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

Identification of Lipids and Cytokines in Plasma and Follicular Fluid before and after Follicle-Stimulating Hormone Stimulation as Potential Markers for Follicular Maturation in Cattle

The process of follicle maturation leading to ovulation is a key milestone in female fertility. It is known that circulating lipids and cytokines play a role in the follicle's ability to go through follicular maturation and the ovulatory processes. However, the specific mechanisms are not well understood. We posit that dysregulation of granulosa cells influences the ovarian environment, which tries to adapt by changing released lipids and cytokines to achieve follicular maturation. Eleven non-lactating adult females underwent estrus synchronization with two injections of PGF2α 14 days apart. Daily blood samples were collected for 28 days to monitor steroid hormone production after the second injection. To understand the potential impacts of lipids and cytokines during ovulation, a low-dose FSH stimulation (FSHLow) was performed after resynchronization of cows, and daily blood samples were collected for 14 days to monitor steroid hormone production until ovariectomies. The lipidomic analysis demonstrated increased circulating diacylglycerides and triacylglycerides during the mid-luteal phase and after FSHLow treatment. Cholesteryl esters decreased in circulation but increased in follicular fluid (FF) after FSHLow. Increased circulating concentrations of TNFα and reduced CXCL9 were observed in response to FSHLow. Therefore, specific circulating lipids and cytokines may serve as markers of normal follicle maturation.

Review: Environment of the ovulatory follicle: modifications and use of biotechnologies to enhance oocyte competence and increase fertility in cattle

The oocyte is the basis of life, supporting development from a fertilized cell to an independent multicellular organism. The oocyte's competence to drive the first cell cycles postfertilization are critical to embryonic survival and subsequent successful pregnancy. Coupled with the complex processes of follicle assembly, activation, differentiation, growth, and terminal maturation, oocyte developmental competence is gradually acquired during oocyte growth and meiotic maturation. Most reproduction management technologies and interventions are centered around these highly coordinated processes, targeting the ovarian follicle and the oocyte within. Thus, our objective was to highlight key aspects of oocyte and follicle development in cattle, and to discuss recent advances in oocyte and follicle-centered reproductive biotechnologies.

IVM Advances for Early Antral Follicle-Enclosed Oocytes Coupling Reproductive Tissue Engineering to Inductive Influences of Human Chorionic Gonadotropin and Ovarian Surface Epithelium Coculture

In vitro maturation (IVM) is not a routine assisted reproductive technology (ART) for oocytes collected from early antral (EA) follicles, a large source of potentially available gametes. Despite substantial improvements in IVM in the past decade, the outcomes remain low for EA-derived oocytes due to their reduced developmental competences. To optimize IVM for ovine EA-derived oocytes, a three-dimensional (3D) scaffold-mediated follicle-enclosed oocytes (FEO) system was compared with a validated cumulus-oocyte complex (COC) protocol. Gonadotropin stimulation (eCG and/or hCG) and/or somatic cell coculture (ovarian vs. extraovarian-cell source) were supplied to both systems. The maturation rate and parthenogenetic activation were significantly improved by combining hCG stimulation with ovarian surface epithelium (OSE) cells coculture exclusively on the FEO system. Based on the data, the paracrine factors released specifically from OSE enhanced the hCG-triggering of oocyte maturation mechanisms by acting through the mural compartment (positive effect on FEO and not on COC) by stimulating the EGFR signaling. Overall, the FEO system performed on a developed reproductive scaffold proved feasible and reliable in promoting a synergic cytoplasmatic and nuclear maturation, offering a novel cultural strategy to widen the availability of mature gametes for ART.

The association of serum phthalate metabolites with biomarkers of ovarian reserve in women of childbearing age

Phthalates (PAEs) are widely used plasticizers drawing increasing concern due to reproductive toxicity. However, studies on serum PAEs metabolites (mPAEs) and their associations with human ovarian function remain very scarce. In this study, from April 2019 to August 2020, a total of 297 women of childbearing age were recruited in Tianjin, China. Eleven mPAEs were analyzed in serum samples and eight mPAEs were detected at frequencies > 65% with median concentrations of 0.43-15.3 ng/mL. In multinomial logistic analysis, an increase in serum mono (2-isobutyl) phthalate (miBP) was associated with decline in antral follicle count (AFC) (OR=1.26, 95% CI: 0.99, 1.61) and 5-mono-(2-ethyl-5-hydroxyhexyl) phthalate (mEHHP) was significantly associated with AFC increase (OR=1.43, 95% CI: 1.06, 1.92), which were aligned with the associations found between mPAEs and AMH through generalized linear regression. In multiple linear regression models, per 10% increase in serum mono (2-ethylhexyl) phthalate (mEHP), mono (2-ethyl-5-oxohexyl) phthalate (mEOHP) (oxo-mEHP), and principal component 1 featured for high concentrations of mono-n-butyl phthalate (mBP), miBP and mEHP were associated with 0.15 (95% CI: -0.29, -0.02), 0.01 (95% CI: -0.01, 0.00) and 0.01 (95% CI: -0.02, 0.00) ln-unit decrease in estradiol (E2) levels, respectively, while mono-[(2-carboxymethyl) hexyl] phthalate (mCMHP) (carboxymethyl-mEHP) was positively associated with 0.05 ln-unit increase of E2 (95% CI: 0.02, 0.08). The observed negative associations between mPAEs and the Anti-Müllerian hormone (AMH) also aligned with the change in AFC. Generalized linear regression also revealed nonlinear associations between mono-ethyl phthalate (mEP), mCMHP and follicle-stimulating hormone (FSH). Overall, serum mEHP and its metabolites were negatively associated with E2. miBP was negatively associated with AFC. The nonlinear associations between mPAEs and FSH, and AMH need further study.

