Oocyte-Somatic Cell Interactions and Implications for Fertility Regulation (Pages: 0-0)


Kenneth P McNatty *,

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In mammals the initiation of ovarian follicular growth occurs as the oocyte enlarges and the immediately adjacent somatic (i.e. granulosa cells) develop a uniformly cuboidal appearance and proliferate. Whilst this transformation is accompanied by the expression of several hundred new genes not expressed in the primordial follicles the key factors responsible for the initiation of growth are not well understood. Nevertheless it has now been established that the oocyte plays an essential role in regulating follicular growth once growth has been initiated at least until follicles develop a dependency on the pituitary hormones LH and FSH for preovulatory maturation. During the period preceding gonadotrophin dependence the oocyte is thought to regulate follicular growth through the secretions of growth factors such as bone morphogenetic protein (BMP)-15 and growth and differentiation factor (GDF)-9 and by interactions with the granulosa cells via an extensive network of gap-junctions. In this way the oocyte is thought to regulate the proliferation and differentiation of its adjacent granulosa cells into two distinct phenotypes namely the cumulus cells (those immediately adjacent to the oocyte) and the mural granulosa cells (those more distantly located from the oocyte). Moreover from studies in sheep it appears that the localised concentrations of BMP-15 within the developing follicle influences the timing of formation of receptors for LH on mural granulosa cells and thus the number of follicles that may go on to ovulate. Currently there is intense interest in determining the molecular forms and mechanisms of action of BMP-15 and GDF-9 and the potential applications of these growth factors for improving fertility in vivo and for use with in vitro technologies to improve IVF outcomes