Selected Manuscripts (pdf) & Abstracts


Neuron accepted

Loss of PYCR2 causes Neurodegeneration by increasing Cerebral Glycine levels via SHMT2

Nature Communications 2020 

Mitochondrial peptide BRAWNIN is essential for vertebrate respiratory 
complex III assembly

Zhang S, Reljić B, Liang C, Kerouanton B, Francisco JC, Peh JH, Mary C, Jagannathan NS, Olexiouk V, Tang C, Fidelito G, Nama S, Cheng RK, Wee CL, Wang LC, Duek Roggli P, Sampath P, Lane L, Petretto E, Sobota RM, Jesuthasan S, Tucker-Kellogg L, Reversade B, Menschaert G, Sun L, Stroud DA, Ho L.

The emergence of small open reading frame (sORF)-encoded peptides (SEPs) is rapidly expanding the known proteome at the lower end of the size distribution. Here, we show that the mitochondrial proteome, particularly the respiratory chain, is enriched for small proteins. Using a prediction and validation pipeline for SEPs, we report the discovery of 16 endogenous nuclear encoded, mitochondrial-localized SEPs (mito-SEPs). Through functional prediction, proteomics, metabolomics and metabolic flux modeling, we demonstrate that BRAWNIN, a 71 a.a. peptide encoded by C12orf73, is essential for respiratory chain complex III (CIII) assembly. In human cells, BRAWNIN is induced by the energy-sensing AMPK pathway, and its depletion impairs mitochondrial ATP production. In zebrafish, Brawnin deletion causes complete CIII loss, resulting in severe growth retardation, lactic acidosis and early death. Our findings demonstrate that BRAWNIN is essential for vertebrate oxidative phosphorylation. We propose that mito-SEPs are an untapped resource for essential regulators of oxidative metabolism.

Nature Communications 2020 

Loss-of-function Mutations in UDP-Glucose 6-Dehydrogenase Are a Novel Cause
of Recessive Developmental Epileptic Encephalopathy.

Hengel H, Bosso-Lefèvre C, Grady G, Szenker-Ravi E, Li H, Pierce S, Lebigot É, Tan TT, Eio MY, Narayanan G, Utami KH, Yau M, Handal N, Deigendesch W, Keimer R, Marzouqa HM, Gunay-Aygun M, Muriello MJ, Verhelst H, Weckhuysen S, Mahida S, Naidu S, Thomas TG, Lim JY, Tan ES, Haye D, Willemsen MAAP, Oegema R, Mitchell WG, Pierson TM, Andrews MV, Willing MC, Rodan LH, Barakat TS, van Slegtenhorst M, Gavrilova RH, Martinelli D, Gilboa T, Tamim AM, Hashem MO, AlSayed MD, Abdulrahim MM, Al-Owain M, Awaji A, Mahmoud AAH, Faqeih EA, Asmari AA, Algain SM, Jad LA, Aldhalaan HM, Helbig I, Koolen DA, Riess A, Kraegeloh-Mann I, Bauer P, Gulsuner S, Stamberger H, Ng AYJ, Tang S, Tohari S, Keren B, Schultz-Rogers LE, Klee EW, Barresi S, Tartaglia M, Mor-Shaked H, Maddirevula S, Begtrup A, Telegrafi A, Pfundt R, Schüle R, Ciruna B, Bonnard C, Pouladi MA, Stewart JC, Claridge-Chang A, Lefeber DJ, Alkuraya FS, Mathuru AS, Venkatesh B, Barycki JJ, Simpson MA, Jamuar SS, Schöls L, Reversade B.

Developmental epileptic encephalopathies are devastating disorders characterized by intractable epileptic seizures and developmental delay. Here, we report an allelic series of germline recessive mutations in UGDH in 36 cases from 25 families presenting with epileptic encephalopathy with developmental delay and hypotonia. UGDH encodes an oxidoreductase that converts UDP-glucose to UDP-glucuronic acid, a key component of specific proteoglycans and glycolipids. Consistent with being loss-of-function alleles, we show using patients' primary fibroblasts and biochemical assays, that these mutations either impair UGDH stability, oligomerization, or enzymatic activity. In vitro, patient-derived cerebral organoids are smaller with a reduced number of proliferating neuronal progenitors while mutant ugdh zebrafish do not phenocopy the human disease. Our study defines UGDH as a key player for the production of extracellular matrix components that are essential for human brain development. Based on the incidence of variants observed, UGDH mutations are likely to be a frequent cause of recessive epileptic encephalopathy.


Am J Hum Genetics Dec 2019 

Homozygous null TBX4 mutations lead to posterior amelia with pelvic and pulmonary hypoplasia.

Ariana Kariminejad , Emmanuelle Szenker-Ravi, Caroline Lekszas, Homa Tajsharghi, Ali-Reza Moslemi, Thomas Naert, Hong Thi Tran, Fatemeh Ahangari, Minoo Rajaei, Mojila Nasseri, Thomas Haaf, Afrooz Azad, Andrea Superti-Furga, Reza Maroofian, Siavash Ghaderi-Sohi, Hossein Najmabadi, Mohammad Reza Abbaszadegan, Kris Vleminckx, Pooneh Nikuei, Bruno Reversade.

The development of hindlimbs in tetrapod species relies specifically on the transcription factor TBX4. In humans, hetero-zygous loss-of-function TBX4 mutations cause dominant Small Patella Syndrome (SPS) due to haploinsufficiency. Here, we characterize a striking clinical entity in four fetuses with complete Posterior Amelia with Pelvis and Pulmonary hypoplasiA (PAPPA). Through exome sequencing, we report that PAPPA syndrome is caused by homozygous TBX4 inactivating mutations during embryogenesis in humans. In two consanguineous couples, we uncover distinct germline TBX4 coding mutations, p.Tyr113* and p.Tyr127Asn, that segregated with SPS in heterozygous parents and with PAPPAS in one available homo-zygous fetus. A complete absence of TBX4 transcripts in this proband with biallelic p.Tyr113* stop-gain mutations revealed nonsense-mediated decay of the endogenous mRNA. CRISPR/Cas9-mediated TBX4 deletion in Xenopus embryos confirmed its restricted role during leg development. We conclude that SPS and PAPPAS are allelic diseases of TBX4 deficiency, a transcription factor that is essential for organogenesis of the lungs, pelvis and hindlimbs in humans.

Journal of Hepatology Nov 2019

Metabolic pathway analyses identify proline biosynthesis pathway as 
a promoter of liver tumorigenesis

Zhaobing Ding, Russell E. Ericksen, Nathalie Escande-Beillard, Qian Yi Lee, Abigail Loh, Simon Denil, Michael Steckel, Andrea Haegebarth, Timothy Shen Wai Ho, Pierce Chow, Han Chong Toh, Reversade B, Sylvia Gruenewald, Weiping Han

BACKGROUND AIM:Under the regulation of various oncogenic pathways, cancer cells undergo adaptive metabolic programming to maintain specific metabolic states that support their uncontrolled proliferation. As it has been difficult to directly and effectively inhibit oncogenic signaling cascades with pharmaceutical compounds, focusing on the downstream metabolic pathways that enable indefinite growth may provide therapeutic opportunities. Thus, we sought to characterize metabolic changes in hepatocellular carcinoma (HCC) development and identify metabolic targets required for tumorigenesis.
METHODS:We compared gene expression profiles of Morris Hepatoma (MH3924a) and DEN (Diethylnitrosamine)-induced HCC models to those of liver tissues from normal and rapidly regenerating liver models, and performed gain- and loss-of-function studies of the identified gene targets for their roles in cancer cell proliferation in vitro and in vivo.
RESULTS:The proline biosynthetic PYCR1 (Pyrroline-5-Carboxylate Reductase 1) was identified as a top up-regulated gene in the HCC models. Knockdown (KD) of PYCR1 potently reduced cell proliferation of multiple HCC cell lines in vitro and tumor growth in vivo. Conversely, overexpression of PYCR1 enhanced the proliferation of the HCC cell lines. Importantly, PYCR1 expression was not elevated in the regenerating liver, and KD or overexpression of PYCR1 had no effect on proliferation of non-cancerous cells. Besides PYCR1, we found that additional proline biosynthetic enzymes, such as ALDH18A1, were upregulated in HCC models and also regulated HCC cell proliferation. Clinical data demonstrated that PYCR1 expression was increased in HCC, correlated with tumor grade, and was an independent predictor of clinical outcome.
CONCLUSION:Enhanced expression of proline biosynthetic enzymes promotes HCC cell proliferation. Inhibition of PYCR1 or ALDH18A1 may be a novel therapeutic strategy to target HCC.

PNAS. Sept. 2019 

Homozygous NLRP1 gain-of-function mutation in siblings 
with recurrent respiratory papillomatosis. 

Scott B. Drutman, Filomeen Haerynck, Franklin L. Zhong, David Hum, Jutte van der Werff Ten, Bosch , Nickolas Hernandez, Serkan Belkaya, Lazaro Lorenzo-Diaz, Gérard Orth, Vincent R. Bonagura, Laurent Abel, Emmanuelle Jouanguy, Reversade B, Jean Laurent Casanova

Institute of Medical Biology, A*STAR,  Singapore 
Institute of Molecular and Cell Biology, A*STAR, Singapore

Juvenile-onset recurrent respiratory papillomatosis (JRRP) is a rare and debilitating childhood disease that presents with recurrent growth of papillomas in the upper airway. Two common human papillomaviruses (HPVs), HPV-6 and -11, are implicated in most cases, but it is still not understood why only a small proportion of children develop JRRP following exposure to these common viruses. We report 2 siblings with a syndromic form of JRRP associated with mild dermatologic abnormalities. Whole-exome sequencing of the patients revealed a private homozygous mutation in NLRP1, encoding Nucleotide-Binding Domain Leucine-Rich Repeat Family Pyrin Domain-Containing 1. We find the NLRP1 mutant allele to be gain of function (GOF) for inflammasome activation, as demonstrated by the induction of inflammasome complex oligomerization and IL-1β secretion in an overexpression system. Moreover, patient-derived keratinocytes secrete elevated levels of IL-1β at baseline. Finally, both patients displayed elevated levels of inflammasome-induced cytokines in the serum. Six NLRP1 GOF mutations have previously been described to underlie 3 allelic Mendelian diseases with differing phenotypes and modes of inheritance. Our results demonstrate that an autosomal recessive, syndromic form of JRRP can be associated with an NLRP1 GOF mutation.


