Evidence that plasminogen activator is not involved in basement membrane penetration at avian gastrulation

We have used the method of radial caseinolysis in agarose to assay for the presence of plasminogen activator in the primitive streak cells of the early chick embryo. These cells are undergoing an epithelial-mesenchymal transformation in the process of the differentiation of mesoderm cells from the ectoderm. In the primitive streak, the epithelial cells, after penetrating the basement membrane, ingress and invade the underlying tissue space as fibroblast-like mesenchyme cells. In contrast to some other early embryonic invasionary and migratory events, we find no evidence for the participation of plasminogen activator in this process.