In vitro evidence that interactions betweenXenopus blastomeres restrict cell migration.

The consistency of the frog blastula's fate map is produced, in part, because the progeny of blastomeres located in dfferent regions do not intermix with one another. We examined the cause for this restriction of intermixing in two types of cultures. In one type of culture, two groups of cells were excised from blastulae and stuck together; the movement of cells between the groups was monitored. Cells migrated more extensively between groups derived from the same region than between groups derived from different regions. In the other type of culture, a single cell was implanted into a group of cells that was excised from the blastula. The rate of division and the extent of migration of the implanted cell's clone were monitored. The implanted cell divided more rapidly among cells from its own region than among cells from a different region. Both experiments show that the restriction of intermixing that occurs between regions of the intact embryo also occurs in vitro. These results indicate that the restriction does not result secondarily from normal morphogenetic movements, which are absent from the explants, but probably from cellular interactions that limit the extent of cell migration. This limitation is correlated with a reduction in the rate of cell division.