Concentrations of steroids and expression of messenger RNA for steroidogenic enzymes and gonadotropin receptors in bovine ovarian follicles of first and second waves and changes in second wave follicles after pulsatile LH infusion

Effects of insulin-like growth factor-1 on the mRNA expression of estradiol receptors, steroidogenic enzymes, and steroid production in bovine follicles

Insulin-like growth factor-1 (IGF-1) plays a crucial role in follicular growth and stimulates steroid hormone production in bovine follicles. Steroid hormones are synthesized through the actions of steroidogenic enzymes, specifically STAR, CYP11A1, HSD3B, and CYP19A1 in both theca cells (TCs) and granulosa cells (GCs), under the influence of gonadotropins. Particularly, estradiol 17β (E2) assumes a central role in follicular development and selection by activating estrogen receptors β (ESR2) in GCs. We assessed ESR2 mRNA expression in GCs of developing follicles and investigated the impact of IGF-1 on the mRNA expression of ESR2, CYP19A1, FSHR, and LHCGR, STAR, CYP11A1, and HSD17B in cultured GCs and TCs, respectively. Additionally, we assessed the influence of IGF-1 on androstenedione (A4), progesterone (P4), and testosterone (T) production in TCs. Small-sized follicles (< 6 mm) exhibited the highest levels of ESR2 mRNA expression, whereas medium-sized follicles (7-8 mm) displayed higher levels than large-sized follicles (≥ 9 mm) (P < 0.05). IGF-1 increased the mRNA expression of ESR2, CYP19A1, and FSHR in GCs of follicles of both sizes, except for FSHR mRNA in medium-sized follicles (P < 0.05). IGF-1 significantly elevated mRNA expression of LHCGR, STAR, CYP11A1, and CYP17B in TCs of small- and medium-sized follicles (P < 0.05). Moreover, IGF-1 augmented the production of A4 and P4 but had no impact on T production in TCs of small- and medium-sized follicles. Taken together, our findings indicate that IGF-1 upregulates steroidogenic enzymes and steroid hormone production, underscoring the crucial role of IGF-1 in follicle development and selection.

Proteomic characterization of bovine granulosa cells in dominant and subordinate follicles

Background

Characterization of molecular factors regulating ovarian follicular development is critical to understanding its functional mechanism of controlling the estrous cycle, determining oocyte competency, and regulating ovulation. In previous studies, we performed next-gene sequencing to investigate the differentially expressed transcripts of bovine follicular granulosa cells (GCs) at the dominant follicle (DF) and subordinate follicle (SF) stages during the first follicular wave. This study aims to investigate the proteomic characterization of GCs of DF and SF in the bovine estrous cycle.

Results

In total, 3409 proteins were identified from 30,321 peptides obtained from liquid chromatograph-mass spectrometer analysis. Two hundred fifty-nine of these proteins were found to be expressed differently in DF and SF. Out of 259, a total of 26 proteins were upregulated (fold change≥2) and 233 proteins were downregulated (fold change≤0.5) in DF. Gene Ontology (GO) analysis of proteome data revealed the biological process, cellular component and molecular function of expressed proteins in DF and SF, while the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed important signaling pathways associated with follicular development such as the PI3K-Akt, estrogen, and insulin signaling pathways. Immunoblotting results of OGN, ROR2, and HSPB1 confirmed the accuracy of the data. Bioinformatics analysis showed that 13 proteins may be linked to follicular development.

Conclusions

Findings from this study will provide useful information for exploring follicular development and function.

Electronic supplementary material

The online version of this article (10.1186/s41065-019-0097-5) contains supplementary material, which is available to authorized users.

