Alteration of cell adhesion system in amphibian ectoderm cells during primary embryonic induction: changes in reaggregation pattern of induced neurectoderm cells and ultrastructural features of the reaggregate.

Cell adhesion was studied during primary embryonic induction. The disaggregation rate and reaggregation patterns were analysed in the ectoderm cells of various developing Cynopus gastrulae and neurulae. The neurectoderm cells disaggregated more slowly with gastrulation, and the neural plate cells of early neurula showed a lesser capacity for disaggregation. Although no differences in reaggregation were found between dorsal and ventral ectoderm at the early gastrula stage, there were significant differences between the induced neurectoderm and the non-induced ventral epidermal cells at the late gastrula stage. Neural plate cells of the early neurula stage were seen to form a chain-like reaggregate, but the ventral epidermal cells of the same embryo formed a cluster-like spherical reaggregate. Scanning electron microscope observations of reaggregates also showed significant differences in adhesive properties between induced neurectoderm and non-induced epidermal cells. The adhesion field of the induced neurectoderm cells was smooth, differing from the distinct ridges of the non-induced epidermal cells. These results suggest that changes in the cell adhesion system, resulting in the formation of a columnar cell shape, may occur immediately after a neural-inducing action.