Localization of myosin in the preimplantation mouse embryo

Myosin was localized in cytoskeletal preparations of preimplantation mouse embryos using indirect immunofluorescent techniques. Blastomeres of 2- and 4-cell embryos exhibited a continuous band of cortical myosin in their apical borders while no cortical myosin was detectable in regions of cell apposition. In 8-cell, 16-cell, and advanced morula-stage embryos the outer group of cells was also characterized by a continuous apical band of cortical myosin, whereas the inner group of apposed cells usually showed no detectable cortical myosin. The possible significance of these observations is discussed.