1426 Deletion of hoxc13 in frogs reveals key steps in the molecular evolution of cornified skin appendages

The evolution of the skin barrier and appendages were major steps in terrestrial vertebrates. Hair keratins are main components mammalian hair, but homologs these proteins also expressed claws reptiles, suggesting that hair have evolved from claw a hairless ancestor. Here, we tested hypothesis keratin their association with evolutionarily conserved even amphibians. We determined proteomes soft epidermis cornified Xenopus frogs. Only contained keratins. Comparison promoter sequences suggested binding sites transcription factor Hoxc13, which is mutated patients ectodermal dysplasia 9 (ECTD9), genes humans mRNA situ hybridization revealed both hoxc13 homolog, krt34, epithelial compartment claws. To test function biallelic knockout was established diploid western clawed frog (Xenopus tropicalis) by use CRISPR/Cas9 subsequent breeding. deletion abolished expression abrogated development X. tropicalis. results this study suggest new model for hard appendages, according to Hoxc13-controlled specific basal tetrapods modifications ancestral program led mammals.