Production and validation of a polyclonal serum against bovine FSH receptor

In ovarian granulosa cells, follicle-stimulating hormone (FSH) regulates the proliferation and differentiation events required for follicular growth and oocyte maturation. FSH actions are mediated exclusively through the FSH receptor (FSHR). In cattle, the FSHR gene expression pattern during folliculogenesis and the implications of this receptor in reproductive disorders have been extensively studied. However, the limited availability of specific antibodies against bovine FSHR has restricted FSHR protein analysis. In the present study, we developed an anti-FSHR polyclonal serum by using a 14-kDa peptide conjugated to maltose binding protein. The antiserum obtained was characterized by western blot of protein extracts from bovine follicles, BGC-1 cells and primary cultures of granulosa cells stimulated with testosterone. Also, the blocking effect of serum on estradiol secretion and cell viability after gonadotropin stimulus was characterized in a functional in vitro assay. A 76-kDa protein, consistent with the predicted molecular size of full-length FSHR, was detected in ovarian tissue. Besides, two immunoreactive bands of 60-kDa and 30-kDa (only in cultured cells) were detected. These bands would be related to some of the isoforms of the receptor. Therefore, immunohistochemical assays allowed detecting FSHR in the cytoplasm of granulosa cells and an increase in its expression as follicles progressed from primordial to large preantral follicles. These results suggest that the anti-FSHR serum here developed has good reactivity and specificity against the native FSHR. Therefore, this antiserum may serve as a valuable tool for future studies of the biological function of FSHR in physiological conditions as well as of the molecular mechanism and functional involvement of FSHR in reproductive disorders.

Changes in ovarian function associated with circulating concentrations of estradiol before a GnRH-induced ovulation in beef cows

These studies were conducted to evaluate causes for differences in circulating concentrations of estradiol before a GnRH-induced ovulation. Beef cows were synchronized by an injection of GnRH on day -7 and an injection of prostaglandin F2α (PGF2α) on day 0. In experiment 1, blood samples were collected every 3 h from PGF2α on day 0 to hour 33 after PGF2α and at slaughter (hour 36 to 42; n = 10). Cows were assigned to treatment group based on circulating concentrations of estradiol (E2): HighE2 vs LowE2. At slaughter, follicular fluid (FF) and granulosa cells were collected from the dominant follicle. In experiment 2, blood samples (n = 30) were collected every 8 h from PGF2α until the dominant follicle was aspirated via ultrasound-guided follicular aspiration to collect FF and granulosa cells (hour 38 to 46). In experiment 1, HighE2 had increased abundance of 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.02), and greater concentrations of estradiol and androstenedione (P ≤ 0.02) in the FF. In experiment 2, HighE2 had increased abundance of CYP11A1, 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.03) vs either LowE2 or GnRHLowE2. There was a tendency (P = 0.07) for LH pulse frequency to be increased in both the GnRHLowE2 and HighE2 compared with LowE2. HighE2 cows experienced increas in circulating concentrations of estradiol compared with LowE2. In conclusion, animals with greater concentrations of circulating estradiol before fixed-time AI experienced an upregulation of the steroidogenic pathway during the preovulatory period.

Molecular aspects of bovine cystic ovarian disease pathogenesis

Cystic ovarian disease (COD) is one of the main causes of reproductive failure in cattle and causes severe economic loss to the dairy farm industry because it increases both days open in the post partum period and replacement rates due to infertility. This disease is the consequence of the failure of a mature follicle to ovulate at the time of ovulation in the estrous cycle. This review examines the evidence for the role of altered steroid and gonadotropin signaling systems and the proliferation/apoptosis balance in the ovary with cystic structures. This evidence suggests that changes in the expression of ovarian molecular components associated with these cellular mechanisms could play a fundamental role in the pathogenesis of COD. The evidence also shows that gonadotropin receptor expression in bovine cystic follicles is altered, which suggests that changes in the signaling system of gonadotropins could play a fundamental role in the pathogenesis of conditions characterized by altered ovulation, such as COD. Ovaries from animals with COD exhibit a disrupted steroid receptor pattern with modifications in the expression of coregulatory proteins. These changes in the pathways of endocrine action would trigger the changes in proliferation and apoptosis underlying the aberrant persistence of follicular cysts.

Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R251/suppl/DC1.

