Biochemical and cytological bases of metamorphosis in Hydractinia echinata

Larvae of the marine hydroid Hydractinia echinata Fleming are induced to settle and metamorphose by contact with bacteria of the genus Alteromonas espejiana (Leitz and Wagner 1992). In previous studies the biochemical mechanism for the activation of the larvae was found to include the signal transduction pathway via the phosphatidylinositol cycle and a role for a kinase C-like enzyme was established. In the present investigation laboratory-reared larvae were immunohistochemically stained with antibodies against kinase C and experiments were conducted to investigate protein phosphorylation during initial metamorphic events. A polyclonal antibody against a synthetic peptide derived from a conserved retion of kinases C binds to an antigen in neurosensory cells of the anterior part of the larvae and corresponding nerve fibres. The Western blot reveals major binding to a protein of M_r (relative molecular mass)=67 and two minor bands at M_r=66 and 48. Assays in vivo show that 3 to 25 min after induction of metamorphosis the phosphorylation of a protein with M_r=30 is enhanced. A hypothesis about the mechanism of induction at the cellular and biochemical level is presented which combines most of the ideas now available from our and other groups.