Acquisition Of Meiotic Competence Research Articles

Effects of oocyte-derived growth factors on the growth of porcine oocytes and oocyte-cumulus cell complexes in vitro.

During oocyte growth and follicle development, oocytes closely communicate with cumulus cells. We examined the effects of oocyte-derived growth factors, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), on the growth and acquisition of meiotic competence of porcine oocytes collected from early antral follicles (1.2–1.5 mm). First, we confirmed that GDF9 and BMP15 mRNAs were expressed almost exclusively in the oocytes. Oocyte–cumulus cell complexes (OCCs) collected from early antral follicles were cultured in growth medium supplemented with 0–100 ng/ml of GDF9 or BMP15 for 5 days. GDF9 dose-dependently increased the OCC diameter, while BMP15 did not. GDF9 and BMP15 had no significant effects on oocyte growth (P > 0.05). When OCCs that had been cultured with 50 and 100 ng/ml BMP15 were subjected to a subsequent maturation culture, they expanded fully by gonadotropic stimulation and 49% and 61% of oocytes matured to metaphase II (MII), respectively. In contrast, GDF9 did not promote cumulus expansion, and < 10% of oocytes matured to MII. Based on the difference in cumulus expansion, we compared the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) and follicle stimulating hormone receptor (FSHR) mRNAs in cumulus cells. The level of LHCGR mRNA was increased in cumulus cells of the BMP15 group, although there were no significant differences in FSHR mRNA levels among the groups. These results suggest that GDF9 promotes the growth of OCCs and that BMP15 promotes LHCGR mRNA expression in cumulus cells during oocyte growth culture, which may contribute to cumulus expansion and oocyte maturation.

Stimulated by retinoic acid gene 8 (STRA8) interacts with the germ cell specific bHLH factor SOHLH1 and represses c‐KIT expression in vitro

STRA8 (Stimulated by Retinoic Acid Gene 8) controls the crucial decision of germ cells to engage meiotic division up and down‐regulating genes involved in the meiotic programme. It has been proven as an amplifier of genes involved in cell cycle control and chromosome events, however, how STRA8 functions as negative regulator are not well understood. In this study, we demonstrate that STRA8 can interact with itself and with other basic Helix‐Loop‐Helix (bHLH) transcription factors through its HLH domain and that this domain is important for its ability to negatively interfere with the Ebox‐mediated transcriptional activity of bHLH transcription factors. Significantly, we show that STRA8 interacts with TCF3/E47, a class I bHLH transcription factors, and with SOHLH1, a gonadal‐specific bHLH, in male germ cells obtained from prepuberal mouse testis. We demonstrated that STRA8, indirectly, is able to exert a negative control on the SOHLH1‐dependent stimulation of c‐KIT expression in late differentiating spermatogonia and preleptotene spermatocytes. Although part of this results were obtained only ‘in vitro’, they support the notion that STRA8 interacting with different transcription factors, besides its established role as ‘amplifier’ of meiotic programme, is able to finely modulate the balance between spermatogonia proliferation, differentiation and acquisition of meiotic competence.

Cortical Granule Distribution and Expression Pattern of Genes Regulating Cellular Component Size, Morphogenesis, and Potential to Differentiation are Related to Oocyte Developmental Competence and Maturational Capacity In Vivo and In Vitro.

Polyspermia is an adverse phenomenon during mammalian fertilization when more than one sperm fuses with a single oocyte. The egg cell is prepared to prevent polyspermia by, among other ways, producing cortical granules (CGs), which are specialized intracellular structures containing enzymes that aim to harden the zona pellucida and block the fusion of subsequent sperm. This work focused on exploring the expression profile of genes that may be associated with cortical reactions, and evaluated the distribution of CGs in immature oocytes and the peripheral density of CGs in mature oocytes. Oocytes were isolated and then processed for in vitro maturation (IVM). Transcriptomic analysis of genes belonging to five ontological groups has been conducted. Six genes showed increased expression after IVM (ARHGEF2, MAP1B, CXCL12, FN1, DAB2, and SOX9), while the majority of genes decreased expression after IVM. Using CG distribution analysis in immature oocytes, movement towards the cortical zone of the oocyte during meiotic competence acquisition was observed. CGs peripheral density decreased with the rise in meiotic competence during the IVM process. The current results reveal important new insights into the in vitro maturation of oocytes. Our results may serve as a basis for further studies to investigate the cortical reaction of oocytes.

Zinc supports transcription and improves meiotic competence of growing bovine oocytes.

