XENOPUS EMBRYONIC-CELL ADHESION TO FIBRONECTIN - POSITION-SPECIFIC ACTIVATION OF RGD SYNERGY SITE-DEPENDENT MIGRATORY BEHAVIOR AT GASTRULATION/

During Xenopus laevis gastrulation, the basic body plan of the embryo is generated by movement of the marginal zone cells of the blastula in to the blastocoel cavity. This morphogenetic process involves cell adh esion to the extracellular matrix protein fibronectin (FN), Regions of FN required for the attachment and migration of involuting marginal z one (IMZ) cells were analyzed in vitro using FN fusion protein substra tes. IMZ cell attachment to FN is mediated by the Arg-Gly-Asp (RGD) se quence located in the type III-10 repeat and by the Pro-Pro-Arg-Arg-Al a-Arg (PPRRAR) sequence in the type III-13 repeat of the Hep II domain , IMZ cells spread and migrate persistently on fusion proteins contain ing both the RGD and synergy site sequence Pro-fro-Ser-Arg-Asn (PPSRN) located in the type III-9 repeat, Cell recognition of the synergy sit e is positionally regulated in the early embryo, During gastrulation, IMZ cells will spread and migrate on FN whereas presumptive pre-involu ting mesoderm, vegetal pole endoderm, and animal cap ectoderm will not . However, animal cap ectoderm cells acquire the ability to spread and migrate on the RGD/synergy region when treated with the mesoderm indu cing factor activin-A. These data suggest that mesoderm induction acti vates the position-specific recognition of the synergy site of FN in v ivo, Moreover, we demonstrate the functional importance of this site u sing a monoclonal antibody that blocks synergy region-dependent cell s preading and migration on FN, Normal IMZ movement is perturbed when th is antibody is injected into the blastocoel cavity indicating that IMZ cell interaction with the synergy region is required for normal gastr ulation.