Disappearance of an epithelial cell surface-specific glycoprotein (Epith-1) associated with epithelial-mesenchymal conversion in sea urchin embryogenesis

Cell surface modification during mesenchyme ingression was examined using a monoclonal antibody (mAb), anti-Epith-1 mAb, raised against a protein (Epi th-1) that was confined to the lateral surface of the epithelial cells in e mbryo of the sea urchin. Tennopleurus hardwicki The mAb epitope was N-glyco sylated oligosaccharides of 160 kDa monomeric Epith-1 protein. The glycopro tein was negatively charged, and its isoelectric point (IP) was 4.98. The m Ab, however, is not immunologically cross-reactive with other sea urchin em bryos including Hemicentrotus pulcherrimus, Strongylocentrotus nudus, and S caphechinus mirabilis. Epith-1 is present initially in the cytoplasm of unf ertilized eggs. Cytoplasmic Epith-1 shifted to the cell surface to be integ rated in plasma membrane during the first cleavage, and remained there duri ng early embryogenesis by retaining the same relative molecular mass (M-r). During primary and secondary mesenchyme ingression periods, however, Epith -1 disappears from the presumptive mesenchyme cell surface that was associa ted with internalization of the protein. In plutei, an additional anti-Epit h-1 mab-positive protein appears at the 142 kDa region, which was not assoc iated with any visible alteration of the histologic localization of the pro tein in larvae. Anti-Epith-1 mAb IgG did not inhibit the reaggregation of e pithelial cells in vitro. which suggests that either the protein is not inv olved in cell-cell adhesion or that the mAb is not recognizing the active s ite of the protein.