The ciliary EVC/EVC2 complex interacts with smo and controls hedgehog pathway activity in chondrocytes by regulating Sufu/Gli3 dissociation and Gli3 trafficking in primary cilia

Hedgehog (Hh) signaling is involved in patterning and morphogenesis of most organs in the developing mammalian embryo. Despite many advances in understanding core components of the pathway, little is known about how the activity of the Hh pathway is adjusted in organ- and tissue-specific developmental processes. Mutations in EVC or EVC2 disrupt Hh signaling in tooth and bone development. Using mouse models, we show here that Evc and Evc2 are mutually required for localizing to primary cilia and also for maintaining their normal protein levels. Consistent with Evc and Evc2 functioning as a complex, the skeletal phenotypes in either single or double homozygous mutant mice are virtually indistinguishable. Smo translocation to the cilium was normal in Evc2-deficient chondrocytes following Hh activation with the Smo-agonist SAG. However, Gli3 recruitment to cilia tips was reduced and Sufu/Gli3 dissociation was impaired. Interestingly, we found Smo to co-precipitate with Evc/Evc2, indicating that in some cells Hh signaling requires direct interaction of Smo with the Evc/Evc2 complex. Expression of a dominantly acting Evc2 mutation previously identified in Weyer's acrodental dysostosis (Evc2d43) caused mislocalization of Evc/Evc2d43 within the cilium and also reproduced the Gli3-related molecular defects observed in Evc2 -/- chondrocytes. Moreover, Evc silencing in Sufu -/- cells attenuated the output of the Hh pathway, suggesting that Evc/Evc2 also promote Hh signaling in the absence of Sufu. Together our data reveal that the Hh pathway involves Evc/Evc2-dependent modulations that are necessary for normal endochondral bone formation. © The Author 2012. Published by Oxford University Press. All rights reserved

Widening the mutation spectrum of EVC and EVC2: ectopic expression of Weyer variants in NIH 3T3 fibroblasts disrupts Hedgehog signaling

Autosomal recessive Ellis-van Creveld syndrome and autosomal dominant Weyer acrodental dysostosis are allelic conditions caused by mutations in EVC or EVC2. We performed a mutation screening study in 36 EvC cases and 3 cases of Weyer acrodental dysostosis, and identified pathogenic changes either in EVC or in EVC2 in all cases. We detected 40 independent EVC/EVC2 mutations of which 29 were novel changes in Ellis-van Creveld cases and 2 were novel mutations identified in Weyer pedigrees. Of interest one EvC patient had a T>G nucleotide substitution in intron 7 of EVC (c.940-150T>G), which creates a new donor splice site and results in the inclusion of a new exon. The T>G substitution is at nucleotide +5 of the novel 5' splice site. The three Weyer mutations occurred in the final exon of EVC2 (exon 22), suggesting that specific residues encoded by this exon are a key part of the protein. Using murine versions of EVC2 exon 22 mutations we demonstrate that the expression of a Weyer variant, but not the expression of a truncated protein that mimics an Ellis-van Creveld syndrome mutation, impairs Hedgehog signal transduction in NIH 3T3 cells in keeping with its dominant effect

De novo mutations in PLXND1 and REV3L cause Mobius syndrome

Mo ̈bius syndrome (MBS) is a neurological disorder that is characterized by paralysis of thefacial nerves and variable other congenital anomalies. The aetiology of this syndrome hasbeen enigmatic since the initial descriptions by von Graefe in 1880 and by Mo ̈bius in 1888,and it has been debated for decades whether MBS has a genetic or a non-genetic aetiology.Here, we reportde novomutations affecting two genes,PLXND1andREV3Lin MBS patients.PLXND1 and REV3L represent totally unrelated pathways involved in hindbrain development:neural migration and DNA translesion synthesis, essential for the replication of endogenouslydamaged DNA, respectively. Interestingly, analysis ofPlxnd1andRev3lmutant mice showsthat disruption of these separate pathways converge at the facial branchiomotor nucleus,affecting either motoneuron migration or proliferation. The finding thatPLXND1andREV3Lmutations are responsible for a proportion of MBS patients suggests thatde novomutations inother genes might account for other MBS patient

Complex genetics of radial ray deficiencies:screening of a cohort of 54 patients

<p>Purpose: Radial ray deficiencies are characterized by unilateral or bilateral absence of varying portions of the radius and thumb. Both isolated and syndromic forms have been described, and although for some of the syndromes the causal gene has been identified, many patients remain without a genetic diagnosis.</p><p>Methods: In this study, a cohort of 54 patients with radial ray deficiencies was screened for genomic aberrations by molecular karyo-typing.</p><p>Results: In 8 of 54 cases, an aberration was detected. Two unrelated patients inherited a 1q21.1 microduplication from a healthy parent, whereas in a third patient, a 16p13.11 microduplication was identified. Two other interesting microdeletions were detected: a 10q24.3 deletion at the split hand-foot malformation (SHFM3) locus and a 7p22.1 deletion including the RAC1 gene.</p><p>Conclusion: The finding of these microduplications may just be coincidental or, alternatively, they may illustrate the broad phenotypic spectrum of these microduplications. Duplications in the 10q24.3 region result in split hand-foot malformations, and our observation indicates that deletions may cause radial ray defects. Finally, a candidate gene for radial ray deficiencies was detected in the 7p22.1 deletion. RAC1 plays an important role in the canonical Wnt pathway and conditional RAC1 knockout mice exhibit truncated-limb defects. Genet Med 2013:15(3):195-202</p>