Effect of the estrous cycle on zinc transporter expression in bovine cumulus-oocyte complexes and oviduct epithelial cells

During the luteal and follicular phases of the estrous cycle, cumulus-oocyte complexes (COC) and oviduct epithelial cells (OEC) undergo notable physiological and morphological changes. Maintaining proper zinc (Zn) homeostasis is crucial in both somatic and germinal mammalian cells. This study aimed to assess the impact of the estrous phase (luteal or follicular) on Zn transporter expression in bovine COC and OEC (BOEC). The expression of Zn transporters Slc39a6 (ZIP6), Slc39a8 (ZIP8), Slc39a14 (ZIP14), Slc30a3 (ZnT3), Slc30a7 (ZnT7), and Slc30a9 (ZnT9) was analyzed in COC and BOEC from cows during the luteal or follicular phases. Gene expression of ZIP6, ZIP14, and ZnT9 was quantified in COC and BOEC. The gene expression in the remaining transporters could not be quantified due to low mRNA levels (ZIP8 and ZnT3 in COC and BOEC; ZnT7 in BOEC) or absence of expression (ZnT7 in COC). In COC, the relative expression (RE) of all three transporters was higher in the luteal phase compared to the follicular phase (P ≤ 0.05). In BOEC, the luteal phase increased the RE of ZIP 6 (P ≤ 0.05), decreased the RE of ZnT9 (P ≤ 0.05), and did not modify the RE of ZIP14 (P > 0.05) compared to the follicular phase. In conclusion, the study reveals differences in the gene expression of ZIP6, ZIP14, and ZnT9 according to the estrous cycle phase in ex vivo samples of bovine COC and OEC.

Physiological high temperatures alter the amino acid metabolism of bovine early antral follicles

Heat stress reduces the developmental competence of bovine oocytes during the growth phase; however, the detailed mechanisms remain unclear. Amino acids play various critical roles in follicular development, including protein synthesis and as energy sources. We performed in vitro growth (IVG) culture of oocyte-cumulus-granulosa complexes (OCGCs) to assess the amino acid metabolism of small follicles at high temperatures. We isolated OCGCs from early antral follicles (0.5-1.0 mm) and subjected them to IVG culture for 12 days. OCGCs in the heat shock group were cultured under a temperature cycle of (38.5°C: 5 h, 39.5°C: 5 h, 40.5°C: 5 h, and 39.5°C: 9 h) to reproduce the body temperature of lactating cows under a hot environment. OCGCs in the control group were cultured at a constant temperature of 38.5°C for 24 h. Of the surviving OCGCs, those showing similar morphology and size between the groups were selected for amino acid analysis. We analyzed the free amino acids and their metabolites in the culture medium and calculated the depletion or appearance of molecular species. The depletion of three essential amino acids (isoleucine, leucine, and valine), two non-essential amino acids (aspartic acid and glycine), and ornithine was higher in the heat shock group (P < 0.05). Alanine depletion was lower in the heat shock group (P < 0.05). We concluded that heat exposure alters the amino acid metabolism of OCGCs isolated from early antral follicles, which might be involved with the diminished developmental potential of oocytes during summer.

Lipopolysaccharide impairs the in vitro growth, steroidogenesis, and maturation of oocyte-cumulus-granulosa cell complexes derived from bovine early antral follicles

In postpartum dairy cows, lipopolysaccharide (LPS) derived from gram-negative bacteria causes uterine or mammary inflammation, resulting in low fertility. The present study aimed to investigate the effect of LPS on the in vitro growth (IVG), steroidogenesis, and maturation of oocyte-cumulus-granulosa cell complexes (OCGCs) derived from bovine early antral follicles. OCGCs were isolated from bovine early antral follicles (0.5-1 mm in diameter) and cultured in vitro for 12 days using media containing 0 (control), 0.01, or 1 μg/mL of LPS. The viability, cavity formation, and oocyte diameter of the OCGCs, as well as the concentrations of estradiol (E2) and progesterone (P4) in the IVG culture media, were determined. After IVG culture, oocytes collected from viable OCGCs were matured in vitro (IVM) in a medium without LPS. The nuclear maturation rate and the mitochondrial membrane potential of oocytes were determined. Bovine oocytes and cumulus-granulosa complexes derived from early antral follicles expressed genes encoding LPS receptor complex, such as toll-like receptor 4 (TLR4). Immunohistochemistry analysis further localized TLR4 expression predominantly in follicular granulosa and theca cells of early antral follicles. The viability of OCGCs and cavity formation in OCGCs were lower in the 0.01 and 1 μg/mL LPS groups than in the control group. No significant difference in oocyte diameter was observed between the treatment groups throughout the culture period. Moreover, E2 production was suppressed in the 0.01 and 1 μg/mL LPS groups from Days 4-8, whereas P4 production increased in the 1 μg/mL LPS group from Days 0-8. The nuclear maturation rate after IVM was lower in the 0.01 and 1 μg/mL LPS groups than in the control group. The mitochondrial membrane potential of post-IVM oocytes was lower in the 0.01 and 1 μg/mL LPS groups than in the control group. Taken together, these results indicate that LPS inhibited the growth and steroidogenesis of OCGCs and the meiosis and mitochondrial function of oocytes derived from early antral follicles. This study suggests that the detrimental effects of LPS on developing oocytes may contribute to long-term decreased fertility in postpartum dairy cows.

