GENETIC-REGULATION OF PREIMPLANTATION MOUSE EMBRYO SURVIVAL

The preimplantation period of mammalian development is characterized b y cleavage of a one-cell embryo to a blastocyst stage embryo. During p reimplantation development, 15%-50% of the embryos die as a result of factors that are largely unknown. Two parameters of preimplantation de velopment, a fast rate of development and a low degree of fragmentatio n, are indicative of good embryo quality. There is mounting evidence t hat genes control both rate of development and degree of fragmentation . We have discovered a gene, Fed (preimplantation embryo development), which controls the rate of preimplantation embryonic cleavage. The Fe d gene is encoded by two similar genes, Q7 and Q9, in the Q region of the mouse major histocompatibility complex (MHC). The Fed gene product is an MHC class Ib protein, the Qa-2 antigen. The mechanisms by which the Red gene controls rate of embryonic cleavage division are being e xplored. In order to understand genetic mechanisms underlying the seco nd criterion of embryo quality, degree of fragmentation, we have begun to assess expression of the genes that could potentially regulate apo ptosis in preimplantation embryos. We have shown that staurosporine ca n induce apoptosis in mouse blastocysts. By using RT-PCR, we have show n that genes encoding proteins in the two major gene families that reg ulate apoptosis, the Bcl-2 and caspase gene families, are present in p reimplantation embryos. We hypothesize that there is a homeostatic mec hanism by which genes that regulate cell survival and those that regul ate cell death determine the overall viability of preimplantation embr yos. J. Exp. Zool. 282:272-279, 1998. (C) 1998 Wiley-Liss, Inc.