The involvement of the Toll-like receptor family in ovulation

Whole-genome association analyses for lifetime reproductive traits in the pig

Profits for commercial pork producers vary in part because of sow productivity or sow productive life (SPL) and replacement costs. During the last decade, culling rates of sows have increased to more than 50% in the United States. Both SPL and culling rates are influenced by genetic and nongenetic factors. A whole-genome association study was conducted for pig lifetime reproductive traits, including lifetime total number born (LTNB), lifetime number born alive (LNBA), removal parity, and the ratio between lifetime nonproductive days and herd life. The proportion of phenotypic variance explained by markers was 0.15 for LTNB and LNBA, 0.12 for removal parity, and 0.06 for the ratio between lifetime nonproductive days and herd life. Several informative QTL regions (e.g., 14 QTL regions for LTNB) and genes within the regions (e.g., SLC22A18 on SSC2 for LTNB) were associated with lifetime reproductive traits in this study. Genes associated with LTNB and LNBA were similar, reflecting the high genetic correlation (0.99 ± 0.003) between these traits. Functional annotation revealed that many genes at the associated regions are expressed in reproductive tissues. For instance, the SLC22A18 gene on SSC2 associated with LTNB has been shown to be expressed in the placenta of mice. Many of the QTL regions showing associations coincided with previously identified QTL for fat deposition. This reinforces the role of fat regulation for lifetime reproductive traits. Overall, this whole-genome association study provides a list of genomic locations and markers associated with pig lifetime reproductive traits that could be considered for SPL in future studies.

The nuclear receptor cofactor receptor-interacting protein 140 is a positive regulator of amphiregulin expression and cumulus cell-oocyte complex expansion in the mouse ovary

The nuclear receptor cofactor receptor-interacting protein 140 (RIP140) is essential for cumulus cell-oocyte complex (COC) expansion, follicular rupture, and oocyte release during ovulation. The expression of many genes necessary for COC expansion is impaired in the absence of RIP140, but the studies herein document that their expression can be restored and COC expansion rescued by treatment with the epidermal growth factor (EGF)-like factor amphiregulin (AREG) both in vitro and in vivo. We demonstrate by several approaches that RIP140 is required for the expression of the EGF-like factors in granulosa cells, but the dependence of genes involved in cumulus expansion, including Ptgs2 Has2, Tnfaip6, and Ptx3, is indirect because they are induced by AREG. Treatment of granulosa cells with forskolin to mimic the effects of LH increases AREG promoter activity in a RIP140-dependent manner that 1) requires an intact cAMP response element in the proximal promoter region of the Areg gene and 2) involves its actions as a coactivator for cAMP response element-binding protein/c-Jun transcription factors. Although human chorionic gonadotropin and AREG coadministration is sufficient to restore ovulation fully in RIP140 heterozygous mice in vivo, both follicular rupture and ovulation remain impaired in the RIP140 null mice. Thus, we conclude that although the level of RIP140 expression in the ovary is a crucial factor required for the transient expression of EGF-like factors necessary for cumulus expansion, it also plays a role in other signaling pathways that induce follicular rupture.

The ovary: basic biology and clinical implications

The classical view of ovarian follicle development is that it is regulated by the hypothalamic-pituitary-ovarian axis, in which gonadotropin-releasing hormone (GnRH) controls the release of the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and that ovarian steroids exert both negative and positive regulatory effects on GnRH secretion. More recent studies in mice and humans indicate that many other intra-ovarian signaling cascades affect follicular development and gonadotropin action in a stage- and context-specific manner. As we discuss here, mutant mouse models and clinical evidence indicate that some of the most powerful intra-ovarian regulators of follicular development include the TGF-beta/SMAD, WNT/FZD/beta-catenin, and RAS/ERK1/2 signaling pathways and the FOXO/FOXL2 transcription factors.

New insights into ovarian function

Infertility adversely affects many couples worldwide. Conversely, the exponential increase in world population threatens our planet and its resources. Therefore, a greater understanding of the fundamental cellular and molecular events that control the size of the primordial follicle pool and follicular development is of utmost importance to develop improved in vitro fertilization as well as to design novel approaches to regulate fertility. In this review we attempt to highlight some new advances in basic research of the mammalian ovary that have occurred in recent years focusing primarily on mouse models that have contributed to our understanding of ovarian follicle formation, development, and ovulation. We hope that these new insights into ovarian function will trigger more research and translation to clinically relevant problems.