IL-6 of follicular fluid and outcome of in vitro fertilization

The quality of an oocyte is influenced by its microenvironment, which includes cumulus cells and follicular fluid, as well as cells of the immune system and their products. The ovarian interleukins, which are secreted by the granulosa cells and other immune cells within the ovaries and follicles, regulate various functions between the cells. IL-6 is a cytokine that is present in the follicular fluid and may affect the quality of oocytes. There are some inconsistencies in the literature regarding the concentration of interleukin 6 in the follicular fluid. The main objective of this study was to examine whether the concentration of interleukin 6 in the follicular fluid affects the outcome of IVF. This study involved 83 patients who underwent IVF. Follicular fluid was used as the biological material for the analysis. Examination of the obtained follicular fluid and collection of oocytes under a stereomicroscope was performed in the embryological laboratory. The concentration of IL-6 in the follicular fluid was analyzed. IVF and ICSI methods were used as the fertilization methods. Pregnancy was confirmed by the positive serum β-hCG level. The software package SPSS 20 was used for statistical data processing. Analysis of the follicular fluid samples showed a correlation between the concentration of IL-6 in the follicular fluid and the outcome of IVF. The concentration of IL-6 in the follicular fluid was higher in patients with confirmed pregnancy (9.55 ± 7.47 ng/ml). Based on our results, we conclude that the concentration of IL-6 affects the outcome of IVF. If the range of IL-6 concentration is between 3,67 ng/ml and 10 ng/ml, we can expect good IVF outcome with vital pregnancy.

When Electrospun Fiber Support Matters: In Vitro Ovine Long-Term Folliculogenesis on Poly (Epsilon Caprolactone) (PCL)-Patterned Fibers

Current assisted reproduction technologies (ART) are insufficient to cover the slice of the population needing to restore fertility, as well as to amplify the reproductive performance of domestic animals or endangered species. The design of dedicated reproductive scaffolds has opened the possibility to better recapitulate the reproductive 3D ovarian environment, thus potentially innovating in vitro folliculogenesis (ivF) techniques. To this aim, the present research has been designed to compare ovine preantral follicles in vitro culture on poly(epsilon-caprolactone) (PCL)-based electrospun scaffolds designed with different topology (Random vs. Patterned fibers) with a previously validated system. The ivF performances were assessed after 14 days under 3D-oil, Two-Step (7 days in 3D-oil and on scaffold), or One-Step PCL protocols (14 days on PCL-scaffold) by assessing morphological and functional outcomes. The results show that Two- and One-Step PCL ivF protocols, when performed on patterned scaffolds, were both able to support follicle growth, antrum formation, and the upregulation of follicle marker genes leading to a greater oocyte meiotic competence than in the 3D-oil system. In conclusion, the One-Step approach could be proposed as a practical and valid strategy to support a synergic follicle-oocyte in vitro development, providing an innovative tool to enhance the availability of matured gametes on an individual basis for ART purposes.

Oocyte quality following in vitro follicle development†

In vitro follicle development (IVFD) is an adequate model to obtain basic knowledge of folliculogenesis and provides a tool for ovarian toxicity screening. IVFD yielding competent oocytes may also offer an option for fertility and species preservation. To promote follicle growth and oocyte maturation in vitro, various culture systems are utilized for IVFD in rodents, domestic animals, wild animals, nonhuman primates, and humans. Follicle culture conditions have been improved by optimizing gonadotropin levels, regulatory factors, nutrient supplements, oxygen concentration, and culture matrices. This review summarizes quality assessment of oocytes generated from in vitro-developed antral follicles from the preantral stage, including oocyte epigenetic and genetic profile, cytoplasmic and nuclear maturation, preimplantation embryonic development following in vitro fertilization, as well as pregnancy and live offspring after embryo transfer. The limitations of oocyte quality evaluation following IVFD and the gaps in our knowledge of IVFD to support proper oocyte development are also discussed. The information may advance our understanding of the requirements for IVFD, with a goal of producing competent oocytes with genetic integrity to sustain embryonic development resulting in healthy offspring.

Ovarian tissue features assessed in bovine fetuses after vitrification and xenotransplantation procedures

Cryopreservation and transplantation of ovarian tissue are proposed methods for the restoration of endocrine function and reproductive potential. Therefore, this study aimed to evaluate the effects of vitrification and xenotransplantation on follicle viability, activation, stromal cell integrity, vascularization, and micronuclei formation. Bovine fetal ovaries were fragmented and assigned to the following groups: Fresh control (FC), ovarian fragments immediately fixed; Vitrified control (VC), ovarian fragments vitrified; Vitrified xenotransplanted (VX), ovarian fragments vitrified and xenotransplanted; and Fresh xenotransplanted (FX), ovarian fragments xenotransplanted. Ovarian fragments were grafted in female BALB/c mice and recovered after 14 days. Follicular viability was preserved (P >  0.05) in VC group. The rate of developing follicles was greater (P <  0.05) in the FX group compared to other groups. Follicular density was higher (P <  0.05) in the VC group than the FC, VX, and FX groups. A decrease (P <  0.05) of stromal cell density was recorded after vitrification (VC vs. FX). Blood vessel density decreased in VC, VX, and FX groups compared with the FC group, and blood vessel density was correlated with follicular viability (positively; P =  0.07) and developing follicles (negatively; P <  0.001). Both vitrification and xenotransplantation groups (VC, VX, and FX) had a greater (P <  0.05) number of cells with one MN compared to the FC group. In summary, our findings showed that both vitrification and xenotransplantation modified blood vessel, follicular and stromal cell densities, follicular viability and activation, and micronuclei formation in ovarian tissue.

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 Three-Dimensional Sodium Alginate Scaffold on Maturation and Developmental Gene Expressions in Fresh and Vitrified Preantral Follicles of Mice

BACKGROUND

Prior to chemotherapy interventions, n vitroi maturation (IVM) of folliclesthrough vitrification can be used to help young people conserve their fertility. The aim of s tudy was to inves tigate effect of sodium alginat scaffold on follicles development and improvement of the culture medium.

