Localization of cytoskeletal proteins in preimplantation mouse embryos

The immunofluorescence technique was used to detect the presence and distribution of actin, alpha-actinin, tubulin and 10 nm filament protein in early mouse embryos. Actin and alpha-actinin stainings showed a distinct concentration to a peripheral layer in the cleavage-stage blastomeres and in trophectoderm cells. Dots of fluorescence appeared in this cortical staining pattern. The distribution of tubulin staining in the blastomere cytoplasm was relatively even with apparent concentration at the perinuclear region and frequently at wide intercellular contact areas. 10 nm filament protein was distributed evenly in the blastomere cytoplasm without cortical concentration of the label. At the blastocyst stage, the trophectoderm cells in blastocyst outgrowths in vitro developed well organized cytoskeletons including both microfilament, microtubule and 10 nm filament elements. Comparable structures were not observed in blastocysts in vivo, or in late hatched blastocysts cultured in suspension. The morphogenetic significance of the observations is discussed.