Autocrine, paracrine and environmental factors influencing embryonic development from zygote to blastocyst

In mammals, embryonic development is the result of a delicate interaction between the genetic program in the chromosomes of each zygote and the female genital tract. Although an accurate formulation of the culture medium allows an increasing proportion of embryos to develop in defined conditions, they are often affected by various degrees of abnormalities. This indicates a persistent inadequacy of the culture systems both with or without somatic cells. Current studies on the physiology of preimplantation embryos and of the oviduct indicate that several factors are involved in this delicate period of cell proliferation and differentiation. These have here been divided in three groups: autocrine factors, mostly growth factors, generated by the embryo for sustaining its own development; paracrine factors, growth factors and specific proteins, generated by the oviduct which reach the conceptus; environmental factors, various substances - i.e. energy substrates, ions, amino acids, vitamins - which generate the "perfect" medium for an embryo to grow. Recent data suggest that successful embryonic development requires the balanced combination of all these factors and culture techniques based on this principle are giving very promising results.