In the last years, many studies focused on the understanding of the possible role of zinc in the control of mammalian oogenesis, mainly on oocyte maturation and fertilization. However, little is known about the role of zinc at earlier stages, when the growing oocyte is actively transcribing molecules that will regulate and sustain subsequent stages of oocyte and embryonic development. In this study, we used the bovine model to gain insights into the possible involvement of zinc in oocyte development. We first mined the EmbryoGENE transcriptomic dataset, which revealed that several zinc transporters and methallothionein are impacted by physiological conditions throughout the final phase of oocyte growth and differentiation. We then observed that zinc supplementation during in vitro culture of growing oocytes is beneficial to the acquisition of meiotic competence when subsequently subjected to standard in vitro maturation. Furthermore, we tested the hypothesis that zinc supplementation might support transcription in growing oocytes. This hypothesis was indirectly confirmed by the experimental evidence that the content of labile zinc in the oocyte decreases when a major drop in transcription occurs in vivo. Accordingly, we observed that zinc sequestration with a zinc chelator rapidly reduced global transcription in growing oocytes, which was reversed by zinc supplementation in the culture medium. Finally, zinc supplementation impacted the chromatin state by reducing the level of global DNA methylation, which is consistent with the increased transcription. In conclusion, our study suggests that altering zinc availability by culture-medium supplementation supports global transcription, ultimately enhancing meiotic competence.

Effects of melatonin on the in vitro growth of early antral follicles and maturation of ovine oocytes

This study aimed to evaluate the effect of melatonin on the in vitro culture and maturation of isolated sheep early antral follicles. Isolated early antral follicles were cultured for 12 d in α-minimum essential medium (MEM+) alone (control) or α-MEM+ added with fixed different concentrations (100, 500, or 1,000 pg/mL) or a sequential concentration of melatonin (MelSeq; day 6 = 100; day 12 = 500 pg/mL). The percentage of morphologically normal follicles was higher (P < 0.05) in 500 pg/mL melatonin than the other treatments at 6 d. Mel 500 also showed a higher rate of fully grown oocytes (P < 0.05) than other treatments. After in vitro culture, reactive oxygen species (ROS) levels in oocytes were similar between Mel 500 and MelSeq, with both being lower (P < 0.05) than other treatments. Oocytes cultured in both Mel 500 and Mel 1000 showed glutathione peroxidase levels similar (P > 0.05) to the control group and higher (P < 0.05) than other treatments. Mitochondrial activity was similar (P > 0.05) among control, Mel 500, and Mel 1000 treatments. Mel 500 treatment presented a higher percentage of germinal vesicle breakdown oocytes than the control group and similar percentages to the other treatments. Follicles cultured in melatonin followed by oocyte maturation with the addition of 500 pg/mL melatonin in maturation medium showed increased (P < 0.05) levels of mitochondrial activity compared to α-MEM+ alone. In conclusion, the concentration of 500 pg/mL of melatonin promotes development and decreases ROS levels of ovine oocytes from in vitro grown early antral follicles. Moreover, melatonin increases mitochondrial activity and promotes the acquisition of meiotic competence of these oocytes.

INFLUÊNCIA DO HEPES NA MATURAÇÃO IN VITRO DE OÓCITOS CANINOS OBTIDOS DE CADELAS EM DIESTRO E ANESTRO

Resumo Diferentemente de outras espécies domésticas, a maturação in vitro (MIV) de oócitos caninos apresenta sucesso limitado. O objetivo deste estudo foi avaliar o efeito do HEPES na maturação in vitro de oócitos caninos obtidos de cadelas em diestro e anestro. Os ovários foram coletados, isolados assepticamente e transportados refrigerados a uma temperatura de 4 ºC. Os complexos cumulus-oócito (CCOs), provenientes das duas fases do ciclo estral, foram submetidos a dois tratamentos: meio TCM-199 com adição de 25 mM de HEPES (GT) e meio sem suplementação (GC). Depois de 72 horas de maturação, os CCOs foram desnudados, fixados e corados com HOESCHT 33342 para avaliação da maturação nuclear. Os oócitos obtidos da fase de anestro e diestro do GT demonstraram, em relação ao grupo GC, maior frequência de oócitos nos estágios de M-II (p&lt;0,01). Comparando-se os diferentes status reprodutivos, observou-se que os oócitos obtidos da fase de diestro apresentaram índices maiores de QVG e M-II. Nossos resultados demonstraram que o HEPES preserva a viabilidade e morfologia oocitária, indispensáveis para a aquisição da competência meiótica, potencializando as taxas de M-II, e que os oócitos obtidos da fase de diestro estão mais aptos a completarem a maturação oocitária.

