Oocyte Factors Research Articles

Spatial distribution of maternal factors in pig mature oocytes

It is known that asymmetrical maternal transcripts play an important role in the cell fate of the early embryo, but few studies are available in mammal oocytes especially in pig. To investigate the spatial factors in pig oocytes, the oriented bisection was established for collecting karyoplasts (NSOs) and cytoplasts (SSOs) with more than 95% efficiency. Subsequently, RNA-Seq and LC-MS/MS analysis were performed on NSOs and SSOs. Although no differentially expressed genes (DEGs) could be detected between NSOs and SSOs, 89 of the differentially expressed proteins (DEPs) were detected, that 58 proteins higher expressed but 31 proteins lower expressed in NSOs compared with SSOs. These DEPs mainly participated in the ‘cell cycle’ and ‘ribosome’ pathway, while the up-regulated DEPs were mainly GO in ‘spindle’ and ‘positive regulation of translation’, and the down-regulated DEPs were in ‘cytosolic small ribosomal subunit’ and ‘mRNA binding’. The up-regulated DEP SIRT5 which are related to the regulation of gene expression, epigenetic were further detected and revealed. A spatial asymmetry of maternal factors at the protein level was firstly detected in pig mature oocytes.

O-006 Oocyte factors as predictors of abnormal, mononucleated and trinucleated, zygotes and assessment of their morphokinetic differences

Abstract Study question Are there oocyte factors associated with the occurrence of mononucleated and trinucleated zygotes after ICSI? Does morphokinetics differ in embryos from normal and abnormal zygotes? Summary answer Formation of 1PN zygotes relates to vitrificated and donor oocytes. 3PN links to age and own oocytes. 1PN embryo morphokinetics are slower than 2PN, 3PN. What is known already In assisted reproduction, after monitoring fertilization, it is common to observe zygotes with one or more than 2 pronuclei. These abnormal zygotes are often discarded due to potential chromosomal abnormalities. The formation of these anomalous zygotes can be attributed to various causes, such as non-activation of the male pronucleus, non-extrusion of the second polar body, etc. Simultaneously, limited data exist on the morphokinetics of abnormal zygotes, explored in a few studies. The embryonic kinetics of 1PN zygotes seem slower than those of 2PN and 3PN zygotes, but further research is needed to confirm this aspect. Study design, size, duration Retrospective multicentre study involved time-lapse monitoring of 28,218 ICSI zygotes (26,252 2PN, 1,190 1PN, and 776 >3PN) generated between January 2019 and December 2023. The study includes donor and patient oocytes with various infertility diagnoses, whether fresh or vitrified. The comparison of embryonic morphokinetics from abnormal/normal zygotes was conducted on 254 embryos from a single centre, with 45 originating from 1PN zygotes, 198 from 2PN zygotes, and 11 from zygotes with 3 or more pronuclei. Participants/materials, setting, methods The study involved 1,053 couples treated in four different centres. Uniform culture media were used, and oocytes were cultivated in time-lapse technology-equipped incubators across all centres. A logistic regression analysis aimed to identify oocyte factors linked to an abnormal pronuclei count. Embryonic morphokinetics were analysed using the CHLOE artificial intelligence system (Fairtility, Israel). Evaluated parameters included: tPNa, tPNf, t2, t3, t4, t5, t6, t7, t8, t9+, tM, tSB, tB, and tEB. Main results and the role of chance Donor oocytes exhibited a 1.32 times higher risk of producing 1PN zygotes than 2PN or 3PN zygotes (p < 0.001). Similarly, vitrified oocytes had a 1.63-fold higher risk of generating 1PN zygotes than 2PN or 3PN zygotes (p < 0.001). Additionally, we found that both the use of own oocytes and advanced age were significantly associated with 3PN zygotes (p < 0.001). Regarding age, the risk increases by 10% for each additional year. The average durations for all morphokinetic parameters of 2PN and 3PN embryos were similar. In contrast, all events, except t3 (p = 0.2), occurred more slowly in embryos derived from 1PN zygotes compared to embryos from 2PN zygotes. Thus, the disappearance of pronuclei had a p-value <0.005, and from t4 to tEB, the p-value was <0.001. When comparing embryos from 1PN and 3PN zygotes, only tPNa, t4, t8, t9+, and tM were significantly different. If only zygotes that reached the blastocyst stage were used for analysis, the results were less conclusive due to a significantly reduced number of cases. Limitations, reasons for caution Embryos were cultured in an EmbryoScope incubator at three centres, while Geri was used in the fourth. Wider implications of the findings Using donor or vitrified oocytes may lead to an increased occurrence of zygotes with 1PN, as will occur with 3PN when patient or aged oocytes are used. The kinetics of embryos from 3PN oocytes resemble those from 2PN, while those from 1PN zygotes exhibit slower kinetics. Trial registration number not applicable

