KS1, AN EPITHELIAL CELL-SPECIFIC GENE, RESPONDS TO EARLY SIGNALS OF HEAD FORMATION IN HYDRA

As a molecular marker for head specification in Hydra, we have cloned an epithelial cell-specific gene which responds to early signals of he ad formation. The gene, designated ks1, encodes a 217-amino acid prote in lacking significant sequence similarity to any known protein. KS1 c ontains a N-terminal signal sequence and is rich in charged residues w hich are clustered in several domains. ks1 is expressed in tentacle-sp ecific epithelial cells (battery cells) as well as in a small fraction of ectodermal epithelial cells in the gastric region subjacent to the tentacles. Treatment with the protein kinase C activator 12-O-tetrade canoylphorbol-13-acetate (TPA) causes a rapid increase in the level of ks1 mRNA in head-specific epithelial cells and also induces ectopic k s1 expression in cells of the gastric region. Sequence elements in the 5'-flanking region of ks1 that are related to TPA-responsive elements may mediate the TPA inducibility of ks1 expression. The pattern of ex pression of ks1 suggests that a ligand-activated diacylglycerol second messenger system is involved in head-specific differentiation.