Distributional Changes in Lysosome-Like Bodies in Mammalian Embryos during the Course of Blastocyst Formation

Distributional changes in lysosome-like bodies (LBs) in mouse, rat, rabbit and bovine embryos during the course of blastocyst formation were studied with acridine orange (AO) staining. AO-stained LBs were distributed throughout the cytoplasm of all round blastomeres in untransformed 8- and 16-cell mouse embryos, 32-cell rabbit embryos and 16-cell bovine embryos, whereas they were observed from the nucleus to the apical cytoplasm of all round blastomeres in 8-cell rat embryos. In morulae of these animals, LBs were present in the entire cytoplasm of inner round blastomeres, and were localized around the nucleus in outer flattened (mouse) and cuboidal (rabbit and cow) blastomeres or the apical cytoplasm in outer flattened (rat) blastomeres. In blastocysts, LBs were present in the entire cytoplasm of inner-cell-mass cells and around the nucleus of trophoblast cells. Such distribution of LBs in mouse embryos was also observed in those developed in vitro. From these results, it was suggested that there is a close relationship between distributional changes in LBs and the transformation and differentiation of blastomeres in mouse, rabbit and bovine embryos