Analysis for the stage specific antigen of the primordial germ cells in the chick embryo.

A monoclonal antibody 2C9 (IgM chi-light chain) was established by fusing the myeloma cells (X63-Ag8-653) with the spleen cells immunized with sexually indifferent gonads from 6-day chick embryos. The 1- to 17-day chick embryos were examined by immunohistochemistry (ABC technique). As a result, the 2C9 antigen first appeared in the cytoplasm of some primordial germ cells (PGCs) of the germinal crescent at 1 day of incubation. The reactivity was also detected in the hypoblastic cells. This antigen may be produced at this stage. After the migrating stage, 2C9-reactive PGCs were increased in number. From this stage to the sexually differentiating stage (7 days of incubation), the 2C9 antibody was reactive all over the cytoplasm of PGCs in both sexes. In the female gonads, the reactivity disappeared at 8 days of incubation, but not in the male. The reactivity of male PGCs was gradually decreased and disappeared until 14 days of incubation. Since the stages of disappearance of this antigen in both sexes seem to depend on the differentiation of the oogonia and spermatogonia, this antigen may disappear in accordance with germ cell differentiation. Cross-reactions were observed in hepatocytes, gastrointestinal endoderm and some mesonephric tubules. By SDS-PAGE and immunoblotting methods, all the extracts from these tissues revealed two bands; 109 kilodalton (kDa) and 64 kDa, suggesting that the 2C9 antibody detects the same molecule in each kind of cells. The 2C9 antibody may be a useful cell-marker and/or probe for analysis of the germ cell differentiation in chick PGCs.