Scale keratin in lizard epidermis reveals amino acid regions homologous with avian and mammalian epidermal proteins.
Small proteins termed beta-keratins constitute the hard corneous material of reptilian scales. In order to study the cell site of synthesis of beta-keratin, an antiserum against a lizard beta-keratin of 15-16 kDa has been produced. The antiserum recognizes beta-cells of lizard epidermis and labels beta-keratin filaments using immunocytochemistry and immunoblotting. In situ hybridization using a cDNA-probe for a lizard beta-keratin mRNA labels beta-cells of the regenerating and embryonic epidermis of lizard. The mRNA is localized free in the cytoplasm or is associated with keratin filaments of beta-cells. The immunolabeling and in situ labeling suggest that synthesis and accumulation of beta-keratin are closely associated. Nuclear localization of the cDNA probe suggests that the primary transcript is similar to the cytoplasmic mRNA coding for the protein. The latter comprises a glycine-proline-rich protein of 15.5 kDa that contains 163 amino acids, in which the central amino acid region is similar to that of chick claw/feather while the head and tail regions resemble glycine-tyrosine-rich proteins of mammalian hairs. This is also confirmed by phylogenetic analysis comparing reptilian glycine-rich proteins with cytokeratins, hair keratin-associated proteins, and claw/feather keratins. It is suggested that different small glycine-rich proteins evolved from progenitor proteins present in basic (reptilian) amniotes. The evolution of these proteins originated glycine-rich proteins in scales, claws, beak of reptiles and birds, and in feathers. Some evidence suggests that at least some proteins contained within beta-keratin filaments are rich in glycine and resemble some keratin-associated proteins present in mammalian corneous derivatives. It is suggested that glycine-rich proteins with the chemical composition, immunological characteristics, and molecular weight of beta-keratins may represent the reptilian counterpart of keratin-associated proteins present in hairs, nails, hooves, and horns of mammals. These small proteins produce a hard type of corneous material due to their dense packing among cytokeratin filaments.
Alibardi
Lorenzo
L
Dipartimento di Biologia Evoluzionistica Sperimentale, University of Bologna, Bologna, Italy. alibardi@biblio.cib.unibo.it
Dalla Valle
Luisa
L
Toffolo
Vania
V
Toni
Mattia
M
D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry* / Q000648:ultrastructure; D001483:Base Sequence; D004817:Epidermis / Q000737:chemistry* / Q000196:embryology* / Q000648:ultrastructure; D005260:Female; D007150:Immunohistochemistry; D007633:Keratins / Q000737:chemistry* / Q000235:genetics; D008116:Lizards / Q000033:anatomy & histology / Q000196:embryology* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D030161:Avian Proteins; D007633:Keratins