MATERIALS AND METHODS

This experimental study was conducted on immature female BALB/c mice (12-14 days). Follicles were gathered mechanically and placed in α-Minimal Essential Medium (α-MEM) containing 5% fetal bovine serum (FBS). Some pre-antral follicles were frozen. The fresh and vitrified follicles were cultured in different concentrations of sodium alginate (0.25%, 0.5%, and 1%) and two dimensional (2D) medium for 12 days. The samples were evaluated for viability percentage, the number of MII-phase oocytes and reactive oxygen specious (ROS) level. Additionally, Gdf9, Bmp15, Bmp7, Bmp4, Gpx, mnSOD and Gcs gene expressions were assessed in the samples.

RESULTS

The highest and lowest percentages of follicle viability and maturation in the fresh and vitrified groups were respectively 0.5% concentration and 2D culture. There was no significant difference among the concentrations of 0.25% and 1%. Viability and maturation of follicles showed a significant increase in the fresh groups in comparison with the vitrified groups. ROS levels in the both fresh and vitrified groups with different concentrations of alginate showed a significant decrease compared to the control group. ROS levels in follicles showed a significant decrease in the fresh groups in comparison with the vitrified groups (P≤0.0001). The highest gene expression levels were observed in the 0.5% alginate (P≤0.0001). Moreover, the viability percentage, follicle maturation, and gene expression levels were higher in the fresh groupsthan the vitrified groups (P≤0.0001).

CONCLUSION

Alginate hydrogel at a proper concentration of 5%, not only helps follicle get mature, but also promotes the expression of developmental genes and reducesthe level of intracellular ROS. Follicular vitrification decreases quality of the follicles, which are partially compensated using a three dimensional (3D) cell culture medium.

Differential molecular and hormonal changes in oocytes, granulosa cells and follicular fluid of pregnant and non-pregnant camels

This study aimed to compare the expression of genes regulating follicles development, survival and steroid hormones secretion in oocytes and granulosa cells (GCs) and study the correlation between their expression and follicular fluid (FF) levels of progesterone (P4) in pregnant and non-pregnant camels. In total, 138 ovarian pairs from slaughtered camels were used. Gene expression and hormonal assay were determined using real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The obtained results revealed that the number of follicles (3-8 mm) was significantly (P < 0.05) lower in pregnant, compared with non-pregnant, camels. P4 level in the FF was significantly (P < 0.05) higher in pregnant, compared with non-pregnant, camels. However, no significant (P > 0.05) difference was noticed in the oestradiol (E2) level. STAR, PTEN, IGF1 and BCL2 mRNA levels were significantly higher in GCs and significantly lower in oocytes of pregnant, compared with non-pregnant, camels. However, follicle-stimulating hormone receptor (FSHR) mRNA level was significantly lower in GCs and oocytes, and the BMP15 mRNA level was significantly lower in oocytes of pregnant, compared with non-pregnant, camels. P4 level in FF was positively correlated with STAR, PTEN, IGF1 and BCL2 mRNA levels in GCs and negatively correlated with BMP15 mRNA levels in oocytes and FSHR mRNA levels in GCs and oocytes of pregnant camels. It could be concluded that pregnancy-induced variations in oocytes and GC expression of BMP15, IGF1, FSHR, STAR, BCL2, and PTEN genes might be associated with a decrease in the number of follicles and an increase in the FF level of P4.

Dingkun Pill replenishes diminished ovarian reserve through the PI3K/AKT/mTOR signaling pathway in TWP-induced mice

ETHNOPHARMACOLOGICAL RELEVANCE

Diminished ovarian reserve (DOR) can lead to poor fertility and shorten the reproductive lifespan of females. The Dingkun Pill (DKP), a traditional Chinese-patented medication, has been an integral part of traditional Chinese medicinal treatment for the management of gynecological diseases for centuries. Relevant clinical studies have shown that DKP is able to protect against DOR, however, its mechanism of action is not yet fully elucidated.

STUDY GOALS

This study was conducted with the aim of exploring the impact of tripterygium wilfordii polyglycosidium (TWP) on the PI3K/AKT/mTOR pathway in the context of the pathophysiology of DOR and the mechanism of action of DKP.

MATERIALS AND METHODS

Eighty female balb/c mice with regular estrous cycles were assigned to Blank, Model, DKP and hormone replacement therapy (HRT) groups in a random manner. With the exception of the Blank group, mice in the other groups were exposed to 40 mg/kg/d TWP suspension for 30 days to DOR induction. Following this, either DKP or hormones were orally administrated to determine their effect on disease progression. During the experiment, changes in body weight and the estrous cycles of the mice were observed. Post treatment, serum sample anti-mullerian hormone (AMH), estradiol (E₂), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were quantified using enzyme-linked immunosorbent assay (ELISA). The mice were then sacrificed in order to harvest their ovaries for hematoxylin and eosin (HE) staining. This process allowed for the assessment of ovarian morphology and follicular quantification. Apoptotic ovarian cells of the ovary were assessed using TUNEL technique, while Caspase-3 and Cytochrome C (Cyt C) expressions of the ovary were examined through immunohistochemistry (IHC). Western blotting analysis was used to quantify levels of Bax, Bcl-2, Caspase-3, Cyt C, mTOR, P-mTOR, AKT, P-AKT, P-PI3K and PI3K proteins, while mRNA levels of Bax, Bcl-2, PI3K, AKT and mTOR were measured in ovarian tissue using RT-PCR.