In vitro culture of sheep early-antral follicles: Milestones, challenges and future perspectives

Early antral follicles (EAFs) represent the transitional stage between pre-antral and antral follicles, containing oocytes that have completed most of their growth phase. Therefore, they offer an easily exploitable reserve for producing mature oocytes and preserving genetic resources, given their higher abundance compared to antral follicles (AFs) and shorter culture period than other pre-antral follicles (PAFs). Despite these advantages, the culture of EAFs remains challenging, and the success rates of in vitro embryo production (IVEP) from EAF-derived oocytes are still far below the standard achieved with fully grown oocytes in ruminant species. The difficulty is related to developing suitable in vitro culture systems tailored with nutrients, growth factors, and other signaling molecules to support oocyte growth. In this review, we focus on the in vitro development of sheep EAFs to provide an informative reference to current research progress. We also summarize the basic aspect of folliculogenesis in sheep and the main achievements and limitations of the current methods for EAF isolation, in vitro culture systems, and medium supplementation. Finally, we highlight future perspectives and challenges for improving EAF culture outcomes.

A refined culture system of oocytes from early antral follicles promotes oocyte maturation and embryo development in cattle

In brief

The proposed culture system improves the current state of in vitro culture of growing oocytes in the bovine species and allows access to the untapped gamete reserve, thus improving reproductive efficiency.

Abstract

The present study aimed to improve the in vitro culture of bovine oocytes collected from early antral follicles (EAFs) to support the progressive acquisition of meiotic and developmental competence. The rationale that drove the development of such a culture system was to maintain as much as possible the physiological conditions that support the oocyte growth and differentiation in vivo. To this extent, oocytes were cultured for 5 days, which parallels the transition from early to medium antral follicles (MAFs) in the bovine, and supports promoting a 3D-like structure were provided. Additionally, the main hormones (follicle-stimulating hormone, estradiol, progesterone, and testosterone) were added in concentrations similar to the ones previously observed in bovine EAFs. The meiotic arrest was imposed using cilostamide. The cultured cumulus-oocyte complexes (COCs) reached a mean diameter of 113.4 ± 0.75 µm and showed a progressive condensation of the chromatin enclosed in the germinal vesicle (GV), together with a gradual decrease in the global transcriptional activity, measured by 5-ethynyl uridine incorporation. The described morpho-functional changes were accompanied by an increased ability to mature and develop to the blastocyst stage in vitro, although not matching the rates obtained by MAF-retrieved oocytes. The described system improves the current state of in vitro culture of growing oocytes in the bovine species, and it can be used to increase the number of gametes usable for in vitro embryo production in animals of high genetic merit or with specific desirable traits.

Effect of heat exposure on the growth and developmental competence of bovine oocytes derived from early antral follicles

In dairy cows, low fertility caused by summer heat stress continues into the cooler autumn season. This can be caused by impaired oocyte quality in small growing follicles during summer. Here, we subjected oocyte-cumulus-granulosa complexes (OCGCs) derived from early antral follicles (0.5-1 mm) to in vitro growth (IVG) culture under two different temperature settings (the control and heat shock groups), and evaluated effects of heat exposure on growth and developmental competence of oocytes, factors affecting the developmental competence of oocytes (steroidogenesis of granulosa cells, oxidative stress in oocytes, and cell-to-cell communication between oocytes and somatic cells). Oocyte diameters after culture were smaller in the heat shock group. Although nuclear maturation and cleavage rates were similar between the groups, blastocyst rates were lower in the heat shock group (0.0%) than in the control group (27.7%), and reduced glutathione (GSH) levels in oocytes were lower in the heat shock group. Supplementation of cysteine, which stimulates GSH synthesis, increased GSH level and improved blastocyst rate of heat shocked oocytes (27.9%). These results suggest that heat exposure impairs the growth and developmental competence of oocytes in early antral follicles through GSH depletion, which can induce low fertility during summer and the following autumn.

Astaxanthin improves the development of the follicles and oocytes through alleviating oxidative stress induced by BPA in cultured follicles

This study is to investigate whether astaxanthin could alleviate the oxidative stress damages of follicles induced by BPA and improve the development of the cultured follicles and oocytes. Compared with BPA group, the survival rate, antrum formation rate, oocyte maturation rate and adherence area of the D8 and D10 follicles of the BPA+Asta group were significantly higher. The estrogen and progesterone in the culture medium of BPA+Asta group were significantly higher. PCNA in D8 and D10 granulosa cells and ERα in D10 granulosa cells of follicles in BPA+Asta group were significantly higher. The levels of malondialdehyde in the follicle culture medium, levels of ROS in the oocytes, the expression levels of caspase 3 and cathepsin B in the oocytes of the BPA+Asta group were significantly lower. However, the mitochondrial membrane potential, and the expression levels of antioxidant genes (CAT, SOD1 and SOD2) and anti-apoptotic gene Bcl-2 in the oocytes in the BPA+Asta group were significantly higher. Astaxanthin improves the development of follicles and oocytes through increasing the antioxidant capacity of follicles and oocytes, and relieving the BPA-induced oxidative stress during follicular development and oocyte maturation.

