In vivo and in vitro cultured mouse preimplantation embryos differ in their display of a teratocarcinoma cell surface antigen: possible binding of an oviduct factor

By use of a monoclonal antibody, 2B5, in indirect immunofluorescence experiments, it was found that both fertilized and unfertilized mouse eggs obtained directly from the oviduct commenced expression of a cell surface antigen at about 5h after ovulation. Surface labelling became intense by 16 h after ovulation and persisted over all blastomeres throughout preimplantation development. In contrast, embryos cultured in vitro did not show appearance of 2B5 antigen until about 48 h after ovulation, at which time they were at the 2- to 4-cell stage. Antigen expression in vitro commonly began on a single blastomere and did not appear consistently over all blastomeres until the 8-cell stage (72h after ovulation). Unfertilized eggs maintained for 72 h in culture did not acquire 2B5 antigen. It is postulated that the absence of 2B5 antigen on 1-cell eggs cultured in vitro may be due either to a failure of normal synthesis by eggs as a result of a deficiency in the culture medium, or alternatively, to absence of a soluble oviduct factor which carries the 2B5 antigen, and which normally becomes bound to the surface of eggs after ovulation. The second of these two possibilities was supported by egg transfer experiments which showed that unfertilized eggs within the oviduct became 2B5 antigenpositive even after their prior fixation in glutaraldehyde. By the 2- to 4-cell stage, however, embryos developed their own capacity for synthesis of 2B5 antigen-positive cell surface molecules. This synthesis was inhibited by tunicamycin, suggesting that the antigenic site involved the sugar component of glycoprotein. The range of tissues within the postimplantation embryo and adult reproductive tracts which labelled with 2B5 antibody was found to be very similar to that known for SSEA-1 monoclonal antibody (Solter & Knowles, 1978; Fox et al. 1981; Fox, Damjanov, Knowles & Solter, 1982), and as further evidence of a relationship between 2B5 and SSEA-1 antigens it was found that ¹²⁵I SSEA-1 antibody could be blocked in its binding to teratocarcinoma cells by preincubation in 2B5 monoclonal antibody.