Location: Avian Disease and Oncology ResearchTitle: The cellular and molecular etiology of the craniofacial defects in the avian ciliopathic mutant talpid2) Author
Submitted to: Development
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/28/2014
Publication Date: 7/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59602
Citation: Chang, C., Schock, E.N., O'Hare, E.A., Dodgson, J.B., Cheng, H.H., Muir, W.M., Edelmann, R.E., Delany, M.E., Brugmann, S.A. 2014. The cellular and molecular etiology of the craniofacial defects in the avian ciliopathic mutant talpid2. Development. 141:3003-3012. Available: http://dev.biologists.org/content/141/15/3003.long. Interpretive Summary: Chicken has been a model species for developmental biology as defects can be readily monitored in embryos. In this submission, using a genomics and molecular biology, the causative gene and likely mutation for talpid 2, characterized by polydactyly, was identified. Specifically, the talpid 2 allele has a deletion that would result in a truncated and probably nonfunctional protein. This study shows the growing power obtained from having the chicken genome sequence and provides the means for a molecular genetic test to screen carriers in commercial populations, if so desired.
Technical Abstract: talpid2 is an avian autosomal recessive mutant with a myriad of congenital malformations, including polydactyly and facial clefting. Although phenotypically similar to talpid3, talpid2 has a distinct facial phenotype and an unknown cellular, molecular and genetic basis. We set out to determine the etiology of the craniofacial phenotype of this mutant. We confirmed that primary cilia were disrupted in talpid2 mutants. Molecularly, we found disruptions in Hedgehog signaling. Post-translational processing of GLI2 and GLI3 was aberrant in the developing facial prominences. Although both GLI2 and GLI3 processing were disrupted in talpid2 mutants, only GLI3 activator levels were significantly altered in the nucleus. Through additional fine mapping and whole-genome sequencing, we determined that the talpid2 phenotype was linked to a 1.4 Mb region on GGA1q that contained the gene encoding the ciliary protein C2CD3. We cloned the avian ortholog of C2CD3 and found its expression was ubiquitous, but most robust in the developing limbs and facial prominences. Furthermore, we found that C2CD3 is localized proximal to the ciliary axoneme and is important for docking the mother centriole to the ciliary vesicle and cell membrane. Finally, we identified a 19 bp deletion in talpid2 C2CD3 that produces a premature stop codon, and thus a truncated protein, as the likely causal allele for the phenotype. Together, these data provide insight into the cellular, molecular and genetic etiology of the talpid2 phenotype. Our data suggest that, although the talpid2 and talpid3 mutations affect a common ciliogenesis pathway, they are caused by mutations in different ciliary proteins that result in differences in craniofacial phenotype.