Vascular endothelial growth factor-A(165) (VEGF-A(165)) stimulates the in vitro development and oocyte competence of goat preantral follicles

Trimethylation profile of histones H3 lysine 4 and 9 in late preantral and early antral caprine follicles grown in vivo versus in vitro in the presence of anethole

This study assessed the histones methylation profile (H3K4me3 and H3K9me3) in late preantral (PA) and early antral (EA) caprine follicles grown in vivo and in vitro, and the anethole effect during in vitro culture of PA follicles. Uncultured in vivo-grown follicles (PA, n = 64; EA, n = 73) were used as controls to assess the methylation profile and genes' expression related to apoptosis cascade (BAX, proapoptotic; BCL2, antiapoptotic), steroidogenesis (CYP17, CYP19A1), and demethylation (KDM1AX1, KDM1AX2, KDM3A). The isolated PA follicles (n = 174) were cultured in vitro for 6 days in α-MEM+ in either absence (control) or presence of anethole. After culture, EA follicles were evaluated for methylation, mRNA abundance, and morphometry. Follicle diameter increased after culture, regardless of treatment. The methylation profile and the mRNA abundance were similar between in vivo-grown PA and EA follicles. Anethole treatment led to higher H3K4me3 fluorescence intensity in EA follicles. The mRNA abundances of BAX, CYP17, and CYP19A1 were higher, and BCL2 and KDM3A were lower in in vitro-grown EA follicles than in vivo-grown follicles. In conclusion, in vitro follicle culture affected H3K4me3 fluorescence intensity, mRNA abundance of apoptotic genes, and steroidogenic and demethylase enzymes compared with in vivo-grown follicles.

The mechanisms that control the preantral to early antral follicle transition and the strategies to have efficient culture systems to promote their growth in vitro

Preantral to early antral follicles transition is a complex process regulated by endocrine and paracrine factors, as well as by a precise interaction among oocyte, granulosa cells and theca cells. Understanding the mechanisms that regulate this step of folliculogenesis is important to improve in vitro culture systems, and opens new perspectives to use oocytes from preantral follicles for assisted reproductive technologies. Therefore, this review aims to discuss the endocrine and paracrine mechanisms that control granulosa cell proliferation and differentiation, formation of the antral cavity, estradiol production, atresia, and follicular fluid production during the transition from preantral to early antral follicles. The strategies that promote in vitro growth of preantral follicles are also discussed.

Effects of vascular endothelial growth factor (VEGF) on the viability, apoptosis and steroidogenesis of yak (Bos grunniens) granulosa cells

Vascular endothelial growth factor (VEGF) is crucial for follicle development through the regulation of granulosa cell (GC) function in some mammals, but its mechanism is unclear in yak (Bos grunniens). Therefore, the objectives of this study were to investigate the effects of VEGF on the viability, apoptosis and steroidogenesis of yak GCs. First, we investigated the localization of VEGF and its receptor (VEGFR2) in yak ovaries by immunohistochemistry analysis and evaluated the effect of culture medium containing different VEGF concentrations and culture times on the viability of yak GCs by Cell Counting Kit-8. Then, optimal treatment with 20 ng/mL VEGF for 24 h was selected to analyze the effects of this compound on intracellular reactive oxygen species levels by DCFH-DA kit, cell cycle and apoptosis by flow cytometry, steroidogenesis by ELISA kit and the expression of the related genes by RT‒qPCR. The results showed that VEGF and VEGFR2 were highly coexpressed in GCs and theca cells. GCs cultured in medium containing 20 ng/mL VEGF for 24 h significantly improved cell viability, decreased ROS production, promoted the transition from G1 phase to S phase (P < 0.05), increased the expression of the CCND1 (P < 0.05), CCNE1, CDK2, CDK4, and PCNA genes (P < 0.01) and decreased the expression of the P53 gene (P < 0.05). This treatment significantly reduced GC apoptosis (P < 0.05) by promoting the expression of BCL2 and GDF9 (P < 0.01) and inhibiting the expression of BAX and CASPASE3 (P < 0.05). VEGF promoted progesterone secretion (P < 0.05) accompanied by increased expression of HSD3B, StAR and CYP11A1 (P < 0.05). Taken together, our findings highlight the beneficial influence exerted by VEGF in improving GC viability and reducing ROS production and the apoptosis rate through the modulation of related gene expression.

Metabolic and secretory recovery of slow frozen-thawed human ovarian tissue in vitro

Within the options available for fertility preservation, cryopreservation of ovarian cortical tissue has become an important technique. Freezing and thawing procedures have been optimized to preserve tissue integrity and viability. However, the improvement of the tissue retransplantation is currently of great interest. Rapid angiogenesis is needed at the retransplantation site to accomplish sufficient blood supply to provide oxygen and nutrients. Many studies address this issue. However, we need to understand the physiology of the thawed tissue to gain further understanding of the complexities of the procedure. As freezing and thawing generally impairs cellular metabolism, we aimed to characterize the changes in metabolic activity and secretion of the angiogenic factor vascular endothelial growth factor-A (VEGF-A) of frozen-thawed ovarian cortical tissue over time. Biopsy punches of ovarian cortical tissue from patients undergoing fertility preservation were maintained in culture without freezing or after a slow-freezing and thawing procedure. VEGF-A secretion was measured after 48 h by ELISA. To examine temporary changes, metabolic activity was assessed for both fresh and frozen-thawed tissue of the same patient. Metabolic activity and VEGF-A secretion were measured at 0, 24 and 48 h in culture. Thawed ovarian cortical tissue secreted significantly less VEGF-A compared to fresh ovarian cortical tissue within 48 h of culture. After thawing, metabolic activity was significantly reduced compared to fresh ovarian cortex but over the course of 48 h, the metabolic activity recovered. Similarly, VEGF-A secretion of thawed tissue increased significantly over 48 h. Here, we have shown that it takes 48 h for ovarian cortical tissue to recover metabolically after thawing, including VEGF-A secretion.

