Isolation and Characterization of cDNA Clones for Epidermis-Specific and Muscle-Specific Genes in Ciona savignyi Embryos

Ascidian eggs and embryos have provided an appropriate experimental system to explore the cellular and molecular mechanisms involved in the embryonic cell specification and pattern formation of the embryo. In Japan, most of the studies of ascidian embryology have been carried out with the large eggs of Halocynthia roretzi. However, for future studies, Ciona species may provide a better experimental system, in particular with respect to the incorporation of genetic approaches. In order to establish Ciona as an experimental system, molecular markers with which to examine cellular differentiation are required. In the present study, we isolated and characterized cDNA clones for two epidermis-specific genes (CsEpi-1 and CsEpi-2) and for two muscle-specific genes (CsMA-1 and CsMu-1). CsEpi-1 encodes a polypeptide with three trefoil domains, while CsMA-1 encodes a muscle-type actin from C. savignyi. Although CsEpi-2 and CsMu-1 transcripts seem to have a poly(A) tail at the 3′ end, we could not find a distinct open reading frame in the sequences. Probes for CsEpi-1, CsMA-1 and CsMu-1 cross-reacted with C. intestinalis embryos. These cDNAs are useful as molecular markers for the specification of epidermis and muscle of Ciona embryos.