Gonadal white adipose tissue is important for gametogenesis in mice through maintenance of local metabolic and immune niches

Gonadal white adipose tissue (gWAT) can regulate gametogenesis via modulation of neuroendocrine signaling. However, the effect of gWAT on the local microenvironment of the gonad was largely unknown. Herein, we ruled out that gWAT had a neuroendocrine effect on gonad function through a unilateral lipectomy strategy, in which cutting off epididymal white adipose tissue could reduce seminiferous tubule thickness and decrease sperm counts only in the adjacent testis and epididymis of the affected gonad. Consistent with the results in males, in females, ovary mass was similarly decreased by lipectomy. We determined that the defects in spermatogenesis were mainly caused by augmented apoptosis and decreased proliferation of germ cells. Transcriptome analysis suggested that lipectomy could disrupt immune privilege and activate immune responses in both the testis and ovary on the side of the lipectomy. In addition, lipidomics analysis in the testis showed that the levels of lipid metabolites such as free carnitine were elevated, whereas the levels of glycerophospholipids such as phosphatidylcholines and phosphatidylethanolamines were decreased, which indicated that the metabolic niche was also altered. Finally, we show that supplementation of phosphatidylcholine and phosphatidylethanolamine could partially rescue the observed phenotype. Collectively, our findings suggest that gWAT is important for gonad function by not only affecting whole-body homeostasis but also via maintaining local metabolic and immune niches.

Plasma profile of follicle-stimulating hormone and sex steroid hormones after a single epidural administration of follicle-stimulating hormone via caudal vertebrae in Holstein dry cows

The conventional follicle-stimulating hormone (FSH) treatment for bovine superstimulation involves multiple intramuscular injections, which is stressful for animals and onerous. We herein investigated whether a single epidural injection of porcine FSH (pFSH) can induce superovulation and peripheral concentrations of pFSH and steroid hormones after the treatment in Holstein dry cows. We intramuscularly administered pFSH twice daily to three cows for 3 days (control) or a single epidural pFSH administration (epidural). Numbers of follicles (≥10 mm in diameter) at estrus and corpora lutea at luteal phase were counted by ultrasonography. Blood was sampled from 0 to 104 h after the first pFSH administration and plasma pFSH, progesterone, androstenedione, testosterone, and estradiol-17β concentrations were measured. Numbers of follicles (control: 18.3 ± 7.5, epidural: 15.7 ± 4.0; mean ± SD) and corpora lutea (control: 7.3 ± 4.2, epidural: 8.0 ± 2.6) were similar between both treatments. Plasma pFSH concentrations were higher in epidural than in control (p < 0.01). Although no significant differences were observed in progesterone, androstenedione, or estradiol-17β concentrations between the groups, testosterone concentrations were slightly lower with the epidural treatment than with the control treatment (p = 0.08). In conclusion, superovulation was induced by a single epidural injection of pFSH, which achieved higher pFSH level than the multiple injections in Holstein dry cows.

Low oxygen environment and astaxanthin supplementation promote the developmental competence of bovine oocytes derived from early antral follicles during 8 days of in vitro growth in a gas-permeable culture device

We evaluated the effects of a constant low (5-5%) and modulated (5-20%) oxygen environments on the in vitro development of bovine oocyte-cumulus-granulosa cell complexes (OCGCs) cultured in the presence or absence of an antioxidant (astaxanthin: Ax). OCGCs were cultured in a gas permeable culture device for 8 days in 5-5% O₂ (±Ax) and 5-20% O₂ (±Ax) culture conditions. In the oxygen modulated culture conditions, the oxygen concentration was switched from 5% to 20% on day 4 of culture. Ax promoted the viability of OCGCs (P < 0.05), but both oxygen and Ax had a significant effect on ROS production levels by OCGCs (P < 0.05). Specifically, ROS levels were significantly lower and higher under 5-5% O₂ (+Ax) and 5-20% O₂ (-Ax) conditions, respectively (P < 0.05), with intermediate levels observed in the 5-5% O₂ (-Ax) and the 5-20% O₂ (+Ax) culture conditions. The steroidogenic pattern was characterized by increasing estradiol-17β but with constant progesterone production levels regardless of culture conditions, suggesting the inhibition of luteinization-like changes in granulosa cells. OCGCs cultured in the 5-20% O₂ (+Ax) had higher nuclear maturation rates (P < 0.05) that were similar to the oocytes grown in vivo. However, there was no clear difference in the subsequent cleavage rates among the 5-5% O₂ (±Ax) and the 5-20% O₂ (+Ax) culture conditions (P > 0.05). A constant low oxygen environment significantly promoted the blastocyst rates (P < 0.05); however, the presence of Ax in the 5-20% O₂ (+Ax) condition also promoted development similar to the OCGCs cultured in the 5-5% O₂ (-Ax) condition (P > 0.05). In conclusion, exposure of OCGCs to constant low oxygen or oxygen modulation in the presence of Ax promotes the healthy development of OCGCs during the 8-day IVG culture using the gas permeable culture device.

