In vitro grown sheep preantral follicles yield oocytes with normal nuclear-epigenetic maturation

In vitro production of meiotically competent oocytes from early antral follicles in sheep

The potential of using long in vitro culture (LIVC) of cumulus-oocyte complexes (COCs) from early antral follicles (EAFs) as an assisted reproductive technology in cattle has shown promising results. This study explored the feasibility of applying this technology to sheep as seasonal breeding animals. Ovaries from sheep were collected during both the breeding and non-breeding seasons. COCs were isolated from EAFs (350-450 μm) and cultured in TCM199 medium supplemented with 0.15 μg/mL Zn sulfate, 10-4IU/mL FSH, 10 ng/mL estradiol, 50 ng/mL testosterone, 50 ng/mL progesterone, and 5 μM Cilostamide. After five days of LIVC, the COCs were submitted to an in vitro maturation procedure. The results indicate successful in vitro development of COCs, evidenced by a significant increase in oocyte diameter (p < 0.000) and the preservation of gap junction communication between oocyte and cumulus cells. The gradual uncoupling was accompanied by a progressive chromatin transition from the non-surrounded nucleolus (NSN) to the surrounded nucleolus (SN) (p < 0.000), coupled with a gradual decrease in global transcriptional activity and an increase in oocyte meiotic competence (p < 0.000). Maintenance of oocyte-cumulus investment architecture, viability, and metaphase II capability was significantly higher in COCs collected during the breeding season (p < 0.000), suggesting higher quality than those obtained during the non-breeding season. In conclusion, our study confirms LIVC feasibility in sheep, emphasizing increased effectiveness during the breeding season in isolating higher-quality COCs from EAFs. These findings can influence improving the LIVC system in mammals with seasonal reproduction.

Generation of mouse and rat xenogeneic ovaries in vitro for production of mouse oocyte

The system forming ovarian follicles is developed to investigate in vitro folliculogenesis in a confined environment to obtain functional oocytes. Several studies have reported the successful generation of fully functional oocytes using mouse-induced pluripotent stem cells (iPSCs) and mouse female germline stem cells (fGSCs) as sources of stem cells for in vitro gametogenesis models. In addition, human oogonia have been generated through heterologous co-culture of differentiated human primordial germ cell-like cells (hPGCLCs) with mouse germline somatic cells, although oocyte formation remains challenging. Thus, studies on in vitro ovarian formation in other species are utilized as an introductory approach for in vitro mammalian gametogenesis by understanding the differences in culture systems between species and underlying mechanisms. In this study, we optimized the method of the entire oogenesis process from rat embryonic gonads. We identified well-maturated MII oocytes from rat gonads using our constructed method. Moreover, we generated the first successful in vitro reconstitution of xenogeneic follicles from mouse primordial germ cells (PGCs) and rat somatic cells. We also established an appropriate culture medium and incubation period for xenogeneic follicles. This method will be helpful in studies of xenogeneic follicular development and oocyte generation.

Exploring the potential use of platelet rich plasma (PRP) from adult and umbilical cord blood in murine follicle culture

Ovarian follicle culture is a powerful tool to study follicular physiology and has potential applications in clinical and commercial settings. Despite remarkable progress, recreating folliculogenesis in vitro remains challenging for many mammalian species. This study investigates the impact of platelet-rich plasma (PRP) derived from adult blood (human platelet lysate, hPL) and umbilical cord blood (Umbilical cord plasma, UCP) on murine pre-antral follicle culture and oocyte maturation. Pre-antral follicles were cultured individually for 10 days with fetal bovine serum (FBS) serving as the control and two PRP sources (hPL and UCP) and their activated forms (Ac-hPL and Ac-UCP). The results suggest that neither hPL nor UCP, regardless of activation status, improved follicle culture outcomes compared to FBS. Interestingly, activation did not significantly impact the main functional outcomes such as maturation rates, survival, and growth. Oestradiol secretion and oocyte diameter, often considered hallmarks of follicle quality, did not show significant differences between matured and non-matured oocytes across the treatment groups. However, gene expression analysis revealed a significant upregulation of Gdf-9 and Bmp-15 mRNA levels in oocytes from the Ac-UCP group, regardless of maturation stage, suggesting that the accumulation of the mRNA could be due to potential challenges in translation in the Ac-UCP group. In conclusion, this study challenges the hypothesis that PRP, as a serum source, could improve follicle culture outcomes compared to FBS, the gold standard in murine follicle culture. Further research is needed to understand the species-specific effects of PRP and explore other potential factors affecting follicle culture and oocyte quality.