The global effect of follicle-stimulating hormone and tumour necrosis factor α on gene expression in cultured bovine ovarian granulosa cells

BACKGROUND

Oocytes mature in ovarian follicles surrounded by granulosa cells. During follicle growth, granulosa cells replicate and secrete hormones, particularly steroids close to ovulation. However, most follicles cease growing and undergo atresia or regression instead of ovulating. To investigate the effects of stimulatory (follicle-stimulating hormone; FSH) and inhibitory (tumour necrosis factor alpha; TNFα) factors on the granulosa cell transcriptome, bovine ovaries were obtained from a local abattoir and pools of granulosa cells were cultured in vitro for six days under defined serum-free conditions with treatments present on days 3-6. Initially dose-response experiments (n = 4) were performed to determine the optimal concentrations of FSH (0.33 ng/ml) and TNFα (10 ng/ml) to be used for the microarray experiments. For array experiments cells were cultured under control conditions, with FSH, with TNFα, or with FSH plus TNFα (n = 4 per group) and RNA was harvested for microarray analyses.

RESULTS

Statistical analysis showed primary clustering of the arrays into two groups, control/FSH and TNFα/TNFα plus FSH. The effect of TNFα on gene expression dominated that of FSH, with substantially more genes differentially regulated, and the pathways and genes regulated by TNFα being similar to those of FSH plus TNFα treatment. TNFα treatment reduced the endocrine activity of granulosa cells with reductions in expression of FST, INHA, INBA and AMH. The top-ranked canonical pathways and GO biological terms for the TNFα treatments included antigen presentation, inflammatory response and other pathways indicative of innate immune function and fibrosis. The two most significant networks also reflect this, containing molecules which are present in the canonical pathways of hepatic fibrosis/hepatic stellate cell activation and transforming growth factor β signalling, and these were up regulated. Upstream regulator analyses also predicted TNF, interferons γ and β1 and interleukin 1β.

CONCLUSIONS

In vitro, the transcriptome of granulosa cells responded minimally to FSH compared with the response to TNFα. The response to TNFα indicated an active process akin to tissue remodelling as would occur upon atresia. Additionally there was reduction in endocrine function and induction of an inflammatory response to TNFα that displays features similar to immune cells.

Transcriptome profiling of granulosa cells of bovine ovarian follicles during growth from small to large antral sizes

Background

At later stages of folliculogenesis, the mammalian ovarian follicle contains layers of epithelial granulosa cells surrounding an antral cavity. During follicle development granulosa cells replicate, secrete hormones and support the growth of the oocyte. In cattle, the follicle needs to grow > 10 mm in diameter to allow an oocyte to ovulate, following which the granulosa cells cease dividing and differentiate into the specialised cells of the corpus luteum. To better understand the molecular basis of follicular growth and granulosa cell maturation, we undertook transcriptome profiling of granulosa cells from small (< 5 mm; n = 10) and large (> 10 mm, n = 4) healthy bovine follicles using Affymetrix microarrays (24,128 probe sets).

Results

Principal component analysis for the first two components and hierarchical clustering showed clustering into two groups, small and large, with the former being more heterogeneous. Size-frequency distributions of the coefficient of variation of the signal intensities of each probe set also revealed that small follicles were more heterogeneous than the large. IPA and GO enrichment analyses revealed that processes of axonal guidance, immune signalling and cell rearrangement were most affected in large follicles. The most important networks were associated with: (A) Notch, SLIT/ROBO and PI3K signalling, and (B) ITGB5 and extracellular matrix signalling through extracellular signal related kinases (ERKs). Upstream regulator genes which were predicted to be active in large follicles included STAT and XBP1. By comparison, developmental processes such as those stimulated by KIT, IHH and MEST were most active in small follicles. MGEA5 was identified as an upstream regulator in small follicles. It encodes an enzyme that modifies the activity of many target proteins, including those involved in energy sensing, by removal of N-acetylglucosamine from serine and threonine residues.

Conclusions

Our data suggest that as follicles enlarge more genes and/or pathways are activated than are inactivated, and gene expression becomes more uniform. These findings could be interpreted that either the cells in large follicles are more uniform in their gene expression, or that follicles are more uniform or a combination of both and that additional factors, such as LH, are additionally controlling the granulosa cells.