RESULTS

The findings revealed that DKP was able to improve levels of serum hormones and promote the recovery of the estrous cycle. DKP augmented the total amount of primordial follicles while reducing the number of follicles that were atretic follicles. The apoptosis index of growing follicles and Bax, Cyt C and Caspase-3 expressions decreased, while the Bcl-2: Bax ratio increased. DKP suppressed levels of phosphorylation and the mRNA expressions of mTOR, AKT and PI3K.

CONCLUSIONS

It was demonstrated that DKP was able to increase ovarian reserves through inhibition of the PI3K/AKT/mTOR signaling pathway, which lead to the suppression of primordial follicle activity and a reduction in levels of apoptosis of early growing follicles. This highlights its potentially beneficial role for the treatment of DOR.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

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.

Interleukin-1β and TNF-α systems in ovarian follicles and their roles during follicular development, oocyte maturation and ovulation

Tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are cytokines that are involved in the development, proliferation and apoptosis of ovarian follicular cells in domestic mammals. The expression of these cytokines in various follicular compartments, depending on the stage of follicle development, demonstrates their involvement in the control of primordial follicle growth up to the preovulatory stage. The mechanism of action of these factors depends on the presence of their receptors that transduce their biological actions. This review shows the expression sites of TNF-α, IL-1β and their receptors in ovarian follicles, and discusses the mechanism of action of these cytokines during follicle development, oocyte maturation and ovulation in domestic animals.

Supplemented powdered coconut water (ACP-406®) promotes growth of goat secondary follicles and oocyte meiotic resumption

The objective of this study was to test the efficiency of powdered coconut water (ACP-406^®) base-medium without or with the addition of supplements on in vitro culture of isolated goat secondary follicles. Follicles were cultured for 18 days in α-MEM or in ACP-406^®, both without supplements (referred to as α-MEM and ACP, respectively), or both supplemented with BSA, insulin, transferrin, selenium, glutamine, hypoxanthine, and ascorbic acid (referred to as α-MEM⁺ and ACP⁺). Follicular morphology, antrum formation, follicular and oocyte diameter, levels of glutathione (GSH), and chromatin configuration after in vitro maturation were evaluated. At the end of culture, ACP-406^® base-medium (without or with supplements) showed a higher (P < 0.05) percentage of normal follicles than α-MEM (without or with supplements). Antrum formation was similar among α-MEM⁺, ACP and ACP⁺, and significantly higher than α-MEM without supplements. The follicular diameter was greater in ACP⁺ than α-MEM, and similar to other treatments. Moreover, fully and daily grown rates were higher (P < 0.05) in ACP-406^® base-medium (without or with supplements) than α-MEM (without or with supplements). Levels of GSH were similar between ACP⁺ and α-MEM⁺ treatments. Both ACP⁺ and α-MEM⁺ allowed meiotic resumption without a significant difference between the two groups. In conclusion, supplemented ACP-406^® base-medium maintained follicular survival and promoted the development as well as meiotic resumption of isolated goat secondary follicles cultured in vitro for 18 days.

Powdered coconut water (ACP 406®) as an alternative base culture medium for in vitro culture of goat preantral follicles enclosed in ovarian tissue

This study evaluated a powdered coconut water solution (ACP 406®) as a base culture medium on the in vitro survival and development of in situ goat preantral follicles. The ovarian fragments were either immediately fixed in Carnoy solution (non-cultured control) or individually cultured for 2 or 6 days. The following culture media (all containing 100 μg/mL penicillin and 100 μg/mL streptomycin) were evaluated: α-MEM (α-MEM alone, without additional supplementation); α-MEM+ (supplemented α-MEM); ACP (ACP®406 alone); or ACP+ (supplemented ACP®406). Additional supplementation includes: 1.25 mg/mL bovine serum albumin, 10 μg/mL insulin, 5.5 μg/mL transferrin, 5 ng/mL selenium, 2 mM glutamine, and 2 mM hypoxanthine. The endpoints (i) follicular morphology; (ii) development; (iii) estradiol production; and (iv) reactive oxygen species (ROS) were recorded. Data were analyzed using chi-square, Turkey, t-test or One-Way ANOVA. Differences were considered significant when P < 0.05. At day 2 of culture, a greater (P < 0.05) percentage of morphologically normal follicles was observed between ACP+ and ACP treatments. Moreover, at day 2 of culture, no hormonal difference (P < 0.05) was observed between ACP+ and both α-MEM treatments. At day 6 of culture when ACP and α-MEM treatments were compared the percentage of healthy follicles were similar (P > 0.05) among treatments. Overall, all treatments had lower primordial follicles (P < 0.05) accompany by greater developing follicles (P < 0.05) percentages than non-cultured control treatment, indicating primordial follicle activation. However, at day 6 of culture, the percentage of primordial follicle development were similar (P > 0.05) among the treatments. Likewise, no differences (P > 0.05) were observed for ROS production and follicular and oocyte diameters among treatments. Therefore, ACP+ has the equivalent efficiency to MEM+ in maintaining the survival and development of goat preantral follicles, representing an alternative plant-based low-cost culture medium for in vitro culture.

Supplementation of culture medium with knockout serum replacement improves the survival of bovine secondary follicles when compared with other protein sources during in vitro culture

The present study evaluated the effect of knockout serum replacement (KSR), fetal bovine serum (FBS) and bovine serum albumin (BSA) on the viability and growth of bovine secondary follicles cultured in vitro for 12 days. To this end, secondary follicles were isolated (185-202 μm) and cultured in vitro in TCM-199+ medium supplemented with KSR (5% and 10%), FBS (5% and 10%) or BSA (3 mg/ml) at 38.5°C with 5% CO2 in air. Follicular diameters were evaluated on days 0, 4, 8 and 12. After 12 days of culture, follicular survival analysis was performing by using calcein-AM and ethidium homodimer. Before and after culture, follicles were fixed in paraformaldehyde for histological evaluation. Follicular diameter at different days of culture were compared using the Kruskal-Wallis test, while the percentages of viable follicles were analyzed by chi-squared test (P < 0.05). Results showed that follicles cultured in the presence of KSR at both concentrations presented higher follicular survival rates than those cultured in control medium alone or supplemented with FBS or BSA. Conversely, the presence of KSR, BSA or FBS did not increase follicular diameter after 12 days of culture. Histology analysis showed that, among the tested treatments, follicles cultured in the presence of KSR had preserved rounded oocytes, juxtaposed granulosa cells and intact basal membrane. In conclusion, supplementation of culture medium with KSR increases the follicular survival of bovine secondary follicles cultured in vitro.

