PATTERNS AND CONTROL OF CELL MOTILITY IN THE XENOPUS-GASTRULA

By comparing cells with respect to several motility-related properties and the ability to migrate on fibronectin, three cell types can be di stinguished in the Xenopus gastrula. These occur in a distinct spatial pattern, thus defining three motility domains which do not correspond to the prospective germ layers. Migratory behavior is confined to a r egion encompassing the anterior mesoderm and endoderm, When stationary animal cap cells are induced to migrate by treatment with activin, ce lls become adhesive at low concentrations of fibronectin, show polariz ed protrusive activity, and form lamellipodia, Adhesion and polarizati on, but not lamellipodia formation, are mimicked by the immediate earl y response gene Mix.1. Goosecoid, another immediate early gene, is wit hout effect when expressed alone in animal cap cells, but it acts syne rgistically with Mix.1 in the control of adhesion, and antagonisticall y in the polarization of protrusive activity. bFGF also induces migrat ion, lamellipodia formation and polarization in animal cap cells, but has no effect on adhesion. By the various treatments of animal cap cel ls, new combinations of motile properties can be generated, yielding c ell types which are not found in the embryo.