INFLUENCE OF THE PREIMPLANTATION-EMBRYO-DEVELOPMENT (PED) GENE ON MOUSE BLASTOCYST DIFFERENTIATION

Mouse preimplantation embryonic cleavage rate is dependent upon the pr esence or absence of the Preimplantation-embryo-development (Ped) gene ; which is linked to the Qa-2 subregion of the H-2 complex. Expression of Qa-2 antigens by fast developing mouse embryos correlates with Fed gene phenotype: Qa-2(a). It is not known if the Fed gene (Qa-2(a)) pa rticipates in cell differentiation in the preimplantation mouse blasto cyst. Therefore, the study objective was to determine the differentiat ion of cells to the inner cell mass (ICM) and trophectoderm (TE) in Qa -2(a) positive (Ped+) and Qa-2(a) negative (Ped-) mouse blastocysts. O ne-cell stage embryos were recovered from the excised oviducts of PMSG (5 IU) and hCG (5 IU) primed virgin female (3-4 weeks) BALB/cByJ (Qa- 2(a): Ped-) and BALB/cJ (Qa-2(a): Ped+) mice mated to fertile males (1 2+ weeks). Embryos were collected, 14 hr after hCG, and cultured in mo dified alpha-MEM, to the hatched blastocyst stage in an atmosphere of 5% CO2 in air, 95% relative humidity at 37 degrees C. Cell differentia tion was determined by differential staining (bis-benzimide and propid ium iodide) and fluorescence microscopy. Data were analyzed by Student s t-test. There was no significant difference in total cell number bet ween BALB/cJ (mean 139) and BALB/cByJ (mean 143) embryos. A significan t difference (p < 0.001) was found in the number of cells differentiat ing to the ICM between BALB/cJ (mean 59.0) and BALB/cByJ (mean 29.0) m ouse embryos. The number of cells differentiating to the TE, between B ALB/cJ (mean 80.0) and BALB/cByJ (mean 114) embryos, approached signif icance (p = 0.062). The results suggest that the Fed gene (Qa-2(a)) ma y have an influential role in preimplantation blastocyst cell differen tiation. Additional studies are warranted to further elucidate the rol e of the Fed gene in preimplantation embryo development and blastocyst formation.