Genomic Organization, Transcriptomic Analysis, and Functional Characterization of Avian α- and β-Keratins in Diverse Feather Forms

Feathers are hallmark avian integument appendages, although they were also present on theropods. They are composed of flexible corneous materials made of alpha- and beta-keratins, but their genomic organization and their functional roles in feathers have not been well studied. First, we made an exhaustive search of alpha- and beta-keratin genes in the new chicken genome assembly (Galgal4). Then, using transcriptomic analysis, we studied alpha- and beta-keratin gene expression patterns in five types of feather epidermis. The expression patterns of beta-keratin genes were different in different feather types, whereas those of alpha-keratin genes were less variable. In addition, we obtained extensive alpha- and beta-keratin mRNA in situ hybridization data, showing that alpha-keratins and beta-keratins are preferentially expressed in different parts of the feather components. Together, our data suggest that feather morphological and structural diversity can largely be attributed to differential combinations of alpha- and beta-keratin genes in different intrafeather regions and/or feather types from different body parts. The expression profiles provide new insights into the evolutionary origin and diversification of feathers. Finally, functional analysis using mutant chicken keratin forms based on those found in the human alpha-keratin mutation database led to abnormal phenotypes. This demonstrates that the chicken can be a convenient model for studying the molecular biology of human