Molecular and morphological differentiation of the mouse blastocyst after manipulations of compaction with cytochalasin D.

Cleavage stage mouse embryos were incubated with cytochalasin D, which inhibited cytokinesis, intercellular adhesion and junction formation but not aspects of the morphological polarization associated with compaction. If the drug was removed when controls had formed blastocysts, the embryos compacted within 1 hr, assembled junctional complexes at the apices of their cells and accumulated fluid to form "blastocyst-like vesicles" within the next 8 to 12 hr. The molecular and morphological development of these blastocyst-like vesicles and embryos cultured continuously in cytochalasin D followed the same temporal sequence as untreated controls, indicating that they are similar to normal intact blastocysts despite their decreased number of cells, altered ploidy and the absence of an overt inner cell mass. Since maturation of the embryo can take place in the absence of the intercellular features of compaction, the cellular polarization of blastomeres may be important for initiating the differentiation of inner cell mass and trophectoderm in the normal compacting morula.