Equine Chorionic Gonadotropin as an Effective FSH Replacement for In Vitro Ovine Follicle and Oocyte Development

The use of assisted reproductive technologies (ART) still requires strategies through which to maximize individual fertility chances. In vitro folliculogenesis (ivF) may represent a valid option to convey the large source of immature oocytes in ART. Several efforts have been made to set up ivF cultural protocols in medium-sized mammals, starting with the identification of the most suitable gonadotropic stimulus. In this study, Equine Chorionic Gonadotropin (eCG) is proposed as an alternative to Follicle Stimulating Hormone (FSH) based on its long superovulation use, trans-species validation, long half-life, and low costs. The use of 3D ivF on single-ovine preantral (PA) follicles allowed us to compare the hormonal effects and to validate their influence under two different cultural conditions. The use of eCG helped to stimulate the in vitro growth of ovine PA follicles by maximizing its influence under FBS-free medium. Higher performance of follicular growth, antrum formation, steroidogenic activity and gap junction marker expression were recorded. In addition, eCG, promoted a positive effect on the germinal compartment, leading to a higher incidence of meiotic competent oocytes. These findings should help to widen the use of eCG to ivF as a valid and largely available hormonal support enabling a synchronized in vitro follicle and oocyte development.

Effects of a gel culture system made of polysaccharides (xanthan gum and locust bean gum) on in vitro bovine oocyte development and gene expression of the granulosa cells

Xanthan gum (XG) and locust bean gum (LBG) are nontoxic polysaccharides that produce culture substrates. The present study examined the effect of XG-LBG gel on in vitro bovine oocyte growth and gene expression in granulosa cells. Oocytes and granulosa cell complexes (OGCs) were cultured in vitro on plastic culture plate (Plate) or XG-LBG gel for 16 days. OGCs formed a dome-like cavity surrounding the oocytes on plate but formed a spherical follicle structure on XG-LBG gel. The total granulosa cell numbers of the OGCs and their survival rate was greater for OGCs cultured on XG-LBG gel than for those cultured on plate. Oocytes grown on XG-LBG gels had higher lipid and mitochondrial content, as well as a larger diameter, than their plate counterparts. When oocytes grown in vitro were subjected to in vitro maturation and fertilization, the normal fertilization rate was significantly higher for oocytes developed on XG-LBG gel than that of oocytes cultured on the plate counterpart. RNAseq of the granulosa cells revealed that genes associated with focal adhesion, phosphatidylinositol 3'-kinase-Akt and Hippo signaling, and regulation of actin cytoskeleton were upregulated in granulosa cells of OGCs cultured on XG-LBG gel compared with those cultured on plate.

Recreating the Follicular Environment: A Customized Approach for In Vitro Culture of Bovine Oocytes Based on the Origin and Differentiation State

The mammalian ovary is a large source of oocytes organized into follicles at various stages of folliculogenesis. However, only a limited number of them can be used for in vitro embryo production (IVEP), while most have yet to complete growth and development to attain full meiotic and embryonic developmental competence. While the in vitro growth of primordial follicles in the ovarian cortex has the potential to produce mature oocytes, it is still at an experimental stage. The population of early antral follicles (EAFs), instead, may represent a reserve of oocytes close to completing the growth phase, which might be more easily exploited in vitro and could increase the number of female gametes dedicated to IVEP.Here we present in vitro culture strategies that have been developed utilizing physiological parameters to support the specific needs of oocytes at distinct stages of differentiation, in order to expand the source of female gametes for IVEP by maximizing the attainment of fertilizable oocytes. Furthermore, these culture systems provide powerful tools to dissect the molecular processes that direct the final differentiation of the mammalian oocyte.

Antioxidant Nobiletin Enhances Oocyte Maturation and Subsequent Embryo Development and Quality

Nobiletin is a polymethoxylated flavonoid isolated from citrus fruits with wide biological effects, including inhibition of reactive oxygen species (ROS) production and cell cycle regulation, important factors for oocyte in vitro maturation (IVM). Therefore, the objective of the present study was to evaluate the antioxidant activity of nobiletin during IVM on matured bovine oocyte quality (nuclear and cytoplasmic maturation; oocyte mitochondrial activity; intracellular ROS and glutathione (GSH) levels) and their developmental competence, steroidogenesis of granulosa cells after maturation, as well as quantitative changes of gene expression in matured oocytes, their cumulus cells, and resulting blastocysts. Bovine cumulus-oocyte complexes were in vitro matured in TCM-199 +10% fetal calf serum (FCS) and 10 ng/mL epidermal growth factor (EGF) (Control) supplemented with 10, 25, 50, or 100 μM of nobiletin (Nob10, Nob25, Nob50, and Nob100, respectively) or 0.1% dimethyl sulfoxide (CDMSO: vehicle for nobiletin dilution). A significantly higher percentage of matured oocytes in metaphase II was observed in Nob25 and Nob50 compared to other groups. Similarly, cleavage rate and cumulative blastocyst yield on Days 7 and 8 were significantly higher for Nob25 and Nob50 groups. Oocytes matured with 25 and 50 μM nobiletin showed a higher rate of migration of cortical granules and mitochondrial activity and a reduction in the ROS and GSH content in comparison with all other groups. This was linked to a modulation in the expression of genes related to metabolism (CYP51A1), communication (GJA1), apoptosis (BCL2), maturation (BMP15 and MAPK1), and oxidative stress (SOD2 and CLIC1). In conclusion, nobiletin offers a novel alternative for counteracting the effects of the increase in the production of ROS during IVM, improves oocyte nuclear and cytoplasmic maturation, and subsequent embryo development and quality in cattle.

