Using the avian mutant talpid² as a disease model for understanding the oral-facial phenotypes of oral-facial-digital syndrome

Oral-facial-digital syndrome (OFD) is a ciliopathy that is characterized byoral-facial abnormalities, including cleft lip and/or palate, broad nasal root, dental anomalies, micrognathia and glossal defects. In addition, these individuals have several other characteristic abnormalities that are typical of a ciliopathy, including polysyndactyly, polycystic kidneys and hypoplasia of the cerebellum. Recently, a subset of OFD cases in humans has been linked to mutations in the centriolar protein C2 Ca²⁺-dependent domain-containing 3 (C2CD3). Our previous work identifiedmutations inC2CD3 as the causal genetic lesion for the avian talpid² mutant. Based on this common genetic etiology, we re-examined the talpid² mutant biochemically and phenotypically for characteristics of OFD.We found that, as in OFD-affected individuals, protein-protein interactions between C2CD3 and oral-facial-digital syndrome 1 protein (OFD1) are reduced in talpid² cells. Furthermore, we found that all common phenotypes were conserved between OFDaffected individuals and avian talpid² mutants. In light of these findings, we utilized the talpid² model to examine the cellular basis for the oralfacial phenotypes present in OFD. Specifically, we examined the development and differentiation of cranial neural crest cells (CNCCs) when C2CD3-dependent ciliogenesis was impaired. Our studies suggest that although disruptions of C2CD3-dependent ciliogenesis do not affect CNCC specification or proliferation, CNCC migration and differentiation are disrupted. Loss of C2CD3-dependent ciliogenesis affects the dispersion and directional persistence of migratory CNCCs. Furthermore, loss of C2CD3-dependent ciliogenesis results in dysmorphic and enlarged CNCC-derived facial cartilages. Thus, these findings suggest that aberrantCNCCmigration and differentiation could contribute to the pathology of oral-facial defects in OFD.