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

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

Method of Isolation and In Vitro Culture of Primordial Follicles in Bovine Animal Model

The mammalian ovary is a substantial source of oocytes arranged into follicles at various stages of folliculogenesis, from the primordial to the ovulatory ones. Primordial follicles constitute the most abundant source of gametes inside the mammalian ovary at any given time.The isolation of a high number of primordial follicles, together with the development of protocols for in vitro follicle growth, would provide a powerful tool to fully exploit the female reproductive potential and boost the rescue and restoration of fertility in assisted reproduction technologies in human medicine, animal breeding, and preservation of threatened species. However, the most significant limitation is the lack of efficient methods for isolating a healthy and homogeneous population of viable primordial follicles suitable for in vitro culture. Here, we provide a fast and high-yield strategy for the mechanical isolation of primordial follicles from limited portions of the ovarian cortex in the bovine animal model.

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.

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.

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.

Therapeutic Potential of In Vitro-Derived Oocytes for the Restoration and Treatment of Female Fertility

Considerable progress has been made with the development of culture systems for the in vitro growth and maturation (IVGM) of oocytes from the earliest-staged primordial follicles and from the more advanced secondary follicles in rodents, ruminants, nonhuman primates, and humans. Successful oocyte production in vitro depends on the development of a dynamic culture strategy that replicates the follicular microenvironment required for oocyte activation and to support oocyte growth and maturation in vivo while enabling the coordinated and timely acquisition of oocyte developmental competence. Significant heterogeneity exists between the culture protocols used for different stages of follicle development and for different species. To date, the fertile potential of IVGM oocytes derived from primordial follicles has been realized only in mice. Although many technical challenges remain, significant advances have been made, and there is an increasing consensus that complete IVGM will require a dynamic, multiphase culture approach. The production of healthy offspring from in vitro-produced oocytes in a secondary large animal species is a vital next step before IVGM can be tested for therapeutic use in humans.

Effect of different vitrification protocols on post thaw viability and gene expression of ovine preantral follicles

The aim of the present study was to establish a vitrification protocol for ovine preantral follicles, which can retain viability after thawing and to evaluate the impact of different vitrification treatments on apoptosis and development-related gene expression. Preantral follicles were isolated from cortical slices of ovaries by the mechanical method of isolation. The isolated preantral follicles (200-300 μm) were randomly assigned into four groups. Group1 - Control Fresh preantral follicles (256 follicles); Group 2- Vitrification treatment A (259 follicles) (Vitrification solution 1 (VS1) - Fetal bovine serum (FBS)10%, Ethylene glycol (EG):1.8 M, Dimethyl sulfoxide (DMSO): 1.4 M, Sucrose-0.3 M for 4 min; VS2- FBS10%, EG:4.5 M, DMSO: 3.5 M, Sucrose:0.3 M for 45 s), Group 3 - Vitr. treatment B (235 follicles) (VS1-FBS 20%, EG:1.3 M, DMSO1.05 M for 15 min, VS2- FBS 20%, EG:2.7 M, DMSO:2.1 M for 5 min) and Group 4-Vitrification treatment C (248 follicles) (VS1-Glycerol(Gly):1.2 M for 3 min, VS2- Gly:1.2 M, EG:3.6 M for 3 min, VS3- Gly3M, EG: 4.5 M for 1 min). Preantral follicles were placed in corresponding vitrification treatments and later plunged immediately into liquid nitrogen (-196 °C). After a week, the follicles were thawed and analyzed for follicular viability by trypan blue dye exclusion method as well as for gene expression. The results showed that the low concentration of cryoprotectants (vitrification treatment B) negatively affected the viability of preantral follicles in comparison with control follicles. There was no significant difference in the viability rates among the Control (87%), Treatment A (79%) and Treatment C (75%). The percentage of viable preantral follicles (73%) derived from Treatment B was significantly decreased (P<0.05%) in comparison to that of control. The expression of apoptotic gene BAK was higher in the vitrification treatment B group. Expressions of the other apoptosis-related genes i.e. Bcl2L1, BAD, BAX, Caspase 3, and Annexin showed no significant difference among the groups. The expression pattern of development competence genes GDF-9 and BMP-15 were higher (P < 0.05) in vitrification treatment A and C, respectively. Expression of NOBOX gene was significantly increased in preantral follicles with Vitrification treatment B compared to the control group. We conclude that both the Vitrification treatment A and Treatment C were the efficient vitrification treatment methods for the vitrification of ovine preantral follicles.