The effect of short-term nutritional supplementation of ewes with lupin grain (Lupinus luteus) on folliculogenesis, the concentrations of hormones and glucose in plasma and follicular fluid and the follicular levels of P450 aromatase and IRS-1, -2 and -4

An experiment was conducted on 48 ewes during follicular and luteal phases of the oestrous cycle to determine the effect of a 5-day lupin grain supplementation (500 g/day) on folliculogenesis, plasma concentrations of glucose, insulin, FSH and oestradiol-17β (E2), follicular fluid concentrations of glucose, E2, androstenedione and progesterone and the levels of P450aromatase and insulin receptor substrate 1 (IRS-1), -2 and -4 in theca and granulosa cells. Average weight did not differ between lupin-fed and control groups. The numbers of follicles were increased (P<0.05; χ2) in the lupin-fed group. The plasma concentrations of glucose (P<0.05; ANOVA) and insulin (P<0.001; ANOVA) were higher in lupin-fed ewes. The plasma concentrations of FSH were not different but those of E2were decreased (P<0.001) in the lupin-fed group. Both the follicular fluid concentration of E2(P<0.05) and the level of P450aromatase in granulosa cells (P<0.05; ANOVA) were decreased in the lupin-fed group, but only during the follicular phase. The level of P450aromatase in granulosa cells was positively correlated with the concentration of E2in follicular fluid (r=0.820;P<0.001; ANOVA). The levels of IRS-1 and -2 in theca and granulosa cell lysates were increased in the lupin-fed group. These data suggest that insulin has a local role in the control of folliculogenesis and is likely to be a mediator of the effects of dietary energy intake on ovulation rate. We suggest that insulin acting through IRS proteins mediates the reproductive actions of insulin in the follicle and that IRS-1 and -2 are nutritionally regulated mediators of the action of insulin in the follicle.

Alteration in localization of steroid hormone receptors and coregulatory proteins in follicles from cows with induced ovarian follicular cysts

Cystic ovarian disease (COD) is an important cause of infertility in cattle. The altered follicular dynamics and cellular differentiation observed in COD may be mediated through a disruption of the expression of steroid receptors and their associated transcriptional cofactors. The aim of this study was to determine the protein expression profiles of ESR1, ESR2, PGR, AR, NCOA3, NCOR2, and PHB2 (REA) in ovarian follicles in an experimental model of COD induced by the administration of ACTH. Ovaries were collected and follicles were dissected from heifers during the follicular phase (control) or from heifers treated with ACTH to induce the formation of ovarian follicular cysts. Ovaries were fixed, sectioned, and stained immunohistochemically for steroid receptors and the associated transcription factors. The relative expression of ESR1 was similar in follicular cysts and in tertiary follicles from both control and cystic cows and was significantly higher than in secondary follicles. The expression of ESR2 in the granulosa was higher in cystic follicles. No differences were seen for PGR. The expression of androgen receptor was significantly increased in tertiary follicles with lower immunostaining in cysts. The expression of NCOA3 was observed in the granulosa and theca with a significantly increased expression in the theca interna of cystic follicles. The highest levels of NCOR2 expression in granulosa, theca interna, and theca externa were observed in cysts. In granulosa cells, NCOR2 levels increase progressively as follicles mature and the treatment had no effect. In summary, ovaries from animals with induced COD exhibited altered steroid receptor expression compared with normal animals, as well as changes in the expression of their regulators. It is reasonable to suggest that in conditions characterized by altered ovulation and follicular persistence, such as COD, changes in the intra-ovarian expression of these proteins could play a role in their pathogenesis.