VEGFA165 can rescue excess steroid secretion, inflammatory markers, and follicle arrest in the ovarian cortex of High A4 cows†

A population of cows with excess androstenedione (A4; High A4) in follicular fluid, with follicular arrest, granulosa cell dysfunction, and a 17% reduction in calving rate was previously identified. We hypothesized that excess A4 in the ovarian microenvironment caused the follicular arrest in High A4 cows and that vascular endothelial growth factor A would rescue the High A4 phenotype. In trial 1, prior to culture, High A4 ovarian cortex (n = 9) had greater numbers of early stage follicles (primordial) and fewer later-stage follicles compared to controls (n = 11). Culture for 7 days did not relieve this follicular arrest; instead, High A4 ovarian cortex had increased indicators of inflammation, anti-Mullerian hormone, and A4 secretion compared to controls. In trial 2, we tested if vascular endothelial growth factor A isoforms could rescue the High A4 phenotype. High A4 (n = 5) and control (n = 5) ovarian cortex was cultured with (1) PBS, (2) VEGFA165 (50 ng/mL), (3) VEGFA165B (50 ng/mL), or (4) VEGFA165 + VEGFA165B (50 ng/mL each) for 7 days. Follicular progression increased with VEGFA165 in High A4 cows with greater early primary, primary, and secondary follicles than controls. Similar to trial 1, High A4 ovarian cortex secreted greater concentrations of A4 and other steroids and had greater indicators of inflammation compared to controls. However, VEGFA165 rescued steroidogenesis, oxidative stress, and fibrosis. The VEGFA165 and VEGFA165b both reduced IL-13, INFα, and INFβ secretion in High A4 cows to control levels. Thus, VEGFA165 may be a potential therapeutic to restore the ovarian steroidogenic microenvironment and may promote folliculogenesis.

Co-culture with peritoneum mesothelial stem cells supports the in vitro growth of mouse ovarian follicles

The important roles played by the ovarian microenvironment and cell interactions in folliculogenesis suggest promising approaches for in vivo growth of ovarian follicles using appropriate scaffolds containing suitable cell sources. In this study, we have investigated the growth of early preantral follicles in the presence of decellularized mesenteric peritoneal membrane (MPM), peritoneum mesothelial stem cells (PMSCs), and conditioned medium (CM) of PMSCs. MPM of mouse was first decellularized; PMSCs were isolated from MPM and cultured and their conditioned medium (CM) was collected. Mouse follicles were separated into four groups: (1) culture in base medium (control), (2) culture in decellularized MPM (DMPM), (3) co-culture with PMSCs (Co-PMSCs), and (4) culture in CM of PMSCs (CM-PMSCs). Qualitative and quantitative assessments were performed to evaluate intact mesenteric peritoneal membrane (IMPM) as well as decellularized ones. After culturing the ovarian follicles, follicular and oocyte diameter, viability, eccentric oocyte percentage, and estradiol hormone amounts were evaluated. Quantitative and qualitative evaluations confirmed removal of cells and retention of the essential fibers in MPM after the decellularization process. Follicular parameters showed that Co-PMSCs better support in vitro growth and development of ovarian follicles than the other groups. The eccentric rate and estradiol production were statistically higher for the Co-PMSCs group than for the CM-PMSCs and control groups. Although the culture of early preantral follicles on DMPM and CM-PMSCs could improve in vitro follicular growth, co-culture of follicles with PMSCs showed even greater improvements in terms of follicular growth and diameter.

Influence of TCM 199B, α-MEM, Waymouth MB 752/1 culture media, VEGF, Estradiol-17β, GDF-9 and FGF on in vitro development of preantral follicles in sheep

A total of 2792 preantral follicles (PFs') isolated from 750 ovaries of sheep were cultured in four different experiments. The efficacy of three commercially available culture media viz., TCM 199B, α-MEM and Waymouth MB 752/1 on the growth of sheep PFs' was tested in experiment I. Among the three media TCM 199B supported better development of PFs' in culture. The remaining experiments established the best concentrations of vascular endothelial growth factor (VEGF), Estradiol-17β (E2), GDF-9, Fibroblast growth factor (FGF) and their best combinations for the in-vitro development of PFs'. Inclusion of VEGF at 10 ng/mL, Estradiol-17β at 5 ng/mL, GDF-9 at 10 ng/mL or FGF at 10 ng/mL individually in a standard medium (SM) (containing FSH, IGF-I, GH and T4) supported better nuclear maturation of the oocytes to MII stage. Different combinations of VEGF, Estradiol-17β, GDF-9 and FGF supplemented in the SM promoted similar overall follicular growth. However, (a) SM + VEGF(10 ng/mL) + E2(5 ng/mL) supported higher increase in the diameter, (b) SM without any supplements induced antrum formation in greater proportion of follicles, and (c) SM + VEGF(10 ng/mL) + GDF 9(10 ng/mL) or SM + E2 (5 ng/mL) + FGF(10 ng/mL) supported high proportion of oocytes to reach MII stage. To conclude, TCM 199B appeared to be a better medium for development of sheep PFs'. VEGF, Estradiol-17 β, GDF-9 and FGF have beneficial influence on the development of sheep PFs' when supplemented in TCM 199B.

Advances in in vitro folliculogenesis in domestic ruminants

The in vitro follicle culture (IVFC) represents an outstanding tool to enhance our understanding of the control of folliculogenesis and to allow the future use of a large number of immature oocytes enclosed in preantral follicles (PFs) in assisted reproductive techniques in humans as well as in others mammalian species including the ruminants. So far, the best results of IVFC were reported from mice with the production of live offspring from primordial follicles cultured in vitro. Live birth has been obtained after the in vitro culture of bovine early antral follicles. However, in other ruminant species, these results have been limited to the production of a variable number of mature oocytes and low percentages of embryos after in vitro culture of goat, buffalo and sheep isolated secondary preantral follicles. The present review presents and discusses the main findings, limitations, and prospects of in vitro folliculogenesis in ruminants focusing on bovine, caprine, and ovine species.

Vitrification of caprine secondary and early antral follicles as a perspective to preserve fertility function

The present study aimed to evaluate the structure, survival and development of isolated caprine (secondary-SEC and early antral-EANT) follicles, after vitrification in the presence of synthetic polymers and in vitro culture. Additionally, transzonal projections (TZPs) and p450 aromatase enzyme were evaluated. After isolation, SEC and EANT follicles were in vitro cultured for six days or vitrified. After one week, SEC and EANT follicles were warmed and also in vitro cultured for six days. Data revealed that the percentage of morphologically normal follicles was similar between fresh and vitrified follicles in both follicular categories and antrum formation rate was similar between fresh and vitrified SEC follicles. Fluorescence by calcein-AM did not show difference between fresh and vitrified (SEC and EANT) follicles, however, the trypan blue test showed low viability for vitrified follicles. The integrity of TZPs was not affected between fresh and vitrified SEC follicles, however, in vitrified EANT follicles, there were signs of TZPs loss. Regarding steroidogenic function, it was observed a positive staining for p450 aromatase enzyme in fresh and vitrified SEC and EANT follicles. It was concluded that SEC follicles seem to be more resistant to vitrification than EANT follicles, as shown by the trypan blue test and TZPs assay. Future studies may confirm this hypothesis, in order to consolidate the use of SEC and EANT follicles as an alternative to ovary cryopreservation.