Nature Communications 2018

Structural basis of RIP2 activation and signaling

Gong Q, Long Z, Zhong FL, Teo DET, Jin Y, Yin Z, Boo ZZ, Zhang Y1, Zhang J, Yang R, Bhushan S, Reversade B, Li Z, Wu B.

Institute of Medical Biology, A*STAR,  Singapore 
Institute of Molecular and Cell Biology, A*STAR, Singapore

Signals arising from bacterial infections are detected by pathogen recognition receptors (PRRs) and are transduced by specialized adapter proteins in mammalian  cells. The Receptor-interacting-serine/threonine-protein kinase 2 (RIPK2 or RIP2)
 is such an adapter protein that is critical for signal propagation of the Nucleotide-binding-oligomerization-domain-containing proteins 1/2 (NOD1 and NOD2). Dysregulation of this signaling pathway leads to defects in bacterial detection and in some cases autoimmune diseases. Here, we show that the Caspase-activation-and-recruitment-domain (CARD) of RIP2 (RIP2-CARD) forms oligomeric structures upon stimulation by either NOD1-CARD or NOD2-2CARD. We reconstitute this complex, termed the RIPosome in vitro and solve the cryo-EM filament structure of the active RIP2-CARD complex at 4.1 A resolution. The structure suggests potential mechanisms by which CARD domains from NOD1 and NOD2 initiate the oligomerization process of RIP2-CARD. Together with structure guided mutagenesis experiments at the CARD-CARD interfaces, we demonstrate molecular mechanisms how RIP2 is activated and self-propagating such signal.

JBC 2018

Human DPP9 represses NLRP1 inflammasome and protects against auto-inflammatory diseases via both peptidase activity and FIIND domain binding.

Franklin L. Zhong, Kim Robinson, Daniel Eng Thiam Teo, Kiat-Yi Tan, Chrissie Lim, Cassandra R. Harapas, Chien-Hsiung Yu, X William H. Xie, Radoslaw M. Sobota, Veonice Bijin Au, Richard Hopkins, Andrea D’Osualdo, John C. Reed, John E. Connolly, Seth L. Masters and Bruno Reversade

Institute of Medical Biology, A*STAR,  Singapore 
Reproductive Biology Laboratory, Amsterdam UMC,  Amsterdam, Netherlands
Institute of Molecular and Cell Biology, A*STAR,  Singapore
Medical Genetics Department, Koç University School of Medicine, Istanbul, Turkey

The inflammasome is a critical molecular complex that activates interleukin-1 driven inflammation in response to pathogen-and danger-associated signals. Germline mutations in the inflammasome sensor NLRP1 cause Mendelian systemic autoimmunity and skin cancer susceptibility, but its endogenous regulation remains less understood. Here we use a proteomics screen to uncover dipeptidyl dipeptidase DPP9 as a novel interacting partner with human NLRP1 and a related inflammasome regulator, CARD8. DPP9 functions as an endogenous inhibitor of NLRP1 inflammasome in diverse primary cell types from human and mice. DPP8/9 inhibition via small molecule drugs and CRISPR/Cas9-mediated genetic deletion specifically activate human NLRP1 inflammasome, leading to ASC speck formation, pyroptotic cell death, and secretion of cleaved interleukin-1. Mechanistically, DPP9 interacts with a unique autoproteolytic domain (FIIND) found in NLRP1 and CARD8. This scaffolding function of DPP9 and its catalytic activity act synergistically to maintain NLRP1 in its inactive state and repress downstream inflammasome activation. We further identified a single patient-derived germline missense mutation in the NLRP1 FIIND domain that abrogates DPP9 binding, leading to inflammasome hyperactivation seen in the Mendelian autoinflammatory disease autoinflammation with arthritis and dyskeratosis. These results unite recent findings on the regulation of murine Nlrp1b by Dpp8/9 and uncover a new regulatory mechanism for the NLRP1 inflammasome in primary human cells. Our results further suggest that DPP9 could be a multifunctional inflammasome regulator involved in human inflammatory diseases.

Nature 2018

RSPO2 inhibition of RNF43 and ZNRF3 governs limb development
independently of LGR4/5/6

Emmanuelle Szenker-Ravi, Umut Altunoglu, Marc Leushacke, Célia Bosso-Lefèvre, Muznah Khatoo, Hong Thi Tran, Thomas Naert, Rivka Noelanders, Amin Hajamohideen, Claire Beneteau, Sergio B. de Sousa, Birsen Karaman, Xenia Latypova, Seher Başaran, Esra Börklü Yücel, Thong Teck Tan, Lena Vlaeminck, Shalini S. Nayak, Anju Shukla, Katta Mohan Girisha, Cédric Le Caignec, Natalia Soshnikova, Zehra Oya Uyguner, Kris Vleminckx, Nick Barker, Hülya Kayserili & Bruno Reversade

Institute of Medical Biology, A*STAR,  Singapore 
Reproductive Biology Laboratory, AMC,  Amsterdam, Netherlands
Institute of Molecular and Cell Biology, A*STAR,  Singapore
National University of Singapore, Department of Paediatrics, Singapore 
Medical Genetics Department, Koç University School of Medicine, Istanbul, Turkey

The four R-spondin secreted ligands (RSPO1–RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers.

eLiFE 2018

A homozygous loss-of-function CAMK2A mutation causes growth delay, frequent seizures and severe intellectual disability

Poh Hui Chia  , Franklin Lei Zhong , Shinsuke Niwa, Carine Bonnard, Kagistia Hana Utami, Ruizhu Zeng, Hane Lee, Ascia Eskin, Stanley F Nelson, William H Xie, Samah Al-Tawalbeh, Mohammad El-Khateeb, Mohammad Shboul, Mahmoud A Pouladi, Mohammed Al-Raqad, Bruno Reversade

Institute of Medical Biology, A*STAR,  Singapore 
Institute of Molecular and Cell Biology, A*STAR, Singapore

Calcium/calmodulin-dependent protein kinase II (CAMK2) plays fundamental roles in synaptic plasticity that underlies learning and memory. Here, we describe a new recessive neurodevelopmental syndrome with global developmental delay, seizures and intellectual disability. Using linkage analysis and exome sequencing, we found that this disease maps to chromosome 5q31.1-q34 and is caused by a biallelic germline mutation in CAMK2A. The missense mutation, p.His477Tyr is located in the CAMK2A association domain that is critical for its function and localization. Biochemically, the p.His477Tyr mutant is defective in self-oligomerization and unable to assemble into the multimeric holoenzyme.In vivo, CAMK2AH477Y failed to rescue neuronal defects in C. elegans lacking unc-43, the ortholog of human CAMK2A. In vitro, neurons derived from patient iPSCs displayed profound synaptic defects. Together, our data demonstrate that a recessive germline mutation in CAMK2A leads to neurodevelopmental defects in humans and suggest that dysfunctional CAMK2 paralogs may contribute to other neurological disorders.

Cancer Cell 2018

Genome-wide CRISPR-Cas9 Screen Identifies Leukemia-Specific Dependence on a Pre-mRNA Metabolic Pathway Regulated by DCPS.

Yamauchi T, Masuda T, Canver MC, Seiler M, Semba Y, Shboul M, Al-Raqad M, Maeda M, Schoonenberg VAC, Cole MA, Macias-Trevino C, Ishikawa Y, Yao Q, Nakano M, Arai F, Orkin SH, Reversade B, Buonamici S, Pinello L, Akashi K, Bauer DE, Maeda T.

Institute of Medical Biology, A*STAR,  Singapore 

To identify novel targets for acute myeloid leukemia (AML) therapy, we performed genome-wide CRISPR-Cas9 screening using AML cell lines, followed by a second screen in vivo. Here, we show that the mRNA decapping enzyme scavenger (DCPS) gene is essential for AML cell survival. The DCPS enzyme interacted with components of pre-mRNA metabolic pathways, including spliceosomes, as revealed by mass spectrometry. RG3039, a DCPS inhibitor originally developed to treat spinal muscular atrophy, exhibited anti-leukemic activity via inducing pre-mRNA mis-splicing. Humans harboring germline biallelic DCPS loss-of-function mutations do not exhibit aberrant hematologic phenotypes, indicating that DCPS is dispensable for human hematopoiesis. Our findings shed light on a pre-mRNA metabolic pathway and identify DCPS as a target for AML therapy.



Am J Hum Genet 2017 

KIAA1109 Variants Are Associated with a Severe Disorder of Brain Development and Arthrogryposis.

Gueneau L, Fish RJ, Shamseldin HE, Voisin N, Tran Mau-Them F, Preiksaitiene E, Monroe GR, Lai A7, Putoux A, Allias F, Ambusaidi Q, Ambrozaityte L, Cimbalistienė L, Delafontaine J, Guex N, Hashem M, Kurdi W, Jamuar SS, Ying LJ, Bonnard C, Pippucci T, Pradervand S, Roechert B, van Hasselt PM, Wiederkehr M, Wright CF; DDD Study, Xenarios I, van Haaften G, Shaw-Smith C, Schindewolf EM, Neerman-Arbez M, Sanlaville D, Lesca G, Guibaud L, Reversade B, Chelly J, Kučinskas V, Alkuraya FS, Reymond A.