Rbpms2 promotes female fate upstream of the nutrient sensing Gator2 complex component Mios

Reproductive success relies on proper establishment and maintenance of biological sex. In many animals, including mammals, the primary gonad is initially ovary biased. We previously showed the RNA binding protein (RNAbp), Rbpms2, is required for ovary fate in zebrafish. Here, we identified Rbpms2 targets in oocytes (Rbpms2-bound oocyte RNAs; rboRNAs). We identify Rbpms2 as a translational regulator of rboRNAs, which include testis factors and ribosome biogenesis factors. Further, genetic analyses indicate that Rbpms2 promotes nucleolar amplification via the mTorc1 signaling pathway, specifically through the mTorc1-activating Gap activity towards Rags 2 (Gator2) component, Missing oocyte (Mios). Cumulatively, our findings indicate that early gonocytes are in a dual poised, bipotential state in which Rbpms2 acts as a binary fate-switch. Specifically, Rbpms2 represses testis factors and promotes oocyte factors to promote oocyte progression through an essential Gator2-mediated checkpoint, thereby integrating regulation of sexual differentiation factors and nutritional availability pathways in zebrafish oogenesis.

Knockdown of KDM5B Leads to DNA Damage and Cell Cycle Arrest in Granulosa Cells via MTF1

KDM5B is essential for early embryo development, which is under the control of maternal factors in oocytes. Granulosa cells (GCs) play a critical role during oocyte mature. However, the role of KDM5B in GCs remains to be elucidated. In the current study, we found that KDM5B expressed highly in the ovaries and located in goat GCs. Using an RNA sequence, we identified 1353 differentially expressed genes in the KDM5B knockdown GCs, which were mainly enriched in cell cycle, cell division, DNA replication and the cellular oxidative phosphorylation regulation pathway. Moreover, we reported a decrease in the percentage of proliferated cells but an increase in the percentage of apoptotic cells in the KDM5B knockdown GCs. In addition, in the KDM5B knockdown GCs, the percentage of GCs blocked at the S phase was increased compared to the NC group, suggesting a critical role of KDM5B in the cell cycle. Moreover, in the KDM5B knockdown GCs, the reactive oxygen species level, the mitochondrial depolarization ratio, and the expression of intracellular phosphorylated histone H2AX (γH2AX) increased, suggesting that knockdown of KDM5B leads to DNA damage, primarily in the form of DNA double-strand breaks (DSBs). Interestingly, we found a down-regulation of MTF1 in the KDM5B knockdown GCs, and the level of cell proliferation, as well as the cell cycle block in the S phase, was improved. In contrast, in the group with both KDM5B knockdown and MTF1 overexpression, the level of ROS, the expression of γH2AX and the number of DNA DSB sites decreased. Taken together, our results suggest that KDM5B inhibits DNA damage and promotes the cell cycle in GCs, which might occur through the up-regulation of MTF1.

Effect of Ovarian Extract on Oocyte Maturation and Early Embryonic Development in Pigs