Lysosomal dysfunction disturbs porcine oocyte maturation and developmental capacity by disorganizing chromosome/cytoskeleton and activating autophagy/apoptosis

Lysosome, an important organelle in eukaryotes, can sequester macromolecules submitted by the endocytosis and autophagy pathways for degradation and recycling. Massive macromolecular turnover is also vital to the growth and development of mammalian oocytes. However, the functional role of lysosomes in the meiotic maturation of mammalian oocytes remains largely unexplored. Here, by treating in vitro matured porcine cumulus-oocyte complexes (COCs) with chloroquine (CQ), a lysosome inhibitor, we showed that regardless of CQ concentration, lysosomal inhibition affected neither the extrusion of the first polar body (PB1), nor the ROS levels. However, CQ treatment dramatically decreased the rates of oocytes with normal chromosome alignment and cytoskeleton organization (P < 0.05), but boosted the rates of oocytes with apoptosis (P < 0.05). Subsequently, after pathenogenetic activation or in vitro fertilization, the death or fragmentation rates of oocytes treated by CQ (both 35 μM and 45 μM) were significantly higher (P < 0.05), whereas the rates of embryo cleavage, embryos developed to blastocysts, and average blastomere number per blastocyst, were all significantly lower (P < 0.05), respectively. Furthermore, CQ (35 μM) treatment activated the autophagy pathway by elevating the LC3 II/I ratio. Taken together, lysosomes could affect porcine oocyte maturation and subsequent developmental capacity partially through the chromosome organization/cytoskeleton assembly and autophagy/apoptosis pathways.

Kaempferol can be used as the single antioxidant in the in vitro culture medium, stimulating sheep secondary follicle development through the phosphatidylinositol 3-kinase signaling pathway

This study evaluated the effect of addition of kaempferol alone or combined with other antioxidants (transferrin, selenium and ascorbic acid) on in vitro culture of sheep isolated secondary follicles and if PI3K pathway is involved in kaempferol action. Secondary follicles were isolated and cultured for 12 days in α-Minimal Essential Medium (α-MEM) supplemented with BSA, insulin, glutamine and hypoxanthine (α-MEM: antioxidant free-medium) or in this medium also added by transferrin, selenium and ascorbic acid (AO: base medium with antioxidants). Moreover, different concentrations of kaempferol (0.1; 1 or 10 μM) were added to the different base media (α-MEM or AO). After culture, glutathione (GSH) levels, mitochondrial activity and meiotic resumption were evaluated. In addition, inhibition of PI3K activity was performed through pretreatment in medium supplemented with LY294002. After 12 days, the percentage of normal follicles was higher (P < 0.05) in AO base medium than the other treatments and similar (P > 0.05) to α-MEM supplemented with 1 or 10 μM kaempferol Moreover, α-MEM plus 1 or 10 μM kaempferol and AO medium showed similar (P > 0.05) follicular diameter, fully-grown oocytes, and GSH levels. However, at the end of the culture, antrum formation was higher (P < 0.05) in α-MEM + 1 μM kaempferol than in AO, and similar (P > 0.05) to α-MEM + 10 μM kaempferol. In addition, oocytes cultured in α-MEM supplemented with 1 μM kaempferol showed greater (P < 0.05) levels of active mitochondria than α-MEM + 10 μM kaempferol and AO medium. The rates of meiotic resumption were similar (P > 0.05) among α-MEM + 1 μM kaempferol and AO medium. LY294002 significantly inhibited antrum formation, follicular diameter and the percentage of fully grown oocytes stimulated by 1 μM kaempferol. In conclusion, 1 μM kaempferol can be used as the single antioxidant present in the base medium, replacing the addition of transferrin, selenium and ascorbic acid during in vitro culture of ovine secondary follicles, maintaining follicular survival, increasing active mitochondria levels, and promoting the oocyte meiotic resumption. Moreover, the development of the ovine secondary follicle stimulated by kaempferol is mediated by PI3K pathway.

Melatonin improves developmental competence of oocyte-granulosa cell complexes from porcine preantral follicles

Melatonin has been reported to improve the survival rate of mouse and goat preantral follicles cultured in vitro. However, the role of melatonin in the development of oocyte-granulosa cell complexes (OGCs) isolated from preantral follicles remains unclear. Cumulus-oocyte complexes were isolated from OGCs cultured in vitro for 18.5 days and were then maturated in vitro for 42 h. The matured oocytes were parthenogenetically activated and were further cultured up to the blastocyst stage. We found that the developmental capacity of oocytes from in vitro cultured OGCs was significantly inferior to that from in vivo grown counterparts. Additionally, a 10^-5 M dose of melatonin added to the medium during in vitro culture of OGCs did not improve oocyte meiotic maturation but enhanced blastocyst rate of parthenogenetically activated embryos. Besides, these beneficial effects could be reversed by luzindole treatment, a melatonin membrane receptor antagonist. mRNA sequencing analysis further revealed that melatonin caused differential expression of 76 genes of which 75 were upregulated and 1 was downregulated in OGCs. Twelve of the 76 genes were identified as potential regulators of metabolic pathways by functional analysis. Taken together, these results indicate that melatonin improves developmental competence of porcine oocyte-granulosa cell complexes.