Institute of Medical Biology, A*STAR,  Singapore 
Reproductive Biology Laboratory, AMC,  Amsterdam, Netherlands
Institute of Molecular and Cell Biology, A*STAR,  Singapore
National University of Singapore, Department of Paediatrics, Singapore 

Whole-exome and targeted sequencing of 13 individuals from 10 unrelated families with overlapping clinical manifestations identified loss-of-function and missense variants in KIAA1109 allowing delineation of an autosomal-recessive multi-system syndrome, which we suggest to name Alkuraya-Kučinskas syndrome (MIM 617822). Shared phenotypic features representing the cardinal characteristics of this syndrome combine brain atrophy with clubfoot and arthrogryposis. Affected individuals present with cerebral parenchymal underdevelopment, ranging from major cerebral parenchymal thinning with lissencephalic aspect to moderate parenchymal rarefaction, severe to mild ventriculomegaly, cerebellar hypoplasia with brainstem dysgenesis, and cardiac and ophthalmologic anomalies, such as microphthalmia and cataract. Severe loss-of-function cases were incompatible with life, whereas those individuals with milder missense variants presented with severe global developmental delay, syndactyly of 2nd and 3rd toes, and severe muscle hypotonia resulting in incapacity to stand without support. Consistent with a causative role for KIAA1109 loss-of-function/hypomorphic variants in this syndrome, knockdowns of the zebrafish orthologous gene resulted in embryos with hydrocephaly and abnormally curved notochords and overall body shape, whereas published knockouts of the fruit fly and mouse orthologous genes resulted in lethality or severe neurological defects reminiscent of the probands' features.

Journal of Investigative Dermatology 2017. 

ENPP1 Mutation Causes Recessive Cole Disease by Altering Melanogenesis.

Chourabi M, Liew MS, Lim S, H'mida-Ben Brahim D, Boussofara L, Dai L, Wong PM, Foo JN, Sriha B, Robinson KS, Denil S, Common JE, Mamaï O, Ben Khalifa Y, Bollen M, Liu J, Denguezli M, Bonnard C, Saad A, Reversade B.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Cole disease is a genodermatosis of pigmentation following a strict dominant mode of inheritance. In this study, we investigated eight patients affected with an overlapping genodermatosis after recessive inheritance. The patients presented with hypo- and hyperpigmented macules over the body, resembling dyschromatosis universalis hereditaria in addition to punctuate palmoplantar keratosis. By homozygosity mapping and whole-exome sequencing, a biallelic p.Cys120Arg mutation in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) was identified in all patients. We found that this mutation, like those causing dominant Cole disease, impairs homodimerization of the ENPP1 enzyme that is mediated by its two somatomedin-B-like domains. Histological analysis revealed structural and molecular changes in affected skin that were likely to originate from defective melanocytes because keratinocytes do not express ENPP1. Consistently, RNA-sequencing analysis of patient-derived primary melanocytes revealed alterations in melanocyte development and in pigmentation signaling pathways. We therefore conclude that germline ENPP1 cysteine-specific mutations, primarily affecting the melanocyte lineage, cause a clinical spectrum of dyschromatosis, in which the p.Cys120Arg allele represents a recessive and more severe form of Cole disease.

Developmental Cell 2017 sept.                                                     

Alternative Progenitor Cells Compensate to Rebuild the Coronary Vasculature in

and Apj-Deficient Hearts

Bikram Sharma, Lena Ho, Gretchen Hazel Ford, Heidi I. Chen, Andrew B. Goldstone, Y. Joseph Woo, Thomas Quertermous, Bruno Reversade, 
Kristy Red-Horse

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Organogenesis during embryonic development occurs through the differentiation of progenitor cells. This process is extraordinarily accurate, but the mechanisms ensuring high fidelity are poorly understood. Coronary vessels of the mouse heart derive from at least two progenitor pools, the sinus venosus and endocardium. We find that the ELABELA (ELA)-APJ signaling axis is only required for sinus venosus-derived progenitors. Because they do not depend on ELA-APJ, endocardial progenitors are able to expand and compensate for faulty sinus venosus development in Apj mutants, leading to normal adult heart function. An upregulation of endocardial SOX17 accompanied compensation in Apj mutants, which was also seen in Ccbe1 knockouts, indicating that the endocardium is activated in multiple cases where sinus venosus angiogenesis is stunted. Our data demonstrate that by diversifying their responsivity to growth cues, distinct coronary progenitor pools are able to compensate for each other during coronary development, thereby providing robustness to organ development.

Am J Hum Genet 2017 

CDK10 Mutations in Humans and Mice Cause Severe Growth Retardation, Spine Malformations, and Developmental Delays

Christian Windpassinger, Juliette Piard, Carine Bonnard, Majid Alfadhel, Shuhui Lim, Xavier Bisteau, Stephane Blouin, Nur’Ain B. Ali, Alvin Yu Jin Ng, Hao Lu, Sumanty Tohari, S. Zakiah A. Talib, Noemi van Hul, Matias J. Caldez, Lionel Van Maldergem, Gokhan Yigit, Hulya Kayserili, Sameh A. Youssef, Vincenzo Coppola, Alain de Bruin, Lino Tessarollo,Hyungwon Choi, Verena Rupp, Katharina Roetzer, Paul Roschger, Klaus Klaushofer, Janine Altmuller, Sudipto Roy, Byrappa Venkatesh, Rudolf Ganger, Franz Grill, Farid Ben Chehida, Bernd Wollnik, Umut Altunoglu, Ali Al Kaissi, Bruno Reversade and Philipp Kaldis

Institute of Medical Biology, A*STAR,  Singapore 
Reproductive Biology Laboratory, AMC,  Amsterdam, Netherlands
Institute of Molecular and Cell Biology, A*STAR,  Singapore
National University of Singapore, Department of Paediatrics, Singapore 
Medical Genetics Department, Koç University School of Medicine, Istanbul, Turkey

In five separate families, we identified nine individuals affected by a previously unidentified syndrome characterized by growth retardation, spine malformation, facial dysmorphisms, and developmental delays. Using homozygosity mapping, array CGH, and exome sequencing, we uncovered bi-allelic loss-of-function CDK10 mutations segregating with this disease. CDK10 is a protein kinase that partners with cyclin M to phosphorylate substrates such as ETS2 and PKN2 in order to modulate cellular growth. To validate and model the pathogenicity of these CDK10 germline mutations, we generated conditional-knockout mice. Homozygous Cdk10-knockout mice died postnatally with severe growth retardation, skeletal defects, and kidney and lung abnormalities, symptoms that partly resemble the disease’s effect in humans. Fibroblasts derived from affected individuals and Cdk10-knockout mouse embryonic fibroblasts (MEFs) proliferated normally; however, Cdk10-knockout MEFs developed longer cilia. Comparative transcriptomic analysis of mutant and wild-type mouse organs revealed lipid metabolic changes consistent with growth impairment and altered ciliogenesis in the absence of CDK10. Our results document the CDK10 loss-of-function phenotype and point to a function for CDK10 in transducing signals received at the primary cilia to sustain embryonic and postnatal development.

Science 2017                                                                                                                   

ELABELA deficiency promotes preeclampsia and cardiovascular malformations in mice

Lena Ho, Marie Van Dijk, Sam Tan Jian Chye, Daniel M. Messerschmidt, Serene C. Chng, Sheena Ong, Ling Ka Yi, Souad Boussata, Grace Hui-Yi Goh, Gijs B. Afink, Chin Yan Lim, N. Ray Dunn, Davor Solter, Barbara B. Knowles, Bruno Reversade

Institute of Medical Biology, A*STAR,  Singapore 
Reproductive Biology Laboratory, AMC,  Amsterdam, Netherlands
Institute of Molecular and Cell Biology, A*STAR,  Singapore
Medical Genetics Department, Koç University School of Medicine, Istanbul, Turkey

Pre-eclampsia (PE) is a gestational hypertensive syndrome affecting between 5 and 8% of all pregnancies. While PE is the leading cause of fetal and maternal morbidity/mortality, its molecular etiology is still unclear. Here, we show that ELABELA (ELA), an endogenous ligand of the apelin receptor (APLNR, or APJ), is a circulating hormone secreted by the placenta. Elabela but not Apelin knockout pregnant mice exhibit PE-like symptoms, including proteinuria and elevated blood pressure due to defective placental angiogenesis. In mice, infusion of exogenous ELA normalizes hypertension, proteinuria, and birth weight. ELA, which is abundant in human placentas, increases the invasiveness of trophoblast-like cells, suggesting that it enhances placental development to prevent PE. The ELA-APLNR signaling axis may offer a new paradigm for the treatment of common pregnancy-related complications, including PE.

Am J Hum Genet 2017 

Loss-of-Function Mutations in LGI4, a Secreted Ligand Involved in Schwann Cell 

Myelination, Are Responsible for Arthrogryposis Multiplex Congenita.

Xue S, Maluenda J, Marguet F, Shboul M, Quevarec L, Bonnard C, Ng AY, Tohari S, Tan TT, Kong MK, Monaghan KG, Cho MT, Siskind CE, Sampson JB, Rocha CT, Alkazaleh F, Gonzales M, Rigonnot L, Whalen S, Gut M, Gut I, Bucourt M, Venkatesh B, Laquerrière A, Reversade Bruno, Melki J

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Arthrogryposis multiplex congenita (AMC) is a developmental condition characterized by multiple joint contractures resulting from reduced or absent fetal movements. Through genetic mapping of disease loci and whole-exome sequencing in four unrelated multiplex families presenting with severe AMC, we identified biallelic loss-of-function mutations in LGI4 (leucine-rich glioma-inactivated 4). LGI4 is a ligand secreted by Schwann cells that regulates peripheral nerve myelination via its cognate receptor ADAM22 expressed by neurons. Immunolabeling experiments and transmission electron microscopy of the sciatic nerve from one of the affected individuals revealed a lack of myelin. Functional tests using affected individual-derived iPSCs showed that these germline mutations caused aberrant splicing of the endogenous LGI4 transcript and in a cell-based assay impaired the secretion of truncated LGI4 protein. This is consistent with previous studies reporting arthrogryposis in Lgi4-deficient mice due to peripheral hypomyelination. This study adds to the recent reports implicating defective axoglial function as a key cause of AMC.

De novo mutations in SMCHD1 cause Bosma arhinia microphthalmia syndrome
and abrogate nasal development.