Various factors in the ovary are known to regulate oocyte maturation and hormone secretory functions; however, the effect of ovarian extract (OE) on oocyte maturation and embryonic development in pigs remains unknown. In this study, we first evaluated whether OE supplementation in the in vitro maturation (IVM) medium alters the oocyte maturation capacity by affecting glucose/amino acid metabolites, meiotic maturation, cumulus cell (CC) expansion, and antioxidants. Various OE concentrations (50, 100, 200, 500, and 5000 μg/mL) were included in the IVM medium. Only the oocytes treated with 100 μg/mL OE exhibited an improved meiotic maturation rate when compared with that of the other groups (non-treated group, 78.6 ± 3.0% vs. 100 μg/mL OE-treated group, 81.6 ± 4.3%); however, the difference was not significant. To observe the changes in glucose and amino acid metabolism in the OE-treated oocytes, we measured the amounts of diverse constituents (glucose, lactate, glutamine, and ammonia) in the IVM medium containing OE. Lactate and ammonia levels in the OE-treated group after 44 h of IVM were higher (p < 0.01) than those in the non-treated group. In addition, the expression of the CC expansion factors (Has2 and Tnfaip6) significantly increased (p < 0.05), whereas the mRNA expression levels of antioxidative enzymes (Sod1, Cat, and Gpx1) significantly diminished (p < 0.05) in the OE-treated group. Moreover, mature oocytes treated with 100 μg/mL OE demonstrated increased subsequent embryonic development rates after 144 h of IVM. Thus, the addition of OE in IVM mediums may improve oocyte maturation capacity which could enhance antioxidative enzyme activation, energy metabolism, and expression of the CC expansion factors in porcine oocytes.

Increased mtDNA mutation frequency in oocytes causes epigenetic alterations and embryonic defects.

Mitochondria are essential for female reproductive processes, yet the function of mitochondrial DNA (mtDNA) mutation in oocytes remains elusive. By employing an mtDNA mutator (Polgm) mouse model, we found the fetal growth retardation and placental dysfunction in post-implantation embryos derived from Polgm oocytes. Remarkably, Polgm oocytes displayed the global loss of DNA methylation; following fertilization, zygotic genome experienced insufficient demethylation, along with dysregulation of gene expression. Spindle-chromosome exchange experiment revealed that cytoplasmic factors in Polgm oocytes are responsible for such a deficient epigenetic remodeling. Moreover, metabolomic profiling identified a significant reduction in the α-ketoglutarate (αKG) level in oocytes from Polgm mice. Importantly, αKG supplement restored both DNA methylation state and transcriptional activity in Polgm embryos, consequently preventing the developmental defects. Our findings uncover the important role of oocyte mtDNA mutation in controlling epigenetic reprogramming and gene expression during embryogenesis. αKG deserves further evaluation as a potential drug for treating mitochondrial dysfunction-related fertility decline.

Mouse oocytes develop in cysts with the help of nurse cells

Mouse germline cysts, on average, develop into six oocytes supported by 24 nurse cells that transfer cytoplasm and organelles to generate a Balbiani body. We showed that between E14.5 and P5, cysts periodically activate some nurse cells to begin cytoplasmic transfer, which causes them to shrink and turnover within 2days. Nurse cells die by a programmed cell death (PCD) pathway involving acidification, similar to Drosophila nurse cells, and only infrequently by apoptosis. Prior to initiating transfer, nurse cells co-cluster by scRNA-seq with their pro-oocyte sisters, but during their final 2days, they cluster separately. The genes promoting oocyte development and nurse cell PCD are upregulated, whereas the genes that repress transfer, such as Tex14, and oocyte factors, such as Nobox and Lhx8, are under-expressed. The transferred nurse cell centrosomes build a cytocentrum that establishes a large microtubule aster in the primordial oocyte that organizes the Balbiani body, defining the earliest oocyte polarity.

DPPA2 and DPPA4 are dispensable for mouse zygotic genome activation and pre-implantation development.

How maternal factors in oocytes initiate zygotic genome activation (ZGA) remains elusive in mammals, partly due to the challenge of de novo identification of key factors using scarce materials. Two-cell (2C)-like cells have been widely used as an in vitro model in order to understand mouse ZGA and totipotency because of their expression of a group of two-cell embryo-specific genes and their simplicity for genetic manipulation. Recent studies indicate that DPPA2 and DPPA4 are required for establishing the 2C-like state in mouse embryonic stem cells in a DUX-dependent manner. These results suggest that DPPA2 and DPPA4 are essential maternal factors that regulate Dux and ZGA in embryos. By analyzing maternal knockout and maternal-zygotic knockout embryos, we unexpectedly found that DPPA2 and DPPA4 are dispensable for Dux activation, ZGA and pre-implantation development. Our study suggests that 2C-like cells do not fully recapitulate two-cell embryos in terms of regulation of two-cell embryo-specific genes, and, therefore, caution should be taken when studying ZGA and totipotency using 2C-like cells as the model system.