Vascular endothelial growth factor A isoforms modulate follicle development in peripubertal heifers independent of diet through diverse signal transduction pathways

Follicular progression during peripuberty is affected by diet. Vascular endothelial growth factor A (VEGFA) induces follicle progression in many species; however, there are limited studies to determine if diet may alter the effects of angiogenic VEGFA165-stimulated follicle progression or antiangiogenic VEGFA165b follicle arrest. We hypothesized that diet affects the magnitude of angiogenic and antiangiogenic VEGFA isoform actions on follicular development through diverse signal transduction pathways. To test this hypothesis, beef heifers in our first trial received Stair-Step (restricted and refeeding) or control diets from 8 to 13 months of age. Ovaries were collected to determine follicle stages, measure vascular gene expression and conduct ovarian cortical cultures. Ovarian cortical cultures were treated with phosphate-buffered saline (control), 50 ng/ml VEGFA165, VEGFA165b, or VEGFA165 + VEGFA165b. The Stair-Step heifers had more primordial follicles (P &lt; 0.0001), greater messenger RNA abundance of vascular markers VE-cadherin (P &lt; 0.0001) and NRP-1 (P &lt; 0.0051) than controls at 13 months of age prior to culture. After culture, VEGFA isoforms had similar effects, independent of diet, where VEGFA165 stimulated and VEGFA165b inhibited VEGFA165-stimulated follicle progression from early primary to antral follicle stages. In vitro cultures were treated with VEGFA isoforms and signal transduction array plates were evaluated. VEGFA165 stimulated expression of genes related to cell cycle, cell proliferation, and growth while VEGFA165b inhibited expression of those genes. Thus, VEGFA isoforms can act independently of diet to alter follicle progression or arrest. Furthermore, follicle progression can be stimulated by VEGFA165 and inhibited by VEGFA165b through diverse signal transduction pathways.

In vitro survival, growth, and maturation of sheep oocytes from secondary follicles cultured in serum-free conditions: impact of a constant or a sequential medium containing recombinant human FSH

This study evaluated the in vitro development and maturation of ovine oocytes from secondary follicles cultured in serum-free medium containing fixed or sequential concentrations of recombinant human FSH (rhFSH). Follicles were cultured in α-MEM⁺ alone or with constant (500, 750, or 1,000 ng/mL) or sequential concentrations of rhFSH (seq. 1: day 6 = 500; day 12 = 750; day 18 = 1,000 ng/mL and seq. 2: day 6 = 100; day 12 = 500; day 18 = 1,000 ng/mL). At the end of the experiment, follicular survival was higher (P < 0.05) in 750 ng/mL rhFSH than the control and 1,000 ng/mL rhFSH. As early as day 6 of culture, antral cavity formation was observed in all treatments. Follicular diameter increased progressively and significantly in all treatments throughout 18 d of culture. Furthermore, addition of rhFSH to the medium promoted a significant increase in the percentage of fully grown oocytes in all treatments compared to α-MEM⁺. Mitochondrial activity was higher in rhFSH treatments than in the control, except in rhFSH seq. 2 (P < 0.05). Maturation rates increased in oocytes from intact follicles cultured in 750 ng/mL rhFSH compared to the control (P < 0.05). In conclusion, rhFSH at 750 ng/mL maintained the survival of secondary follicles cultured in serum-free medium, improved oocyte growth, mitochondrial activity, and oocyte maturation.

In vitro growth and development of isolated secondary follicles from vitrified caprine ovarian cortex

The aim of this study was to evaluate the viability, antrum formation and in vitro development of isolated secondary follicles from vitrified caprine ovarian cortex in a medium previously established for fresh isolated secondary follicles, in the absence (α-minimum essential medium (α-MEM+) alone) or presence of FSH and vascular endothelial growth factor (VEGF; α-MEM++FSH+VEGF). Ovarian fragments were distributed among five treatments (T1 to T5): fresh follicles were fixed immediately (T1), follicles from fresh tissue were cultured in vitro in α-MEM+ (T2) or α-MEM++FSH+VEGF (T3) and follicles from vitrified tissue were cultured in vitro in α-MEM+ (T4) or α-MEM++FSH+VEGF (T5). After 6 days of culture, treated follicles (T2, T3, T4 and T5) were evaluated for morphology, viability and follicular development (growth, antrum formation and proliferation of granulosa cells by Ki67 and argyrophilic nucleolar organiser region (AgNOR) staining). The levels of reactive oxygen species (ROS) in the culture media were also assessed. Overall, morphology of vitrified follicles was altered (P<0.05) compared with the fresh follicles. Follicular viability, antrum formation and ROS were similar between treatments (P>0.05). The average overall and daily follicular growth was highest (P<0.05) in T3. Granulosa cells in all treatments (T1, T2, T3, T4 and T5) stained positive for Ki67. However, fresh follicles from T3 had significantly higher AgNOR staining (P<0.05) compared with follicles of T1, T2, T4 and T5. In conclusion, secondary follicles can be isolated from vitrified and warmed ovarian cortex and survive and form an antrum when growing in an in vitro culture for 6 days.

Anti-Müllerian hormone reduces growth rate without altering follicular survival in isolated caprine preantral follicles cultured in vitro

The aim of the present study was to evaluate the effect of anti-Müllerian hormone (AMH), with and without FSH, on the in vitro development of isolated caprine preantral follicles, as well as follicular steroid production and mRNA levels of AMH, hormone receptors (AMH and FSH), CYP19A1 (cytochrome P450, family 19, subfamily A, polypeptide 1), CYP17 (cytochrome P450, family 17, subfamily A, polypeptide 1), HSD3B (3-beta-hydroxysteroid dehydrogenase) and Myc (myelocytomatosis oncogene). Isolated secondary follicles were cultured in minimum essential medium alpha (α-MEM+) alone or supplemented with 50ng mL^-1 AMH and/or 100ng mL^-1 FSH added sequentially on different days of culture. Follicles were cultured for a total of 18 days, with different media during the first (Days 0-9) and second (Days 10-18) halves of the culture period, resulting in six treatment groups, as follows: α-MEM+/α-MEM+, FSH/FSH, AMH/AMH, AMH+FSH/AMH+FSH, AMH/FSH, and FSH/AMH. Follicle development was evaluated on the basis of follicular growth, oocyte maturation and steroid secretion. There was a decrease in follicular growth rate in the AMH, AMH+FSH and AMH/FSH treatment groups compared with α-MEM+ and FSH treatment groups (P<0.05). However, the different culture conditions had no effect on rates of meiotic resumption and steroid secretion (P>0.05). Moreover, follicles cultured in the presence of FSH had lower levels of AMH receptor type II (AMHRII) mRNA compared with non-cultured control (freshly isolated follicles), and the AMH and AMH/FSH treatment groups. In conclusion, AMH reduces the follicular growth rate of isolated goat preantral follicles in vitro without affecting follicular survival.

