Investigating the Homology of Feathers and Scales using High-throughput Genomics

Meeting Abstract

123.8  Tuesday, Jan. 7 15:00  Investigating the Homology of Feathers and Scales using High-throughput Genomics MUSSER, JM*; WAGNER, GP; PRUM, RO; Yale University; Yale University; Yale University

Feathers are an early avian innovation that facilitated the evolution of flight, greater thermoregulation, and other facets of avian life. However, the molecular basis for the evolution of feathers is poorly understood, and the homology of feathers to other skin derivatives, especially scales, remains contentious. Here, we investigate feather novelty and homology by comparing transcriptomes from different stages of developing feathers, different scales, and claws. Transcriptomes were assayed at different developmental stages and in multiple species, including two distantly related birds, Chicken (Gallus gallus) and Emu (Dromaius novaehollandiae), and American Alligator (Alligator mississipiensis). We found that in early development feathers and scutate scales, an asymmetric avian scale, share similar gene expression compared to other scales and claws. However, as development progresses gene expression in feathers becomes distinct, suggesting later stages of feather development are novel. This close relationship between feathers and scutate scales in early development, and subsequent unique expression in later feather development is supported independently by transcriptomes from both epidermis and dermis, as well as across multiple avian species. Further, to complement our transcriptome data, we used immunohistochemistry to compare spatial patterns of expression of the transcription cofactor &beta-catenin, the earliest known molecule expressed in feathers. We found that &beta-catenin is expressed in similar spatial patterns in early developing feathers and scutate scales. These complementary results suggest feathers share similar molecular pathways to scutate scales in early development, and that feathers may have evolved via elaboration of an asymmetric scutate type scale.

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