GROWTH FACTORS IN FOLLICULAR DEVELOPMENT

Malfunction of granulosa cells results in follicular atresia, oocyte
degeneration, sterility and impairment of a variety of physiological
processes that depend on ovarian steroids. The purpose of the present
proposal is to provide insight into the intricate cellular and molecular
mechanisms involved in gonadotropin regulated folliculogenesis in general
and granulosa cell function in particular. Because conventional granulosa
cell cultures result in the loss of follicular structure and alteration in
cell functions, we have developed an alternative approach to study
follicular functions by use of isolated intact preantral follicles from the
hamster ovary and a long-term culture system for their in vitro
development. This technique opens an entirely new dimension to study
directly the physiology and biochemistry of proliferating follicular cells
in their native, follicular microenvironment. We have determined that
follicular cells in these cultures synthesize cAMP and steroids,
proliferate in response to gonadotropins; express gonadotropin receptors as
well as unique follicular proteins. We have observed that mitogenic action
of FSH is transduced via EGF. Radioimmunoassay data, Western blotting and
immunoprecipitation studies indicated that the hamster ovary has both EGF,
TGF beta1 and beta2-like proteins, and EGF receptors. However, the
cellular and molecular changes during development of the follicles and the
roles of growth factors in these processes remain to be determined. I
hypothesize that gonadotropin and steroid regulation of follicular cell
proliferation and differentiation depend upon critical modulation of the
activities of ovarian growth factors (e.g., EGF and TGFs-beta) and their
receptors. Disruption of this process results in malfunctions in granulosa
cells and sterility. The present study will focus on one important
question: (1) Do gonadotropins regulate folliculogenesis by modulating
ovarian EGF and TGFs-beta (beta1 and beta2) activities? The study will
involve (1) immunohistochemical analyses of growth factor expression and
their hormonal control during in vivo and in vitro follicular development;
(2) biochemical analyses of growth factor effects on follicular growth and
steroidogenesis, and (3) immunohistochemical and biochemical assessment of
EGF- receptors during hormonal control of follicular development.
Identification of the pathway for gonadotropin action in intact ovarian
follicles will significantly add to our knowledge of the fundamental
mechanisms of folliculogenesis.