Abstract

Mouse pre‐implantation development appears to be under the control of paracrine and autocrine growth factors. The epithelium of the oviduct and the uterus together, with the population of macrophages and lymphocytes present in the reproductive tract from the onset of pregnancy, are thought to be the major sources of paracrine growth factors targeted to the developing embryos. Some of the growth factors are synthesized by both uterine epithelial cells and activated lympho‐hematopoietic cells, suggesting a partial overlap of the regulatory signals used by the reproductive and lympho‐hematopoietic systems. Such growth factors may be the long sought‐after mediators of the synchrony between the pre‐implantation embryo and the sex‐steroid hormone‐induced changes in the uterus.