Relationship between growth of the preovulatory follicle and its steroidogenic activity on the onset and expression of estrus behavior in CIDR-treated Bos indicus cows: an observational study

Estrus synchronization induces cows to gather in sexually active groups (SAGs) composed of females displaying mounting activity. Although this technique promotes the enhancement of sexual behavior, there are cows in estrus (CE) that delay estrus expression and also cows not displaying estrus (CNDE) even in the presence of a preovulatory follicle (PF). To elucidate the physiological mechanisms of the delay in the onset of estrus or absence of estrus behavior, an observational study was undertaken in 17 Bos indicus cows treated with exogenous progesterone (CIDR) to synchronize estrus and to monitor follicular growth and its steroidogenic activity. After SAGs formation, cows were ovariectomized at 24, 48, and 72 h post-CIDR. Among ovariectomized groups there were only 9 CE which: 1) showed differences in the onset of estrus; 2) displayed distinctive follicular growth patterns; and 3) at 72 h produced the highest intrafollicular estradiol concentration, and showed a linear trend to increase expression of P450scc and P450arom. Comparison of CE vs. CNDE showed that: 1) both groups had progesterone levels indicative of cyclic activity, and a PF which grew at a similar rate and size; 2) CE showed a stronger association between time and growth; and 3) CE produced more intrafollicular estradiol and progesterone, together with the expression of higher levels of P450arom. Results suggest that pending on the pattern of growth of the PF and its steroidogenic potential to produce estradiol, the onset and expression of estrus behavior may be delayed probably until the establishment of the appropriate conditions to ensure ovulation.

Gene expression pattern of adiponectin and adiponectin receptors in dominant and atretic follicles and oocytes screened based on brilliant cresyl blue staining

Adiponectin and its receptors (AdipoR1 and AdipoR2) are novel endocrine systems that act at various levels to control male and female fertility. The aim of this study was to determine whether adiponectin and its receptors gene expression levels differ between dominant follicle (DF) and atretic follicle (AF) and also between oocytes which were stained positively and negatively with brilliant cresyl blue (BCB(+) and BCB(-)). Based on estradiol/progesterone ratio, follicles from ovaries were classified as AFs and DFs. The stages of estrous cycle (follicular or luteal phases) were defined by macroscopic observation of the ovaries and the uterus. Oocytes were stained with BCB for 90 min. The relative expression of adiponectin, AdipoR1 and AdipoR2 mRNA in theca and cumulus cells and oocytes of different follicles were determined by quantitative real time PCR. Adiponectin and its receptors genes were clearly expressed higher (P<0.05) in theca and cumulus cells and oocytes of DFs than those of AFs during the follicular and luteal phases. BCB(+) oocytes showed a higher (P<0.05) expression of adiponectin and its receptors compared with their BCB(-) counterparts. Positive correlation (r>0.725, P<0.001) was observed between adiponectin mRNA level in ovarian cells of DFs and follicular fluid E2 concentration in follicular phase. Adiponectin mRNA abundance in ovarian cells of AFs showed a significant negative correlation with follicular fluid progesterone concentration in follicular and luteal phases (r<-0.731, P<0.001). This work has revealed the novel association of adiponectin and its receptors genes with follicular dominance and oocyte competence, thereby opening several new avenues of research into the mechanisms of dominance and competence in animal and human.

Differential expression of focimatrix and steroidogenic enzymes before size deviation during waves of follicular development in bovine ovarian follicles

During the growth of bovine follicles, one emerges from a wave as the largest and dominant follicle. What regulates dominance is not known but candidates include oestradiol, transforming growth factor beta beta1 (TGFB1), and recently CYP11AI (cholesterol side-chain cleavage) and focal intra-epithelial matrix (focimatrix). To examine this, pairs of bovine ovaries with 2 or more follicles of equal size (>5mm) and hence in a wave before deviation, were collected at an abattoir (6.7+/-SEM 0.1mm diameter; n=14 animals, 35 follicles in total). These follicles were dissected and follicular fluid collected to measure progesterone and oestradiol concentrations. A portion of the follicle wall was processed for histological classification of health or atresia and granulosa cells were harvested for quantitative RT-PCR of focimatrix components [COL4A1 (collagen type IV alpha1), LAMB2 (laminin beta2) and HSPG2 (perlecan)], steroidogenic enzymes [CYP11A1 and CYP19A1] and TGFB1. For statistical analyses follicles within each animal were grouped into either the highest (oestradiol, CYP11A1) or lowest (TGFB1) expression (n=14) for comparison with the remaining follicles (n=21). When grouped on oestradiol no other parameters differed significantly, and when grouped on TGFB1 some parameters were different however the levels were also lower, and not higher as expected. When grouped on CYP11A1 other parameters were significantly elevated in the high CYP11A1 group (COL4A1P<0.05; LAMB2P<0.01; HSPG2P<0.01 and CYP19A1P<0.001). This suggests that steroidogenesis and focimatrix might be important in a follicle attaining dominance.

