Temporal and Spatial Expression of Major Histocompatibility Complex Class I H-2K in the Early Mouse Embryo1

The pattern of expression of major histocompatibility complex class I H-2K in early mouse embryos was determined through reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization methods. H-2K transcripts were detected in all stages of preimplantation embryos from oocyte to blastocyst. In the blastocyst, transcripts were found in both trophectoderm and inner cell mass. Quantitative RT-PCR revealed that in CD-1 mice H-2Kq transcript levels per oocyte/embryo were 71 +/- 13 in oocyte, 150 +/- 9 in 2-cell embryos, 220 +/- 22 in 8-cell embryos, and 560 +/- 86 in blastocysts. By RT-PCR, H-2Kq mRNA was also detected in postimplantation staged (7.5-, 8.5-, and 9.5-day) embryos. Examination of components of the 7.5-day conceptus revealed the highest levels in the ectoplacental cone (EPC), followed by the decidua, and finally the embryo. The spatial distribution of H-2K transcripts in decidua was very heterogeneous, whereas the low levels in the embryo were found to be uniform throughout. Both cell types of the EPC contained H-2K transcripts. In the 9.5-day embryo, high transcript levels were observed over the developing liver above a background of constitutive expression everywhere else.