Control of H-2 antigen and beta 2-microglobulin gene expression in mouse trophoblast cell clones.

We have investigated the expression of H-2 antigen and beta 2-microglobulin in recently established mouse trophoblast cell clones. These clones, derived from C57BL/6 (H-2b) or BALB/c (H-2d) strains, synthesized extra-embryonic endoderm- and trophectoderm-specific cytoskeletal proteins, termed "Endo A" and "Endo B," and no detectable SSEA-1 embryonic antigen. Flow microfluorometry indicated that H-2 antigen expression on the cell surface of trophoblast cells was very low, corresponding to 2-5% of the amounts found on differentiated teratocarcinoma cells (12-1a) and BALB/c 3T3 cells, respectively. Expression of beta 2-microglobulin was reduced to approximately equal to 14% of the amounts found on 12-la cells. Immunoprecipitation and polyacrylamide gel electrophoretic analysis indicated that the synthesis of H-2 antigen and beta 2-microglobulin in the trophoblast cells was lower than that found in normal spleen cells. In addition low, but unequal, levels of mRNA specific for H-2 antigen and beta 2-microglobulin were found in trophoblast cells by blot hybridization with cDNA probes. The low mRNA levels may be due to transcriptional control of the genes encoding H-2 antigen and beta 2-microglobulin.