IMMUNOLOCALIZATION OF OVIDUCTIN IN ENDOCYTIC COMPARTMENTS IN THE BLASTOMERES OF DEVELOPING EMBRYOS IN THE GOLDEN-HAMSTER

We have previously localized an antigen of oviductal origin in the zona pellucida of superovulated hamster ova. This antigen is a high-molecular-weight glycoprotein that is secreted by the nonciliated secretory cells of the oviduct and later is transferred to the zona pellucida of the oocyte during oviductal transit. This glycoprotein is rich in N-acetyl-D-galactosamine residues and has been designated Hamster Oviductin-1. In the present study, we have examined the intracellular localization of the oviductin in the blastomeres of developing embryos of the golden hamster. Seventeen cycling females were used for the localization and detection of the oviductin in oviductal oocytes and early embryos. Thin sections of hamster 1-cell oocytes, and 2-cell, and 8-cell embryos, embedded in Lowicryl and then incubated with the monoclonal antibody against the oviductin, revealed a homogenous distribution of antigenic sites in the matrix of the zona pellucida. While immunogold labeling was completely absent in the cytoplasm of 1-cell ova prior to fertilization, labeling was found associated with coated pits and coated vesicles and with flocculent material in the perivitelline space of fertilized eggs. In addition to these labeled endocytic structures, many endosomes, multivesicular bodies, and secondary lysosomes were also found to be labeled heavily in the cytoplasm of developing embryos. Our results indicate that following the transfer of Hamster Oviductin-1 to the zona pellucida of oocytes during transit in the oviduct and subsequent to fertilization, some of the oviductin associated with the zona pellucida appears to be internalized by blastomeres of the embryo and further processed through the endosomal/lysosomal pathway.