GSE67875
A molecular shift in limb identity underlies the convergent evolution and development of feathered feet
The genetic and developmental mechanisms that control the decision between scale and feather growth – two profoundly different epidermal appendages, and an important developmental shift in the evolution of birds from their dinosaurian ancestors – remain poorly understood. Domestic pigeons display dramatic variation in foot epidermal appendages within a single species, and classical studies suggest that a small number of genes control much of this variation; thus pigeons provide a tractable model to understand skin appendage specification and variation. Here we show that feathered feet in pigeons are the consequence of a partial transformation of limb-type identity mediated by cis-regulatory changes in the hindlimb-specific transcription factor Pitx1 and forelimb-specific transcription factor Tbx5. We also demonstrate that ectopic hindlimb expression of Tbx5 is associated with the development of foot feathers in domestic chickens, suggesting that similar developmental mechanisms underlie phenotypic convergence in avian lineages that diverged over 100 MYA. These results show how qualitative and quantitative changes in expression of regional patterning genes can generate localized changes in organ fate and morphology, and provide a viable molecular mechanism for the evolution of hindlimb scale and feather distribution in dromaeosaurs. Overall design: Examination of H3K27ac status in embryonic limb buds from two domestic pigeon breeds, racing homer and Indian fantail