Cell proliferation in the ectoderm of the Xenopus embryo: development of substratum requirements for cytokinesis.

The requirements for cell division in ectodermal blastomeres of the early Xenopus embryo were studied. Isolated blastomeres divide autonomously on nonadhesive agar in a simple salt solution up to the midblastula stage. After the midblastula transition, cell-cell contact is required for blastomere division. In isolated blastomeres of that stage, cytokinesis fails, but nuclear division continues normally for some time. Cell-cell contact as a prerequisite for blastomere division can be replaced by culturing blastomeres on an appropriate substratum. Clonal growth of isolated blastomeres is supported by a variety of protein substrata, indicating rather unspecific substratum requirements. Different substrata which do not support blastomere division can affect different steps in cytokinesis.