Pamlin, a primary mesenchyme cell adhesion protein, in the basal lamina of the sea urchin embryo.

Pamlin, a primary mesenchyme cell (PMC) adhesion protein, was isolated from the blastocoel of embryos of the sea urchin Hemicentrotus pulcherrimus. PMCs isolated from mesenchyme blastulae bound exclusively to pamlin. Pamlin is a distinctive extracellular matrix (ECM) component from reported ECM molecules in sea urchin embryos in its motility on SDS-PAGE gels both with and without 2-mercaptoethanol and histological localization. A monoclonal antibody was raised against pamlin, and this protein was immunoaffinity purified. The Mr of pamlin shown by SDS-PAGE gel analysis under nonreduced conditions was 255 kDa. Under reduced conditions, pamlin was cleaved to 180-, 52-, and 23-kDa subunits, indicating the 255-kDa protein is an SS-bonded heterotrimer. PMCs bound exclusively to the 52-kDa subunit. Mannose residues occur in the larger two subunits, but not in the smallest subunit. Pamlin does not run into 4% nondenatured PAGE gels, suggesting that the native glycoprotein forms a large polymeric supramolecular configuration in vivo. Immunohistochemistry showed that pamlin is seen on the entire basal lamina in the blastocoel and hyaline layer of mesenchyme blastulae. In vitro PMC migration assays on pamlin show that an optimum amount of pamlin for PMC migration was 2.5 micrograms/ml and that a synthetic RGDS peptide inhibited PMC migration dose dependently.