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.

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.

In Vitro Folliculogenesis in Mammalian Models: A Computational Biology Study

In vitro folliculogenesis (ivF) has been proposed as an emerging technology to support follicle growth and oocyte development. It holds a great deal of attraction from preserving human fertility to improving animal reproductive biotechnology. Despite the mice model, where live offspring have been achieved,in medium-sized mammals, ivF has not been validated yet. Thus, the employment of a network theory approach has been proposed for interpreting the large amount of ivF information collected to date in different mammalian models in order to identify the controllers of the in vitro system. The WoS-derived data generated a scale-free network, easily navigable including 641 nodes and 2089 links. A limited number of controllers (7.2%) are responsible for network robustness by preserving it against random damage. The network nodes were stratified in a coherent biological manner on three layers: the input was composed of systemic hormones and somatic-oocyte paracrine factors; the intermediate one recognized mainly key signaling molecules such as PI3K, KL, JAK-STAT, SMAD4, and cAMP; and the output layer molecules were related to functional ivF endpoints such as the FSH receptor and steroidogenesis. Notably, the phenotypes of knock-out mice previously developed for hub.BN indirectly corroborate their biological relevance in early folliculogenesis. Finally, taking advantage of the STRING analysis approach, further controllers belonging to the metabolic axis backbone were identified, such as mTOR/FOXO, FOXO3/SIRT1, and VEGF, which have been poorly considered in ivF to date. Overall, this in silico study identifies new metabolic sensor molecules controlling ivF serving as a basis for designing innovative diagnostic and treatment methods to preserve female fertility.

Genome-wide profile in DNA methylation in goat ovaries of two different litter size populations

Although some studies have investigated the DNA methylation modification in goat ovaries, it is not understood DNA methylation related to goat litter size. This investigation was designed to explore the DNA methylation status in the ovaries of high litter size and low litter size groups using whole-genome bisulfite sequencing (WGBS). We found that there was global difference on DNA methylation in high litter size and low litter size goat ovaries. Many differentially methylated region-related genes (DMGs) were found in the ovaries of these two different goat populations. Moreover, enrichment analysis discovered that many DMGs were involved in gamete development, reproductive system development, wingless-type MMTV integration site family (WNT) signalling pathways and mitogen-activated protein kinase 1 (MAPK) signalling pathways. The data indicated that DNA methylation in goat ovaries may play important roles in the folliculogenesis, the oocyte ovulation rate and finally the litter size. This study provides a comprehensive analysis of genome-wide DNA methylation patterns in ovaries of high and low litter size goat which helps the understanding of ovarian DNA methylation in relation to goat fertility capability.

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.

