Skin-specific expression of ictacalcin, a homolog of the S100 genes, during zebrafish embryogenesis.

Full-length cDNA coding for the ictacalcin gene, a homolog of the S100 genes, was isolated in zebrafish and mapped on linkage group 16 using the LN54 radiation hybrid panel. The homology and phylogenetic analyses, based on the deduced amino acid sequences, showed the orthologous relationship of ictacalcin genes between zebrafish and other fish species. However, ictacalcin genes constitute an out-group with respect to other members of the S100 gene family. This result supports the findings that fish ictacalcin genes are new members of the S100 gene family and may have evolved after the divergence of teleosts and tetrapods. The zebrafish ictacalcin gene was zygotically transcribed from 12 hours postfertilization onward and was stably expressed throughout adulthood. During zebrafish embryogenesis, the ictacalcin gene was specifically expressed in striated epidermal cells covering the entire embryo. The ictacalcin staining in keratinocytes of striated epithelia was absent in the cytoplasm surrounding the nuclei, but it was highly concentrated in the peripheral margin. Tissues enriched with epithelia folds, such as olfactory epithelium, hatching gland, pectoral fin buds, urogenital opening, and pharynx, showed a robust ictacalcin expression. The strikingly heavy staining of ictacalcin in the pharyngeal region provides us with an early marker to follow the pharynx formation in zebrafish embryos.