P–498 Patient’s pregnancy rates after IVF fresh embryo transfer positively correlates to the number of visual connections to live blastocyst development images of own embryos

Abstract Study question Looking at time-lapse images of own embryos during the five days of culture, as a patient’s active behaviour, may help to increase pregnancy rates? Summary answer The number of visual connections to live blastocyst development images of own embryos positively correlates to patient’s pregnancy rates after fresh single blastocyst transfer. What is known already In human reproduction, despite the evidence that infertility itself and reproductive treatments can produce anxiety and stress, the impact of emotions on pregnancy outcomes is unknown and probably underestimated. The interaction between psyche, nervous, immune and endocrine systems (PNIE) is well known and has been applied to understand and treat different pathological conditions. Patient’s active behaviour during IVF treatments appears to be a positive strategy to decrease women’s anxiety and stress, thus to increase fertility quality of life and pregnancy outcomes. Study design, size, duration Retrospective comparative study of 934 patients undergoing fresh IVF cycles during three years. To avoid any bias related to oocyte and embryo factors, we only included egg donation cycles in the study, and ≥3BB (Gardner score) single embryo transfers. All embryo cultures were performed in time-lapse incubator and patients could connect on-line to their embryo’s images before single blastocyst transfer. We evaluated the impact of visual connections to live embryo images on pregnancy rates. Participants/materials, setting, methods On day one of embryo culture, consenting patients received an individualized and secure link allowing them to connect on-line to images of their own embryos any time during the five days of culture. Patients were divided in five groups depending on the number of on-line visualisations (A = 0; B = 1–10; C = 11–20; D = 21–30; E > 30). Pregnancy and clinical pregnancy rates were compared between the five groups. Chi-square test for a large contingency table was performed to compare all groups Main results and the role of chance The distribution of patients in the five groups, based on number of visualizations, resulted as follows: 287 in group A; 328 in group B; 156 in group C; 80 in group D; 83 in group E. The five groups were homogeneous and there were no statistically significant differences in recipient’s ages (A 42.8±3.9 years; B 41.9±3.9 years; C 41.8±4.5 years; D 42.8±4.1 years; E 41.9±4.4 years) and in donor’s ages (A 25.5±4.3 years; B 26.9±4.4 years; C 27.1±4.2 years; D 26.4±4.5 years; E 26.5±4.1 years) among the five groups. We observed a progressive positive trend between the number of on-line visualisations and pregnancy rates, reaching statistical significance for group E (>30 visualizations) compared to the others groups. In group E, pregnancy rates and clinical pregnancy rates per fresh single blastocyst transfer were respectively 72.3% and 65.1%, significantly higher when compared to the others groups (p < 0.01, p < 0.001): group A 61% and 50.9%, group B 63.1% and 56.1%, group C 64.1% and 55.1%, group D 65% and 53.8%. Limitations, reasons for caution Time-lapse incubator is needed as well as a strong informatics setting to ensure secure and personalised on-line connection to each patient at any time during the five days of culture. Endocrine and endometrial biomarkers should be proposed and evaluated in further clinical trials to better understand these results. Wider implications of the findings: Repeated on-line visualization of own embryos images before fresh blastocyst transfer enhances pregnancy rates in IVF cycles. We propose that repeated visual stimuli of images produces a positive emotional connection between patients and their own developing embryos, thus reducing anxiety and enhancing recipient’s endometrial receptivity. Trial registration number Not applicable

Identification of differentially abundant mRNA transcripts and autocrine/paracrine factors in oocytes and follicle cells of mud crabs

The late vitellogenic stage of the mud crab is characterized by large and obvious follicle cells as well as an enlarged oocyte nucleus and a prominent germinal vesicle (GV). The aim of this study was evaluation of functions of oocytes and follicle cells during meiosis as well as at identifying associated ovarian autocrine/paracrine factors using comparative transcriptomics. The results from the KEGG pathway analysis indicated DNA replication, nucleotide excision repair, spliceosome and the ribosome pathways were highly associated with oocyte maturation across both transcriptomes. In addition, there was a larger abundance of mRNA transcripts for cell cycle-related genes in the oocyte, as well as cyclin A, cyclin B and CKS1B in the GV than at the time of germinal vesicle breakdown (GVBD). These findings indicate these cell cycle-related genes might be involved in GVBD induction. Results when there was localization of ligands and the respective receptors of VEGF, TGFβ propeptide and BMP9/10 indicated these proteins might be autocrine/paracrine factors. Results from functional analysis of VEGF, TGFβ propeptide and BMP9/10 in oocyte maturation using RNA interference revealed that these proteins might be involved in oocyte maturation by regulating cyclin abundance. This is the first study on the functions of VEGF in oocyte maturation in invertebrates.