Christopher T. Gordon, Shifeng Xue, Gökhan Yigit, Hicham Filali, Kelan Chen, Nadine Rosin, Koh-ichiro, Yoshiura, Myriam Oufadem, Tamara J. Beck, Ruth McGowan, Alex C. Magee, Janine Altmüller, Camille Dion, Holger Thiele, Alexandra D. Gurzau, Peter Nürnberg, Dieter Meschede, Wolfgang Mühlbauer, Nobuhiko Okamoto, Vinod Varghese, Rachel Irving, Sabine Sigaudy, Denise Williams, S. Faisal Ahmed, Carine Bonnard, Mung Kei Kong, Ilham Ratbi, Nawfal Fejjal, Meriem Fikri, Siham Chafai Elalaoui, Hallvard Reigstad, Christine Bole-Feysot, Patrick Nitschké, Nicola Ragge, Nicolas Lévy, Gökhan Tunçbilek, Audrey S.M. Teo, Michael L. Cunningham, Abdelaziz Sefiani, Hülya Kayserili, James M. Murphy, Chalermpong Chatdokmaiprai, Axel M. Hillmer, Duangrurdee Wattanasirichaigoon, Stanislas Lyonnet, Frédérique Magdinier, Asif Javed, Marnie E. Blewitt, Jeanne Amiel, Bernd Wollnik, Bruno Reversade

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Bosma arhinia microphthalmia syndrome (BAMS) is an extremely rare and striking condition characterized by complete absence of the nose with or without ocular defects. We report here that missense mutations in the epigenetic regulator SMCHD1 mapping to the extended ATPase domain of the encoded protein cause BAMS in all 14 cases studied. All mutations were de novo where parental DNA was available. Biochemical tests and in vivo assays in Xenopus laevis embryos suggest that these mutations may behave as gain-of-function alleles. This finding is in contrast to the loss-of-function mutations in SMCHD1 that have been associated with facioscapulohumeral muscular dystrophy (FSHD) type 2. Our results establish SMCHD1 as a key player in nasal development and provide biochemical insight into its enzymatic function that may be exploited for development of therapeutics for FSHD.


CELL 2016  

Germline NLRP1 Mutations Cause Skin Inflammatory and Cancer Susceptibility Syndromes via Inflammasome Activation.

Zhong FL, Mamaï O, Sborgi L, Boussofara L, Hopkins R, Robinson K, Szeverényi I, Takeichi T, Balaji R, Lau A, Tye H, Roy K, Bonnard C, Ahl PJ, Jones LA, Baker P, Lacina L, Otsuka A, Fournie PR, Malecaze F, Lane EB, Akiyama M, Kabashima K, Connolly JE, Masters SL, Soler VJ, Omar SS, McGrath JA, Nedelcu R, Gribaa M, Denguezli M, Saad A, Hiller S, Bruno Reversade 

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Inflammasome complexes function as key innate immune effectors that trigger inflammation in response to pathogen- and danger-associated signals. Here, we report that germline mutations in the inflammasome sensor NLRP1 cause two overlapping skin disorders: multiple self-healing palmoplantar carcinoma (MSPC) and familial keratosis lichenoides chronica (FKLC). We find that NLRP1 is the most prominent inflammasome sensor in human skin, and all pathogenic NLRP1 mutations are gain-of-function alleles that predispose to inflammasome activation. Mechanistically, NLRP1 mutations lead to increased self-oligomerization by disrupting the PYD and LRR domains, which are essential in maintaining NLRP1 as an inactive monomer. Primary keratinocytes from patients experience spontaneous inflammasome activation and paracrine IL-1 signaling, which is sufficient to cause skin inflammation and epidermal hyperplasia. Our findings establish a group of non-fever inflammasome disorders, uncover an unexpected auto-inhibitory function for the pyrin domain, and provide the first genetic evidence linking NLRP1 to skin inflammatory syndromes and skin cancer predisposition.

eLiFE. 2016  

The Apelin receptor enhances Nodal/TGFβ signaling to ensure proper cardiac development.

Deshwar AR, Chng SC, Ho L, Reversade B, Scott IC.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

The Apelin receptor (Aplnr) is essential for heart development, controlling the early migration of cardiac progenitors. Here we demonstrate that in zebrafish Aplnr modulates Nodal/TGFβ signaling, a key pathway essential for mesendoderm induction and migration. Loss of Aplnr function leads to a reduction in Nodal target gene expression whereas activation of Aplnr by a non-peptide agonist increases the expression of these same targets. Furthermore, loss of Aplnr results in a delay in the expression of the cardiogenic transcription factors mespaa/ab. Elevating Nodal levels in aplnra/b morphant and double mutant embryos is sufficient to rescue cardiac differentiation defects. We demonstrate that loss of Aplnr attenuates the activity of a point source of Nodal ligands Squint and Cyclops in a non-cell autonomous manner. Our results favour a model in which Aplnr is required to fine-tune Nodal output, acting as a specific rheostat for the Nodal/TGFβ pathway during the earliest stages of cardiogenesis.

eLiFE. 2016  

Quantitative imaging reveals real-time Pou5f3-Nanog complexes driving dorsoventral mesendoderm patterning in zebrafish

Mireia Perez Camps , Jing Tian , Serene Chng, Kaiping Sem , Thankiah Sudhaharan, Cathleen Teh, Malte Wachsmuth , Vladimir Korzh , Sohail Ahmed, Bruno Reversade.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Formation of the three embryonic germ layers is a fundamental developmental process that initiates differentiation. How the zebrafish pluripotency factor Pou5f3 (homologous to mammalian Oct4) drives lineage commitment is unclear. Here, we introduce fluorescence lifetime imaging microscopy and fluorescence correlation spectroscopy to assess the formation of Pou5f3 complexes with other transcription factors in real-time in gastrulating zebrafish embryos. We show, at single-cell resolution in vivo, that Pou5f3 complexes with Nanog to pattern mesendoderm differentiation at the blastula stage. Later, during gastrulation, Sox32 restricts Pou5f3-Nanog complexes to the ventrolateral mesendoderm by binding Pou5f3 or Nanog in prospective dorsal endoderm. In the ventrolateral endoderm, the Elabela/Aplnr pathway limits Sox32 levels, allowing the formation of Pou5f3-Nanog complexes and the activation of downstream BMP signalling. This quantitative model shows that a balance in the spatiotemporal distribution of Pou5f3-Nanog complexes, modulated by Sox32, regulates mesendoderm specification along the dorsoventral axis.

Am J Hum Genet. 2016 

Loss-of-function mutations in ELMO2 cause intraosseous vascular malformation by impeding RAC1 signaling

Arda Cetinkaya, Jingwei Rachel Xiong, Ibrahim Vargel, Kemal Kosemehmetoglu, Halil Ibrahim Canter, Omer Faruk Gerdan,Nicola Longo, Ahmad Alzahrani, Mireia Perez Camps, Ekim Zihni Taskiran,Simone Laupheimer, Lorenzo D. Botto, Eeswari Paramalingam, Zeliha Gormez, Elif Uz, Bayram Yuksel, Sxevket Ruacan, Mahmut Sxamil Sagıroglu, Tokiharu Takahashi, Bruno Reversade, Nurten Ayse Akarsu

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Vascular malformations are non-neoplastic expansions of blood vessels that arise due to errors during angiogenesis. They are a heterogeneous group of sporadic or inherited vascular disorders characterized by localized lesions of arteriovenous, capillary, or lymphatic origin. Vascular malformations that occur inside bone tissue are rare. Herein, we report loss-of-function mutations in ELMO2 (which translates extracellular signals into cellular move-ments) that are causative for autosomal-recessive intraosseous vascular malformation (VMOS) in five different families. Individuals with VMOS suffer from life-threatening progressive expansion of the jaw, craniofacial, and other intramembranous bones caused by malformed blood vessels that lack a mature vascular smooth muscle layer. Analysis of primary fibroblasts from an affected individual showed that absence of ELMO2 correlated with a significant downregulation of binding partner DOCK1, resulting in deficient RAC1-dependent cell migration. Unexpectedly, elmo2-knockout zebrafish appeared phenotypically normal, suggesting that there might be human-specific ELMO2 requirements in bone vasculature homeostasis or genetic compensation by related genes. Comparative phylogenetic analysis indicated that elmo2 originated upon the appearance of intramembranous bones and the jaw in ancestral vertebrates, implying that elmo2 might have been involved in the evolution of these novel traits. The present findings highlight the necessity of ELMO2 for maintaining vascular integrity, specifically in intramembranous bones.

Am J Hum Genet. 2016 

De Novo Loss-of-Function Mutations in USP9X Cause a Female-Specific Recognizable Syndrome with Developmental Delay and Congenital Malformations.

Reijnders MR, Zachariadis V, Latour B, Jolly L, Mancini GM, Pfundt R, Wu KM, van Ravenswaaij-Arts CM, Veenstra-Knol HE, Anderlid BM, Wood SA, Cheung SW, Barnicoat A, Probst F, Magoulas P, Brooks AS, Malmgren H, Harila-Saari A, Marcelis CM, Vreeburg M, Hobson E, Sutton VR, Stark Z, Vogt J, Cooper N, Lim JY, Price S, Lai AH, Domingo D, Bruno Reversade ; DDD Study, Gecz J, Gilissen C, Brunner HG, Kini U, Roepman R, Nordgren A, Kleefstra T.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Academic Medical Centre & VU University Medical Center, Reproductive Biology Laboratory, Amsterdam, the Netherlands.

Mutations in more than a hundred genes have been reported to cause X-linked recessive intellectual disability (ID) mainly in males. In contrast, the number of identified X-linked genes in which de novo mutations specifically cause ID in females is limited. Here, we report 17 females with de novo loss-of-function mutations in USP9X, encoding a highly conserved deubiquitinating enzyme. The females in our study have a specific phenotype that includes ID/developmental delay (DD), characteristic facial features, short stature, and distinct congenital malformations comprising choanal atresia, anal abnormalities, post-axial polydactyly, heart defects, hypomastia, cleft palate/bifid uvula, progressive scoliosis, and structural brain abnormalities. Four females from our cohort were identified by targeted genetic testing because their phenotype was suggestive for USP9X mutations. In several females, pigment changes along Blaschko lines and body asymmetry were observed, which is probably related to differential (escape from) X-inactivation between tissues. Expression studies on both mRNA and protein level in affected-female-derived fibroblasts showed significant reduction of USP9X level, confirming the loss-of-function effect of the identified mutations. Given that some features of affected females are also reported in known ciliopathy syndromes, we examined the role of USP9X in the primary cilium and found that endogenous USP9X localizes along the length of the ciliary axoneme, indicating that its loss of function could indeed disrupt cilium-regulated processes. Absence of dysregulated ciliary parameters in affected female-derived fibroblasts, however, points toward spatiotemporal specificity of ciliary USP9X (dys-)function.