Morphological classification of bovine ovarian follicles

Follicle classification is an important aid to the understanding of follicular development and atresia. Some bovine primordial follicles have the classical primordial shape, but ellipsoidal shaped follicles with some cuboidal granulosa cells at the poles are far more common. Preantral follicles have one of two basal lamina phenotypes, either a single aligned layer or one with additional layers. In antral follicles <5 mm diameter, half of the healthy follicles have columnar shaped basal granulosa cells and additional layers of basal lamina, which appear as loops in cross section ('loopy'). The remainder have aligned single-layered follicular basal laminas with rounded basal cells, and contain better quality oocytes than the loopy/columnar follicles. In sizes >5 mm, only aligned/rounded phenotypes are present. Dominant and subordinate follicles can be identified by ultrasound and/or histological examination of pairs of ovaries. Atretic follicles <5 mm are either basal atretic or antral atretic, named on the basis of the location in the membrana granulosa where cells die first. Basal atretic follicles have considerable biological differences to antral atretic follicles. In follicles >5 mm, only antral atresia is observed. The concentrations of follicular fluid steroid hormones can be used to classify atresia and distinguish some of the different types of atresia; however, this method is unlikely to identify follicles early in atresia, and hence misclassify them as healthy. Other biochemical and histological methods can be used, but since cell death is a part of normal homoeostatis, deciding when a follicle has entered atresia remains somewhat subjective.

The absence of corpus luteum formation alters the endocrine profile and affects follicular development during the first follicular wave in cattle

We previously established a bovine experimental model showing that the corpus luteum (CL) does not appear following aspiration of the preovulatory follicle before the onset of LH surge. Using this model, the present study aimed to determine the profile of follicular development and the endocrinological environment in the absence of CL with variable nadir circulating progesterone (P4) concentrations during the oestrous cycle in cattle. Luteolysis was induced in heifers and cows and they were assigned either to have the dominant follicle aspirated (CL-absent) or ovulation induced (CL-present). Ultrasound scanning to observe the diameter of each follicle and blood collection was performed from the day of follicular aspiration or ovulation and continued for 6 days. The CL-absent cattle maintained nadir circulating P4throughout the experimental period and showed a similar diameter between the largest and second largest follicle, resulting in co-dominant follicles. Oestradiol (E2) concentrations were greater in the CL-absent cows than in the CL-present cows at day −1, day 1 and day 2 from follicular deviation. The CL-absent cows had a higher basal concentration, area under the curve (AUC), pulse amplitude and pulse frequency of LH than the CL-present cows. After follicular deviation, the CL-absent cows showed a greater basal concentration, AUC and pulse amplitude of growth hormone (GH) than the CL-present cows. These results suggest that the absence of CL accompanying nadir circulating P4induces an enhancement of LH pulses, which involves the growth of the co-dominant follicles. Our results also suggest that circulating levels of P4and E2affect pulsatile GH secretion in cattle.

Exposure to human chorionic gonadotropin during in vitro maturation does not improve the maturation rate and developmental potential of immature oocytes from patients with polycystic ovary syndrome

OBJECTIVE

To investigate the effects of human chorionic gonadotropin (hCG) in culture medium on the in vitro maturation (IVM) and subsequent developmental potential of human immature oocytes.

DESIGN

Prospective, randomized study.

SETTING

Reproductive Medicine Center, First Affiliated Hospital of Wenzhou Medical College, People's Republic of China.

PATIENT(S)

62 women with polycystic ovary syndrome (PCOS) undergoing IVM treatment.

