Endocrine Abstracts

Germ cell-somatic cell communication in the ovary is essential for follicle and oocyte development. This communication may take place via gap junctions or via paracrine mediated signalling through the secretion of growth factors. Over the past ten to fifteen years there has been a major change in how the oocyte is perceived within the context of the ovarian follicle. The original view of the oocyte as a passenger benefiting from the nutrients provided by gap-junction coupled somatic cells has been supplanted by one in which the oocyte is very much in (or at least sharing) the driving seat. This shift has come about through the identification of oocyte-secreted growth factors that have been shown to control the proliferation and differentiation of the companion granulosa cells. These studies have greatly advanced our understanding of paracrine signalling pathways in the process of follicle development.

In contrast to these advances in paracrine signalling, little work has been performed to determine whether gap junctions play a role in signalling between the oocyte and granulosa cell compartments. This is particularly relevant in the control of meiotic progression in the oocyte, where it has been proposed that cAMP and calcium play a major role in the control of entry into the first meiotic division. Using isolated cumulus-oocyte complexes and a FRET-based cAMP sensor we have shown that FSH, acting via receptors on the cumulus cells, leads to an increase in cAMP in the oocyte. Similarly, induction of an increase in Calcium in the cumulus cells results in this signal being propagated to the oocyte. These studies demonstrate that second messengers may propagate from the cumulus cells, where they have one function, to the oocyte where they may play a role in regulating meiotic maturation.