title: Convergent evolution of cysteine-rich proteins in feathers and hair.
abstract: BACKGROUND
  Feathers and hair consist of cornified epidermal keratinocytes in which proteins are crosslinked via disulfide bonds between cysteine residues of structural proteins to establish mechanical resilience. Cysteine-rich keratin-associated proteins (KRTAPs) are important components of hair whereas the molecular components of feathers have remained incompletely known. Recently, we have identified a chicken gene, named epidermal differentiation cysteine-rich protein (EDCRP), that encodes a protein with a cysteine content of 36%. Here we have investigated the putative role of EDCRP in the molecular architecture and evolution of feathers.
  
  
  RESULTS
  Comparative genomics showed that the presence of an EDCRP gene and the high cysteine content of the encoded proteins are conserved among birds. Avian EDCRPs contain a species-specific number of sequence repeats with the consensus sequence CCDPCQ(K/Q)(S/P)V, thus resembling mammalian cysteine-rich KRTAPs which also contain sequence repeats of similar sequence. However, differences in gene loci and exon-intron structures suggest that EDCRP and KRTAPs have not evolved from a common gene ancestor but represent the products of convergent sequence evolution. mRNA in situ hybridization demonstrated that chicken EDCRP is expressed in the subperiderm layer of the embryonic epidermis and in the barbule cells of growing feathers. This expression pattern supports the hypothesis that feathers are evolutionarily derived from the subperiderm.
  
  
  CONCLUSIONS
  The results of this study suggest that convergent sequence evolution of avian EDCRP and mammalian KRTAPs has contributed to independent evolution of feathers and hair, respectively.
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Lazarettgasse 14, 1090, Vienna, Austria. bettina.strasser@meduniwien.ac.at.
authors.forename: Bettina
authors.initials: B
authors.lastname: Strasser
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Lazarettgasse 14, 1090, Vienna, Austria. veronika.mlitz@meduniwien.ac.at.
authors.forename: Veronika
authors.initials: V
authors.lastname: Mlitz
authors.affiliation: Department of Medical Biochemistry, Medical University of Vienna, Vienna, Austria. marcela.hermann@meduniwien.ac.at.
authors.forename: Marcela
authors.initials: M
authors.lastname: Hermann
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Lazarettgasse 14, 1090, Vienna, Austria. erwin.tschachler@meduniwien.ac.at.
authors.forename: Erwin
authors.initials: E
authors.lastname: Tschachler
authors.affiliation: Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Lazarettgasse 14, 1090, Vienna, Austria. leopold.eckhart@meduniwien.ac.at.
authors.forename: Leopold
authors.initials: L
authors.lastname: Eckhart
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001717:Birds / Q000235:genetics / Q000378:metabolism; D002645:Chickens / Q000235:genetics; D019143:Evolution, Molecular; D005241:Feathers / Q000737:chemistry* / Q000378:metabolism; D006197:Hair / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008322:Mammals / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D030161:Avian Proteins; D009124:Muscle Proteins; D016271:Proto-Oncogene Proteins c-myc; C081447:cysteine-rich protein, avian