INTERVENTION(S)

Immature oocytes were retrieved from unstimulated ovaries of women with PCOS. We tried three different culture systems in this experiment. In group A, oocytes were cultured in the medium containing M199 + 20% fetal bovine serum (FBS) + 75 mIU/mL recombinant follicle-stimulating hormone (FSH) + 0.5 IU/mL recombinant hCG. In group B, oocytes were cultured in hCG-free IVM medium (M199 + 20% FBS + 75 mIU/mL recombinant FSH) for 10 hours, then transferred to the same medium as used for group A. In group C, oocytes were cultured only in hCG-free IVM medium. After the oocytes had matured in vitro, fertilization and embryo transfer were performed.

MAIN OUTCOME MEASURE(S)

Rates of maturation, fertilization, cleavage, implantation, clinical pregnancy, miscarriage, and live birth.

RESULT(S)

For groups A, B, and C, the maturation rates at 32 and 48 hours were 46.02% and 69.25%; 43.72% and 64.51%; and 51.87% and 67.51%, respectively. Relatively satisfactory clinical results and implantation rates were obtained in all three groups. No statistically significant differences among groups A, B, and C were found in the rates of maturation, fertilization, cleavage, implantation, clinical pregnancy, miscarriage, or live birth.

CONCLUSION(S)

The results of our study indicated that the addition of hCG to in vitro culture medium did not improve the maturation rate or development potential of immature oocytes. For the IVM and development of immature oocytes from women with PCOS, hCG appears to be unnecessary.

Localization of Oestrogen Receptors Within Various Bovine Ovarian Cell Types at Different Stages of the Oestrous Cycle

In the present study oestrogen receptor alpha(ERalpha) and oestrogen receptor beta (ERbeta) mRNA were localized in various ovarian cell types of 23 cows at different stages of the oestrous cycle. ERalpha was detected by immunohistochemistry and the localization of ERbeta mRNA was examined using in situ hybridization. The immunostaining of ERalpha was low in the ovarian follicles, tunica albuginea and surface epithelium, but high in cells of the deep stroma and superficial stroma, which indicates a functional role of ERalpha in the cells surrounding the follicles. In contrast, ERbeta mRNA scores were low to moderate in primordial and primary follicles, and increased with the development of the follicle. ERbeta mRNA scores were higher in cystic follicles than in obliterative follicles. In the corpora lutea and corpora albicantia the scores for ERbeta mRNA were moderate. Furthermore, in the corpora lutea, ERbeta mRNA levels showed cyclic variations and were low during early dioestrus. The correlation between plasma progesterone levels and the score for ER was low and negative in all ovarian cell types. This study demonstrates the predominant role of ERbeta over ERalpha in bovine ovarian structures. Furthermore, the colocalization of both ERbeta mRNA and ERalpha in most cell types suggests possible interactions between both ER subtypes.

Histological Characteristics and Steroid Concentration of Ovarian Follicles at Different Stages of Development in Pregnant and Non-pregnant Dairy Cows

The aim of the study was to investigate the histological characteristics and steroid concentrations in follicular fluid of different populations of follicles at different stages of development, during pregnancy and the oestrous cycle in cows. Follicles from ovaries collected at a slaughterhouse were allocated into three size categories (small, 2-5.9 mm; medium, 6-13.9 mm; and large, 14-20 mm) in pregnant and non-pregnant cows. Slices were stained with HE and PAS for histological analysis. Follicular fluid was pooled according to size and pregnancy status and estradiol, testosterone and progesterone concentrations in follicular fluid were determined by RIA. Characteristics of healthy follicles did not differ, regardless of follicle size or pregnancy status. Total histological atresia was significantly higher in pregnant cows than in non-pregnant cows (p < 0.05). Estradiol increased and testosterone decreased significantly, while follicles increased in size, in both non-pregnant and pregnant cows (p < 0.05). Nonpregnant cows had the highest estradiol values in follicles of all sizes. Medium and large follicles from pregnant cows showed the lowest testosterone concentration (p < 0.05). Progesterone levels increased with follicle size only in non-pregnant animals. In large follicles, progesterone concentration was significantly higher in non-pregnant cows than in pregnant cows (p < 0.05). Considering steroid concentration and histological findings, most large follicles might be atretic during pregnancy in cattle.

