THE ROLE OF GROWTH-FACTORS IN EMBRYO PRODUCTION

Despite the successful in vitro culture of preimplantation embryos from a number of mammalian species, such embryos are at a developmental disadvantage when compared to their in vivo counterparts. This disadvantage can be overcome to some extent by adding growth factors, or washings from the reproductive tract. It has become clear within the past few years that the oviduct and uterus contain growth factors that can stimulate cellular proliferation, and in some cases, differentiation of preimplantation embryos. These growth factors act along a paracrine pathway by binding to specific receptors on embryonic cells. In addition, the embryo itself produces some autocrine growth factors. The study of these growth factors and their receptors has led to some general conclusions. There are several growth factors that stimulate cellular proliferation, although the precise pathway they utilize is not known. Similarly, it is conceivable there are synergistic interactions of different growth factors required for optimal early development. We summarize information regarding the role of the insulin family of peptides in preimplantation mammalian development and describe some other relevant studies.