In vivo and in vitro strategies to support caprine preantral follicle development after ovarian tissue vitrification

The aim of the present study was to compare fresh and vitrified goat ovarian tissue after autotransplantation and in vitro culture. Adult goats were completely ovariectomised and each ovarian pair was sliced and distributed among six different treatment groups: fresh control, fresh transplant, fresh culture, vitrified control, vitrified transplant and vitrified culture. Follicular morphology, development, growth, density, revascularisation and hormone production were evaluated in all groups. Three antral follicles (two in the fresh transplant and one in the vitrified transplant groups) were observed on the surface of the graft 90 days after transplantation. The percentage of morphologically normal follicles was similar in the fresh control, fresh transplant and vitrified transplant groups. The percentage of developing (transition, primary and secondary) follicles was higher after in vitro culture of fresh or vitrified tissue. Transplantation resulted in a lower follicle density. Serum oestradiol concentrations remained constant during the entire transplantation period. In contrast, progesterone production decreased significantly. Expression of CD31 mRNA was lower in fresh culture. In conclusion, restoration of goat ovarian function can be successfully achieved following transplantation of both fresh and vitrified goat ovarian tissue. However, transplantation induced higher follicle loss than in vitro culture.

The effects of activated omental extract on nuclear and cytoplasmic in vitro maturation of rat oocytes

Objective:

The role of growth factors, including vascular endothelial growth factor of activated omentum on mitosis is clearly known, though not on all the aspects of in vitro oocyte maturation. This study was designed to assess the effect of activated-omental extract (AOE) on in vitro maturation (IVM) of rat cumulus-oocyte complexes (COCs).

Materials and Methods:

In this experimental study, the COCs were incubated in Ham’s F-10 supplemented with either 20% AOE, 20% fetal bovine serum (FBS) or serum-free media. Post-culture COCs were studied according to the cumulus cells (CCs) expansion, nuclear maturation and cytoplasmic maturation. Cumuli expansion was evaluated by inverted microscope without staining; nuclear maturation was assessed by aceto-orcein staining (light microscope) and cytoplasmic maturation was also observed by TEM.

Results:

Expansion of CCs and nuclear maturation of the oocytes in in vitro for 24 hr was significantly higher in AOE- and FBS-supplemented groups (P=0.000 and 0.013) and (P=0.004 and 0.014), respectively, compared to serum-free group. At ultra-structural level, after 24 hr, both FBS and AOE-supplemented media showed uniformly wide perivitelline space (PVS). After 12 hr, the cortical granules were found in the oocytes cultured in FBS and AOE-supplemented media. Within 24 hr, both granules and mitochondria were large without any detectable topographic tendency across the ooplasm. In AOE and FBS-supplemented oocytes, the number and size of microvilli were more than those in serum-free one.

Conclusion:

Although AOE supplementation induced a higher rate of the CCs expansion, and resuming meiosis, it was not as potent as FBS to provide cytoplasmic maturation of rat oocytes.

Ovarian tissue culture in the presence of VEGF and fetuin stimulates follicle growth and steroidogenesis

Ovarian tissue cryopreservation together with follicle culture provides a promising technique for fertility preservation in cancer patients. The study aimed to evaluate follicle parameters in a culture medium supplemented with VEGFA165 and/or fetuin. Vitrified-warmed ovarian cortical pieces were divided randomly into four culture groups consisting of basic culture medium (control), and the basic culture medium supplemented with VEGFA165, fetuin or both. After six days of culture, we evaluated the following: percentage of resting, primary and secondary growing follicles; survival rate; steroid hormones production; levels of reactive oxygen species, lipid peroxidation and total antioxidant capacity; and developmental and antioxidant gene expression. The addition of VEGFA165 alone or in combination with fetuin to the culture medium caused resting follicle activation and increased the number of growing follicles. In the VEGFA165 group, we found a significant increase in the concentrations of 17β-estradiol at day 6 and progesterone from 4th day of the culture period. In the VEGFA165 + fetuin group, the concentration of 17β-estradiol rose at day 4 of the culture period. The levels of BMP15, GDF9 and INHB mRNAs were increased in all treated groups. In the fetuin and fetuin + VEGFA165 groups, we observed a high level of total antioxidant capacity and expression of SOD1 and CAT genes, low reactive oxygen species and lipid peroxidation levels and increased number of viable follicles. In conclusion, the present study provides useful evidence that supplementation of culture medium with VEGFA165 + fetuin leads to primordial follicle activation and development and increased percentage of healthy secondary growing follicles.

Fibrin-alginate hydrogel supports steroidogenesis, in vitro maturation of oocytes and parthenotes production from caprine preantral follicles cultured in group

This study aimed to establish a culture system that improves the in vitro development of caprine preantral follicles. In a first experiment, follicles were encapsulated as a single unit per bead and cultured singly or in groups or with five follicles in the same alginate (ALG) bead for 18 days. In a subsequent experiment, the "five follicles per bead" design was chosen to culture in ALG, fibrin-alginate (FA) or hyaluronate (HA) for 18 days. In a third experiment, we chose the five follicles per bead in FA to culture for 30 days. The culture set-up of five follicles per ALG bead increased antrum formation and follicle diameter compared to the other culture designs (p < .05). Moreover, under this condition, 44.44% of the oocytes from in vitro cultured preantral follicles reached meiotic resumption. A significant increase of follicle diameter occurred in attachment system and FA (p < .05), but the ALG condition reached the highest among all groups on day 18 (p < .05). Follicles encapsulated in matrix produced more estradiol and progesterone than attachment system (p < .05). The expression of MMP-9 mRNA was higher in FA than in other groups (p < .05) and similar to antral follicles from in vivo control (p > .05). Only FA group resulted in oocytes matured. After 30 days, oocytes from preantral follicles in vitro grown in FA developed to eight-cell parthenotes. In conclusion, a culture system using FA supported the development of caprine preantral follicles cultured in group and included in the same bead of hydrogel, improving the oocyte maturation and producing parthenotes.