Progress and challenges in developing organoids in farm animal species for the study of reproduction and their applications to reproductive biotechnologies

Within the past decades, major progress has been accomplished in isolating germ/stem/pluripotent cells, in refining culture medium and conditions and in establishing 3-dimensional culture systems, towards developing organoids for organs involved in reproduction in mice and to some extent in humans. Haploid male germ cells were generated in vitro from primordial germ cells. So were oocytes, with additional support from ovarian cells and subsequent follicle culture. Going on with the female reproductive tract, spherical oviduct organoids were obtained from adult stem/progenitor cells. Multicellular endometrial structures mimicking functional uterine glands were derived from endometrial cells. Trophoblastic stem cells were induced to form 3-dimensional syncytial-like structures and exhibited invasive properties, a crucial point for placentation. Finally, considering the embryo itself, pluripotent embryonic cells together with additional extra-embryonic cells, could self-organize into a blastoid, and eventually into a post-implantation-like embryo. Most of these accomplishments have yet to be reached in farm animals, but much effort is devoted towards this goal. Here, we review the progress and discuss the specific challenges of developing organoids for the study of reproductive biology in these species. We consider the use of such organoids in basic research to delineate the physiological mechanisms involved at each step of the reproductive process, or to understand how they are altered by environmental factors relevant to animal breeding. We evaluate their potential in reproduction of animals with a high genetic value, from a breeding point of view or in the context of preserving local breeds with limited headcounts.

Signalling pathways and mechanistic cues highlighted by transcriptomic analysis of primordial, primary, and secondary ovarian follicles in domestic cat

In vitro growth (IVG) of dormant primordial ovarian follicles aims to produce mature competent oocytes for assisted reproduction. Success is dependent on optimal in vitro conditions complemented with an understanding of oocyte and ovarian follicle development in vivo. Complete IVG has not been achieved in any other mammalian species besides mice. Furthermore, ovarian folliculogenesis remains sparsely understood overall. Here, gene expression patterns were characterised by RNA-sequencing in primordial (PrF), primary (PF), and secondary (SF) ovarian follicles from Felis catus (domestic cat) ovaries. Two major transitions were investigated: PrF-PF and PF-SF. Transcriptional analysis revealed a higher proportion in gene expression changes during the PrF-PF transition. Key influencing factors during this transition included the interaction between the extracellular matrix (ECM) and matrix metalloproteinase (MMPs) along with nuclear components such as, histone HIST1H1T (H1.6). Conserved signalling factors and expression patterns previously described during mammalian ovarian folliculogenesis were observed. Species-specific features during domestic cat ovarian folliculogenesis were also found. The signalling pathway terms "PI3K-Akt", "transforming growth factor-β receptor", "ErbB", and "HIF-1" from the functional annotation analysis were studied. Some results highlighted mechanistic cues potentially involved in PrF development in the domestic cat. Overall, this study provides an insight into regulatory factors and pathways during preantral ovarian folliculogenesis in domestic cat.

Evaluating the Effects of Different Concentrations of Human Follicular Fluid on Growth, Development, and PCNA Gene Expression of Mouse Ovarian Follicles

Follicle culture in vitro provides a method for investigating stages of folliculogenesis that can lead to preserving fertility through cryopreservation techniques. This study aims to assess the effects of various concentrations of human follicular fluid (hFF) on growth, development, and expression of the proliferating cell nuclear antigen (PCNA) gene in mouse ovarian follicles in vitro. Preantral follicles were isolated from 14-day NMRI mouse ovaries. The follicles were cultured in basic media enriched with FBS, FSH, and insulin-transferrin-selenium, and supplemented with different concentrations of hFF (10, 20, and 30%) for 12 days. During the culture period, survival rate and follicular maturation, follicular diameter, levels of estrogen and progesterone secretion, and PCNA gene expression rate were evaluated. Survival rate, maturation, and antrum formation were significantly higher in the 10% hFF group than in the 20 and 30% hFF groups. On day 4, follicle diameter in the 10% hFF group was also higher than in the 20 and the 30% hFF group. In comparison with other groups, significantly higher estrogen and progesterone production levels were measured in the 10% hFF group. PCNA gene expression was also higher with 10 than 20 and 30% hFF concentrations. The present study suggests that addition of 10% hFF to mice ovarian preantral follicle culture media enhances follicle growth and oocyte maturation.

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.

