The invasion of cultured cell layers and intact epithelia.

This paper concerns the invasive behaviour of a migratory embryonic cell type, the primordial germ cell (PGC) of the anuran amphibian Xenopus laevis. Scanning electron microscopy of isolated PGCs shows that they invade layers of cells derived from adult Xenopus mesentery, and the epithelium of the intact mesentery itself. This invasion is at least partly due to the stimulation by the PGCs of process formation in both cultured and intact epithelial cells. These broad lamellipodia move over the surface of the PGCs and eventually enclose them. We have documented previously that active invasion by the PGC also takes place, though the relative roles of these two components of the invasive process are unknown. We also demonstrate that these properties are not mediated by any contaminating cellular or extracellular material on the isolated PGCs, since their removal by trypsin does not alter the invasive behaviour.