Am J Hum Genet. 2016 

Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility.

Mbarek H, Steinberg S, Nyholt DR, Gordon SD, Miller MB, McRae AF, Hottenga JJ, Day FR, Willemsen G, de Geus EJ, Davies GE, Martin HC, Penninx BW, Jansen R, McAloney K, Vink JM, Kaprio J, Plomin R, Spector TD, Magnusson PK, Reversade B, Harris RA, Aagaard K, Kristjansson RP, Olafsson I, Eyjolfsson GI, Sigurdardottir O, Iacono WG, Lambalk CB, Montgomery GW, McGue M, Ong KK, Perry JRB, Martin NG, Stefánsson H, Stefánsson K, Boomsma DI.

Institute of Medical Biology, A*STAR, Singapore, Singapore.
Academic Medical Centre & VU University Medical Center, Reproductive Biology Laboratory, Amsterdam, the Netherlands.

Spontaneous dizygotic (DZ) twinning occurs in 1%-4% of women, with familial clustering and unknown physiological pathways and genetic origin. DZ twinning might index increased fertility and has distinct health implications for mother and child. We performed a GWAS in 1,980 mothers of spontaneous DZ twins and 12,953 control subjects. Findings were replicated in a large Icelandic cohort and tested for association across a broad range of fertility traits in women. Two SNPs were identified (rs11031006 near FSHB, p = 1.54 × 10(-9), and rs17293443 in SMAD3, p = 1.57 × 10(-8)) and replicated (p = 3 × 10(-3) and p = 1.44 × 10(-4), respectively). Based on ∼90,000 births in Iceland, the risk of a mother delivering twins increased by 18% for each copy of allele rs11031006-G and 9% for rs17293443-C. A higher polygenic risk score (PRS) for DZ twinning, calculated based on the results of the DZ twinning GWAS, was significantly associated with DZ twinning in Iceland (p = 0.001). A higher PRS was also associated with having children (p = 0.01), greater lifetime parity (p = 0.03), and earlier age at first child (p = 0.02). Allele rs11031006-G was associated with higher serum FSH levels, earlier age at menarche, earlier age at first child, higher lifetime parity, lower PCOS risk, and earlier age at menopause. Conversely, rs17293443-C was associated with later age at last child. We identified robust genetic risk variants for DZ twinning: one near FSHB and a second within SMAD3, the product of which plays an important role in gonadal responsiveness to FSH. These loci contribute to crucial aspects of reproductive capacity and health.


Current Biology. 2015                                                                                    

Gmnc Is a Master Regulator of the Multiciliated Cell Differentiation Program

Feng Zhou, Vijay Narasimhan, Mohammad Shboul, Yan Ling Chong, Bruno Reversade, Sudipto Roy

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Multiciliated cells (MCCs) differentiate hundreds of motile cilia that generate mechanical force required to drive fluid movement over epithelia [1 and 2]. For example, metachronal beating of MCC cilia in the mammalian airways clears mucus that traps inhaled pathogens and pollutants. Consequently, abnormalities in MCC differentiation or ciliary motility have been linked to an expanding spectrum of human airway diseases [3, 4,5 and 6]. The current view posits that MCC precursors are singled out by the inhibition of Notch signaling. MCC precursors then support an explosive production of basal bodies, which migrate to the apical surface, dock with the plasma membrane, and seed the growth of multiple motile cilia. At the center of this elaborate differentiation program resides the coiled-coil-containing protein Multicilin, which transcriptionally activates genes for basal body production and the gene for FoxJ1, the master regulator for basal body docking, cilia formation, and motility [7 and 8]. Here, using genetic analysis in the zebrafish embryo, we discovered that Gmnc is a novel determinant of the MCC fate. Like Multicilin, Gmnc is a coiled-coil-containing protein of the Geminin family. We show that Gmnc functions downstream of Notch signaling, but upstream of Multicilin in the developmental pathway controlling MCC specification. Moreover, we find that loss of Gmnc in Xenopus embryos also causes loss of MCC differentiation and that overexpression of the protein is sufficient to induce supernumerary MCCs. Together, our data identify Gmnc as an evolutionarily conserved master regulator functioning at the top of the hierarchy of transcription factors involved in MCC differentiation.

Cell Stem Cell. 2015                                                                          

ELABELA Is an Endogenous Growth Factor that Sustains hESC Self-Renewal 

via the PI3K/AKT Pathway

Lena Ho, Shawn Y.X. Tan, Sheena Wee, Yixuan Wu, Sam J.C. Tan, Navin B. Ramakrishna, Serene C. Chng, Srikanth Nama, Iwona Sczerbineska, Winston Chan, Stuart Avery, Norihiro Tsuneyoshi, Huck Hui Ng, Jayantha Gunaratne, N. Ray Dunn, Bruno Reversade

Institute of Medical Biology, A*STAR, Singapore, Singapore.

ELABELA (ELA) is a peptide hormone required for heart development that signals via the Apelin Receptor (APLNR, APJ). ELA is also abundantly secreted by human embryonic stem cells (hESCs), which do not express APLNR. Here we show that ELA signals in a paracrine fashion in hESCs to maintain self-renewal. ELA inhibition by CRISPR/Cas9-mediated deletion, shRNA, or neutralizing antibodies causes reduced hESC growth, cell death, and loss of pluripotency. Global phosphoproteomic and transcriptomic analyses of ELA-pulsed hESCs show that it activates PI3K/AKT/mTORC1 signaling required for cell survival. ELA promotes hESC cell-cycle progression and protein translation and blocks stress-induced apoptosis. INSULIN and ELA have partially overlapping functions in hESC medium, but only ELA can potentiate the TGFβ pathway to prime hESCs toward the endoderm lineage. We propose that ELA, acting through an alternate cell-surface receptor, is an endogenous secreted growth factor in human embryos and hESCs that promotes growth and pluripotency.

Am J Hum Genet.2015 

Recurrent De Novo Mutations Affecting Residue Arg138 of Pyrroline-5-Carboxylate

Synthase Cause a Progeroid Form of Autosomal-Dominant Cutis Laxa.

Björn Fischer-Zirnsak, Nathalie Escande-Beillar, Jaya Ganesh, Yu Xuan Tan, Mohammed Al Bughaili, Angela E. Lin, Inderneel Sahai, Paulina Bahena, Sara L. Reichert, Abigail Loh, Graham D. Wright, Jaron Liu, Elisa Rahikkala, Eniko K. Pivnick, Asim F. Choudhri, Ulrike Krüger, Tomasz Zemojtel, Conny van Ravenswaaij-Arts, Roya Mostafavi, Irene Stolte-Dijkstra, Sofie Symoens, Leila Pajunen, Lihadh Al-Gazali, David Meierhofer, Peter N. Robinson, Stefan Mundlos, Camilo E. Villarroel, Peter Byers, Amira Masri, Stephen P. Robertson, Ulrike Schwarze, Bert Callewaert, Bruno Reversade, Uwe Kornak

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Progeroid disorders overlapping with De Barsy syndrome (DBS) are collectively denoted as autosomal-recessive cutis laxa type 3 (ARCL3). They are caused by biallelic mutations in PYCR1 or ALDH18A1, encoding pyrroline-5-carboxylate reductase 1 and pyrroline-5-carboxylate synthase (P5CS), respectively, which both operate in the mitochondrial proline cycle. We report here on eight unrelated individuals born to non-consanguineous families clinically diagnosed with DBS or wrinkly skin syndrome. We found three heterozygous mutations in ALDH18A1 leading to amino acid substitutions of the same highly conserved residue, Arg138 in P5CS. A de novo origin was confirmed in all six probands for whom parental DNA was available. Using fibroblasts from affected individuals and heterologous overexpression, we found that the P5CS-p.Arg138Trp protein was stable and able to interact with wild-type P5CS but showed an altered sub-mitochondrial distribution. A reduced size upon native gel electrophoresis indicated an alteration of the structure or composition of P5CS mutant complex. Furthermore, we found that the mutant cells had a reduced P5CS enzymatic activity leading to a delayed proline accumulation. In summary, recurrent de novo mutations, affecting the highly conserved residue Arg138 of P5CS, cause an autosomal-dominant form of cutis laxa with progeroid features. Our data provide insights into the etiology of cutis laxa diseases and will have immediate impact on diagnostics and genetic counseling.

eLiFE. 2015 May 27. 

The hormonal peptide Elabela guides angioblasts to the midline

during vasculogenesis

 Helker C. S. M.,  Schuermann A, Pollmann C , Chng S C, Kiefer F ,  Reversade B, Herzog W 

Institute of Medical Biology, A*STAR, Singapore, Singapore.

A key step in the de novo formation of the embryonic vasculature is the migration of endothelial precursors, the angioblasts, to the position of the future vessels. To form the first axial vessels, angioblasts migrate towards the midline and coalesce underneath the notochord. Vascular endothelial growth factor (Vegf) has been proposed to serve as a chemoattractant for the angioblasts and to regulate this medial migration. Here we challenge this model and instead demonstrate that angioblasts rely on their intrinsic expression of Apelin receptors (Aplnr, APJ) for their migration to the midline. We further show that during this angioblast migration Apelin receptor signaling is mainly triggered by the recently discovered ligand Elabela (Ela). As neither of the ligands Ela or Apelin (Apln) nor their receptors have previously been implicated in regulating angioblast migration, we hereby provide a novel mechanism for regulating vasculogenesis, with direct relevance to physiological and pathological angiogenesis.

Human Molecular Genetics. 2015 Feb 24. 

Loss of the Scavenger mRNA Decapping Enzyme DCPS Causes Syndromic Intellectual Disability with Neuromuscular Defects.

