Cytoplasmic polarity develops at compaction in rat and mouse embryos.

Cells of both rat and mouse morulae can be stained vitally to reveal an asymmetry in the organization of their cytoplasm. In each cell of the rat 8-cell-embryo a column of organelles develops between the nucleus and the embryo periphery as revealed by toluidine blue, acridine orange and horseradish peroxidase (HRP). Although cells of the mouse morula lack the blatant asymmetric distribution of organelles observed in rat cells, a long pulse (greater than 3 h) of HRP to compact 8-cell mouse embryos revealed a distinct restricted localization of the enzyme not evident at earlier pre-compaction stages. The cytoplasmic polarity generated in these embryos can be demonstrated in cells of intact embryos, and also in cells disaggregated from embryos before vital staining.