Relationships between the antral follicle count, steroidogenesis, and secretion of follicle-stimulating hormone and anti-Müllerian hormone during follicular growth in cattle

BACKGROUND

The antral follicle count (AFC) in mammalian ovaries positively correlates with female fertility. To clarify the causes of differences in fertility between low and high AFC cows, we investigated follicular growth dynamics and hormone concentrations in plasma, follicular fluid, and in vitro growth (IVG) media at different stages of follicular growth.

METHODS

Seven cows were divided into high AFC (n = 4, > 30 follicles) and low AFC (n = 3, < 30 follicles) groups based on the peak AFC detected by ultrasonography. These cows were subjected to estrous synchronization, daily ovarian ultrasonography, and blood collection. Their follicular fluid was collected from dominant follicles at different stages (selection, luteal, and ovulatory phases). In another experiment, we cultured oocyte-cumulus-granulosa cell complexes collected from early antral follicles (< 1 mm) for 12 days. Estradiol-17β (E₂), testosterone (T), progesterone (P₄), and anti-Müllerian hormone (AMH) concentrations in follicular fluids and plasma were measured. Plasma follicle-stimulating hormone (FSH) concentrations were examined. E₂, P₄, and AMH concentrations were also measured in IVG media.

RESULTS

The numbers of small (< 4 mm) and intermediate (4-8 mm) follicles were larger in the high AFC group than in the low AFC group (P < 0.05). The number of intermediate follicles was stable in the low AFC group, indicating consistent development. However, the number of these follicles fluctuated in the high AFC group. Plasma FSH concentrations were higher, whereas E₂ and T concentrations were lower in the low AFC group (P < 0.05). E₂ concentrations and the E₂/P₄ ratio in ovulatory follicles and IVG media on day 8 were higher in the high AFC group (P < 0.05). AMH concentrations in plasma and IVG media (P < 0.01) were higher in the high AFC group.

CONCLUSIONS

The weaker response to FSH of granulosa cells caused low E₂ production in the low AFC group, resulting in high FSH concentrations and the consistent development of intermediate follicles. Conversely, higher E₂ concentrations suppressed FSH secretion in the high AFC group. Granulosa cells in the high AFC group had the ability to produce more AMH than those in the low AFC group throughout IVG culture.

Astaxanthin improves the developmental competence of in vitro-grown oocytes and modifies the steroidogenesis of granulosa cells derived from bovine early antral follicles

In this study we investigated the effect of astaxanthin (Ax), which exhibits strong antioxidant activity, during invitro growth (IVG) on the developmental competence of oocytes and steroidogenesis of granulosa cells derived from early antral follicles. Bovine oocyte–cumulus–granulosa complexes collected from early antral follicles were cultured for 12 days in the presence or absence (control) of 500µM Ax. The viability of oocytes and antrum formation in the granulosa cell layer during IVG culture were greater in the presence than absence of Ax (P&lt;0.05). Regardless of Ax treatment, 17β-oestradiol production increased during IVG culture; however, progesterone production was significantly lower in the presence than absence of Ax (P&lt;0.05). Reactive oxygen species levels were lower in Ax-treated oocytes than in controls after IVG (P&lt;0.05). Although nuclear maturation and cleavage rates did not differ between the Ax-treated and control groups, Ax treatment led to weaker cathepsin B activity in oocytes and better blastocyst rates than in controls (P&lt;0.05). Accordingly, Ax treatment during IVG increased the total number of cells in blastocysts (P&lt;0.05). These results indicate that Ax supplementation of IVG medium improves the quality of bovine oocytes due to its antioxidative effects on growing oocytes and its suppression of the luteinisation of granulosa cells.

Comparative transcriptome analysis of rumen papillae in suckling and weaned Japanese Black calves using RNA sequencing

The length and density of rumen papillae starts to increase during weaning and growth of ruminants. This significant development increases the intraruminal surface area and the efficiency of VFA (acetate, propionate, butyrate, etc.) uptake. Thus, it is important to investigate the factors controlling the growth and development of rumen papillae during weaning. This study aimed to compare the transcriptomes of rumen papillae in suckling and weaned calves. Total RNA was extracted from the rumen papillae of 10 male Japanese Black calves (5 suckling calves, 5 wk old; 5 weaned calves, 15 wk old) and used in RNA-sequencing. Transcript abundance was estimated and differentially expressed genes were identified and these data were then used in Ingenuity Pathway Analysis (IPA) to predict the major canonical pathways and upstream regulators. Among the 871 differentially expressed genes screened by IPA, 466 genes were upregulated and 405 were downregulated in the weaned group. Canonical pathway analysis showed that "atherosclerosis" was the most significant pathway, and "tretinoin," a derivative of vitamin A, was predicted as the most active upstream regulator during weaning. Analyses also predicted IgG, lipopolysaccharides, and tumor-necrosis factor-α as regulators of the microbe-epithelium interaction that activates rumen-related immune responses. The functional category and the up-regulators found in this study provide a valuable resource for studying new candidate genes related to the proliferation and development of rumen papillae from suckling to weaning Japanese Black calves.