HIRA contributes to zygote formation in mice and is implicated in human 1PN zygote phenotype.

Elucidating the mechanisms underpinning fertilisation is essential to optimising IVF procedures. One of the critical steps involves paternal chromatin reprogramming, in which compacted sperm chromatin packed by protamines is removed by oocyte factors and new histones, including histone H3.3, are incorporated. HIRA is the main H3.3 chaperone governing this protamine-to-histone exchange. Failure of this step results in abnormally fertilised zygotes containing only one pronucleus (1PN), in contrast to normal two-pronuclei (2PN) zygotes. 1PN zygotes are frequently observed in IVF treatments, but the genotype-phenotype correlation remains elusive. We investigated the maternal functions of two other molecules of the HIRA complex, Cabin1 and Ubn1, in mouse. Loss-of-function Cabin1 and Ubn1 mouse models were developed: their zygotes displayed an abnormal 1PN zygote phenotype. We then studied human 1PN zygotes and found that the HIRA complex was absent in 1PN zygotes that lacked the male pronucleus. This shows that the role of the HIRA complex in male pronucleus formation potentially has coherence from mice to humans. Furthermore, rescue experiments in mouse showed that the abnormal 1PN phenotype derived from Hira mutants could be resolved by overexpression of HIRA. We have demonstrated that HIRA complex regulates male pronucleus formation in mice and is implicated in humans, that both CABIN1 and UBN1 components of the HIRA complex are equally essential for male pronucleus formation, and that rescue is feasible.

A primate perspective on oocytes and transgenerational PCOS.

'Androgenized' rodent models are widely used to explore the pathophysiology underlying human polycystic ovary syndrome (PCOS), including reproductive and metabolic dysfunction. Based on a recent study using a dihydrotestosterone (DHT)-treated murine model, it has been proposed that prenatal androgen excess alone can predispose to transgenerational transmission of PCOS. From RNA sequencing analysis of metaphase II (MII) oocytes of androgenized lineages, the authors speculated that oocyte factors, including up-regulation of cytotoxic granulosa-associated RNA binding protein-like 1 (TiaL1), are sufficient to promote disease transfer across generations. Although this is an intriguing concept, it was not considered in the context of earlier publications in which the transcriptomes of human MII oocytes from PCOS women undergoing IVF were compared with women without PCOS. In one of these papers, a number of differentially expressed genes in PCOS MII oocytes (TIAL1 was not differentially expressed) were found to have putative response elements in their promoters for androgen receptors and peroxisome proliferating receptor gamma, providing a mechanism for how excess androgens and/or metabolic defects associated with PCOS might affect female germ cells.

A Gatekeeping Role of ESR2 to Maintain the Primordial Follicle Reserve.

Over the entire reproductive lifespan in mammals, a fixed number of primordial follicles serve as the source of mature oocytes. Uncontrolled and excessive activation of primordial follicles can lead to depletion of the ovarian reserve. We observed that disruption of estrogen receptor β (ESR2) signaling results in increased activation of primordial follicles in Esr2-null (Esr2-/-) rats. However, follicle assembly was unaffected, and the total number of follicles remained comparable between neonatal wild-type and Esr2-/- ovaries. While the activated follicle counts were increased in Esr2-/- ovary, the number of primordial follicles were markedly decreased. Excessive recruitment of primordial follicles led to premature ovarian senescence in Esr2-/- rats and was associated with reduced levels of serum AMH and estradiol. Disruption of ESR2 signaling through administration of a selective antagonist (PHTPP) increased the number of activated follicles in wildtype rats, whereas a selective agonist (DPN) decreased follicle activation. In contrast, primordial follicle activation was not increased in the absence of ESR1, indicating that the regulation of primordial follicle activation is ESR2 specific. Follicle activation was also increased in Esr2 mutants lacking the DNA binding domain, suggesting a role for the canonical transcriptional activation function. Both primordial and activated follicles express ESR2, suggesting a direct regulatory role for ESR2 within these follicles. We also detected that loss of ESR2 augmented the activation of AKT, ERK, and mTOR pathways. Our results indicate that the lack of ESR2 upregulated both granulosa and oocyte factors, which can facilitate AKT and mTOR activation in Esr2-/- ovaries leading to increased activation of primordial follicles.

