[Effect of a short-term disturbance of the cell contacts on the mesodermal differentiation of clawed toad embryos]

The differentiation of the presumptive mesoderm explants from different sectors of the early gastrula marginal zone was compared with that of the identical explants placed just after explantation into a medium free of divalent cations for 30 s. The development of the treated dorsal explants differed from that of control explants by the presence of well differentiated forebrain structures and the development of the explants from more ventral zones by a decrease in the occurrence of blood cells and nondifferentiated endoderm and an increase in occurrence of epithelioid structures, which form frequently deep invaginations. The shape of the treated explants was more organized and differentiated than that of the control explants. A conclusion has been reached that the development of epithelioid and forebrain structures in the explants is stimulated after a short-term disturbance of cell contacts.