Technologies for the Production of Fertilizable Mammalian Oocytes

Women affected by ovarian pathologies or with cancer can usually preserve fertility by egg/embryo freezing. When oocyte retrieval is not feasible, the only option available is ovarian tissue cryopreservation and transplantation. The culture of follicles isolated from fresh or cryopreserved ovaries is considered still experimental, although this procedure is considered safer, because the risk of unintentional spreading of cancer cells eventually present in cryopreserved tissue is avoided. Animal and human small follicles can be cultured in vitro, but standardized protocols able to produce in vitro grown oocytes with the same developmental capacity of in vivo grown oocytes are not available yet. In fact, the different sizes of follicles and oocytes, the hormonal differences existing between mono- (e.g., human, goat, cow, and sheep) and poly-ovulatory (rodents and pig) species, and the incomplete identification of the mechanisms regulating the oocyte–follicle and follicle–ovary interrelationships affect the outcome of in vitro culture. From all these attempts, however, new ideas arise, and the goal of assuring the preservation of female reproductive potential appears a more realistic possibility. This review surveys and discusses advances and challenges of these technologies that, starting from a simple attempt, are now approaching the biosynthesis of a functional engineered ovary.

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.

Influence of follicle-stimulating hormone concentrations on the integrity and development of bovine follicles cultured in vitro

This study investigated the in vitro culture of bovine follicles included in ovarian tissue for 2 or 6 days (D2 or D6), with the addition of different concentrations of follicle-stimulating hormone (FSH) (0, 10, 50, 100 or 200 ng/ml). Data were compared for follicular development, morphological integrity and diameter of follicles and oocytes. Ovaries (n = 10) from Nelore cows (n = 5) were divided into fragments (n = 11 per ovary) and were immediately fixed in Bouin’s solution (D0) or were individually cultured for 2 or 6 days in one of the described concentrations of FSH and then processed for histology. Compared with the rates of follicular development at D2 for minimal essential medium (MEM) (75.0%) and 50 ng/ml of FSH (71.1%), the best rates of follicular development at D2 were obtained with 10 (84.7%), 100 (87.5%) and 200 ng/ml of FSH (85.0%; P<0.05). After 6 days of cultivation, there were no differences among treatments regarding follicular growth. The morphological integrity of preantral follicles was better maintained by 100 ng/ml FSH for 2 and 6 days of cultivation (51.2 and 40.4%, respectively; P<0.05) than that for MEM (D2: 30.9%, D6: 20.8%), 10 (D2: 39.2%, D6: 22.8%), 50 (D2: 30.4%, D6: 28.8%) and 200 ng/ml FSH (D2: 45.2%, D6: 36.8%). FSH at 100 ng/ml provided the highest mean diameter averages: 34.5±10.8 µm at D2 and 33.2±12.5 µm at D6 (P<0.05). We concluded that the medium supplemented with 100 ng/ml FSH during in vitro culture provided appropriate conditions for the development and morphological integrity of preantral follicles in cattle.

Direct actions of androgen, estrogen and anti-Müllerian hormone on primate secondary follicle development in the absence of FSH in vitro

STUDY QUESTION

What are effects of androgen, estrogen and anti-Müllerian hormone (AMH), independent of FSH action, on the development and function of primate follicles from the preantral to small antral stage in vitro?

SUMMARY ANSWER

Androgen and estrogen, but not AMH, promote follicle survival and growth in vitro, in the absence of FSH. However, their growth-promoting effects are limited to the preantral to early antral stage.

WHAT IS KNOWN ALREADY

FSH supports primate preantral follicle development in vitro. Androgen and estrogen augment follicle survival and growth in the presence of FSH during culture.

STUDY DESIGN SIZE, DURATION

Nonhuman primate model; randomized, control versus treatment groups. Rhesus macaque (n = 6) secondary follicles (n = 24 per animal per treatment group) were cultured for 5 weeks.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicles were encapsulated in 0.25% (w/v) alginate and cultured individually in modified alpha minimum essential media with (i) FSH (1 ng/ml; control), (ii) no FSH, (iii) no FSH + estradiol (E2; 100 pg/ml)/dihydrotestosterone (DHT; 50 ng/ml) and (iv) no FSH + AMH (50 ng/ml). In a second experiment, follicles were cultured with (i) FSH (1 ng/ml), (ii) no FSH, (iii) no FSH + E2 (1 ng/ml), (iv) no FSH + DHT (50 ng/ml) and (v) no FSH + E2/DHT. Follicle survival, antrum formation and growth pattern were evaluated. Progesterone (P4), E2 and AMH concentrations in culture media were measured.

MAIN RESULTS AND THE ROLE OF CHANCE

In the first experiment, FSH deprivation significantly decreased (P < 0.05) follicle survival rates in the no FSH group (16 ± 5%), compared to CTRL (66 ± 9%). E2/DHT (49 ± 5%), but not AMH (27 ± 8%), restored follicle survival rate to the CTRL level. Similarly, antrum formation rates were higher (P < 0.05) in CTRL (56 ± 6%) and E2/DHT groups (54 ± 14%), compared to no FSH (0 ± 0%) and AMH (11 ± 11%) groups. However, follicle growth rate after antrum formation and follicle diameter at week 5 was reduced (P < 0.05) in the E2/DHT group (405 ± 25 μm), compared to CTRL (522 ± 29 μm). Indeed, the proportion of fast-grow follicles at week 5 was higher in CTRL (29% ± 5), compared to E2/DHT group (10 ± 3%). No fast-grow follicles were observed in no FSH and AMH groups. AMH levels at week 3 remained similar in all groups. However, media concentrations of P4 and E2 at week 5 were lower (P < 0.05, undetectable) in no FSH, E2/DHT and AMH groups, compared to CTRL (P4 = 93 ± 10 ng/ml; E2 = 4 ± 1 ng/ml). In the second experiment, FSH depletion diminished follicle survival rate (66 ± 8% in control versus 45 ± 9% in no FSH, P = 0.034). E2 plus DHT (31.5 ± 11%) or DHT alone (69 ± 9%) restored follicle survival rate to the control (FSH) level as expected. Also, E2 plus DHT or DHT alone improved antrum formation rate. However, in the absence of FSH, E2 plus DHT or DHT alone did not support growth, in terms of follicle diameter, or steroid (P4 or E2) production after the antral stage.

