Localization of Luteinizing Hormone Receptor Messenger Ribonucleic Acid Expression in Ovarian Cell Types during Follicle Development and Ovulation*

Heat stress inhibits ovarian follicular development in mammalian species. We hypothesized that heat stress inhibits the function of follicular granulosa cells and suppresses follicular development. To test this, immature female rats were injected with pregnant mare serum gonadotropin (PMSG) at 48 h after the start of temperature treatment (control: 25 8C, 50% RH; heat stress: 35 8C, 70% Relative Humidity). The ovaries and granulosa cells of follicles at different developmental stages were analyzed for gonadotropin receptor levels and aromatase activity; estradiol levels were measured in follicular fluid. Before injection, heat stress diminished only the amount of FSH receptor on granulosa cells of antral follicles. During PMSG-stimulated follicular development, heat stress strongly inhibited gonadotropin receptor levels and aromatase activity in granulosa cells, and estradiol levels in the follicular fluid of early antral, antral and preovulatory follicles. To examine apoptosis and mRNA levels of bcl-2 and bax in granulosa cells, follicles harvested 48 h after PMSG injection were cultured in serum-free conditions. Heat-stressed granulosa cells showed a time-dependent increase in apoptosis. The bcl-2 mRNA levels were similar in control and heat-stressed granulosa cells; bax mRNA levels were increased in heat-stressed granulosa cells. According to these results, heat stress inhibits expression of gonadotropin receptors in granulosa cells and attenuates estrogenic activity of growing follicles, granulosa cells of heat-stressed follicles are susceptible to apoptosis, and the bcl2/bax system is not associated with heat-stress-induced apoptosis of granulosa cells. Our study suggests that decreased numbers and function of granulosa cells may cause ovarian dysfunction in domestic animals in summer.

Section: Discussionmentioning

confidence: 56%

Heat stress diminishes gonadotropin receptor expression and enhances susceptibility to apoptosis of rat granulosa cells

Shimizu¹,

Ohshima²,

Ozawa³

et al. 2005

“…As mentioned previously, LH acts on the outermost, mural granulosa cells of the follicle; cumulus cells and oocytes lack LH receptors (Peng et al 1991, Eppig et al 1997. The LH signal must therefore be transmitted from the mural granulosa cells to the oocyte.…”

Section: How Does Lh Trigger Meiotic Resumption?mentioning

confidence: 89%

“…LH receptors are located on the mural granulosa cells but not on the cumulus cells or the oocyte (Peng et al 1991, Eppig et al 1997, so the mechanism(s) by which LH stimulates oocyte maturation is indirect. Although much is known about LH signaling in the mural granulosa cells (Richards et al 2002), how the LH signal is passed on to the oocyte is incompletely understood.…”

Section: Introductionmentioning

confidence: 99%

Stops and starts in mammalian oocytes: recent advances in understanding the regulation of meiotic arrest and oocyte maturation

Mehlmann¹

2005

437

307

Mammalian oocytes grow and undergo meiosis within ovarian follicles. Oocytes are arrested at the first meiotic prophase, held in meiotic arrest by the surrounding follicle cells until a surge of LH from the pituitary stimulates the immature oocyte to resume meiosis. Meiotic arrest depends on a high level of cAMP within the oocyte. This cAMP is generated by the oocyte, through the stimulation of the G s G-protein by the G-protein-coupled receptor, GPR3. Stimulation of meiotic maturation by LH occurs via its action on the surrounding somatic cells rather than on the oocyte itself. LH induces the expression of epidermal growth factor-like proteins in the mural granulosa cells that act on the cumulus cells to trigger oocyte maturation. The signaling pathway between the cumulus cells and the oocyte, however, remains unknown. This review focuses on recent studies highlighting the importance of the oocyte in producing cAMP to maintain arrest, and discusses possible targets at the level of the oocyte on which LH could act to stimulate meiotic resumption.

“…This is achieved through activation of intrafollicular signaling and gene expression pathways leading to CCs expansion, meiosis resumption, oocyte final maturation, and ovulation in most mammalian species including mouse (Panigone et al 2008), pig (Kawashima et al 2008), cow (Hyttel et al 1997, and human (Filicori 1999, Feuerstein et al 2007. Although it has been established that LH triggers key functions in both oocyte and cumulus, there are questions about the presence of LH receptor proteins in CCs membrane, suggesting an indirect induction pathway (Peng et al 1991) probably through the EGFR (epidermal growth factor receptor) pathway (Panigone et al 2008, Reizel et al 2010.…”

Section: Introductionmentioning

confidence: 99%

Cumulus cell gene expression following the LH surge in bovine preovulatory follicles: potential early markers of oocyte competence

Assidi¹,

Dieleman²,

Sirard³

2010

Cumulus cells (CCs) are essential for oocytes to reach full development competency and become fertilized. Many major functional properties of CCs are triggered by gonadotropins and governed by the oocyte. Consequently, cumulus may reflect oocyte quality and is often used for oocyte selection. The most visible function of CCs is their ability for rapid extracellular matrix expansion after the LH surge. Although unexplained, LH induces the final maturation and improves oocyte quality. To study the LH signaling and gene expression cascade patterns close to the germinal vesicle breakdown, bovine CCs collected at 2 h before and 6 h after the LH surge were hybridized to a custom-made microarray to better understand the LH genomic action and find differentially expressed genes associated with the LH-induced oocyte final maturation. Functional genomic analysis of the 141 overexpressed and 161 underexpressed clones was performed according to their molecular functions, gene networks, and cell compartments. Following real-time PCR validation of our gene lists, some interesting pathways associated with the LH genomic action on CCs and their possible roles in oocyte final maturation, ovulation, and fertilization are discussed. A list of early potential markers of oocyte competency in vivo and in vitro is thereafter suggested. These early biomarkers are a preamble to understand the LH molecular pathways that trigger the final oocyte competence acquisition process in bovine.