Transfer and Localisation of Maternal Serum Antigens by Mouse Preimplantation Embryos and Oviductal Epithelium

Two hours after systemic injection of bovine plasma albumin (BPA) into pregnant mice, albumin-like antigen was detected by indirect immunohistological methods within the cytoplasm of oviductal and preimplantation uterine embryos whether ovulation was spontaneous or induced by hormone injection. Although fluorescence, localising antigen similar to or identical with the systemically injected foreign protein, was present in embryos in all oviductal regions and at all cleavage stages, the intraembryonic location of the transferred serum molecules differed with embryo stage. Most ootids and two-celled blastomeres contained large intracytoplasmic areas of intense fluorescence randomly associated with non-fluorescent or dimly fluorescent areas in the same cell. By four- and eight-celled stages, albumin-like antigen was localised at the periphery of blastomeres; less was found deep within embryos. By morula and blastocyst stages, blastomeres differed from each other in fluorescence intensity although intracellular fluorescence was homogeneous. Transferred BPA antigen, present in both pronuclei, probably was absent from blastomere nuclei. Ootid zonae pellucidae contained BPA antigen but none was detected in zonae surrounding cleaving embryos. Little foreign albumin was detected in oviductal epithelium.
It is concluded that morphological, as well as biochemical, differentiation occurs during mammalian cleavage and it is suggested that maternal macromolecular contributions to mammalian preimplantation embryos may be necessary for normal development in vivo .