Caprine ovarian follicle requirements differ between preantral and early antral stages after IVC in medium supplemented with GH and VEGF alone or in combination

The aim of the present study was to evaluate the effect of growth hormone (GH) and vascular endothelial growth factor (VEGF) added alone, sequentially or in combination, in the presence of insulin at physiological concentration (10 ng/mL) on the IVC of two different follicular categories: preantral (experiment 1; Exp.1) and early antral (experiment 2; Exp.2). Isolated follicles were individually cultured for 24 (Exp.1) and 18 days (Exp.2) in the following treatments: αMEM⁺ (Control), or Control medium supplemented with 50 ng/mL GH (GH), 100 ng/mL VEGF (VEGF), the combination of both (GH + VEGF), GH during the first 12 days and VEGF from Day 12 until the end of the culture (GH/VEGF) and vice versa (VEGF/GH). At the end of the culture, cumulus-oocyte complexes from in vitro-grown follicles were recovered and subjected to IVM. The following end points were evaluated: Follicle morphology, growth rates and antrum formation, production of estradiol, progesterone and testosterone, oocyte viability and meiotic stage, as well as relative expression of LHR, Amh, HAS2, PTGS2, CYP17, CYP19A1, and 3βHSD. A considerable amount of viable fully grown oocytes were recovered after the IVC of early antral follicles in all treatments. Nevertheless, the GH treatment presented the highest percentage of fully grown oocytes (60%), mean oocyte diameter (117.74 ± 2.61 μm), and meiotic resumption (50%). Furthermore, GH treatment produced higher (P < 0.05) rates of metaphase II oocytes than all the other treatments, and similar LHR, Amh, and PTGS2 transcript levels to in vivo. Contrary to early antral follicles, preantral follicles were not affected by medium supplementation. In conclusion, the addition of GH to a culture medium containing physiological concentrations of insulin improves oocyte growth and maturation after the IVC of goat early antral follicles.

Ovarian follicle development in vitro and oocyte competence: advances and challenges for farm animals

During the last 2 decades, research on in vitro preantral follicle growth and oocyte maturation has delivered fascinating advances concerning the knowledge of processes regulating follicle growth and the developmental competence of oocytes. These advances include (1) information about the role of several hormones and growth factors on in vitro activation of primordial follicles; (2) increased understanding of the intracellular pathway involved in the initiation of primordial follicle growth; (3) the growth of primary and secondary follicles up to antral stages; and (4) production of embryos from oocytes from in vitro grown preantral follicles. This review article describes these advances, especially in regard farm animals, and discusses the reasons that limit embryo production from oocytes derived from preantral follicles cultured in vitro.

Anethole improves the in vitro development of isolated caprine secondary follicles

The aim of this study was to investigate the effect of three concentrations of anethole (30, 300, and 2000 μg/mL) on survival, antrum formation, follicular diameter, and oocyte maturation in the caprine species. The study also evaluated the effects of anethole on transcripts of ICAM-1, CAV-1, TIMP-2, and PAI-1 genes and levels of reactive oxygen species (ROS) in isolated goat preantral ovarian follicles before and after in vitro culture for 18 days. Preantral follicles were isolated from goat ovaries and individually cultured in alpha minimum essential medium modified (α-MEM⁺), defined as the control treatment, α-MEM⁺ supplemented with ascorbic acid at a concentration of 100 μg/mL (AA), or α-MEM⁺ supplemented with three different concentrations of anethole (30, 300, 2000 μg/mL) for a period of 18 days. Treatments were named as α-MEM⁺, AA, AN30, AN300, and AN2000, respectively. After culture, the follicles were opened, the cumulus oocytes complex (COCs) were removed and matured in vitro. The walls of the follicles were used for the quantitation of mRNA by quantitative real-time polymerase chain reaction. Finally, the medium collected at the end of culture was used for the measurements of ROS. After 18 days of culture, the AA treatment showed the percentage of intact follicles and follicular diameter significantly higher compared with the other treatments. However, daily growth rate, antrum formation, and also oocyte diameter were similar among the treatments. In addition, compared with AA, the rate of oocytes for in vitro maturation (diameter ≥ 110 μm) and the meiosis resumption rate were significantly higher in the treatments AN30 and AN2000, respectively. When assessing gene related to remodeling of the basement membrane, significant differences in mRNA levels for ICAM-1, CAV-1, TIMP-2, and PAI-1 were observed in comparison with Day 0, i.e., in the noncultured control. In addition, the ROS from Day 12, all treatments with the addition of anethole have significantly lower values of ROS than α-MEM⁺ and AA. In conclusion, the addition of anethole to the in vitro culture medium was able to improve the development of goat preantral follicles by reducing concentrations of ROS and increasing the percentage of oocytes able to resume meiosis.

Bone Morphogenetic Protein-6 (BMP-6) Stimulates the Antrum Formation by the Regulation of its Signalling Pathway in Caprine Pre-antral Follicles Cultured In Vitro

BMP-6 has been found to be important to ovarian cells and oocyte, as well as to uterus. Thus, this study investigated the effect of bone morphogenetic protein (BMP-6) and recombinant follicle-stimulating hormone (rFSH) alone or in combination on the in vitro culture (IVC) of isolated caprine secondary follicles (Experiment 1) and the mRNA levels for BMP receptors/Smad signalling pathway (BMPR1A, BMPR2, SMAD1, SMAD4, SMAD5, SMAD6, SMAD7 and SMAD8) in vivo and in vitro using BMP-6 (Experiment 2). Secondary follicles were cultured in αMEM(+) alone (control medium) or supplemented with BMP-6 at 1 or 10 ng/ml and rFSH alone or the combination of both BMP-6 concentrations and rFSH. The results from Experiment 1 showed that the antrum formation rate was higher in the BMP-6 at 1 ng/ml (p < 0.05) than in MEM. In Experiment 2, the mRNA expression for BMPR2, SMAD1, SMAD5 and SMAD6 was detected in non-cultured control and after in vitro culture (MEM and 1 ng/ml BMP-6); while the expression of SMAD7 and SMAD8 mRNA was only detected after IVC, SMAD4 was only detected in the BMP-6 at 1 ng/ml treatment. In conclusion, the low BMP-6 concentration positively influenced antrum formation and ensured normal mRNA expression for BMP receptor and Smads after IVC of caprine secondary follicles.

