MESODERMAL CELL-ADHESION TO FIBRONECTIN-RICH FIBRILLAR EXTRACELLULAR-MATRIX IS REQUIRED FOR NORMAL RANA-PIPIENS GASTRULATION

New observations on thin strips of cells from the leading edge of the involuting presumptive mesoderm explanted onto FN-coated substrata show a striking preferential cellular emigration from the leading edge of explants. Microinjected probes (Fab' anti-FN, Fab' anti-integrin and RGD-peptides) that disrupt cell adhesion to the FN-matrix on basal surface of the blastocoel roof also disrupt normal anuran gastrulation, producing blocked embryos with no adhesion of leading edge mesodermal cells to the blastocoel roof, abnormal epiboly, and defects of mesodermal cell spreading across the basal surface of the blastocoel roof toward the animal pole. These results show that the FN-rich fibrillar extracellular matrix on the basal surface of the blastocoel roof is required for normal gastrulation in Rana pipiens embryos.