β-keratins of differentiating epidermis of snake comprise glycine-proline-serine-rich proteins with an avian-like gene organization

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Abstract

β-keratins of reptilian scales have been recently cloned and characterized in some lizards. Here we report for the first time the sequence of some β-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' β-keratins. Cloning and Southern blotting analysis suggest that snake β-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 β-keratin transcripts almost exclusively in differentiating oberhautchen and β-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 β-strand regions in the central region, likely involved in the formation of a fibrous framework of β-keratins. This region was possibly present in basic reptiles that originated reptiles and birds. Developmental Dynamics 236:1939–1953, 2007. © 2007 Wiley-Liss, Inc.

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