Pamlin-induced tyrosine phosphorylation of SUp62 protein in primary mesenchyme cells during early embryogenesis in the sea urchin, Hemicentrotus pulcherrimus

Ingression of primary mesenchyme cells (PMC) is associated with the encounter of basal lamina including pamlin. It was found that sea urchin embryos have a protein that binds antihuman focal adhesion kinase (FAK) antibodies, yet it has a 62 kDa homo-dimeric structure. Thus, this protein was distinctive from known FAK, and was named SUp62. In mesenchyme blastulae, one of the subunits increased its apparent molecular mass slightly but distinctively, then restored the original molecular mass in early gastrulae. This temporal and stage-specific shifting of the molecular mass was associated with the occurrence of tyrosine phosphorylation of a subunit that did not increase the apparent molecular mass. Herbimycin A induced the hyperphosphorylation of tyrosine residues of SUp62, and inhibited the occurrence of molecular mass shifting. Immunohistochemistry showed a strong positive signal of SUp62 and phosphotyrosine in PMC. Herbimycin A also severely but reversibly inhibited PMC dissociation, migration and gastrulation. Tyrosine phosphorylation of SUp62 was induced when PMC were incubated with pamlin in vitro, and it was initiated within 10 min after onset of the incubation. It reached its peak in 1 h, and declined gradually in the next 1 h, indicating that pamlin-induced tyrosine phosphorylation of SUp62 occurs closely associated with acquiring PMC migration activity.