Comparative Genomics Identifies Epidermal Proteins Associated with the Evolution of the Turtle Shell

Comparative Genomics Identifies Epidermal Proteins Associated with the Evolution of the Turtle Shell

Abstract

The evolution of reptiles, birds, and mammals was associated with the origin of unique integumentary structures. Studies on lizards, chicken, and humans have suggested that the evolution of major structural proteins of the outermost, cornified layers of the epidermis was driven by the diversification of a gene cluster called Epidermal Differentiation Complex (EDC). Turtles have evolved unique defense mechanisms that depend on mechanically resilient modifications of the epidermis. To investigate whether the evolution of the integument in these reptiles was associated with specific adaptations of the sequences and expression patterns of EDC-related genes, we utilized newly available genome sequences to determine the epidermal differentiation gene complement of turtles. The EDC of the western painted turtle (Chrysemys picta bellii) comprises more than 100 genes, including at least 48 genes that encode proteins referred to as beta-keratins or corneous beta-proteins. Several EDC proteins have evolved cysteine/proline contents beyond 50% of total amino acid residues. Comparative genomics suggests that distinct subfamilies of EDC genes have been expanded and partly translocated to loci outside of the EDC in turtles. Gene expression analysis in the European pond turtle (Emys orbicularis) showed that EDC genes are differentially expressed in the skin of the various body sites and that a subset of beta-keratin genes within the EDC as well as those located outside of the EDC are expressed predominantly in the shell. Our findings give strong support to the hypothesis that the evolutionary innovation of the turtle shell involved specific molecular adaptations of epidermal differentiation.

Grafik Top
Authors
  • Schmidt, Heiko A.
  • Holthaus, Karin Birgit
  • Strasser, Bettina
  • Sipos, Wolfgang
  • Mlitz, Veronika
  • Sukseree, Supawadee
  • Weissenbacher, Anton
  • Tschalter, Erwin
  • Alibardi, Lorenzo
  • Eckhart, Leopold
Grafik Top
Shortfacts
Category
Journal Paper
Divisions
Bioinformatics and Computational Biology
Journal or Publication Title
Molecular Biology and Evolution
ISSN
0737-4038
Publisher
Oxford Journals - Molecular Biology and Evolution
Place of Publication
OXFORD OX2 6DP, ENGLAND
Page Range
pp. 726-737
Volume
33/3
Date
April 2016
Export
Grafik Top