From Science Daily:
In the study, the working group led by Leopold Eckhart investigated the genes responsible for the skin layers of the shell of the European terrapin and a North American species of turtle, in order to compare them with the genes of human skin.
The study findings suggest that a hard shell was formed as the result of mutations in a group of genes known as the Epidermal Differentiation Complex (EDC). Comparisons of genome data from various reptiles suggest that the EDC mutations responsible occurred when turtles split off from other reptiles around 250 million years ago.
What is remarkable is that the basic organisation of the EDC genes is similar in humans and turtles. This leads to the conclusion that the prototypical EDC genes developed in a common ancestor, who lived 310 million years ago and was similar to modern reptiles.
In the case of turtles, these genes developed so as to form proteins that bring about a significant hardening in the outer layer of skin, intensified cross-linking and hence the formation of a shell. In humans, the EDC genes protect the skin from the penetration of microbes and allergens. More.
Has anyone documented this in life forms more closely related to humans than turtles are? On the face of it, the similarity seems odd otherwise.
See also: Humans and birds evolved different, “sing” alike? Researchers: They use exact same physical mechanism to make their vocal cords move and thus produce sound.
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Here’s the 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. Open access – Karin Brigit Holthaus, Bettina Strasser, Wolfgang Sipos, Heiko A. Schmidt, Veronika Mlitz, Supawadee Sukseree, Anton Weissenbacher, Erwin Tschachler, Lorenzo Alibardi, Leopold Eckhart. Comparative genomics identifies epidermal proteins associated with the evolution of the turtle shell. Molecular Biology and Evolution, 2015; msv265 DOI: 10.1093/molbev/msv265