Relationship between the antral follicle count in bovine ovaries from a local abattoir and steroidogenesis of granulosa cells cultured as oocyte-cumulus-granulosa complexes

The antral follicle count (AFC) is used as an indicator of cow fertility. We herein investigated the relationship between AFC and the steroidogenesis of granulosa cells and confirmed the developmental competence of oocytes derived from early antral follicles (0.5–1.0 mm) using in vitro growth culture. Slaughterhouse-derived ovaries were divided into high (≥ 25) and low (< 25) AFC groups based on AFC (≥ 2.0 mm). Oocyte-cumulus-granulosa complexes (OCGCs) collected from early antral follicles were cultured for 12 days. The total number, viability, and diameter of granulosa cells and estradiol-17β and progesterone production during the culture were evaluated. Surviving oocytes on day 12 were subjected to in vitro maturation, and their volume and nuclear status were evaluated. Some oocytes were subjected to the evaluation of developmental competence to blastocysts. Although the total number and viability of granulosa cells did not differ between the groups, granulosa cell diameters were smaller in the high AFC group than in the low AFC group. The estradiol-17β and progesterone ratio on day 8 was higher in the high AFC group than in the low AFC group. Oocyte volumes and nuclear maturation rates were greater in the high AFC group than in the low AFC group. The development rate to blastocysts was 9.1% in the high AFC group, while no oocytes developed to blastocysts in the low AFC group. Therefore, estradiol-17β production by granulosa cells appears to be greater in high AFC cattle than in low AFC cattle, thereby promoting the acquisition of oocyte competence.

Follicular factors determining granulosa cell number and developmental competence of porcine oocytes

PURPOSE

Granulosa cell (GC) number in follicles is a simple characteristic of follicles. The present study examined the hypothesis that follicular fluid (FF) determines GC number and oocyte developmental ability and revealed the molecular background determining the number of follicular GCs.

METHODS

FF was collected from antral follicles (3-5 mm in diameter), after which the number of GCs per follicle was determined for each donor gilt using real time PCR targeting single copy gene. GCs were analyzed by next-generation RNA sequencing and IPA pathway analysis.

RESULTS

When oocyte cumulus cell-oocyte-complexes (COCs) were cultured in maturation medium containing 10% of each individual FF, the rate of development to the blastocyst stage was significantly correlated with the number of GCs in the donor gilt. In addition, when GCs were cultured in medium containing FF, the proliferative activity of the GCs was also significantly correlated to the number of GCs in the donor gilt. Moreover, when the FFs were categorized based on the number of GCs in the follicle, it was found that supplementation of culture media with GC-rich FF improved the developmental ability of oocytes compared to those supplemented with GC-poor FF. RNA sequencing and a pathway analysis of GCs from GC-rich and -poor follicles revealed the key regulatory pathway determining GC number in follicles.

CONCLUSION

GC number may be a useful marker for "good" follicles and oocytes, and the characteristics of the FFs determine granulosa cell number and oocyte developmental ability.

Estradiol benzoate treatment before ovum pick-up increases the number of good quality oocytes retrieved and improves the production of transferable embryos in Japanese Black cattle

The aim of this study was to evaluate the efficacy of treatment with estradiol benzoate (EB) at luteal phase prior to the ovum pick-up (OPU) during in vitro production of transferable embryos in Japanese Black cattle. A total of 15 cows were used as oocyte donors for OPU. Of those, four donors were randomly allocated (three times) into each of two treatment groups as a crossover study, and OPU session was carried out six times per one donor. Another eleven donors were used in a paired difference test by one crossover trial. Donors in the control group received no hormonal treatment; whereas, donors in the EB group received 1 mg of EB as a single injection. First, we observed dynamics of ovarian follicles and emergence of follicular wave after EB injection using transrectal ultrasonography. The number and proportion of medium-sized follicles with 4 to 6 mm in diameter increased gradually and achieved a peak at 72 and 96 hours after EB injection. The OPU was performed 88 hours after EB injection. The EB-treated donors had a higher proportion of follicles with 4 to 6 mm in diameters at the time of OPU. The stimulation with EB significantly increased the numbers of follicles aspirated, and the good quality cumulus-oocyte complexes per OPU. Furthermore, in the EB group, the percentage of transferable blastocysts was significantly greater than that in the control group (P<0.05). In conclusion, a single EB injection before OPU increases the number of medium-sized follicles and can produce more transferable embryos.

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Efficacy of one-shot treatment with 1 mg of estradiol benzoate (EB) at luteal phase prior to the ovum pick-up (OPU) for in vitro production of transferable embryos in Japanese Black cattle was investigated.

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The donors had a higher proportion of follicles with 4 to 6 mm in diameter at 72 and 96 hours after EB i.m. injection.

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The stimulation with EB before OPU increased significantly the number of good quality cumulus-oocyte complexes, and the percentage of blastocysts or transferable embryos after in vitro fertilization.