LIMITATIONS REASONS FOR CAUTION

This study is limited to in vitro effects of E2, DHT and AMH during the interval from the secondary to small antral stage of macaque follicular development. In addition, the primate follicle pool is heterogeneous and differs between animals; therefore, even though only secondary follicles were selected, follicle growth and developmental outcomes might differ from one animal to another.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides novel information on the possible actions of estrogen and androgen during early follicular development in primates. Our results suggest that sequential exposure of preantral follicles to local factors, e.g. E2 and DHT, followed by gonadotropin once the follicle reaches the antral stage, may better mimic primate folliculogenesis in vivo.

STUDY FUNDING/COMPETING INTEREST(S)

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Center for Translational Research on Reproduction and Infertility 5P50HD071836, and the NIH Primate Centers Program 8P510D011092. There are no conflicts of interest.

Reduced nucleic acid methylation impairs meiotic maturation and developmental potency of pig oocytes

Oocyte meiosis is a complex process coordinated by multiple endocrinal and molecular circuits. Recently, N⁶-methyladenosine (m⁶A) epigenetic modification on RNA is revealed to be important for meiotic maturation. However, the molecular mechanism of how m⁶A modification exerts its effect on oocyte maturation is largely unknown. Here, we showed that endogenous m⁶A writers (Mettl3 and Wtap) and eraser (Fto) elevated their transcript levels during meiotic maturation of pig oocytes. From germinal vesicle (GV) to metaphase II (MII) stages, global m⁶A level significantly increased, and existed mostly in ooplasm. Methyl donor (betaine, 16 mM) treatment of porcine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM) significantly boosted nucleic acid m⁶A level within oocytes, but unchanged meiotic process and oocyte subsequent development. By contrast, methylation inhibitor (cycloleucine, 20 mM) reduced nucleic acid m⁶A level, and significantly decreased the germinal vesicle breakdown (GVBD) rate, the extrusion rate of the first polar body, and the cleavage and blastocyst rates of parthenotes. In addition, in cycloleucine-treated oocytes Wtap increased but Lin28 decreased their abundances significantly, along with the higher incidence of spindle defects and chromosome misalignment. Furthermore, pT161-CDK1 protein level in pig oocytes was confirmed to be decreased after cycloleucine treatment for 24 h. Taken together, chemical induced reduction of nucleic acid m⁶A methylation during pig oocyte meiosis could impair meiotic maturation and subsequent development potency, possibly through down-regulating pluripotency marker Lin28 mRNA abundance and disturbing MPF-regulated chromosome/spindle organization.

The local regulation of folliculogenesis by members of the transforming growth factor superfamily and its relevance for advanced breeding programmes

Regulation of the growth and maturation of the ovarian follicle is critical for normal reproductive function. Alterations in this growth can lead to pathological conditions, such as cystic follicles, reduced oocyte quality, or an abnormal endocrine environment leading to poor fertility. Alterations in follicular growth also influence the number of follicles ovulating and thus can change litter size. Both endocrine factors, such as follicle stimulating hormone and luteinizing hormone, as well as local factors, are known to regulate follicular growth and development. This review will focus on the role of local factors in regulation of ovarian follicular growth in ruminants, with a focus on members of the transforming growth factor superfamily. The potential role of these factors in regulating proliferation, apoptosis, steroidogenesis and responsiveness to gonadotrophins will be considered.

Isolation and in vitro culture of ovarian stem cells in Chinese soft-shell turtle (Pelodiscus sinensis)

Gonadal cell lines provide valuable tools for studying gametogenesis, sex differentiation, and manipulating germ cells in reproductive biology. Female germline stem cells have been characterized and isolated from ovaries of mammalian species, including mice and human, but there has been very few studies on female germline stem cells in reptiles. Here, we described an ovarian stem cell-like line isolated and cultured from the Chinese soft-shell turtle (Pelodiscus sinensis), designated as PSO1. The cells showed high alkaline phosphatase activity with a normal diploid karyotype. As shown by reverse transcription-polymerase chain reaction, the cells were positive for the expression of germ cell-specific genes, vasa and dazl, as well as a stem cell marker, nanog, but negative for the expression of the folliculogenesis-specific gene, figla. Likewise, through fluorescent immunostaining analyses, both the Dazl and Vasa proteins were detected abundantly in the cytoplasm of perinuclear region, whereas Nanog and PCNA were dominantly observed in the nuclei in PSO1 cells. Moreover, PSO1 cells transfected with pCS2:h2b-egfp could properly express the fusion protein in the nuclei. Taken together, the findings suggested that the germline stem cells exist in the ovary of juvenile Chinese soft-shell turtle and these cells can be isolated for a long-term in vitro culture under experimental conditions. This study has provided a valuable basis for further investigations on the molecular mechanisms whereby the germline stem cells develop and differentiate into gametes in turtles. Also, it has paved the way for studies on oogenesis in turtles, even in the other reptiles.

