| Description |
Recent studies on the development of embryos of the amphibian, Xenopus laevis, utilizing the intracellular marker, horseradish peroxidase, have shown that blastomeres are segregated into groups, called ancestral cell groups, at the 512-cell stage. The progeny of blastomeres of an ancestral cell group disperse, intermingle, and exclusively populate a characteristic region of the tail bud embryo called a compartment; the progeny of blastomeres of different ancestral cell groups do not intermingle. That is, cells do not disperse beyond their compartmental boundary. The present studies were designed to determine the nature of the mechanism that restricts the mingling of the progeny of blastomeres of different ancestral cell groups. Because the cells of an ancestral cell group did not sort out after they were intermixed with other cells, dispersal of the progeny of blastomeres of an ancestral cell group is probably not restricted by the formation of ancestral cell group-selective adhesions. Because the progeny of blastomeres of different ancestral cell groups did not intermingle in vitro, whereas the progeny of blastomeres of the same ancestral cell group did intermingle, ancestral cell group-specific mingling restriction seems to result from an interaction between cells of different ancestral cell groups. Additionally, because the cells that did not intermingle were about four times larger than those that did intermingle, the mingling restriction may involve an inhibition of cell division. To test this possibility, an individual labeled blastomere was implanted into a group of blastomeres excised from either the same or from a different ancestral cell group and the resulting progeny were counted. The results suggest that cells of different ancestral cell groups interact to mutually inhibit one another's division. Furthermore, the progeny of blastomeres that divided only once or twice remained coherent, whereas the progeny of blastomeres that underwent more divisions were dispersed. These results suggest that mingling of cells of different ancestral cell groups may be restricted because the cells of adjacent ancestral cell groups mutually inhibit migration by inhibiting one another's division. |