Insulin improves in vitro survival of equine preantral follicles enclosed in ovarian tissue and reduces reactive oxygen species production after culture

This study investigated the effect of insulin concentration on the in vitro culture of equine preantral follicles enclosed in ovarian tissue. Ovarian tissue samples were immediately fixed (noncultured control) or cultured for 1 or 7 days in α-MEM(+) supplemented with 0 ng/mL, 10 ng/mL, or 10 μg/mL insulin. Ovarian tissues were processed and analyzed by classical histology. Culture medium samples were collected after 1 and 7 days of culture for steroid and reactive oxygen species (ROS) analyses. The percentage of morphologically normal follicles was greater (P < 0.001) in insulin-treated groups after 1 day of culture; likewise, more (P < 0.02) normal follicles were observed after 7 days of culture in medium supplemented with 10-ng/mL insulin. Furthermore, an increase (P < 0.01) in developing (transition, primary, and secondary) follicles between Days 1 and 7 of culture was observed only with the 10-ng/mL insulin treatment. ROS production after 1 or 7 days of culture was lower (P < 0.0001) in medium with 10-ng/mL insulin than the other treatments. Ovarian tissues containing preantral follicles were able to produce estradiol and progesterone after 1 and 7 days of culture; however, treatments did not differ in steroid production. In conclusion, the use of a physiological concentration (10 ng/mL) of insulin rather than the previously reported concentration (10 μg/mL) for in vitro culture of equine preantral follicles improved follicular survival and growth and lowered oxidative stress. Results from this study shed light on new perspectives for producing an appropriate medium to improve equine preantral follicle in vitro survival and growth.

The base medium affects ultrastructure and survival of bovine preantral follicles cultured in vitro

The aim of this study was to determine the effectiveness of minimum essential medium alpha modification (α-MEM), tissue culture medium 199 (TCM-199), and McCoy's medium (McCoy's) on IVC of preantral follicles included in the bovine ovarian cortex (in situ). Bovine ovarian fragments were cultured in α-MEM, TCM-199, or McCoy supplemented ((+)) with glutamine, insulin, transferrin, selenium, ascorbic acid, BSA, penicillin, streptomycin, and HEPES buffer in 24-well plates, at 37 °C and 5% CO2 for 1 or 7 days. The morphology of follicles, normal, primordial and development (primary and secondary), as well as viability and morphometric variables of follicles and oocytes were assessed. The morphology and morphometry of preantral follicles were analyzed by ANOVA followed by the Tukey and Dunnett tests, and viability variables were determined by the chi-square test. The results showed that TCM-199(+) reduced significantly (P < 0.05) the percentage of morphologically normal and viable follicles after 7 days of culture compared to the control. Similar results were observed in McCoy(+), in which the percentage of viable follicles after 7 days of culture was significantly lower (P < 0.05) than in the control. However, it was similar (P > 0.05) between α-MEM(+) and TCM-199(+). Moreover, follicular diameters in McCoy(+) and TCM-199(+) were significantly smaller (P < 0.05) than in control and α-MEM(+) after 7 days of culture. In addition, the ultrastructure of preantral follicles was similar between the control and α-MEM(+) after 7 days of culture. In conclusion, α-MEM(+) showed to be the most effective medium to preserve morphology, morphometry and ultrastructure of bovine preantral follicles, ensuring their viability and growth after in situ culture.

The Paracrine Effect of Transplanted Human Amniotic Epithelial Cells on Ovarian Function Improvement in a Mouse Model of Chemotherapy-Induced Primary Ovarian Insufficiency

Human amnion epithelial cells (hAECs) transplantation via tail vein has been reported to rescue ovarian function in mice with chemotherapy-induced primary ovarian insufficiency (POI). To test whether intraperitoneally transplanted hAECs could induce therapeutic effect and to characterize the paracrine effect of transplanted hAECs, we utilized a chemotherapy induced mice model of POI and investigated the ability of hAECs and conditioned medium collected from cultured hAECs (hAECs-CM) to restore ovarian function. We found that transplantation of hAECs or hAECs-CM either 24 hours or 7 days after chemotherapy could increase follicle numbers and partly restore fertility. By PCR analysis of recipient mice ovaries, the presence of SRY gene was only detected in mice transplanted with male hAECs 24 hours following chemotherapy. Further, the gene expression level of VEGFR1 and VEGFR2 in the ovaries decreased, although VEGFA increased 2 weeks after chemotherapy. After treatment with hAECs or hAEC-CM, the expression of both VEGFR1 and VEGFR2 increased, consistent with the immunohistochemical analysis. In addition, both hAECs and hAECs-CM treatment enhanced angiogenesis in the ovaries. The results suggested that hAECs-CM, like hAECs, could partly restore ovarian function, and the therapeutic function of intraperitoneally transplanted hAECs was mainly induced by paracrine-mediated ovarian protection and angiogenesis.

Balance of insulin and FSH concentrations improves the in vitro development of isolated goat preantral follicles in medium containing GH

The aim of this study was to evaluate the effect of different combinations of insulin and FSH concentrations in culture media containing GH on the in vitro follicle morphology, antrum formation, growth rates, estradiol (E2) production, oocyte viability and maturation as well as gene expression for FSHR, GHR, INSR, CYP19A1, CYP17, 3ßHSD. Secondary follicles were individually cultured for 18 days in a basic medium containing 50ng/mL GH supplemented with low insulin concentration (INS-LW: 10ng/mL) or high insulin concentration (INS-HG: 10μg/mL) alone or with a fixed FSH concentration (FSH100: 100ng/mL) or with increasing FSH concentrations (FSH-SEQ: 100ng/mL, days 0-6; 500ng/mL, days 6-12; 1000ng/mL days 12-18). In the INS-LW treatment was observed a higher (P<0.05) incidence of normal follicles at day 18 of culture. However, overall higher (P<0.05) follicular growth, oocyte diameter and meiotic resumption rates were obtained using INS-HG+FSH 100. The INS-HG and INS-HG+FSH100 treatments showed higher E2 production and mRNA levels for CYP19A1, CYP17, 3βHSD when compared to INS-LW and INS-LW+FSH100. However, the addition of increasing FSH concentration, regardless of insulin concentration, did not improve the follicular growth, meotic resumption, E2 production or gene expression of steroidogenic enzymes when compared with INS-HG+FSH100. In conclusion, in presence of GH, a basic medium supplemented with 10μg/mL insulin and 100μg/mL FSH throughout the culture period, improves follicular and oocyte growth, oocyte meiotic resumption and E2 production from isolated preantral caprine follicles cultured in vitro.

