IMMUNOLOGICAL STUDIES ON THE SETTLEMENT-INDUCING PROTEIN COMPLEX (SIPC) OF THE BARNACLE BALANUS-AMPHITRITE AND ITS POSSIBLE INVOLVEMENT IN LARVA-LARVA INTERACTIONS

Immunological investigation has revealed that a settlement-inducing pr otein complex (SIPC), which induces cypris settlement of the barnacle Balanus amphitrite, is synthesized during larval development and accum ulates in the cypris larva. We previously purified the SIPC from adult B. amphitrite, which was active when bound to a substratum. The SIPC is a glycoprotein of high molecular mass, consisting of three major su bunits of 76, 88 and 98 kDa with lentil lectin (LCA)-binding sugar cha ins. In the present study, we prepared antiserum against each LCA-bind ing subunit of SIPC, and performed immunoblot analyses. Immunoblotting of adult extracts showed that anti-76-kDa antibody reacted only with the 76-kDa protein, whereas anti-88-kDa and anti-98-kDa antibodies rea cted with both the 88-kDa and the 98-kDa proteins. Immunoblotting of l arval extracts indicated that reactivity of the 76-kDa protein to anti -76-kDa antiserum increased during larval development and cyprid extra cts reacted strongly. Moreover, by using immunostaining we found that the SIPC was contained in 'footprints' of cyprids, which have been sho wn to act as a settlement-inducing pheromone, and is secreted onto the antennular attachment discs. The results suggest that the SIPC (or SI PC-like proteins) is involved in both adult-larva and larva-larva inte ractions during settlement of the barnacle B. amphitrite.