PREIMPLANTATION DEVELOPMENT OF THE MAMMALIAN EMBRYO AND ITS REGULATION BY GROWTH-FACTORS

Preimplantation development in mammals involves both the development o f the embryo and the preparation of the uterus in anticipation of blas tocyst implantation. Preparation of the uterus for implantation is pri marily under the control of the ovarian sex steroids, estrogen and pro gesterone. Increasing evidence is revealing that their effects on cell proliferation and differentiation in the uterus are mediated by local ly produced growth factors and cytokines. In contrast, preimplantation development of the embryo to the blastocyst stage appears to be indep endent of exogenous growth factors. implantation, the point at which t he blastocyst forms a more intimate association with the maternal tiss ues, is regulated by the uterine expression of leukemia inhibitory fac tor (LIF), LIF is required both io promote embryo attachment and for d ecidualization of the uterus. In the absence of LIF, neither of these events occur. Uterine expression of LIF al the time of implantation ha s been described in many species, suggesting that LIF may be of genera l significance in regulating embryo implantation in mammals. (C) 1997 Wiley-Liss, Inc.