The differential transcriptome and ontology profiles of floating and cumulus granulosa cells in stimulated human antral follicles

Communication between various ovarian cell types is a prerequisite for folliculogenesis and ovulation. In antral follicles granulosa cells divide into two distinct populations of mural and cumulus granulosa cells (CGC), enveloping the antrum and surrounding the oocyte, respectively. Both cell types, with the mural compartment in excess, contribute to the floating granulosa cell (FGC) population in the follicular fluid. The aim of this study was to compare the transcriptomes of FGC and CGC in stimulated antral follicles obtained from 19 women undergoing IVF-ICSI procedure. FGC were obtained from follicular fluid during the follicle puncture procedure and CGC were acquired after oocyte denudation for micromanipulation. Gene expression analysis was conducted using the genome-wide Affymetrix transcriptome array. The expression profile of the two granulosa cell populations varied significantly. Out of 28 869 analysed transcripts 4480 were differentially expressed (q-value < 10(-4)) and 489 showed > or =2-fold difference in the expression level with 222 genes up-regulated in FGC and 267 in CGC. The transcriptome of FGC showed higher expression of genes involved in immune response, hematological system function and organismal injury, although CGC had genes involved in protein degradation and nervous system function up-regulated. Cell-to-cell signalling and interaction pathways were noted in both cell populations. Furthermore, numerous novel transcripts that have not been previously described in follicular physiology were identified. In conclusion, our results provide a solid basis for future studies in follicular biology that will help to identify molecular markers for oocyte and embryo viability in IVF.

Control of ovulation in mice by progesterone receptor-regulated gene networks

The mid-cycle surge of luteinizing hormone (LH) induces ovulation, a process during which a fertilizable oocyte is released from a mature ovarian follicle. Although ovulation is a physiologically well-characterized event, the underlying molecular pathways remain poorly understood. Progesterone receptor (PGR), which mediates the biological effects of the steroid hormone progesterone, has emerged as a key regulator of ovulation in mice. The development of a progesterone-receptor-null (Pgr-null) mouse model confirmed a critical role of this hormone in ovulation because in these mutant mice, mature pre-ovulatory follicles fail to release the oocytes. This animal model has thus presented a unique opportunity to study the molecular pathways underlying ovulation. Gene-expression profiling experiments by several groups, using the ovaries of Pgr-null mice, revealed novel gene networks, which act downstream of PGR to control ovulation. These genes encode diverse molecules such as proteases, transcription factors, cell-adhesion molecules, modulators of vascular activities and regulators of inflammation. Functional analyses using gene-knockout mouse models have confirmed that some of these factors play critical roles during ovulation. The knowledge gained from these studies has helped us to understand better the molecular mechanisms that facilitate the release of oocytes from pre-ovulatory follicles. Further analysis of the role of molecular regulators of ovulation will help identify useful molecular targets that would allow the development of improved contraceptives and new therapeutics for anovulatory infertility.

Toll-like receptor signaling in hen ovarian granulosa cells is dependent on stage of follicle maturation

The recent identification of toll-like receptor (TLR) signaling within ovarian granulosa cells has broad implications for ovarian physiology. Functions of TLRs within granulosa cells of the laying hen are of particular interest due to the method of transovarian transmission of Salmonella enteritidis, which results in egg contamination. This study utilized hen granulosa cells to evaluate the expression and function of Gallus TLR-signaling at distinct stages of follicular maturity. Data presented herein demonstrate the presence of TLR2, TLR4, and TLR15 mRNAs in undifferentiated granulosa cells from prehierarchal follicles and differentiated granulosa cells from preovulatory follicles, together with mRNAs encoding adaptor proteins and signaling components required for TLR signaling gene. Treatment with lipopolysaccharide (LPS) or LH, in vitro, led to the differential regulation of TLRs based on the stage of follicle maturation, with the largest (F1) follicle granulosa cells having the most rapid response. Furthermore, treatment with LPS resulted in attenuation of agonist-induced progesterone synthesis in undifferentiated, but not differentiated, granulosa cells. Additionally, undifferentiated granulosa cells were significantly more sensitive to LPS-induced apoptosis than differentiated granulosa cells from the F1 follicle. Together, these data provide evidence for a complete and functional TLR signaling pathway in hen granulosa cells, with effects on steroidogenesis and cell viability dependent upon stage of maturation. These differences may reflect the susceptibility of granulosa cells at early stages of maturation to undergo apoptosis in response to select pathogenic stimuli, thus attenuating transovarian transmission, whereas granulosa cells from preovulatory follicles are comparably resistant to LPS-mediated apoptosis.