Cross-linking of Qa-2 protein, the Ped gene product, increases the cleavage rate of C57BL/6 preimplantation mouse embryos

The Qa-2 protein, a glycosylphosphatidylinositol (GPI)-linked major histocompatibility complex (MHC) Class Ib molecule found on the surface of mouse T-cells and preimplantation embryos, is the product of the preimplantation embryo development (Ped) gene. The Ped gene regulates the rate of early embryonic development and subsequent embryo survival. T-cells treated with anti-Qa-2 monoclonal antibody (mAb) and cross-linked with a secondary antibody, in the presence of a co-stimulatory signal, undergo increased proliferation. The purpose of this study was to determine whether cross-linking of Qa-2 similarly affects preimplantation embryos. We cross-linked Qa-2 protein on the surface of C57BL/6 2-cell and 8-cell embryos, in the presence of 4/5-phorbol-12-myristate-13-acetate (PMA), and assessed the percentage of embryos reaching the blastocyst stage, the percentage hatching from the zona pellucida, [3H-thymidine] incorporation into DNA, and the total number of cells per embryo as measures of embryonic cleavage rate. Both 2-cell and 8-cell embryos increased their cleavage rates 48 h after cross-linking of Qa-2, compared with control embryos (P < 0.05). Our results indicate that a Qa-2 protein cross-linking mechanism may be one way by which this protein regulates the rate of preimplantation mouse embryo development.