Ovine oocytes display a similar germinal vesicle configuration and global DNA methylation at prepubertal and adult ages

Epigenetic mechanisms are thought to be involved in the reduced developmental capacity of early prepubertal ewe oocytes compared to their adult counterparts. In this study, we have analyzed the global DNA methylation pattern and in vitro meiotic and developmental competence of oocytes at the germinal vesicle (GV) stage obtained from adult and 3-month-old donors. All oocytes were aspirated from antral follicles with a diameter ≥3 mm, and DNA methylation on 5-methylcytosine was detected by immunofluorescence using an anti-methyl cytosine antibody. The main global chromatin configuration pattern shown by both prepubertal and adult ovine oocytes corresponded to condensed chromatin localized close to the nuclear envelope (the SNE pattern). Immunofluorescence showed that a global bright nuclear staining of 5-methylcytosine (5-mC) occurred in all germinal vesicle stage oocytes and matched the propidium iodide staining pattern. The total fluorescence intensity values of lamb GVs were not lower than those observed in adult GVs. The meiotic competence and cleavage rates were similar in adult and prepubertal oocytes, however, the developmental competence of embryos to reach blastocysts was higher for adult oocytes than lamb oocytes (p<0.0001). In conclusion, our results indicate that adult-size oocytes derived from 3 to 4 month old prepubertal ewes show similar GV morphology and DNA methylation staining patterns to those obtained from adult animals, despite exhibiting a lower developmental competence.

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.

Innovative multi-protectoral approach increases survival rate after vitrification of ovarian tissue and isolated follicles with improved results in comparison with conventional method

Background

In recent years, autotransplantation of cryopreserved ovarian tissue became a promising approach to preserve female fertility. The slow freezing is the most effective technique which resulted in greater live birth incidence so far. Despite that, interest to vitrification of the ovarian tissue is swiftly growing, thereby undermining the necessity for further improvements in the technique. In present study, we evaluated possibilities to increase follicle survival rates adopting innovative multi-protectoral vitrification protocols, applied to the slivers of ovarian cortex or isolated early-antral follicles, frozen individually. These experimental protocols have been compared with with validated vitrification and slow freezing ones, clinically used for female fertility preservation.

Results

The results showed that third tested variation of experimental vitrification protocol, with four cryoprotectants in relatively low concentrations and applied to pieces of ovarian tissue at 0 °C during equilibration, increased survival rate of ovine ovarian tissue and improved results in comparison with conventional vitrification method. This variation of experimental protocol showed significant increase in percentage of follicles with good morphology (69,3%) in comparison with only commercially available vitrification protocol for ovarian tissue (62,1%). Morphology results were confirmed by TUNEL assay. Analysis of estradiol and progesterone production by cultured individual follicles after freezing/thawing revealed that steroids secretion remained significantly higher after multi-protectoral vitrification and slow freezing protocol, when follicles after standard vitrification protocol demonstrated decline in steroidogenic activity.

Conclusions

The multi-protectoral approach represents a workable solution to improve vitrification outcome on ovarian tissue and isolated follicles. The reduction of individual cryoprotectants concentrations, while maintaining their sufficient cumulative level in the final freezing solution, helps to increase efficiency of the procedure. Moreover, equilibration with lower temperatures helped to decrease even further the toxic effects of cryoprotectants and preserve original quality of ovarian tissue. Therefore, multi-protectoral vitrification can be suggested as an improved method for the clinical cryopreservation of ovarian tissue.

Genome-wide analysis of DNA Methylation profiles on sheep ovaries associated with prolificacy using whole-genome Bisulfite sequencing

Background

Ovulation rate and litter size are important reproductive traits in sheep with high economic value. Recent work has revealed a potential link between DNA methylation and prolificacy. However, a genome-wide study that sought to identify potential DNA methylation sites involved in sheep prolificacy indicated that it is still unknown. Here, we aimed to investigate the genome-wide DNA methylation profiles of Hu sheep ovaries by comparing a high-prolificacy group (HP, litter size of three for at least 2 consecutive lambings) and low prolificacy group (LP, litter size of one for at least 2 consecutive lambings) using deep whole-genome bisulfite sequencing (WGBS).

