UP-REGULATION OF A HYDRA-VULGARIS CPKC GENE IS TIGHTLY COUPLED TO THEDIFFERENTIATION OF HEAD STRUCTURES

Two different cDNA clones from Hydra (HvPKC1a and HvPKC1b) were charac terized, which encode members of the cPKC family of protein kinase Cs (PKCs). The two predicted proteins differ only in their amino-terminal sequences and thus probably represent the products of alternatively s pliced mRNAs from a single gene. In situ hybridization with a probe re cognizing sequences in common between the two mRNAs detects HvPKC1 RNA in all parts of the adult polyp except the foot. The mRNA is containe d in ecto-and endodermal epithelial cells as well as a certain subset of gland cells and pairs of interstitial cells. During head and foot f ormation, induced by either regeneration, budding, lithium treatment o r repeated application of a diacylglycerol, HvPKC1 expression is upreg ulated immediately prior to the evagination of tentacles and downregul ated by foot formation. Although PKC activity is clearly inducible in vitro by diacylglycerol and a tumour promoting phorbol ester, structur al features detected in the regulatory domains of HvPKC1a and Ib indic ate that endogenous activators for Hydra PKC might differ from those o f other organisms. The results corroborate the hypothesis that signal transduction systems using protein kinase C are key elements controlli ng the formation of head structures in Hydra.