The phorbol ester TPA induces metamorphosis in Red Sea coral planulae (Cnidaria: Anthozoa)

Controlled experiments on the metamorphosis of marine invertebrate larvae require artificial inducers. These inducers can be used for studying the involvement of known signal transduction pathways in settlement and metamorphosis. The ability of the tumor-promoting phorbol ester TPA (12-O-tetradecanoylphorbol-13-acetate) to induce metamorphosis in planulae of the Red Sea soft coral species Heteroxenia fuscescens, Xenia umbellata, Dendronephthya hemprichii, Litophyton arboreum and Parerythropodium fulvum fulvum, and the stony coral Stylophora pistillata, was examined by using various concentrations of TPA. The chemical induced metamorphosis in all six species. The effect was unspecific and concentration-related. For all the corals except for X. umbellata the highest mean percentages of metamorphosis were obtained with 8.1 x 10^-7-10^-9 M TPA. For X. umbellata, the percentage of metamorphosis was lower, and was obtained within a wider TPA concentration range. The present results, along with previous studies on Hydrozoa and Scyphozoa, demonstrate that TPA is the first common artificial inducer for these classes of Cnidaria. TPA is known to activate the enzyme protein kinase C (PKC) and therefore plays an important role in studying the phosphatidylinositol signal transduction system. Evidence for the involvement of this pathway in triggering metamorphosis has already been reported for Hydrozoa and Scyphozoa. Our results suggest that PKC is also involved in initiating metamorphosis in Anthozoa.