Results

First, our results demonstrated lower expression levels of DNA methyltransferase (DNMT) genes in the ovaries of the HP group than that in the ovaries of the LP group. Both groups showed similar proportions of methylation at CpG sites but different proportions at non-CpG sites. Subsequently, we identified 70,899 differential methylated regions (DMRs) of CG, 16 DMRs of CHG, 356 DMRs of CHH and 12,832 DMR-related genes(DMGs). Gene Ontology (GO) analyses revealed that some DMGs were involved in regulating female gonad development and ovarian follicle development. Finally, we found that 10 DMGs, including BMP7, BMPR1B, CTNNB1, FST, FSHR, LHCGR, TGFB2 and TGFB3, are more likely to be involved in prolificacy of Hu sheep, as assessed by correlation analysis and listed in detail.

Conclusions

This study revealed the global DNA methylation pattern of sheep ovaries associated with high and low prolificacy groups, which may contribute to a better understanding of the epigenetic regulation of sheep reproductive capacity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4068-9) contains supplementary material, which is available to authorized users.

Molecular evidence that follicle development is accelerated in vitro compared to in vivo

In this study, we systematically compared the morphological, functional and molecular characteristics of granulosa cells and oocytes obtained by a three-dimensional in vitro model of ovine ovarian follicular growth with those of follicles recovered in vivo. Preantral follicles of 200 µm diameter were recovered and cultured up to 950 µm over a 20-day period. Compared with in vivo follicles, the in vitro culture conditions maintained follicle survival, with no difference in the rate of atresia. However, the in vitro conditions induced a slight decrease in oocyte growth rate, delayed antrum formation and increased granulosa cell proliferation rate, accompanied by an increase and decrease in CCND2 and CDKN1A mRNA expression respectively. These changes were associated with advanced granulosa cell differentiation in early antral follicles larger than 400 µm diameter, regardless of the presence or absence of FSH, as indicated by an increase in estradiol secretion, together with decreased AMH secretion and expression, as well as increased expression of GJA1, CYP19A1, ESR1, ESR2, FSHR, INHA, INHBA, INHBB and FST. There was a decrease in the expression of oocyte-specific molecular markers GJA4, KIT, ZP3, WEE2 and BMP15 in vitro compared to that in vivo. Moreover, a higher percentage of the oocytes recovered from cultured follicles 550 to 950 µm in diameter was able to reach the metaphase II meiosis stage. Overall, this in vitro model of ovarian follicle development is characterized by accelerated follicular maturation, associated with improved developmental competence of the oocyte, compared to follicles recovered in vivo.

Differentiation of Mouse Primordial Germ Cells into Functional Oocytes In Vitro

Various complex molecular events in oogenesis cannot be observed in vivo. As a bioengineering technique for female reproductive tissues, in vitro culture systems for female germ cells have been used to analyze oogenesis and preserve germ cells for over 20 years. Recently, we have established a new methodological approach for the culture of primordial germ cells (PGCs) and successfully obtained offspring. Our PGC culture system will be useful to clarify unresolved mechanisms of fertility and sterility from the beginning of mammalian oogenesis, before meiosis. This review summarizes the history of culture methods for mammalian germ cells, our current in vitro system, and future prospects for the culture of germ cells.

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.

Amburana cearensis leaf extract maintains survival and promotes in vitro development of ovine secondary follicles

The antioxidant properties of Amburana cearensis extract may be a useful substitute for standard cell culture medium. Thus, the aim of this study was to evaluate the effect of this extract, with or without supplementation, on in vitro survival and development of sheep isolated secondary follicles. After collection of the ovaries, secondary follicles were isolated and cultured for 18 days in α-MEM+ supplemented with bovine serum albumin, insulin, transferrin, selenium, glutamine, hypoxanthine and ascorbic acid (control medium) or into medium composed of different concentrations of A. cearensis extract without supplements (Amb 0.1; 0.2 or 0.4 mg/ml) or A. cearensis extract supplemented with the same substances described above for α-MEM+ supplementation. The A. cearensis supplemented medium was named Amb 0.1+; 0.2+ or 0.4+ mg/ml. There were more morphologically normal follicles in Amb 0.1 or Amb 0.4 mg/ml than in the control medium (α-MEM+) after 18 days of culture. Moreover, the percentage of antrum formation was significantly higher in Amb 0.1 or Amb 0.2 mg/ml than in α-MEM+ and Amb 0.1+ mg/ml, and similar to the other treatments. All A. cearensis extract media induced a progressive and significant increase in follicular diameter throughout the culture period. In conclusion, this study showed that 0.1 mg/ml of this extract, without supplementation, maintains follicular survival and promotes the development of ovine isolated secondary follicles in vitro. This extract can be an alternative culture medium for preantral follicle development.