Relationship between in vitro growth of bovine oocytes and steroidogenesis of granulosa cells cultured in medium supplemented with bone morphogenetic protein-4 and follicle stimulating hormone

Bone morphogenetic protein-4 (BMP-4) and FSH play important regulatory roles in follicular growth and steroidogenesis in vivo. The purpose of this study was to investigate the effects of BMP-4 and FSH on in vitro growth (IVG) and steroidogenesis of bovine oocyte-cumulus-granulosa complexes (OCGCs). We cultured OCGCs collected from early antral follicles (0.5-1 mm) in medium without BMP-4 and FSH for 4 days and investigated the appearance of OCGCs and their steroidogenesis. During the first 4 days of IVG, morphologically normal OCGCs produced more estradiol-17β (E₂), but less progesterone (P₄). Morphologically normal OCGCs were subjected to an additional culture in medium supplemented with BMP-4 (0, 10, and 50 ng/mL) and FSH (0 and 0.5 ng/mL) until day 12. We examined the viability and steroidogenesis of OCGCs after 8 and 12 days of culture. Oocyte growth, characteristics of granulosa cells, and the maturational competence of oocytes were also investigated. On day 8, the viability of OCGCs cultured without FSH was higher in the 10 ng/mL BMP-4 group than in the 50 ng/mL BMP-4 group (P < 0.05). No significant difference was observed in the viability of groups cultured with FSH, regardless of the addition of BMP-4, and FSH improved the viability of 50 ng/mL BMP-4 group similar to 10 ng/mL BMP-4 group. The total number of granulosa cells was larger in 10 ng/mL BMP-4 group cultured with FSH than in 50 ng/mL BMP-4 group cultured with FSH on day 8 (P < 0.05). E₂ production decreased from days 8-12, and P₄ production increased throughout IVG culture, regardless of the addition of BMP-4 and FSH (P < 0.05). No significant differences in E₂ production were observed between groups from days 4-8, regardless of whether BMP-4 was added without FSH; however, E₂ production in the group cultured with 50 ng/mL BMP-4 was suppressed by FSH. BMP-4 suppressed E₂ production from days 8-12, regardless of whether FSH was added. The group cultured with 10 ng/mL BMP-4 without FSH showed the lowest P₄ production among all groups for all culture periods. OCGCs that produced mature oocytes tended to secrete more E₂ and less P₄ than OCGCs that produced immature oocytes. In conclusion, until day 8 of the IVG culture, P₄ production by OCGCs was suppressed by the addition of 10 ng/mL BMP-4 in the absence of FSH, without inhibiting E₂ production. These conditions appear to mimic growing follicles until day 8 and mimic degenerating follicles from days 8-12 of culture.

Brain-derived neurotrophic factor promotes human granulosa-like tumor cell steroidogenesis and proliferation by activating the FSH receptor-mediated signaling pathway

Brain-derived neurotrophic factor (BDNF) and FSH receptor (FSHR) are expressed in ovarian granulosa cells, and play important roles in regulating follicle growth and oocyte maturation. Studies have linked the BDNF-associated signaling pathway to FSHR mRNA expression in the regulation of follicle development, but the mechanisms remain unknown. In the current study, we found that BDNF stimulated the secretion of estradiol and progesterone, and increased the proliferation of KGN cells (human granulosa-like tumor cell line). BDNF treatment also increased phosphorylated and ubiquitinated FSHR, and activated cAMP/PKA/CREB signaling pathway. Moreover, inhibition of BDNF expression by siRNA markedly reduced the estradiol secretion and down-regulated FSHR, aromatase and phosphorylated CREB; meanwhile, FSH treatment partly alleviated the effects of BDNF siRNA on KGN cells. These findings suggested that BDNF modulates graunlosa cell functions and the action probably mediated by FSHR-coupled signaling pathway, to affect aromatase-mediated steroidogenesis. These results provide an alternative target to optimize ovarian granulosa cell function.

MicroRNA-764-3p regulates 17β-estradiol synthesis of mouse ovarian granulosa cells by targeting steroidogenic factor-1

Previous studies have reported that microRNA-764-3p (miR-764-3p) is one of the most up-regulated microRNAs (miRNAs) in TGF-β1-stimulated mouse ovarian granulosa cells. However, little is known about the roles and mechanisms of miR-764-3p in granulosa cell function during follicular development. In this study, we found that overexpression of miR-764-3p inhibited 17β-estradiol (E2) synthesis of granulosa cells through directly targeting steroidogenic factor-1 (SF-1). MiR-764-3p inhibited SF-1 by affecting its messenger RNA (mRNA) stability, which subsequently suppressed the expression levels of Cyp19a1 gene (aromatase, a downstream target of SF-1). In addition, SF-1 was involved in regulation of miR-764-3p-mediated Cyp19a1 expression in granulosa cells which contributed, at least partially, to the effects of miR-764-3p on granulosa cell E2 release. These results suggest that miR-764-3p functions to decrease steroidogenesis by targeting SF-1, at least in part, through inactivation of Cyp19a1. Taken together, our data provide mechanistic insights into the roles of miR-764-3p on E2 synthesis. Understanding of potential miRNAs affecting estrogen synthesis will help to diagnose and treat steroid-related diseases.

