Ultrastructural localization of cytoplasmic phosphatases in preimplantation mouse embryos

The appearance and localization of the cytoplasmic phosphatases [acid phosphatase (AcPase) as a marker of lysosomes, TPPase as a marker of the Golgi apparatus, and NDPase (IDPase) as enzymatic marker of the endoplasmic reticulum (ER)] were cytochemically studied on the ultrastructural level in secondary oocytes and in preimplantation mouse embryos. The detectable AcPase activity, located on the inner surface of the membrane delimiting some cytoplasmic vacuoles (lysosomes and autophagic vacuoles), appears at the eight-cell stage and grows pregressively stronger up to the blastocyst stage. Golgi-associated reaction for TPPase was detectable in oocytes, dropped in one-cell embryos and became negative in the two-cell embryos. The reaction for TPPase and IDPase was present in plasma membranes of oocytes and early embryos and appeared in the delimiting membrane of some cytoplasmic vesicles in eight-cell embryos. Some activity of IDPase was found in small segments of the ER at the morula and blastocyst stage. The observed results suggest that the lysosomes are the first organelles in early embryos showing activity of the marker enzymes of the phosphatase type, while the activity of other marker enzymes is mainly concentrated in the plasma membrane of blastomeres. It cannot be excluded, however, that positive reaction for TPPase and IDPase in the plasma membrane results from nonspecific action of other phosphatases.