The role of changes in cell contact behavior in amphibian gastrulation

Five different methods were used to examine cell contact behavior in normal and interspecific hybrid embryos in an attempt to elucidate the role of cell surface adhesiveness in gastrulation. In normal embryos and viable hybrid embryos, all cells show an increasing tendency to attach to glass in vitro with advancing developmental age. Presumptive mesodermal cells from early gastrulae show a high ability to attach to glass and to reaggregate. The rate of disaggregation of whole embryos shows marked decreases with advancing age from the blastula to late gastrula period. Binary combinations of explanted embryonic germ layer fragments from early gastrulae undergo movements that are reminiscent of portions of gastrulation. At the level of fine structure, cell contacts become increasingly intimate from the blastula to late gastrula period. In hybrid embryos which undergo developmental arrest at the onset of gastrulation, there is a lack of gastrular morphogenetic behavior in some or all portions of the embryo. In those portions of arrested hybrids where some morphogenesis is evident, there is “quasi‐normal” cell contact behavior. Most often, however, there is no recognizable gastrulation and a striking departure from the normal pattern of cell contact behavior. These results show that extent of changes in cell contact behavior and extent of normal gastrulation correlate positively. This suggests that changes in cell surface properties, resulting in the formation of stronger intercellular adhesions, are necessary for the morphogenetic movements of gastrulation.