Influence of vascular endothelial growth factor and Cysteamine on in vitro bovine oocyte maturation and subsequent embryo development

The objective of this study was to investigate the effect of VEGF and Cysteamine during in vitro maturation (IVM) of bovine oocytes on GSH content and developmental competence. For this purpose, experiments were designed to evaluate the effect of 0, 100, 300, and 500 ng/mL VEGF in IVM medium on: GSH content in oocytes and cumulus cells (Exp. 1) and subsequent embryo development (Exp. 2). Also, influence of adding 500 ng/mL VEGF and 100 μM Cysteamine to IVM medium on GSH content in oocytes and cumulus cells (Exp. 3) and oocyte developmental capacity (Exp. 4) were evaluated. Oocytes were matured in: a) Control; b) VEGF 0-3 h; c) Cysteamine 4-24 h; d) VEGF 0-3 h + Cysteamine 4-24 h; and e) VEGF + Cysteamine 24 h. The results showed that: i) VEGF did not alter GSH content in oocytes and cumulus cells; (ii) supplementation of 300 and 500 ng/mL VEGF increased blastocyst yield; (iii) the presence of VEGF + Cysteamine simultaneously during 24 h improved GSH content but not embryo development; and (iv) the presence of VEGF during the first 3 h + Cysteamine from 4 to 24 h increased GSH concentrations and subsequent embryo development. In conclusion, the addition of VEGF and Cysteamine in two sequential steps to maturation medium result in an improvement of cytoplasmic maturation, with a positive impact on oocyte developmental capacity by increasing the efficiency of in vitro blastocyst production. However, the effect was detrimental when both VEGF and Cysteamine were present during 24 of IVM.

In vitro culture of bovine preantral follicles: a review

Preantral follicles are the majority of the ovarian follicle population and their use as a source of homogeneous oocytes for bovine reproductive biotechnologies could result in a substantial advance in this field. However, while in other species embryos and offspring have been produced, in bovine species the results have been limited to the follicular activation of small (primordial) preantral follicles and formation of early antral follicles from large (secondary) preantral follicles after in vitro culture. Therefore, this review will highlight the basic aspects of bovine folliculogenesis by focusing on preantral follicles, the methods of harvesting preantral follicles, the main results from in vitro follicular culture during the last 20 years, and the potential candidate substances (basic supplements, growth factors, and hormones) for improving the efficiency of in vitro follicle growth.

In vitro development of bovine secondary follicles in two- and three-dimensional culture systems using vascular endothelial growth factor, insulin-like growth factor-1, and growth hormone

The aim of this study was to evaluate the development and estradiol production of isolated bovine secondary follicles in two-dimensional (2D, experiment 1) and three-dimensional (3D using alginate, experiment 2) long-term culture systems in the absence (control group; only α-MEM(+)) or presence of vascular endothelial growth factor (VEGF), insulin-like growth factor-1, or GH alone, or a combination of all. A total of 363 isolated secondary follicles were cultured individually for 32 days at 38.5 °C in 5% CO2 in a humidified incubator with addition of medium (5 μL) every other day. In 2D culture system, follicular growth and antrum formation rates were higher (P < 0.05) in VEGF treatment compared with the other treatments. In 3D culture system, only estradiol concentration was greater (P < 0.05) in the GH than in the control group, whereas the other end points were similar (P > 0.05). In summary, this study demonstrated that the benefits of using a certain type of medium supplement depended on the culture system (2D vs. 3D). Vascular endothelial growth factor was an effective supplement for the in vitro culture of bovine secondary follicles when the 2D culture system was used, whereas GH only affected estradiol production using the 3D culture system. This study sheds light on advancements in methodology to facilitate subsequent studies on bovine preantral follicle development.

Alginate hydrogel matrix stiffness influences the in vitro development of caprine preantral follicles

This study examined caprine follicular development in different concentrations of alginate matrix to determine the optimal conditions for culture. Caprine preantral follicles were cultured in a two-dimensional system (control) or a three-dimensional encapsulated system in 0.25%, 0.5%, or 1% alginate (ALG 0.25, ALG 0.5, and ALG 1, respectively). A higher percentage of morphologically normal follicles developed in ALG 0.5 and ALG 1 than in ALG 0.25 or the control (P < 0.05). The rate of antrum formation, however, was higher in ALG 0.25 than in ALG 0.5 and ALG 1 conditions (P < 0.05), but similar to the control. Follicles cultured in ALG 0.25 had higher growth rates and meiotic resumption than those cultured in ALG 0.5, ALG 1, or the control (P < 0.05). Moreover, follicles cultured in ALG 0.25 had higher levels of estradiol and progesterone than those cultured in ALG 0.5, ALG 1, or the control, as well as higher levels of CYP19A1 and HSD3B mRNA. In conclusion, a three-dimensional system that uses ALG 0.25 fosters the in vitro development of caprine preantral follicles and increases the rate of meiotic resumption.

In vitro development of secondary follicles from pre-pubertal and adult goats cultured in two-dimensional or three-dimensional systems

The aim of this study was to evaluate the influence of two-dimensional (2D) and three-dimensional (3D) alginate culture systems on in vitro development of pre-antral caprine follicles. In addition, the influence of the reproductive age of the ovary donor on the in vitro culture success was investigated. Pre-antral follicles from pre-pubertal or adult goats were isolated and cultured directly on a plastic surface (2D) or encapsulated in an alginate-based matrix (3D). After 18 days, the oocytes underwent in vitro maturation (IVM) and in vitro fertilization (IVF) to produce embryos. The 3D system showed higher rates of follicle survival, lower rates of oocyte extrusion, and a greater number of recovered oocytes for IVM and IVF (P < 0.05). Only pre-antral follicles from adult animals produced MII oocytes and embryos. The estradiol concentrations increased from day 2 to day 12 of culture in all groups tested (P < 0.05). Conversely, progesterone concentrations were lower in 3D-cultured follicles than in 2D-cultured follicles, with differences on days 2 and 6 of culture (P < 0.05). We provide compelling evidence that a 2D or 3D alginate in vitro culture system offers a promising approach to achieving full in vitro development of caprine pre-antral follicles to produce mature oocytes that are capable of fertilization and viable embryos.

