FOLLICULAR DEVELOPMENT THROUGH PREANTRAL STAGES - SIGNALING VIA GROWTH-FACTORS

Although gonadotrophins, particularly FSH, are the primary pituitary r egulators of ovarian folliculogenesis, the involvement of ovarian-deri ved growth factors in follicular growth and maturation has become incr easingly apparent over the past decade. Regulators of ovarian somatic cells can be broadly divided into (I) mitogenic factors, and (2) diffe rentiation-induction factors, based on two primary cellular requiremen ts, that is, proliferation and differentiation that are fundamental to folliculogenesis and ovarian functions. In this article, direct as we ll as indirect evidence is presented that highlights the roles of epid ermal growth factor - a mitogen, and transforming growth factor beta - a differentiation-induction factor, in modulating gonadotrophin actio n in the ovary, particularly in the preantral follicles. An exquisitel y timed and regionalized expression of these two types of peptide fact or, along with their membrane receptors, may determine the differentia l success of follicle development, hence, allowing selection of the be st oocytes for fertilization and subsequent development.