Ng C, Shboul M, Taverniti V, Bonnard C, Lee H, Eskin A, Nelson SF, Al-Raqad M, Altawalbeh S, Séraphin B, Reversade B.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

mRNA decay is an essential and active process that allows cells to continuously adapt gene expression to internal and environmental cues. There are two mRNA degradation pathways: 3' to 5' and 5' to 3'. The DCPS protein is the scavenger mRNA decapping enzyme which functions in the last step of the 3' end mRNA decay pathway. We have identified a DCPS pathogenic mutation in a large family with three affected individuals presenting with a novel recessive syndrome consisting of craniofacial anomalies, intellectual disability and neuromuscular defects. Using patient's primary cells, we show that this homozygous splice mutation results in a DCPS loss-of-function allele. Diagnostic biochemical analyses using various m7G cap derivatives as substrates reveal no DCPS enzymatic activity in patient's cells. Our results implicate DCPS and more generally RNA catabolism, as a critical cellular process for neurological development, normal cognition and organismal homeostasis in humans.


Neuron. 2014 Dec 22. 

Katanin p80 Regulates Human Cortical Development by Limiting Centriole and Cilia Number.

Hu WF, Pomp O, Ben-Omran T, Kodani A, Henke K, Mochida GH, Yu TW, Woodworth MB, Bonnard C, Raj GS, Tan TT, Hamamy H, Masri A, Shboul M, Al Saffar M, Partlow JN, Al-Dosari M, Alazami A, Alowain M, Alkuraya FS, Reiter JF, Harris MP, Reversade B, Walsh CA.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Katanin is a microtubule-severing complex whose catalytic activities are well characterized, but whose in vivo functions are incompletely understood. Human mutations in KATNB1, which encodes the noncatalytic regulatory p80 subunit of katanin, cause severe microlissencephaly. Loss of Katnb1 in mice confirms essential roles in neurogenesis and cell survival, while loss of zebrafish katnb1 reveals specific roles for katnin p80 in early and late developmental stages. Surprisingly, Katnb1 null mutant mouse embryos display hallmarks of aberrant Sonic hedgehog signaling, including holoprosencephaly. KATNB1-deficient human cells show defective proliferation and spindle structure, while Katnb1 null fibroblasts also demonstrate a remarkable excess of centrioles, with supernumerary cilia but deficient Hedgehog signaling. Our results reveal unexpected functions for KATNB1 in regulating overall centriole, mother centriole, and cilia number, and as an essential gene for normal Hedgehog signaling during neocortical development.

Journal of Investigative Dermatology. 2014 Jul 22. 

Multiple Self-Healing Palmoplantar Carcinoma: A Familial Predisposition to Skin Cancer with Primary Palmoplantar and Conjunctival Lesions.

Mamaï O, Boussofara L, Denguezli M, Escande-Beillard N, Kraeim W, Merriman B, Ben Charfeddine I, Stevanin G, Bouraoui S, Amara A, Mili A, Nouira R, H'mida D, Sriha B, Gribaa M, Saad A, Reversade B.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Familial keratoacanthomas (KAs) are characterized by the appearance of multiple epithelial tumors that are believed to arise from adjoining hair follicles (Schwartz, 1994). These lesions, which phenotypically and histologically resemble squamous cell carcinomas (SCCs) (Cribier et al., 1999), have a fast evolution and spontaneous regression. To date, four familial forms of multiple KAs have been described: (1) multiple self-healing squamous epithelioma (MSSE; Smith, 1948); (2) the Grzybowski syndrome (Grzybowski, 1950); (3) the Witten–Zak syndrome (Witten and Zak, 1952); and 4) the Muir-Torre syndrome (Muir et al., 1967). The Muir-Torre syndrome (MIM#158320) is caused by mutations in the DNA-repair genes MSH2/MLH1 (Bapat et al., 1996; Kruse et al., 1998), and MSSE (MIM#132800) is due to mutations in TGFBR1 (Goudie et al., 2011), but the causative genes underlying the other two familial KAs are still not known. We describe here, in a five-generation Tunisian family comprising 27 affected individuals with autosomal dominant transmission of palmoplantar KAs, an unreported syndrome that we have named multiple self-healing palmoplantar carcinoma MSPC. MSPC has the distinctive feature of mainly affecting epithelial tissues that are devoid of hair follicles, such as palmoplantar skin and the conjunctival epithelium.


Developmental Cell. 2013 Dec;(27):1-9.                                  

ELABELA: A Hormone Essential for Heart Development Signals via the Apelin Receptor

Chng SHo L, Tian JReversade B

Institute of Medical Biology, A*STAR, Singapore, Singapore.

We report here the discovery and characterization of a gene, ELABELA (ELA), encoding a conserved hormone of 32 amino acids. Present in human embryonic stem cells, ELA is expressed at the onset of zebrafish zygotic transcription and is ubiquitous in the naive ectodermal cells of the embryo. Using zinc-finger-nuclease-mediated gene inactivation in zebrafish, we created an allelic series of ela mutants. ela null embryos have impaired endoderm differentiation potential marked by reduced gata5 and sox17 expression. Loss of Ela causes embryos to develop with a rudimentary heart or no heart at all, surprisingly phenocopying the loss of the apelin receptor (aplnr), which we show serves as Ela's cognate G protein-coupled receptor. Our results reveal the existence of a peptide hormone, ELA, which, together with APLNR, forms an essential signaling axis for early cardiovascular development.

Human Genetics. 2013 Nov 1. 

C5orf42 is the major gene responsible for OFD syndrome type VI.

Lopez E, Thauvin-Robinet C, Reversade B, Khartoufi NE, Devisme L, Holder M, Ansart-Franquet H, Avila M, Lacombe D, Kleinfinger P, Kaori I, Takanashi JI, Le Merrer M, Martinovic J, Noël C, Shboul M, Ho L, Güven Y, Razavi F, Burglen L, Gigot N, Darmency-Stamboul V, Thevenon J, Aral B, Kayserili H, Huet F, Lyonnet S, Le Caignec C, Franco B, Rivière JB, Faivre L, Attié-Bitach T.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Oral-facial-digital syndrome type VI (OFD VI) is a recessive ciliopathy defined by two diagnostic criteria: molar tooth sign (MTS) and one or more of the following: (1) tongue hamartoma (s) and/or additional frenula and/or upper lip notch; (2) mesoaxial polydactyly of one or more hands or feet; (3) hypothalamic hamartoma. Because of the MTS, OFD VI belongs to the "Joubert syndrome related disorders". Its genetic aetiology remains largely unknown although mutations in the TMEM216 gene, responsible for Joubert (JBS2) and Meckel-Gruber (MKS2) syndromes, have been reported in two OFD VI patients. To explore the molecular cause(s) of OFD VI syndrome, we used an exome sequencing strategy in six unrelated families followed by Sanger sequencing. We identified a total of 14 novel mutations in the C5orf42 gene in 9/11 families with positive OFD VI diagnostic criteria including a severe fetal case with microphthalmia, cerebellar hypoplasia, corpus callosum agenesis, polydactyly and skeletal dysplasia. C5orf42 mutations have already been reported in Joubert syndrome confirming that OFD VI and JBS are allelic disorders, thus enhancing our knowledge of the complex, highly heterogeneous nature of ciliopathies. 

Mol Biol Cell. 2013 July 31. 

Nuclear-localized Asunder regulates cytoplasmic dynein localization via its role in the Integrator complex.

Jodoin JN, Sitaram P, Albrecht TR, May SB, Shboul M, Lee E, Reversade B, Wagner EJ, Lee LA.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

We previously reported that Asunder (ASUN) is essential for recruitment of dynein motors to the nuclear envelope (NE) and nucleus-centrosome coupling at the onset of cell division in cultured human cells and Drosophila spermatocytes, though the mechanisms underlying this regulation remain unknown. We have also recently identified ASUN as a functional component of Integrator (INT), a multi-subunit complex required for 3'-end processing of small nuclear RNAs (snRNAs). We now provide evidence that ASUN acts in the nucleus in concert with other INT components to mediate recruitment of dynein to the NE. Knockdown of other individual INT subunits in HeLa cells recapitulates the loss of perinuclear dynein in ASUN-siRNA cells. Forced localization of ASUN to the cytoplasm via mutation of its nuclear localization sequence (NLS) blocks its capacity to restore perinuclear dynein in both cultured human cells lacking ASUN and Drosophila asun spermatocytes. Additionally, the levels of several INT subunits are reduced at G2/M when dynein is recruited to the NE, suggesting that INT does not directly mediate this step. Taken together, our data support a model in which a nuclear INT complex promotes recruitment of cytoplasmic dynein to the NE, possibly via a mechanism involving RNA processing.

Development.  2013 Jan 14. 

Lim CY, Reversade B, Knowles BB, Solter D.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Cellular differentiation during embryogenesis involves complex gene regulation to enable the activation and repression of genes. Here, we show that mesodermal competence is inhibited in Xenopus embryos depleted of histones H3 and H3.3, which fail to respond to Nodal/Activin signaling and exhibit concomitant loss of mesodermal gene expression. We find that transcriptional activation in gastrula embryos does not correlate with promoter deposition of H3.3. Instead, gastrulation defects in H3.3/H3-deficient embryos are partially rescued with concurrent depletion of the linker histone H1A. In addition, we show that linker histone H1-induced premature loss of mesodermal competence in animal cap explants can be abrogated with the overexpression of nucleosomal H3.3/H3. Our findings establish a chromatin-mediated regulatory mechanism in which a threshold level of H3 is required to prevent H1-induced gene repression, and thus facilitate mesodermal differentiation in response to inductive signaling.


Nature Genetics. 2012 Nov;44(11):1272-6.

