TEMPORAL AND SPATIAL EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I H-2K IN THE EARLY MOUSE EMBRYO

The pattern of expression of major histocompatibility complex class I H-2K in early mouse embryos was determined through reverse transcripti on-polymerase chain reaction (RT-PCR) and in situ hybridization method s. H-2K transcripts were detected in all stages of preimplantation emb ryos from oocyte to blastocyst. In the blastocyst, transcripts were fo und in both trophectoderm and inner cell mass. Quantitative RT-PCR rev ealed that in CD-1 mice H-2K(q) transcript levels per oocyte/embryo we re 71 +/- 13 in oocyte, 150 +/- 3 in 2-cell embryos, 220 +/- 22 in 8-c ell embryos, and 560 +/- 86 in blastocysts. By RT-PCR, H-2K(q) mRNA wa s also detected in postimplantation staged (7.5-, 8.5-, and 9.5-day) e mbryos. Examination of components of the 7.5-day conceptus revealed th e highest levels in the ectoplacental cone (EPC), followed by the deci dua, and finally the embryo. The spatial distribution of H-2K transcri pts in decidua was very heterogeneous, whereas the low levels in the e mbryo were found to be uniform throughout. Both cell types of the EPC contained H-2K transcripts. In the 9.5-day embryo, high transcript lev els were observed over the developing liver above a background of cons titutive expression everywhere else.