Preimplantation growth factor physiology.

The robust independence of preimplantation embryo development in vitro suggests that the developmental programme is autonomous. The rapid accumulation of evidence during the last decade for participation of many hormones, growth factors and their receptors in these early stages of embryogenesis has challenged this conclusion. In this review, the insulin and epidermal growth factor families, which have been best studied in mice, are used to illustrate the different roles growth factors may play in preimplantation physiology and the circuits that possibly mediate their participation. Tumour necrosis factor alpha, an inhibitory factor and growth hormone previously considered to be restricted to orchestrating postnatal growth and development, is also discussed. In the absence of results indicating the existence of a master regulatory factor, the data support the hypothesis that the redundancy of growth factor actions may provide fail-safe protection to the preimplantation developmental programme.