Gonadotropin requirements for dominant follicle selection in GnRH agonist-treated cows

A study was conducted to examine the effects of gonadotropins on ovarian follicular development and differentiation in GnRH agonist (GnRHa)-treated cattle. Holstein cows were allotted into two pre-treatment groups: controls (n = 5) and GnRHa-treated (n = 9). Ovaries were removed from control cows on day 5 following a synchronized estrus. Treatment with GnRHa resulted in follicular arrest at <5 mm. Following follicular arrest, GnRHa-treated cows received a constant infusion of FSH for 96 h (GnRHa/FSH), with a randomly selected subset receiving hourly pulses of LH in addition to FSH during the last 48 h of infusion (GnRHa/FSH + LH). At the end of infusion, ovaries were removed, follicles were counted and measured, and follicular fluid samples were collected from large follicles (>10 mm). Differences in expression of mRNA for LH receptor, FSH receptor, cytochrome P450 side-chain cleavage, 3β-hydroxysteroid dehydrogenase, cytochrome P450 17α-hydroxylase (P450c17) and cytochrome P450 aromatase were determined in large follicles using in situ hybridization. The number of large follicles did not differ between GnRHa/FSH-treated and GnRHa/FSH + LH-treated cows (P = 0.64), but was greater than control animals (P ≤ 0.004). Follicular fluid concentrations of estradiol-17β and androstenedione were highest in GnRHa/FSH + LH-treated cows (P ≤ 0.04), intermediate in control cows, and lowest in GnRHa/FSH-treated cows. Hybridization intensity of P450c17 was greater in GnRHa/FSH + LH-treated versus control or GnRHa/FSH-treated cows (P ≤ 0.03). These results indicate that while FSH can support bovine follicular growth >10 mm, LH increases androgen production and expression of P450c17.

Gene transcription and regulation of oocyte maturation

The developmental potential of an embryo is dependent on the developmental potential of the oocyte from which it originates. The process of oocyte maturation is critical for the efficient application of biotechnologies such as in vitro embryo production and mammalian cloning. However, the overall efficiency of in vitro maturation remains low because oocytes matured in vitro have a lower developmental competence than oocytes matured in vivo. Furthermore, oocytes that have been exposed to gonadotropins have greater developmental competence than oocytes matured in the absence of gonadotropins. By understanding the molecular mechanisms underlying gonadotropin-induced maturation, improvement in oocyte maturation technologies may be expected as procedures to manipulate specific factors involved in signalling for resumption of meiosis are identified. The present review will focus on transcriptional mechanisms underlying the maturation of mammalian oocytes in vitro, as well as on the acquisition of oocyte developmental competence. In addition, a working model for the transcriptional control of mammalian oocyte maturation is proposed.

Temporal relationships between FSH receptor, type 1 insulin-like growth factor receptor, and aromatase expression during FSH-induced differentiation of bovine granulosa cells maintained in serum-free culture

A serum-free culture system has been developed in ruminants that allows gonadotrophin-responsive induction of oestradiol (E2) production by non-differentiated granulosa cells (GC) from small antral follicles. Critical determinants are dose of FSH and insulin-like growth factor (IGF), and the plating density of the GC. Over the first 16 h of culture when cells remained as a dispersed monolayer, expression declined in FSH receptors (FSHr) (P <0.001), IGF type 1 receptor (IGF-1r) (P <0.08) and p450 arom (CYP19, P <0.001). Characteristic GC clusters formed from 16 h and further enlarged between 24 and 48 h, accompanied by marked increases in FSHr (P <0.01), IGF-1r (P <0.05), and p450 arom (P <0.01) expression, and preceded induction and subsequent peak E2 production, at 96 and 144 h, respectively (P <0.01). In conclusion, isolation and dispersion of GC appears to induce reversion to an immature state resulting in loss of receptor expression. Re-establishment of cell-cell communications in the presence of FSH and IGF results in receptor up-regulation and induction of cellular differentiation.