Evidence for the involvement of PI-signaling and diacylglycerol second messengers in the initiation of metamorphosis in the hydroid Hydractinia echinata Fleming
Leitz, T.; Müller, W.A.
Developmental Biology 121(1): 82-89
1987
ISSN/ISBN: 0012-1606 PMID: 3032714 DOI: 10.1016/0012-1606(87)90140-0
Accession: 017893403
Metamorphosis of the planula larvae into polyps does not occur spontaneously but depends on the reception of external trigger stimuli. Artificially, metamorphosis can be initiated by a pulse-type application of Cs+ or tumor-promoting phorbol esters (W. A. Muller (1985) Differentiation 29, 216-222). In the present study we examined the putative involvement of the phosphatidylinositol system in signal transduction. Planulae of Hydractinia echinata were preincubated with [3H]-inositol. Upon exposure of the larvae to Cs+ the label in inositol trisphosphate (InsP3) increased twofold as early as 15 sec after addition of Cs+. Within the first 60 sec the levels of inositol monophosphate (InsP1) and inositol bisphosphate (InsP2) were also elevated compared to the values in nonstimulated larvae. After 1 and 3 hr, respectively, of incubation with Cs+, only the label in InsP2 was increased. When applied to saponin-permeabilized larvae, InsP3 did not induce metamorphosis. But 1,2-dioctanoyl-glycerol (diC8) was effective in inducing metamorphosis with a half-maximal effective concentration of 9 .mu.M. The percentage of metamorphosed animals after the application of 5 .mu.M diC8 (30 mM Cs+) was increased by the simultaneous application of 1 .mu.M (0.1 .mu.M) of the diacylglycerol kinase inhibitor R 59022. The results are interpreted as evidence for the involvement of the PI-signaling/diacyglycerol transduction system in the initiation of metamorphosis of planula larvae of H. echinata.