Resveratrol-induced mitochondrial synthesis and autophagy in oocytes derived from early antral follicles of aged cows

Mitochondrial numbers increase during oocyte growth. In this study, we collected oocytes and granulosa cell complexes (OGCs) from early antral follicles (EAFs) of aged cows (> 120 months of age) and examined the effects of resveratrol on mitochondrial generation, degradation, and quality in oocytes grown in vitro. We also examined the effects of resveratrol on gene expression of the granulosa cells. Resveratrol (20 µM) enhanced the expression of SIRT1 and induced autophagy in both granulosa cells and oocytes derived from aged cows. Culturing the OGCs with resveratrol increased mitochondrial DNA copy numbers in oocytes grown in vitro. Furthermore, resveratrol increased the ATP content in oocytes and improved the developmental ability of the oocytes to the blastocyst stage. Gene expression profiles in granulosa cells, as evaluated by next-generation sequencing technology, revealed that resveratrol enhanced the expression of EIF2-related genes but downregulated the expression of mammalian target of rapamycin (mTOR)-, inflammation-, and cholesterol homeostasis-related genes in granulosa cells. In conclusion, resveratrol affected both oocytes and granulosa cells derived from aged cows and improved the quality of oocytes grown in vitro through upregulation of mitochondrial biogenesis and degradation in growing oocytes and conditioning of granulosa cells.

Exposure of female macaques to Western-style diet with or without chronic T in vivo alters secondary follicle function during encapsulated 3-dimensional culture

Increased adiposity and hyperandrogenemia alter reproductive parameters in both animal models and women, but their effects on preantral follicles in the ovary remain unknown. We recently reported that Western-style diet (WSD) consumption over 1 year, with or without chronic exposure to elevated circulating T, increased the body fat percentage, elicited insulin resistance, suppressed estradiol and progesterone production, as well as altered the numbers, size, and dynamics of antral follicles in the ovary during the menstrual cycle in female macaques. Therefore, experiments were designed to compare the WSD and WSD+T effects to age-matched controls on the survival, growth, and function of isolated secondary follicles during 5 weeks of encapsulated 3-dimensional culture. Follicle survival significantly declined in the WSD and WSD+T groups compared with the control (CTRL) group. Although media progesterone levels were comparable among groups, androstenedione and estradiol levels were markedly reduced in the WSD and WSD+T groups compared with the CTRL group at week 5. Anti-Müllerian hormone levels peaked at week 3 and were lower in the WSD+T group compared with the WSD or CTRL group. Vascular endothelial growth factor levels also decreased at week 5 in the WSD+T group compared with the WSD or CTRL group. After human chorionic gonadotropin exposure, only antral follicles developed from the CTRL group yielded metaphase II oocytes. Thus, WSD with or without T exposure affects the cohort of secondary follicles in vivo, suppressing their subsequent survival, production of steroid hormones and local factors, as well as oocyte maturation in vitro.

Effects of reaggregated granulosa cells and oocytes derived from early antral follicles on the properties of oocytes grown in vitro

In this study, we examined the effects of reconstructed oocyte-granulosa cell complexes (OGCs) on the development of porcine oocytes derived from early antral follicles (EAFs; 0.5-0.7 mm in diameter). When denuded oocytes were cocultured with granulosa cells derived from other EAFs, the oocytes and granulosa cells aggregated to form OGCs after 2 days of culture. After 14 days of culture, we compared cell number, oocyte diameter, and oocyte chromatin configuration in unmanipulated (natural) OGCs, reconstructed OGCs, and OGCs collected from antral follicles (AFs, 3.0-6.0 mm in diameter). The diameters of oocytes from reconstructed OGCs grown in vitro were not different from those of oocytes from natural OGCs, although they were significantly smaller than those of oocytes from antral follicle (AF) OGCs. Oocyte chromatin configuration did not differ among the 3 OGC groups, but the oocyte nuclear maturation rate was lower in the reconstructed OGCs and higher in the AF OGCs. However, when the in vitro culture period for the reconstructed OGCs was extended by 2 days, the nuclear maturation rate of oocytes from reconstructed OGCs was similar to that of oocytes from natural OGCs. In addition, blastocysts were successfully obtained from oocytes from reconstructed OGCs. In conclusion, we established an innovative culture method that allows oocytes and granulosa cells from EAFs to reaggregate as reconstructed OGCs, which yield oocytes with the ability to develop to the blastocyst stage.

Age-associated changes in bovine oocytes and granulosa cell complexes collected from early antral follicles

PURPOSE

To assess the age-associated changes in oocytes and granulosa cells derived from early antral follicles (EAFs).

METHOD

Gene expression analysis of granulosa cells of the EAFs using a genome analyzer (Illumina) and in vitro culture of oocyte-granulosa cell complexes (OGCs) of EAFs (400-700 μm in diameter) collected from ovaries of aged (>120 months) and young (<50 months) cows.

RESULTS

Gene expression profiles in granulosa cells of EAFs of aged cows, which included changes in genes that encode chaperone proteins and antioxidants. In vivo development of EAFs, as determined by oocyte diameter of EAFs and AFs (3-6 mm in diameter), appeared to be impaired in aged cows and the OGCs of aged cows contained low GSH compared to younger counterparts. When the OGCs were cultured in a medium containing low estradiol (E2, 0.1 μg/mL), the ratio of antrum formation was higher for OGCs from aged animals than that from young animals, while higher abnormal fertilization rate and lower total cell number of the blastocysts were observed in the OGCs of aged cows compared with those of young cows. On the contrary, when the OGCs were cultured in a medium containing 10 μg/mL E2, the ratio of antrum formation and fertilization outcome was comparable between the two age groups, whereas the total cell number of the blastocysts was still low in the aged group.

CONCLUSION

Aging affects the gene expression profiles of the granulosa cells, and impairs in vitro developmental ability of OGCs collected from EAFs.