Follicle-Stimulating Hormone Increases Gap Junctional Communication Between Somatic and Germ-Line Follicular Compartments During Murine Oogenesis1

Germ cells develop in intimate contact and communication with somatic cells of the gonad. In female mammals, oocyte development depends crucially on gap junctions that couple it to the surrounding somatic granulosa cells of the follicle, yet the mechanisms that regulate this essential intercellular communication remain incompletely understood. Follicle-stimulating hormone (FSH) drives the terminal stage of follicular development. We found that FSH increases the steady-state levels of mRNAs encoding the principal connexins that constitute gap junctions and cadherins that mediate cell attachment. This increase occurs both in granulosa cells, which express the FSH-receptor, and in oocytes, which do not. FSH also increased the number of transzonal projections that provide the sites of granulosa cell-oocyte contact. Consistent with increased connexin expression, FSH increased gap junctional communication between granulosa cells and between the oocyte and granulosa cells, and it accelerated oocyte development. These results demonstrate that FSH regulates communication between the female germ cell and its somatic microenvironment. We propose that FSH-regulated gap junctional communication ensures that differentiation processes occurring in distinct cellular compartments within the follicle are precisely coordinated to ensure production of a fertilizable egg.