Location: Avian Disease and Oncology Laboratory
Title: The cellular and molecular etiology of the craniofacial defects in the avian ciliopathic mutant talpid2 Authors
|Chang, Ching-Fang -|
|Schock, Elizabeth -|
|O'Hare, Elizabeth -|
|Dodgson, Jerry -|
|Muir, William -|
|Edelmann, Richard -|
|Delany, Mary -|
|Brugmann, Samantha -|
Submitted to: Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 28, 2014
Publication Date: N/A
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 line exhibiting a myriad of congenital malformations including polydactyly and facial clefting. Although phenotypically similar to its sister strain 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, both in the axoneme and basal bodies, were disrupted in talpid2 mutants. Furthermore, disruptions in Hedgehog signaling occur in talpid2 embryos and 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 Gli3A levels were significantly altered in the nucleus. Through additional fine-mapping and whole genome sequencing, we determined the talpid2 phenotype was linked to a 1.4 Mb region on GGA1q that contained the ciliary protein C2CD3. We cloned the avian ortholog of C2CD3 and found its expression was localized to the developing limbs and facial prominences. The likely causal allele for talpid2 is a 19 bp deletion in C2CD3 that produces a premature stop codon and thus a truncated protein, although we cannot eliminate a linked missense mutation (Ala782Pro) or a combination of the two as being causative. Furthermore, we found that the C2CD3 protein was localized proximal to the ciliary axoneme, suggesting a function in the ciliary transition zone or transition fibers. Together, these data provide insight into the cellular, molecular and genetic etiology of the talpid2 phenotype. Our data suggest that, whereas talpid2 and talpid3 affect a common ciliogenesis pathway, they are caused by mutations in different ciliary proteins and lead to subtle differences in phenotype.