Expression of osteopontin in the head process late in gastrulation in the rat.

Osteopontin (OPN) is a secreted, glycosylated phosphoprotein. Previous studies have implicated OPN in calcification/decalcification and inflammation. We became interested in developmental expression of OPN because of our previous findings that suggest OPN may play a role in formation of new vascular layers after injury, and because of our observation of developmental regulation in vascular smooth muscle cells. While OPN was expressed at low levels in vessels, only late in development, examination of very early expression patterns revealed a surprising finding. OPN was expressed exclusively in the head process, on day 9.0 late in gastrulation in the rat. In vitro studies of vascular smooth muscle cells have previously demonstrated that OPN promotes cell adhesion and migration. It is suggested that OPN may promote migration of cells, during gastrulation, via integrins which may be present in the head process or overlying ectoderm.