title: 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.
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria Dipartimento di Scienze Biologiche, Geologiche ed Ambientali (BiGeA), University of Bologna, Bologna, Italy.
authors.forename: Karin Brigit
authors.initials: KB
authors.lastname: Holthaus
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
authors.forename: Bettina
authors.initials: B
authors.lastname: Strasser
authors.affiliation: Clinical Department for Farm Animals and Herd Management, University of Veterinary Medicine Vienna, Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sipos
authors.affiliation: Center for Integrative Bioinformatics Vienna (CIBIV), Max F. Perutz Laboratories, Medical University of Vienna, University of Vienna, Vienna, Austria.
authors.forename: Heiko A
authors.initials: HA
authors.lastname: Schmidt
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
authors.forename: Veronika
authors.initials: V
authors.lastname: Mlitz
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
authors.forename: Supawadee
authors.initials: S
authors.lastname: Sukseree
authors.affiliation: Vienna Zoo, Vienna, Austria.
authors.forename: Anton
authors.initials: A
authors.lastname: Weissenbacher
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
authors.forename: Erwin
authors.initials: E
authors.lastname: Tschachler
authors.affiliation: Dipartimento di Scienze Biologiche, Geologiche ed Ambientali (BiGeA), University of Bologna, Bologna, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Alibardi
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria leopold.eckhart@meduniwien.ac.at.
authors.forename: Leopold
authors.initials: L
authors.lastname: Eckhart
mesh_terms: D000595:Amino Acid Sequence; D060105:Animal Shells; D000818:Animals; D005075:Biological Evolution; D017124:Conserved Sequence; D004817:Epidermis / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D005786:Gene Expression Regulation; D016678:Genome; D023281:Genomics / Q000379:methods; D005810:Multigene Family; D010802:Phylogeny; D011506:Proteins / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D014178:Translocation, Genetic; D014426:Turtles / Q000145:classification / Q000235:genetics*
chemical_list: D011506:Proteins
keywords: gene duplication.; gene family; integument; skin; turtles