Type I and type II cytokeratin cDNAs from the zebrafish (Danio rerio) and expression patterns during early development

Full-length cDNAs of a type I (zfCKI), and a type II (zfCKII) cytokeratin f rom the adult zebrafish, Danio rerio, were characterized and their expressi ons studied during early development and in the adult. The 1426 bp long zfC KI cDNA encodes a 46.7 kD protein, whereas the 2398 bp zfCKII cDNA encodes a protein of 58.6 kD, zfCKI and zfCKII each have a central rod domain that is characteristic of intermediate filaments and which share 73 % -91 % and 87 %-93 % similarity, respectively, with those of type I and type Il cytoke ratins from zebrafish, goldfish, and the rainbow trout. The central rod dom ains of zfCKI and zfCKII also contain the IF signature motif, IR[T/E]YR[K/R ]LL[D/E]. zfCKI has, in addition, a leucine-zipper motif at a.a. residues 1 84-205 and 191-212. Both zfCKI and zfCKII mRNAs are expressed in the epider mis of the zebrafish, zfCKII mRNA was both maternally inherited and zygotic ally transcribed and was detected from the one-cell embryo to adult stages. zfCKII tvas also strongly expressed specifically during the 20-somites, pr otruding-mouth, and adult stages. In the adult, it was uniformly expressed in the skin, fins and scale epidermis. In contrast, zfCKI mRNA was undetect able in the oocyte but was zygotically transcribed from the epiboly stage o nwards. Its expression in the skin was strong only up to the swimming larva stage and was weak and patchy in the adult. Both zfCKI and zfCKII were exp ressed in the neurons and glial cells of the brain and spinal cord. In the adult eye, zfCKI and zfCKII were expressed in the ganglion cell layer and t he retina, but zfCKII was also strongly expressed in the cornea as well as in chondrocytes in the skull.