Exosomal and Non-Exosomal Transport of Extra-Cellular microRNAs in Follicular Fluid: Implications for Bovine Oocyte Developmental Competence

Cell-cell communication within the follicle involves many signaling molecules, and this process may be mediated by secretion and uptake of exosomes that contain several bioactive molecules including extra-cellular miRNAs. Follicular fluid and cells from individual follicles of cattle were grouped based on Brilliant Cresyl Blue (BCB) staining of the corresponding oocytes. Both Exoquick precipitation and differential ultracentrifugation were used to separate the exosome and non-exosomal fraction of follicular fluid. Following miRNA isolation from both fractions, the human miRCURY LNA™ Universal RT miRNA PCR array system was used to profile miRNA expression. This analysis found that miRNAs were present in both exosomal and non-exosomal fraction of bovine follicular fluid. We found 25 miRNAs differentially expressed (16 up and 9 down) in exosomes and 30 miRNAs differentially expressed (21 up and 9 down) in non-exosomal fraction of follicular fluid in comparison of BCB- versus BCB+ oocyte groups. Expression of selected miRNAs was detected in theca, granulosa and cumulus oocyte complex. To further explore the potential roles of these follicular fluid derived extra-cellular miRNAs, the potential target genes were predicted, and functional annotation and pathway analysis revealed most of these pathways are known regulators of follicular development and oocyte growth. In order to validate exosome mediated cell-cell communication within follicular microenvironment, we demonstrated uptake of exosomes and resulting increase of endogenous miRNA level and subsequent alteration of mRNA levels in follicular cells in vitro. This study demonstrates for the first time, the presence of exosome or non-exosome mediated transfer of miRNA in the bovine follicular fluid, and oocyte growth dependent variation in extra-cellular miRNA signatures in the follicular environment.

Targeting angiogenesis in the pathological ovary

The ovary is a key tissue in the study of physiological neo-vascularisation in the adult and its study has highlighted important molecules involved in the regulation of angiogenesis in vivo. These include vascular endothelial growth factor, delta-like ligand 4, thrombospondin-1, prokineticin-1 and prostaglandin E2. Targeting these molecular pathways has therapeutic potential and their manipulation has an increasing preclinical and clinical role in the management of the pathological ovary. Targeting angiogenic pathways has utility in the promotion of ovarian angiogenesis to improve tissue and follicle survival and function as well as the prevention and management of ovarian hyperstimulation syndrome. There is a theoretical possibility that targeting angiogenesis may improve the function of the polycystic ovary and a real role for targeting angiogenesis in ovarian cancer.

Insulin-like growth factor II (IGF-II) and follicle stimulating hormone (FSH) combinations can improve the in vitro development of grown oocytes enclosed in caprine preantral follicles

OBJECTIVE

Evaluate the possible role of IGF-II alone or in association with FSH on in vitro development of isolated caprine preantral follicles.

METHODS

Preantral follicles (≥150 μm) were isolated from goat ovaries and cultured for 18 days in basic αMEM medium (control) or supplemented with IGF-II alone at 20 or 50 ng/ml, named IGF20 and IGF50, respectively, or in combination with recombinant FSH (FSH, IGF20F or IGF50F). During in vitro culture, the follicles were analyzed by using morphology criteria, antrum formation and growth rate as parameters. After 18 days of follicular culture, oocytes equal to or larger than 110 μm were used for in vitro maturation (IVM). Oocyte viability and meiosis resumption were assessed by fluorescence microscopy after labeling with calcein-AM, ethidium homodimer and Hoechst 33342.

RESULTS

The IGF20 treatment was the only treatment capable of maintaining the percentage of morphologically normal follicles from D0 until D6 and from D12 to D18 (p>0.05), while in all other treatments the percentage of morphologically normal follicles decreased progressively during 18 days of in vitro culture (p<0.05). At D18, all treatments with IGF-II or FSH resulted in a significantly higher percentage of normal follicles when compared to αMEM alone. The IGF50F treatment provided a significantly higher early antrum formation rate when compared to αMEM and FSH alone. The addition of IGF-II alone (20 or 50 ng/ml) or in combination with FSH prevented oocyte degeneration after IVM. Moreover, the FSH treatment demonstrated a lower percentage of oocyte degeneration when compared to control (4.35% vs. 26.3%, respectively; p<0.05). Regarding meiosis resumption, the IGF20F treatment was the only treatment that significantly differed from αMEM alone. All treatments except the control (αMEM alone) presented oocytes at metaphase II.

CONCLUSION

IGF-II associated with FSH stimulated in vitro follicular development, oocyte viability and meiotic resumption of caprine oocytes after IVM.

Vascular endothelial growth factor-induced expression of its receptors and activation of the MAPK signaling pathway during ovine oocyte maturation in vitro

The vascular endothelial growth factor (VEGF) has beneficial effects on ovine oocytes during in vitro maturation and their subsequent early embryonic development, but the biochemical pathway underlying this effect has not been elucidated. Therefore, the focus of the present study was to investigate the activation of the mitogen-activated protein kinase (MAPK) pathway in response to the addition of VEGF to the maturation medium, and to study the subcellular localization of VEGF and its receptors during ovine oocyte maturation. We concluded that: (1) VEGF mainly localized in the cytoplasm, whereas its receptors, fms-tyrosine kinase-1 and kinase domain region (KDR), were localized on the plasma membrane of oocytes; (2) the addition of 5 ng/mL VEGF increased the percentage of oocytes with extruded first polar bodies (50.9 ± 2.2% vs. 34.6 ± 2.9%; treatment vs. control, respectively; P < 0.01) and the rate of oocytes competent to undergo nuclear maturation (70.6 ± 0.9% vs. 62.9 ± 1.9%, P < 0.01); and (3) as the expression of VEGF, fms-tyrosine kinase-1, and KDR increased after supplementation with 5 ng/mL, expression of VEGF, mitogen-activated protein kinase kinase (MEK), and MAPK mRNA, as well as MAPK phosphorylation, were stimulated in a time-dependent manner. We inferred that, in a paracrine manner, exogenous VEGF bound to KDR, its main receptor, and then activated the MAPK signaling pathway, which promoted maturation of ovine oocytes. However, the VEGF system also had an autocrine regulatory loop that contributed to creating an environment optimal for oocyte maturation.