New epidermal keratin genes from Xenopus laevis: hormonal and regional regulation of their expression during anuran skin metamorphosis

Xenopus larval keratin (XLK) was isolated by gel electrophoresis of protein s of tadpole skin. Screening of an expression cDNA library of tail tissues by specific polyclonal antibodies against XLK produced XLK cDNA (xlk). Its complete nucleotide and predicted amino acid sequences revealed that XLK wa s a new member of type II keratin. Screening of a cDNA library of adult Xen opus skin using an oligonucleotide probe which had been designed from well- conserved N-terminal amino acid sequences of the rod domain of type I kerat in produced two cDNAs, xak-a and xak-b, which were found to be new members of type I keratin gene. Northern blot analysis showed that ilk was expresse d exclusively in the larval skin whereas xak-a and xak-b were expressed exc lusively in the adult skin. Their expression level was regulated in a regio n- and metamorphic stage- dependent manner during larval skin development. mRNA in situ hybridization experiments identified the cells that expressed xlk, and xak-a and uak-b as larva- specific epidermal cells (skein cells an d basal cells), and adult suprabasal epidermal cells, respectively. These t hree genes were found to be late responsive to thyroid hormone. Phylogeneti c relationships of these keratins with known ones are discussed. (C) 2001 E lsevier Science B.V. All rights reserved.