Expression Pattern of Early Transcription Factors in Porcine Oocytes and Embryos

Expression Pattern of Early Transcription Factors in Porcine Oocytes and Embryos

Evaluation of comparison of clinical outcome treated oocyte with ionomycin and strontium chloride in infertile couple with previous failed in vitro fertilization

Introduction: Several factors are involved in failed fertilization following intracytoplasmic sperm injection (ICSI), which could be related to sperm, oocyte factors and/or both. Failure in oocyte activation is considered as the most important factor in failed fertilization after ICSI. To overcome this shortcoming, artificial oocyte activation (AOA) after ICSI has been suggested. Commonly, ionomycin and strontium chloride are used as the most efficient agents for oocyte activation in the clinic. In this study, for the first time, the clinical results of ionomycin and strontium chloride were compared on sister oocytes of couples who previously have had fertilization failure after ICSI. Methods: In this intervention study, 14 couples with male factor infertility and previous failed fertilization after ICSI were included in this study. Oocytes of their wives were divided into two groups. Half of the oocytes after ICSI were treated with ionomicin and other half were treated with strontium chloride. Then, fertilization rate, embryo quality and pregnancy status were compared through SPSS 18 software, Paired sample t-test and chi-square test. Results: Percentage of fertilization rate was significantly higher in oocytes that were activated using strontium chloride compared to those that were activated with ionomycin (p<0.0001). Although, the pregnancy rate was insignificantly higher in strontium chloride group than ionomycin group (p=0.387), but the quality of embryo was similar between the two groups (p=0.924). Conclusion: In infertile men with previous failed fertilization after ICSI, the use of strontium chloride can also be recommended for oocyte activation.

Evaluation of members of the TGFß superfamily as candidates for the oocyte factors that control mouse cumulus expansion and steroidogenesis

Oocytes secrete factors that control cumulus and granulosa functions, including cumulus expansion and steroid hormone production. Some members of the transforming growth factor ß (TGFß) superfamily influence these activities, yet it is still not determined conclusively whether any of these superfamily members are the previously reported oocyte-secreted factors. The aim of this study was to examine the effects of TGFß1 and growth differentiation factor 9 (GDF-9) on cumulus expansion and progesterone production by mouse oocytectomized (OOX) complexes in culture. TGFß1 mimics the effects of oocytes by both enabling cumulus expansion and inhibiting progesterone production; however, neutralizing antibodies to TGFß1 in cultures of cumulus-oocyte complexes (COCs) or in co-cultures of OOX complexes failed to inhibit the ability of oocytes to enable cumulus expansion or inhibit progesterone production. Activin A had no effect on progesterone production by OOX complexes. In experiments using oocytes obtained from mice with deficient expression of GDF-9, OOX complexes cultured in the presence of heterozygous oocytes were capable of full expansion, whereas OOX complexes cultured with oocytes from GDF-9 null mice did not expand. Similarly, GDF-9 null oocytes failed to suppress FSH-induced progesterone production by OOX complexes. These results support the hypothesis that GDF-9 is the cumulus expansion enabling factor produced by mouse oocytes and that GDF-9 also inhibits cumulus progesterone production; however, the possibility remains that loss of GDF-9 may indirectly affect the ability of oocytes to produce the factors that regulate cumulus cell activity.

A Method for Zebrafish Follicle Transplantation into Recipient Mothers for the Generation of Fertilizable Eggs and Viable Offspring.

