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Archosaurian beta-keratins and the origin of feathers



From: Ben Creisler
bcreisler@gmail.com


A new online paper:

Matthew J. Greenwold & Roger H. Sawyer (2013)
Molecular Evolution and Expression of Archosaurian β-Keratins:
Diversification and Expansion of Archosaurian β-Keratins and the
Origin of Feather β-Keratins.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution (advance online publication)
DOI: 10.1002/jez.b.22514
http://onlinelibrary.wiley.com/doi/10.1002/jez.b.22514/abstract

The Archosauria consist of two living groups, crocodilians, and birds.
Here we compare the structure, expression, and phylogeny of the beta
(β)-keratins in two crocodilian genomes and two avian genomes to gain
a better understanding of the evolutionary origin of the feather
β-keratins. Unlike squamates such as the green anole with 40
β-keratins in its genome, the chicken and zebra finch genomes have
over 100 β-keratin genes in their genomes, while the American
alligator has 20 β-keratin genes, and the saltwater crocodile has 21
β-keratin genes. The crocodilian β-keratins are similar to those of
birds and these structural proteins have a central filament domain and
N- and C-termini, which contribute to the matrix material between the
twisted β-sheets, which form the 2–3 nm filament. Overall the
expression of alligator β-keratin genes in the integument increases
during development. Phylogenetic analysis demonstrates that a
crocodilian β-keratin clade forms a monophyletic group with the avian
scale and feather β-keratins, suggesting that avian scale and feather
β-keratins along with a subset of crocodilian β-keratins evolved from
a common ancestral gene/s. Overall, our analyses support the view that
the epidermal appendages of basal archosaurs used a diverse array of
β-keratins, which evolved into crocodilian and avian specific clades.
In birds, the scale and feather subfamilies appear to have evolved
independently in the avian lineage from a subset of archosaurian claw
β-keratins. The expansion of the avian specific feather β-keratin
genes accompanied the diversification of birds and the evolution of
feathers.