Spatio-temporal expression of pamlin during early embryogenesis in sea urchin and importance of N-linked glycosylation for the glycoprotein function

Expression of pamlin, a heterotrimeric primary mesenchyme cell (PMC) adhesion glycoprotein, and its role during early embryogenesis were examined using immunochemistry and microinjection of pamlin to tunicamycin-treated embryos of the sea urchin, Hemicentrotus pulcherrimus. Pamlin faintly detected in egg cortex before fertilization was strongly expressed in the hyaline layer after fertilization. The embryonic apical surface retained pamlin throughout early embryogenesis, whereas pamlin on the basal surface showed a dynamic change of spatio-temporal distribution from morula to gastrula stage. Pamlin distributed on the entire basal surface of the ectoderm before onset of invagination gradually disappeared from the presumptive archenteron during gastrulation, and then was restricted to the apical tuft region and the PMC sessile sites in early gastrulae. Tunicamycin, an inhibitor of N-glycosydically linked carbohydrate formation, inhibited PMC migration and gastrulation. Tunicamycin also inhibited the assembly of mannose moieties of 180 and 52 kDa subunits of pamlin. Pamlin microinjection to the tunicamycin-treated embryos rescued them from this morphogenetic disturbance. PMCs did not bind to pamlin isolated from the tunicamycin-treated embryos. The present study indicated that pamlin plays an essential role in PMC migration, its termination and gastrulation, and the presence of N-glycosydically linked carbohydrate moieties that contain mannose are necessary to preserve the biological function of pamlin.