Effect of bone morphogenetic proteins 2 and 4 on survival and development of bovine secondary follicles cultured in vitro

This study evaluated the effect of bone morphogenetic proteins 2 (BMP2) and 4 (BMP2) on follicle development and mRNA expression for GDF9, Cyclin B1, BMPR1A, BMPR1B, BMPRII, FSHR and SMAD1 in bovine secondary follicles cultured in vitro. Isolated secondary follicles were cultured for 18 days in TCM199⁺ medium alone or supplemented with BMP2 (10 ng/mL), BMP4 (100 ng/mL) or combination of both BMP2 and 4. Real-time PCR was used to analyze mRNA levels in fresh and cultured follicles. After 18 days of culture, follicles cultured with BMP2 alone or with BMP4 alone had larger diameters when compared to control (P < .05). In addition, all treatments promoted antrum formation and maintained a high viability rate through the growing period. The presence of BMP2, BMP4 or both together did not influence mRNA expression for the tested genes. However, the in vitro culture induces down-regulation for mRNA expression of BMPR1A. In conclusion, the addition of BMP2 or BMP4 alone in cultured medium promotes follicular growth and antrum formation in bovine follicles after 18 days of in vitro culture.

Effects of FSH addition to an enriched medium containing insulin and EGF after long-term culture on functionality of equine ovarian biopsy tissue

The effect of FSH supplementation on an enriched cultured medium containing insulin (10 ng/mL) and EGF (50 ng/mL) was investigated on in vitro culture of equine ovarian biopsy tissue. Ovarian tissue fragments were collected from mares (n = 10) and distributed in the following treatments: noncultured control, cultured control, and cultured + FSH. Both treated groups were cultured for 7 or 15 days. The end points evaluated were: follicular morphology, estradiol levels in the culture medium, fluorescence intensity for TUNEL, EGFR and Ki-67 detection, and gene expression of GDF-9, BMP-15, and Cyclin-D2 in the ovarian tissue. After seven days of culture, medium supplemented with FSH had a similar (P > 0.05) percentage of morphologically normal follicles compared to the noncultured control group. Estradiol levels increased (P < 0.05) from Day 7 to Day 15 of culture for both treated groups. No difference (P > 0.05) was observed for TUNEL and EGFR intensity between the noncultured control group and the treated groups after 15 days of culture. Ki-67 intensity did not differ (P > 0.05) between treated groups after 15 days of culture, but decreased (P < 0.05) when compared with the noncultured control group. Similar (P > 0.05) mRNA expression for GDF-9, BMP-15, and Cyclin-D2 was observed among all treatments after 15 days of culture. In conclusion, an enriched medium supplemented or not with FSH was able to maintain the functionality of equine ovarian biopsy tissue after a long-term in vitro culture.

Microfluidic Encapsulation of Ovarian Follicles for 3D Culture

The ovarian follicle that contains one single oocyte is the fundamental functional tissue unit of mammalian ovary. Therefore, isolation and in vitro culture of ovarian follicles to obtain fertilizable oocytes are regarded as a promising strategy for women to combat infertility. In this communication, we performed a brief survey of studies on microfluidic encapsulation of ovarian follicles in core-shell hydrogel microcapsules for biomimetic 3D culture. These studies highlighted that recapitulation of the mechanical heterogeneity of the extracellular matrix in ovary is crucial for in vitro culture to develop early pre-antral follicles to the antral stage, and for the release of cumulus-oocyte complex (COC) from antral follicles in vitro. The hydrogel encapsulation-based biomimetic culture system and the microfluidic technology may be invaluable to facilitate follicle culture as a viable option for restoring women's fertility in the clinic.

Effect of Heat Stress on Reproduction in Dairy Cows: Insights into the Cellular and Molecular Responses of the Oocyte

Among the components of the female reproductive tract, the ovarian pool of follicles and their enclosed oocytes are highly sensitive to hyperthermia. Heat-induced alterations in small antral follicles can be expressed later as compromised maturation and developmental capacity of the ovulating oocyte. This review summarizes the most up-to-date information on the effects of heat stress on the oocyte with an emphasis on unclear points and open questions, some of which might involve new research directions, for instance, whether preantral follicles are heat resistant. The review focuses on the follicle-enclosed oocytes, provides new insights into the cellular and molecular responses of the oocyte to elevated temperature, points out the role of the follicle microenvironment, and discusses some mechanisms that might underlie oocyte impairment. Mechanisms include nuclear and cytoplasmic maturation, mitochondrial function, apoptotic pathways, and oxidative stress. Understanding the mechanism by which heat stress compromises fertility might enable development of new strategies to mitigate its effects.

Dimethyl Sulfoxide Perturbs Cell Cycle Progression and Spindle Organization in Porcine Meiotic Oocytes

Meiotic maturation of mammalian oocytes is a precisely orchestrated and complex process. Dimethyl sulfoxide (DMSO), a widely used solvent, drug, and cryoprotectant, is capable of disturbing asymmetric cytokinesis of oocyte meiosis in mice. However, in pigs, DMSO’s effect on oocyte meiosis still remains unknown. We aimed to evaluate if DMSO treatment will affect porcine oocyte meiosis and the underlying molecular changes as well. Interestingly, we did not observe the formation of the large first polar body and symmetric division for porcine oocytes treated with DMSO, contrary to findings reported in mice. 3% DMSO treatment could inhibit cumulus expansion, increase nuclear abnormality, disturb spindle organization, decrease reactive oxygen species level, and elevate mitochondrial membrane potential of porcine oocytes. There was no effect on germinal vesicle breakdown rate regardless of DMSO concentration. 3% DMSO treatment did not affect expression of genes involved in spindle organization (Bub1 and Mad2) and apoptosis (NF-κB, Pten, Bcl2, Caspase3 and Caspase9), however, it significantly decreased expression levels of pluripotency genes (Oct4, Sox2 and Lin28) in mature oocytes. Therefore, we demonstrated that disturbed cumulus expansion, chromosome alignment, spindle organization and pluripotency gene expression could be responsible for DMSO-induced porcine oocyte meiotic arrest and the lower capacity of subsequent embryo development. Our results provide new insights on DMSO’s effect on porcine oocyte meiosis and raise safety concerns over DMSO’s usage on female reproduction in both farm animals and humans.