Growth Promoting Activity of Oocytes on Granulosa Cells Is Decreased upon Meiotic Maturation

Abstract

An increasing body of evidence indicates that the oocyte plays an active role in the control of ovarian follicle development in mammals. In the present study, we have examined the role of oocytes in regulating granulosa cell proliferation. Rat and bovine oocytes cocultured with rat granulosa cells stimulated granulosa cell DNA synthesis and DNA content in the cultures. FSH or cAMP further amplified this effect. Poor-quality oocytes showed a marked decrease in their stimulatory effect. Stimulation of DNA synthesis by bovine oocytes seems to be cell-type specific, since Swiss 3T3 fibroblasts and CCL-64 mink lung epithelial cells were not responsive, while primary cultures of rat and bovine granulosa cells and the bovine granulosa cell line BGC-1 showed significant responses. Oocyte-conditioned medium produced only a slight stimulation of rat granulosa cell DNA synthesis. However, the effect of oocyte coculture was dependent on the total incubation volume, suggesting that the growth promoting activity was mediated by a soluble factor. The stimulation elicited by bovine oocytes was evident even in the presence of maximally effective doses of transforming growth factor-beta or tumor necrosis factor-alpha, indicating that neither of these growth factors was responsible for this effect. In vitro maturation of bovine oocytes was associated with a marked decrease in the stimulatory activity. This decrease was partially prevented when maturation was blocked by addition of cycloheximide. Comparison of the developmental pattern of the secretion of the growth promoting activity with that of the cumulus expansion-enabling factor indicated that both activities can be dissociated. Our data suggest the existence of a very labile factor produced by the oocyte before completion of the first meiotic division that promotes granulosa cell proliferation.

Effects of species differences on oocyte regulation of granulosa cell function

“…These findings are consistent with their known roles on ovarian follicular development in vivo (Juengel & McNatty 2005). Collectively, the aforementioned results are consistent with previous reports showing dose-related effects of mouse, rat or bovine oocytes on 3 H-thymidine incorporation by rodent GC (Vanderhyden et al 1992, Lanuza et al 1998, Otsuka & Shimasaki 2002, Gilchrist et al 2004. Despite a dose response effect of rat oocyte numbers on 3 H-thymidine incorporation by rat GC, 3 H-thymidine incorporation in rat DO-GC co-incubations was only reduced after blocking the action of GDF9 and not of BMP15.…”

“…However, it is known that when the health of follicles based on GC criteria is assessed, BMP15 and GDF9 mRNA are significantly lower in atretic compared with healthy follicles . Moreover, Lanuza et al (1998) have reported that poor quality bovine oocytes are less effective than good quality oocytes in stimulating 3 H-thymidine uptake by rat GC.…”

“…One approach to examining the effects of species differences of oocytes on GC is to test the effects of oocytes from a high ovulation rate phenotype against GC from a low ovulation rate phenotype and vice versa. Hitherto, the oocyte-GC co-incubation model has been used extensively to determine the roles of oocytes or oocyte-derived growth factors on the regulation of GC function (Vanderhyden et al 1992, Lanuza et al 1998, Otsuka & Shimasaki 2002, Gilchrist et al 2004. This model has also been used to test the role of GDF9 from murine oocytes on murine GC using an immunoneutralisation approach with a GDF9-specific MAB (Gilchrist et al 2004).…”

Growth and Differentiation of Small Ovarian Follicles in Mammals: Problems and Future Perspectives.

“…At the same time, the oocyte regulates a broad range of granulosa cell functions through the release of paracrine signals. Germ cells stimulate granulosa cell proliferation and differentiation [45][46][47][48], modulates steroidogenesis [49], expression of the c-kit ligand [50], LH receptor (LHR [51]), hyaluronic acid (HA) synthesis [52] and urokinasetype plasminogen activator (uPA [53]). As antral follicle is formed, a gradient of oocyte-secreted factors directs the specialization of the surrounding granulosa cells, referred to as cumulus cells, in a s p e c i f i c p h e n o t y p e , i n o r d e r t o c r e a t e a microenvironment capable to better respond to the oocyte requirements.…”

Effects of Oxygen Tension on Survival and Growth In Vitro of Bovine Oocytes from Early Antral Follicles

“…In addition to the communication through gap junctions, both granulosa cells and oocytes produce paracrine factors [19,20], which are important in the regulation of oocyte growth and follicular development. For example, growth differentiation factor-9, which is produced by oocytes, promotes granulosa cell proliferation [21][22][23], and regulates granulosa cell differentiation [24][25][26][27][28]. Moreover, oocytes seem to promote the formation of follicular antrum [29,30], so that there is a bidirectional regulatory loop between the oocytes and their companion granulosa cells [31,32].…”