In zebrafish and other externally developing animals, maternal effect gene products significantly contribute to embryonic and larval development. Several methods exist for both forward and reverse genetic manipulation of maternal gene products, yet it remains technically difficult to interfere with maternal gene products. Therefore, alternative methods to manipulate maternal factors in oocytes remain of interest. Here we describe a method which allows manipulation and subsequent transplantation of stage I-II follicles of zebrafish into recipient mothers where donor oocytes can develop into mature eggs and produce viable offspring. Additionally, we describe a simple microinjection protocol for injecting reporter constructs into follicles as a proxy for manipulating maternal effect genes.

126 Regulation of initiation of follicle growth and dynamics of early follicular development in the sheep.

Primordial follicles embedded in the ovarian cortex are the source of developing follicles. Follicle growth activation and development up to the small antral follicle stage are controlled by cell interactions. The sheep ovary offers an appropriate non-rodent model to study these interactions, thanks to the development of in vitro and in vivo experimental approaches, ex vivo molecular analyses and in silico mathematical modeling. Each primordial follicle, composed of an oocyte surrounded by a single layer of quiescent granulosa cells, relies on nutrients and growth factors supplied by the surrounding stroma of connective tissue. In vitro cultures of ovarian cortex have shown that primordial follicles are activated by the lifting of mechanisms maintaining quiescence, some of them involving AMH secreted by already growing follicles. Afterwards, follicle development is supported by a finely tuned molecular dialog between the growing oocyte and proliferating granulosa cells. The isolation of preantral follicles and their development in vitro as individual follicles perturb this dialog, leading to an acceleration of follicular maturation. In vivo, mutations in the oocyte factors BMP15, GDF9 or their receptor BMPR1B also impair this dialog, leading to an imbalance between oocyte growth and cell proliferation, which can be reproduced by models for cell dynamics. During the growth of preantral follicles, the recruitment and differentiation of theca cells from the ovarian stroma provide them with a structural and vascularized support. In vivo exposure of sheep fetal ovaries to testosterone imprints the stroma cells so that the expression of genes involved in extracellular matrix organization and cell-cell adhesion is affected in theca at adulthood; this leads to a lower ovarian tissue rigidity that can account for the accelerated follicle growth observed in androgenized ewes. A better knowledge of cell interactions during early follicular development will help to improve the biotechnology methods of fertility preservation.

Disparate IVF Outcomes and the Role of Uterine and Oocyte Factors

Infertility has become an important public health issue, with over 12% of the U.S. population being affected. Moreover, the role of race and ethnicity has become increasingly recognized as an important contributor to health outcomes. Despite in vitro fertilization (IVF) playing a significant role in helping many women achieve their reproductive goals, data show disparities in IVF outcomes among racial and ethnic minority groups. This review examines the literature on disparities in IVF outcomes among black, Asian, and Hispanic women. Data analyzed show that black and Asian women have decreased clinical pregnancy and live-birth rates compared to white women and increased rates of pregnancy loss and fetal growth restriction. While consistent findings have not been identified among Hispanic women, likely due to inadequate studies among Hispanic women, limited epidemiologic data suggest decreased clinical pregnancy and live-birth rates among Hispanic women, while clinic based studies show no differences in outcomes when compared to white women. The biological plausibility associated with these disparate outcomes suggests a role for obesity, fibroids, and impaired endometrial hormonal milieu affecting outcomes among black women, while variation in ovarian reserve and endometrial hormonal milieu may contribute to poorer outcomes among Asian women. Keywords: In vitro fertilization (IVF), disparities, fibroids, minorities, race, ethnicity.

Chromatin Accessibility Impacts Transcriptional Reprogramming in Oocytes

SummaryOocytes have a remarkable ability to reactivate silenced genes in somatic cells. However, it is not clear how the chromatin architecture of somatic cells affects this transcriptional reprogramming. Here, we investigated the relationship between the chromatin opening and transcriptional activation. We reveal changes in chromatin accessibility and their relevance to transcriptional reprogramming after transplantation of somatic nuclei into Xenopus oocytes. Genes that are silenced, but have pre-existing open transcription start sites in donor cells, are prone to be activated after nuclear transfer, suggesting that the chromatin signature of somatic nuclei influences transcriptional reprogramming. There are also activated genes associated with new open chromatin sites, and transcription factors in oocytes play an important role in transcriptional reprogramming from such genes. Finally, we show that genes resistant to reprogramming are associated with closed chromatin configurations. We conclude that chromatin accessibility is a central factor for successful transcriptional reprogramming in oocytes.