Pohler E, Mamai O, Hirst J, Zamiri M, Horn H, Nomura T, Irvine AD, Moran B, Wilson NJ, Smith FJ, Goh CS, Sandilands A, Cole C, Barton GJ, Evans AT, Shimizu H, Akiyama M, Suehiro M, Konohana I, Shboul M, Teissier S,Boussofara L, Denguezli M, Saad A, Gribaa M, Dopping-Hepenstal PJ, McGrath JA, Brown SJ, Goudie DR, Reversade B, Munro CS, McLean WH.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Palmoplantar keratodermas (PPKs) are a group of disorders that are diagnostically and therapeutically problematic in dermatogenetics. Punctate PPKs are characterized by circumscribed hyperkeratotic lesions on the palms and soles with considerable heterogeneity. In 18 families with autosomal dominant punctate PPK, we report heterozygous loss-of-function mutations in AAGAB, encoding α- and γ-adaptin-binding protein p34, located at a previously linked locus at 15q22. α- and γ-adaptin-binding protein p34, a cytosolic protein with a Rab-like GTPase domain, was shown to bind both clathrin adaptor protein complexes, indicating a role in membrane trafficking. Ultrastructurally, lesional epidermis showed abnormalities in intracellular vesicle biology. Immunohistochemistry showed hyperproliferation within the punctate lesions. Knockdown of AAGAB in keratinocytes led to increased cell division, which was linked to greatly elevated epidermal growth factor receptor (EGFR) protein expression and tyrosine  phosphorylation. We hypothesize that p34 deficiency may impair endocytic recycling of growth factor receptors such as EGFR, leading to increased signalling and cellular proliferation.

Nature Genetics. 2012 May 13;44(6):703-13.

Mutations in IRX5 impair craniofacial development and germ cell migration
via SDF1.

Bonnard C, Strobl AC, Shboul M, Lee H, Merriman B, Nelson SF,Ababneh OH, Uz E, Guran T, Kayserili H, Hamamy H, Reversade B.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Using homozygosity mapping and locus resequencing, we found that alterations in the homeodomain of the IRX5 transcription factor cause a recessive congenital disorder affecting face, brain, blood, heart,bone and gonad development. We found through in vivo modeling in Xenopus laevis embryos that Irx5 modulates the migration of progenitor cell populations in branchial arches and gonads by repressing Sdf1. We further found that transcriptional control by Irx5 is modulated by direct protein-protein interaction with two GATA zinc-finger proteins, GATA3 and TRPS1; disruptions of these proteins also cause craniofacial dysmorphisms. Our findings suggest that IRX proteins integrate combinatorial transcriptional inputs to regulate key signaling molecules involved in the ontogeny of multiple organs during embryogenesis and homeostasis.



Nature Genetics. 2011 Sep;41(9):1016-21.  

Goudie DRD'Alessandro MMerriman BLee HSzeverényi IAvery SO'Connor BDNelson SFCoats SEStewart A,Christie LPichert GFriedel JHayes IBurrows NWhittaker SGerdes AMBroesby-Olsen SFerguson-Smith MA,Verma CLunny DPReversade BLane EB.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Multiple self-healing squamous epithelioma (MSSE), also known as Ferguson-Smith disease (FSD), is an autosomal-dominant skin cancer condition characterized by multiple squamous-carcinoma-like locally invasive skin tumors that grow rapidly for a few weeks before spontaneously regressing, leaving scars. High-throughput genomic sequencing of a conservative estimate (24.2 Mb) of the disease locus on chromosome 9 using exon array capture identified independent mutations in TGFBR1 in three unrelated families. Subsequent dideoxy sequencing of TGFBR1 identified 11 distinct monoallelic mutations in 18 affected families, firmly establishing TGFBR1 as the causative gene. The nature of the sequence variants, which include mutations in the extracellular ligand-binding domain and a series of truncating mutations in the kinase domain, indicates a clear genotype-phenotype correlation between loss-of-function TGFBR1 mutations and MSSE. This distinguishes MSSE from the Marfan syndrome-related disorders in which missense mutations in TGFBR1 lead to developmental defects with vascular involvement but no reported predisposition to cancer.



Am J Hum Genet. 2010 Dec;10;87(6):768-78.

Tian J, Ling L, Shboul M, Lee H, O'Connor B, Merriman B, Nelson SF, Cool S, Ababneh OH, Al-Hadidy A, Masri A, Hamamy H, Reversade B.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

We delineated a syndromic recessive preaxial brachydactyly with partial duplication of proximal phalanges to 16.8 Mb over 4 chromosomes. High-throughput sequencing of all 177 candidate genes detected a truncating frameshift mutation in the gene CHSY1 encoding a chondroitin synthase with a Fringe domain. CHSY1 was secreted from patients' fibroblasts and was required for synthesis of chondroitin sulfate moieties. Noticeably, its absence triggered massive production of JAG1 and subsequent NOTCH activation, which could only be reversed with a wild-type but not a Fringe catalytically dead CHSY1 construct. In vitro, depletion of CHSY1 by RNAi knockdown resulted in enhanced osteogenesis in fetal osteoblasts and remarkable upregulation of JAG2 in glioblastoma cells. In vivo, chsy1 knockdown in zebrafish embryos partially phenocopied the human disorder; it increased NOTCH output and impaired skeletal, pectoral-fin, and retinal development. We conclude that CHSY1 is a secreted FRINGE enzyme required for adjustment of NOTCH signaling throughout human and fish embryogenesis and particularly during limb patterning.



Nature Genetics. 2009 Sep;41(9):1016-21.  

Mutations in PYCR1 cause cutis laxa with progeroid features.

Reversade B, Escande-Beillard N, Dimopoulou V, Fischer B, Chng S C, Li Y, Shboul M, et al.

Institute of Medical Biology, A*STAR, Singapore, Singapore.

Autosomal recessive cutis laxa (ARCL) describes a group of syndromal disorders that are often associated with a progeroid appearance, lax and wrinkled skin, osteopenia and mental retardation. Homozygosity mapping in several kindreds with ARCL identified a candidate region on chromosome 17q25. By high-throughput sequencing of the entire candidate region, we detected disease-causing mutations in the gene PYCR1. We found that the gene product, an enzyme involved in proline metabolism, localizes to mitochondria. Altered mitochondrial morphology, membrane potential and increased apoptosis rate upon oxidative stress were evident in fibroblasts from affected individuals. Knockdown of the orthologous genes in Xenopus and zebrafish led to epidermal hypoplasia and blistering that was accompanied by a massive increase of apoptosis. Our findings link mutations in PYCR1 to altered mitochondrial function and progeroid changes in connective tissues.



EMBO J. 2007 Jun 20;26(12):2955-65. 

The opposing homeobox genes Goosecoid and Vent1/2 self-regulate Xenopus patterning.

Sander V, Reversade B, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California-Los Angeles, 675 Charles Young Drive South, Los Angeles, CA 90095, USA.

We present a loss-of-function study using antisense morpholino (MO) reagents for the organizer-specific gene Goosecoid (Gsc) and the ventral genes Vent1 and Vent2. Unlike in the mouse Gsc is required in Xenopus for mesodermal patterning during gastrulation, causing phenotypes ranging from reduction of head structures-including cyclopia and holoprosencephaly-to expansion of ventral tissues in MO-injected embryos. The overexpression effects of Gsc mRNA require the expression of the BMP antagonist Chordin, a downstream target of Gsc. Combined Vent1 and Vent2 MOs strongly dorsalized the embryo. Unexpectedly, simultaneous depletion of all three genes led to a rescue of almost normal development in a variety of embryological assays. Thus, the phenotypic effects of depleting Gsc or Vent1/2 are caused by the transcriptional upregulation of their opposing counterparts. A principal function of Gsc and Vent1/2 homeobox genes might be to mediate a self-adjusting mechanism that restores the basic body plan when deviations from the norm occur, rather than generating individual cell types. The results may shed light on the molecular mechanisms of genetic redundancy.




Cell. 2006 Jan 13;124(1):147-59.

Embryonic dorsal-ventral signaling: secreted frizzled-related proteins as inhibitors of tolloid proteinases.

Lee HX, Ambrosio AL, Reversade B, De Robertis EM.

Howard Hughes Medical Institute, Department of Biological Chemistry, University of California, Los Angeles, CA 90095, USA.

Here we report an unexpected role for the secreted Frizzled-related protein (sFRP) Sizzled/Ogon as an inhibitor of the extracellular proteolytic reaction that controls BMP signaling during Xenopus gastrulation. Microinjection experiments suggest that the Frizzled domain of Sizzled regulates the activity of Xolloid-related (Xlr), a metalloproteinase that degrades Chordin, through the following molecular pathway: Szl -| Xlr -| Chd -| BMP --> P-Smad1 --> Szl. In biochemical assays, the Xlr proteinase has similar affinities for its endogenous substrate Chordin and for its competitive inhibitor Sizzled, which is resistant to enzyme digestion. Extracellular levels of Sizzled and Chordin in the gastrula embryo and enzyme reaction constants were all in the 10(-8) M range, consistent with a physiological role in the regulation of dorsal-ventral patterning. Sizzled is also a natural inhibitor of BMP1, a Tolloid metalloproteinase of medical interest. Furthermore, mouse sFRP2 inhibited Xlr, suggesting a wider role for this molecular mechanism.
Commented in:



Cell. 2005 Dec 16;123(6):1147-60.

Regulation of ADMP and BMP2/4/7 at opposite embryonic  poles generates a self-regulating morphogenetic field.

Reversade B, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA.

Embryos have the ability to self-regulate and regenerate normal structures after being sectioned in half. How is such a morphogenetic field established? We discovered that quadruple knockdown of ADMP and BMP2/4/7 in Xenopus embryos eliminates self-regulation, causing ubiquitous neural induction throughout the ectoderm. ADMP transcription in the Spemann organizer is activated at low BMP levels. When ventral BMP2/4/7 signals are depleted, Admp expression increases, allowing for self-regulation. ADMP has BMP-like activity and signals via the ALK-2 receptor. It is unable to signal dorsally because of inhibition by Chordin. The ventral BMP antagonists Sizzled and Bambi further refine the pattern. By transplanting dorsal or ventral wild-type grafts into ADMP/BMP2/4/7-depleted hosts, we demonstrate that both poles serve as signaling centers that can induce histotypic differentiation over considerable distances. We conclude that dorsal and ventral BMP signals and their extracellular antagonists expressed under opposing transcriptional regulation provide a molecular mechanism for embryonic self-regulation.  
Commented in:  
 Cell. 2005 Dec 16;123(6):982-4.

Bmp signaling: turning a half into a whole.

Kimelman D, Pyati UJ.

Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195, USA.

