A monoclonal antibody, MA21, recognizes a surface component that is present on F9 teratocarcinoma cells and that appears vectorially on the trophectoderm of peri-implantation-stage mouse blastocysts

A monoclonal antibody (MAb) “MA21”, derived from lymphoid tissue of a multiparous mouse and selected for binding to mouse teratocarcinoma cell line F9, recognizes a surface antigen that appears on peri-implantation-stage mouse blastocysts. In indirect immunofluorescence assays, MAb MA21 does not bind to I-cell-through morula-stage embryos, nor to early, 3.5-day post-coitum (p.c.) blastocysts. When 3.5-day p.c. blastocysts are maintained 17 h in vitro and then assayed, MAb MA21 binds to a limited number of trophectoderm cells that are centered at the embryonic pole. As culture time lengthens, the number of antigen-expressing trophectoderm cells increases, forming a cap that spreads from the embryonic pole into the abembryonic region. Embryos maintained 48 h in vitro bind MAb MA21 over as much as 100% of the trophectoderm surface. MAb MA21 does not bind to the inner cell mass. When mouse pregnancy uteri are assayed by the immunoperoxidase method, MAb MA21 binds to extra-embryonic ectoderm and trophectoderm of 5-day p.c. implanted blastocysts, but does not bind to 6-day p.c. blastocysts. MAb MA21 recognizes a component with an estimated mol. wt of 44,000 from NP-40 detergent extracts of F9 cells and peri-implantation-stage mouse blastocysts. The component appears to be firmly associated with the plasma membrane; it is resistant to removal by high salt or moderate concentrations of non-ionic detergent.