Beta-keratins of differentiating epidermis of snake comprise glycine-proline-serine-rich proteins with an avian-like gene organization.
Beta-keratins of reptilian scales have been recently cloned and characterized in some lizards. Here we report for the first time the sequence of some beta-keratins from the snake Elaphe guttata. Five different cDNAs were obtained using 5'- and 3'-RACE analyses. Four sequences differ by only few nucleotides in the coding region, whereas the last cDNA shows, in this region, only 84% of identity. The gene corresponding to one of the cDNA sequences has a single intron present in the 5'-untranslated region. This genomic organization is similar to that of birds' beta-keratins. Cloning and Southern blotting analysis suggest that snake beta-keratins belong to a family of high-related genes as for geckos. PCR analysis suggests a head-to-tail orientation of genes in the same chromosome. In situ hybridization detected beta-keratin transcripts almost exclusively in differentiating oberhautchen and beta-cells of the snake epidermis in renewal phase. This is confirmed by Northern blotting that showed, in this phase, a high expression of two different transcripts whereas only the longer transcript is expressed at a much lower level in resting skin. The cDNA coding sequences encoded putative glycine-proline-serine rich proteins containing 137-139 amino acids, with apparent isoelectric point at 7.5 and 8.2. A central region, rich in proline, shows over 50% homology with avian scale, claw, and feather keratins. The prediction of secondary structure shows mainly a random coil conformation and few beta-strand regions in the central region, likely involved in the formation of a fibrous framework of beta-keratins. This region was possibly present in basic reptiles that originated reptiles and birds.
Dalla Valle
Luisa
L
Dipartimento di Biologia, Università di Padova, Padova, Italy.
Nardi
Alessia
A
Belvedere
Paola
P
Toni
Mattia
M
Alibardi
Lorenzo
L
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001717:Birds / Q000235:genetics*; D002454:Cell Differentiation / Q000235:genetics*; D017812:Colubridae / Q000235:genetics* / Q000378:metabolism; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D005998:Glycine / Q000235:genetics; D008969:Molecular Sequence Data; D011392:Proline / Q000235:genetics; D012694:Serine / Q000235:genetics; D053800:beta-Keratins / Q000235:genetics* / Q000378:metabolism
D053800:beta-Keratins; D012694:Serine; D011392:Proline; D005998:Glycine