In a famous experiment over a century ago, Hans Spemann demonstrated that amphibians have a remarkable ability to compensate for perturbations to the embryo. In this issue of Cell, Reversade and De Robertis (2005) uncover the basis of this phenomenon. They demonstrate that interactions between bone morphogenetic proteins (Bmps) and their inhibitors on both the dorsal and ventral sides of the early Xenopus embryo are involved in creating the body plan.
Commented in:
 Development. 2005 Aug;132(15):3381-92.

Depletion of Bmp2, Bmp4, Bmp7 and Spemann organizer signals induces massive brain formation in Xenopus embryos.

Reversade B, Kuroda H, Lee H, Mays A, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, CA 90095-1662, USA.

To address the patterning function of the Bmp2, Bmp4 and Bmp7 growth factors, we designed antisense morpholino oligomers (MO) that block their activity in Xenopus laevis. Bmp4 knockdown was sufficient to rescue the ventralizing effects caused by loss of Chordin activity. Double Bmp4 and Bmp7 knockdown inhibited tail development. Triple Bmp2/Bmp4/Bmp7 depletion further compromised trunk development but did not eliminate dorsoventral patterning. Unexpectedly, we found that blocking Spemann organizer formation by UV treatment or beta-Catenin depletion caused BMP inhibition to have much more potent effects, abolishing all ventral development and resulting in embryos having radial central nervous system (CNS) structures. Surprisingly, dorsal signaling molecules such as Chordin, Noggin, Xnr6 and Cerberus were not re-expressed in these embryos. We conclude that BMP inhibition is sufficient for neural induction in vivo, and that in the absence of ventral BMPs, Spemann organizer signals are not required for brain formation.


Genes Dev.
2005 May 1;19(9):1022-7.

Default neural induction: neuralization of dissociated Xenopus cells is mediated by Ras/MAPK activation.

Kuroda H, Fuentealba L, Ikeda A, Reversade B, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, CA 90095-1662, USA.

Xenopus embryonic ectodermal cells dissociated for three or more hours differentiate into neural tissue instead of adopting their normal epidermal fate. This default type of neural induction occurs in the absence of Spemann's organizer signals and is thought to be caused by the dilution of endogenous BMPs into the culture medium. Unexpectedly, we observed that BMP ligands continue to signal in dissociated cells. Instead, cell dissociation induces a sustained activation of the Ras/MAPK pathway, which causes the phosphorylation of Smad1 at sites that inhibit the activity of this transcription factor. It is this activation of Ras/MAPK that is required for neuralization in dissociated ectoderm.

Development. 2005 May;132(10):2489-99.

Sirenomelia in Bmp7 and Tsg compound mutant mice: requirement for Bmp signaling in the development of ventral posterior mesoderm.

Zakin L, Reversade B, Kuroda H, Lyons KM, De Robertis EM.

Howard Hughes Medical Institute, and Department of Biological Chemistry, University of California, Los Angeles, CA 90095-1662, USA.

Sirenomelia or mermaid-like phenotype is one of the principal human congenital malformations that can be traced back to the stage of gastrulation. Sirenomelia is characterized by the fusion of the two hindlimbs into a single one. In the mouse, sirens have been observed in crosses between specific strains and as the consequence of mutations that increase retinoic acid levels. We report that the loss of bone morphogenetic protein 7 (Bmp7) in combination with a half dose or complete loss of twisted gastrulation (Tsg) causes sirenomelia in the mouse. Tsg is a Bmp- and chordin-binding protein that has multiple effects on Bmp metabolism in the extracellular space; Bmp7 is one of many Bmps and is shown here to bind to Tsg. In Xenopus, co-injection of Tsg and Bmp7 morpholino oligonucleotides (MO) has a synergistic effect, greatly inhibiting formation of ventral mesoderm and ventral fin tissue. In the mouse, molecular marker studies indicate that the sirenomelia phenotype is associated with a defect in the formation of ventroposterior mesoderm. These experiments demonstrate that dorsoventral patterning of the mouse posterior mesoderm is regulated by Bmp signaling, as is the case in other vertebrates. Sirens result from a fusion of the hindlimb buds caused by a defect in the formation of ventral mesoderm.

 Development. 2003 Sep;130(17):4047-56.

The pro-BMP activity of Twisted gastrulation is independent of BMP binding.

Oelgeschlager M, Reversade B, Larrain J, Little S, Mullins MC, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California-Los Angeles, Los Angeles, CA 90095-1662, USA.

The determination of the vertebrate dorsoventral body axis is regulated in the extracellular space by a system of interacting secreted molecules consisting of BMP, Chordin, Tolloid and Twisted Gastrulation (Tsg). Tsg is a BMP-binding protein that forms ternary complexes with BMP and Chordin. We investigated the function of Tsg in embryonic patterning by generating point mutations in its two conserved cysteine-rich domains. Surprisingly, Tsg proteins with mutations in the N-terminal domain were unable to bind BMP, yet ventralized the embryo very effectively, indicating strong pro-BMP activity. This hyperventralizing Tsg activity required an intact C-terminal domain and could block the anti-BMP activity of isolated BMP-binding modules of Chordin (CRs) in embryonic assays. This activity was specific for CR-containing proteins as it did not affect the dorsalizing effects of Noggin or dominant-negative BMP receptor. The ventralizing effects of the xTsg mutants were stronger than the effect of Chordin loss-of-function in Xenopus or zebrafish. The results suggest that xTsg interacts with additional CR-containing proteins that regulate dorsoventral development in embryos.


Developmental Cell.
2003 Feb;4(2):219-30.

Chordin is required for the Spemann organizer transplantation phenomenon in Xenopus embryos.

Oelgeschlager M, Kuroda H, Reversade B, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA.

We analyzed the Chordin requirement in Xenopus development. Targeting of both chordin Xenopus laevis pseudoalleles with morpholino antisense oligomers (Chd-MO) markedly decreased Chordin production. Embryos developed with moderately reduced dorsoanterior structures and expanded ventroposterior tissues, phenocopying the zebrafish chordino mutant. A strong requirement for Chordin in dorsal development was revealed by experimental manipulations. First, dorsalization by lithium chloride treatment was completely blocked by Chd-MO. Second, Chd-MO inhibited elongation and muscle differentiation in Activin-treated animal caps. Third, Chd-MO completely blocked the induction of the central nervous system (CNS), somites, and notochord by organizer tissue transplanted to the ventral side of host embryos. Unexpectedly, transplantations into the dorsal side revealed a cell-autonomous requirement of Chordin for neural plate differentiation.



 Nat Cell Bio.  2002 Aug;4(8):599-604.

Connective-tissue growth factor (CTGF) modulates cell signalling by BMP and TGF-beta.

Abreu JG, Ketpura NI, Reversade B, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Riverside, 9095-1662, USA.

Connective-tissue growth factor (CTGF) is a secreted protein implicated in multiple cellular events including angiogenesis, skeletogenesis and wound healing. It is a member of the CCN family of secreted proteins, named after CTGF, cysteine-rich 61 (CYR61), and nephroblastoma overexpressed (NOV) proteins. The molecular mechanism by which CTGF or other CCN proteins regulate cell signalling is not known. CTGF contains a cysteine-rich domain (CR) similar to those found in chordin and other secreted proteins, which in some cases have been reported to function as bone morphogenetic protein (BMP) and TGF-beta binding domains. Here we show that CTGF directly binds BMP4 and TGF-beta 1 through its CR domain. CTGF can antagonize BMP4 activity by preventing its binding to BMP receptors and has the opposite effect, enhancement of receptor binding, on TGF-beta 1. These results show that CTGF inhibits BMP and activates TGF-beta signals by direct binding in the extracellular space.

 Development. 2001 Nov;128(22):4439-47.

Proteolytic cleavage of Chordin as a switch for the dual activities of Twisted gastrulation in BMP signaling.

Larrain J, Oelgeschlager M, Ketpura NI, Reversade B, Zakin L, De Robertis EM.

Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, CA 90095-1662, USA.

Dorsoventral patterning is regulated by a system of interacting secreted proteins involving BMP, Chordin, Xolloid and Twisted gastrulation (Tsg). We have analyzed the molecular mechanism by which Tsg regulates BMP signaling. Overexpression of Tsg mRNA in Xenopus embryos has ventralizing effects similar to Xolloid, a metalloprotease that cleaves Chordin. In embryos dorsalized by LiCl treatment, microinjection of Xolloid or Tsg mRNA restores the formation of trunk-tail structures, indicating an increase in BMP signaling. Microinjection of Tsg mRNA leads to the degradation of endogenous Chordin fragments generated by Xolloid. The ventralizing activities of Tsg require an endogenous Xolloid-like activity, as they can be blocked by a dominant-negative Xolloid mutant. A BMP-receptor binding assay revealed that Tsg has two distinct and sequential activities on BMP signaling. First, Tsg makes Chordin a better BMP antagonist by forming a ternary complex that prevents binding of BMP to its cognate receptor. Second, after cleavage of Chordin by Xolloid, Tsg competes the residual anti-BMP activity of Chordin fragments and facilitates their degradation. This molecular pathway, in which Xolloid switches the activity of Tsg from a BMP antagonist to a pro-BMP signal once all endogenous full-length Chordin is degraded, may help explain how sharp borders between embryonic territories are generated.

 PNAS. 2000 Dec 19;97(26):14388-93.

Gene expression profiles in normal and Otx2-/- early gastrulating mouse embryos.

Zakin L, Reversade B, Virlon B, Rusniok C, Glaser P, Elalouf JM, Brulet P.

Unite d'Embyologie Moleculaire, Unite de Recherche Associee 1947, Centre National de la Recherche Scientifique, and Laboratoire de Genomique des Microorganismes Pathogenes, Institut Pasteur, 25 Rue du Docteur Roux, 75724, Paris Cedex 15, France.

The mouse Otx2 gene is a homeobox transcription factor required as early as gastrulation for the proper development of the head. We compared gene expression profiles in wild-type and Otx2(-/-) 6.5 days postcoitum embryos by using a serial analysis of gene expression assay adapted to microdissected structures. Among a broader list, the study of six genes found to be differentially expressed allows defining a role for Otx2 in the orchestration of cell movements leading to the adequate organization of the embryo before gastrulation.