Fresh and vitrified bovine preantral follicles have different nutritional requirements during in vitro culture

The aim of this study was to compare the efficiency of different media for the in vitro culturing of fresh and vitrified bovine ovarian tissues. Fragments of the ovarian cortex were subjected to vitrification and histological and viability analyses or were immediately cultured in vitro using the alfa minimum essential medium, McCoy's 5A medium (McCoy), or medium 199 (M199). Samples of different culture media were collected on days 1 (D1) and 5 (D5) for quantification of reactive oxygen species and for hormonal assays. In non-vitrified (i.e., fresh) ovarian tissue cultures, the percentage of morphologically normal follicles was significantly greater than that recorded for the other media (e.g., M199). In the case of previously vitrified tissues, the McCoy medium was significantly superior to the other media in preserving follicular morphology up until the last culture day (i.e., D5), thus maintaining a similar percentage from D1 to D5. Reactive oxygen species levels were higher in D1 vitrified cultured tissues, but there were no differences in the levels among the three media after 5 days. The hormonal assays showed that in the case of previously vitrified tissues, at D5, progesterone levels increased on culture in the M199 medium and estradiol levels increased on culture in the McCoy medium. In conclusion, our results indicate that the use of M199 would be recommended for fresh tissue cultures and of McCoy for vitrified tissue cultures.

Post-ovulatory ageing of mouse oocytes affects the distribution of specific spindle-associated proteins and Akt expression levels

The aim of this study has been to determine the effects of in vivo post-ovulatory ageing (POA) on the distribution of spindle-associated proteins, histone H3/H4 post-translational modifications and on v-akt murine thymoma viral oncogene homolog 1 (Akt) expression levels. To this end, oocytes were retrieved 13, 29 and 33h after human chorionic gonadotrophin (hCG) treatment. The presence and distribution at the meiotic spindle of acetylated tubulin, γ-tubulin, polo kinase-1 and Ser473/Thr308 phosphorylated Akt (pAkt) as well as histone H3 and H4 acetylation and phosphorylation levels were assayed via immunofluorescence. Akt expression levels were determined via reverse transcription-polymerase chain reaction and western blotting analyses. Spindles from oocytes recovered 13h and 29h after hCG treatment showed similar levels of acetylated tubulin but ageing induced: (1) translocation of γ-tubulin from spindle poles to microtubules, (2) absence of Thr308- and Ser473-pAkt in 76% and 30% of oocytes, respectively, and (3) a significant reduction in phosphorylation levels of serine 10 on histone 3. At 29h, a significant decrease in Akt mRNA, but not in pAkt or Akt protein levels, was recorded. By contrast, protein content significantly decreased 33h after hCG. We conclude that POA impairs oocyte viability and fertilisability by altering the expression levels and spindle distribution of proteins that are implicated in cell survival and chromosome segregation. Together, these events could play a role in oocyte apoptosis.

Epigenetic disturbances in in vitro cultured gametes and embryos: implications for human assisted reproduction

Although assisted reproductive technology (ART) has become a routine practice for human infertility treatment, the etiology of the increased risks for perinatal problems in ART-conceived children is still poorly understood. Data from mouse experiments and the in vitro production of livestock provide strong evidence that imprint establishment in late oocyte stages and reprogramming of the two germline genomes for somatic development after fertilization are vulnerable to environmental cues. In vitro culture and maturation of oocytes, superovulation, and embryo culture all represent artificial intrusions upon the natural development, which can be expected to influence the epigenome of the resultant offspring. However, in this context it is difficult to define the normal range of epigenetic variation in humans from conception throughout life. With the notable exception of a few highly penetrant imprinting mutations, the phenotypic consequences of any observed epigenetic differences between ART and non-ART groups remain largely unclear. The periconceptional period is not only critical for embryonal, placental, and fetal development, as well as the outcome at birth, but suboptimal in vitro culture conditions may also lead to persistent changes in the epigenome influencing disease susceptibilities later in life. The epigenome appears to be most plastic in the late stages of oocyte and the early stages of embryo development; this plasticity steadily decreases during prenatal and postnatal life. Therefore, when considering the safety of human ART from an epigenetic point of view, our main concern should not be whether or not a few rare imprinting disorders are increased, but rather we must be aware of a functional link between interference with epigenetic reprogramming in very early development and adult disease.

Exposure to mono-n-butyl phthalate disrupts the development of preimplantation embryos

Dibutyl phthalate (DBP), a widely used phthalate, is known to cause many serious diseases, especially in the reproductive system. However, little is known about the effects of its metabolite, mono-n-butyl phthalate (MBP), on preimplantation embryo development. In the present study, we found that treatment of embryos with 10–3 M MBP impaired developmental competency, whereas exposure to 10–4 M MBP delayed the progression of preimplantation embryos to the blastocyst stage. Furthermore, reactive oxygen species (ROS) levels in embryos were significantly increased following treatment with 10–3 M MBP. In addition, 10–3 M MBP increased apoptosis via the release of cytochrome c, whereas immunofluorescent analysis revealed that exposure of preimplantation embryos to MBP concentration-dependently (10–5, 10–4 and 10–3 M) decreased DNA methylation. Together, the results indicate a possible relationship between MBP exposure and developmental failure in preimplantation embryos.

Genomic imprints as a model for the analysis of epigenetic stability during assisted reproductive technologies

Gamete and early embryo development are important stages when genome-scale epigenetic transitions are orchestrated. The apparent lack of remodeling of differential imprinted DNA methylation during preimplantation development has lead to the argument that epigenetic disruption by assisted reproductive technologies (ARTs) is restricted to imprinted genes. We contend that aberrant imprinted methylation arising from assisted reproduction or infertility may be an indicator of more global epigenetic instability. Here, we review the current literature on the effects of ARTs, including ovarian stimulation,in vitrooocyte maturation, oocyte cryopreservation, IVF, ICSI, embryo culture, and infertility on genomic imprinting as a model for evaluating epigenetic stability. Undoubtedly, the relationship between impaired fertility, ARTs, and epigenetic stability is unquestionably complex. What is clear is that future studies need to be directed at determining the molecular and cellular mechanisms giving rise to epigenetic errors.

H3K9 trimethylation precedes DNA methylation during sheep oogenesis: HDAC1, SUV39H1, G9a, HP1, and Dnmts are involved in these epigenetic events

The oocyte, to become a fully mature gamete, has to acquire a correct pattern of DNA methylation on its genome; this epigenetic event represents the major point of the molecular mechanisms that occur during postnatal oogenesis. It is known that an intimate link exists between DNA methylation and histone posttranslational modifications, such as trimethylation of lysine 9 on histone 3 (H3K9me3), that is essential in the silencing of gene transcription. What remains unclear is the precise sequence of these two epigenetic events and the protein expression of the enzymes that catalyze this epigenetic maturation during oogenesis. To identify the key molecules involved in global DNA methylation and H3K9me3, a biological network-based computational model was realized. Then, the spatiotemporal distribution of the proteins, identified from the biological network, was assessed during postnatal oogenesis. The results obtained suggest the existence of a sequential cascade of events in which H3K9me3 is the primary step followed by DNA methylation. These two epigenetic marks are realized due to the recruitment of the HDAC1, SUV39H1, G9a, HP1, and Dnmt3a, which were always localized in the nuclei of the oocytes and were dependent on chromatin configuration. These results involving DNA methylation and H3K9me3 are crucial in defining the oocyte developmental competence.