Growing Oocytes Need Zinc: Zinc Deficiency in the Preantral Ovarian Follicle

ObjectiveTo evaluate the effect of zinc deficiency on oocyte development in the preantral ovarian follicle – a novel developmental stage for micronutrient investigation.MethodsOocyte‐granulosa cell complexes were collected from preantral ovarian follicles of 14 day old CD‐1 mice and cultured on collagen membranes under control, zinc‐deficient, or rescue conditions. Oocyte diameter was measured from brightfield images taken with an Olympus DP20 microscope digital camera. Chromatin arrangement and nucleolar development was observed after DAPI staining. Gene expression was measured with qPCR. Meiotic competence was measured by exposing cultured oocyte‐granulosa cell complexes to Epidermal Growth Factor (EGF) to mimic the in‐vivo ovulatory signal (maturation media). The ability of the oocytes to undergo meiotic division was assessed 24 hours after EGF treatment.ResultsZinc deficiency disrupted oocyte growth in vitro. Zinc deficient oocytes were smaller than control or rescue on day 4 (p&lt;0.001) and 6 (p&lt;0.05), but not day 10 of cell culture. Zinc deficiency impacted nuclear development; zinc deficient oocytes were more likely to have multiple nucleoli on day 6 (p&lt;0.001), but not day 10 of cell culture. Differentiation of somatic cells was also impaired; zinc‐deficient granulosa cell gene expression was consistent with a preantral, undifferentiated phenotype, even after 10 days of culture. Preantral somatic cell markers lhcgr, ar, pcsk6, and fosb were elevated compared with control (p&lt;0.05 for all). Preantral zinc deficiency reduced the meiotic potential of cultured oocytes. After EGF treatment, oocytes matured in zinc deficient media were less likely to resume meiosis and reach the meiotic stage required for fertilization (chi square p&lt;0.001). The meiotic defect was seen in zinc‐deficient oocytes even when transferred to maturation media containing zinc.ConclusionsPrior to entering the pool of antral ovulatory follicles, oocytes and the surrounding somatic cells undergo a period of growth and differentiation. This phase is known as preantral oocyte development and may last 3–5 months in humans. This study shows that zinc deficiency impairs multiple preantral developmental milestones including oocyte growth, oocyte nuclear maturation, and somatic cell differentiation. Most notably, the acquisition of meiotic competence – a benchmark of oocyte fertility and viability – was severely reduced by zinc deficiency. The meiotic defect was noted in zinc‐deficient cultured oocytes even when they were transferred to maturation media containing zinc, indicating a zinc requirement during development, rather than during meiotic resumption. These results demonstrate that zinc is required in oocyte development earlier than previously reported, and that even short periods of zinc deficiency may impact fertility months later. These results may impact our understanding of prenatal micronutrient supplementation, as well as optimal methods for in‐vitro oocyte maturation.Support or Funding InformationNIH ‐HD074831‐01This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Influence of epidermal growth factor (EGF) supplementation at different times of &lt;i&gt;in vitro&lt;/i&gt; maturation of canine oocytes

The aim of this study was to evaluate the influence of epidermal growth factor (EGF) on in vitro maturation of canine oocytes at different times of the process. Ovaries were collected from 55 bitches considered healthy and aseptically isolated, immersed in physiological solution (0.9% NaCl) and transported under refrigeration. Grade 1 cumulus-oocyte complexes (COCs) were selected and divided into two groups: control group (CG) and treatment group (TG). In CG 698 grade I COCs were placed in 4-well plates containing TCM-199 medium supplemented with 25 mM HEPES, 100 IU/mL penicillin, 100 mg/mL streptomycin, 26 mM sodium bicarbonate, 1.5 mM sodium pyruvate, 2.9 mM sodium lactate pentahydrate, 0.6 mM cysteine, 0.03 IU/mL hCG, 0.5 μg/mL FSH, 20 μg/mL estrogen at 38.5ºC in a humidified atmosphere of 5% CO2 in times of 24 h, 48 h, and 72 h. In TG 547 COCs received the same maturation medium plus 10 ηg/mL EGF. Logistic regression models (SAS, 2011) were constructed in order to estimate the chances of oocytes being observed at nuclear maturation stages in different culture times (24 h, 48 h, and 72 h). Based on the results found EGF-supplemented medium showed 2.56 times more chances of having an oocyte at metaphase I (M-I) than medium without EGF (p &lt; 0.0001). The results of this study demonstrated that the time of 72 h showed 5.88 times more chances of having an oocyte at metaphase II (M-II) compared to time of 24 h (p = 0.0001) and 7.69 times more chance than time of 48 h (p = 0.0001). The chances of finding an oocyte at M-II were also 9.09 times higher in medium supplemented with EGF than in medium without EGF (p = 0.0001). Thus, these results demonstrated the essential importance of EGF at different moments of oocyte maturation, being a key component for the acquisition of meiotic competence in bitches, increasing the M-I and M-II rates.

Spatio-Temporal Gene Expression Profiling during In Vivo Early Ovarian Folliculogenesis: Integrated Transcriptomic Study and Molecular Signature of Early Follicular Growth.

BackgroundThe successful achievement of early ovarian folliculogenesis is important for fertility and reproductive life span. This complex biological process requires the appropriate expression of numerous genes at each developmental stage, in each follicular compartment. Relatively little is known at present about the molecular mechanisms that drive this process, and most gene expression studies have been performed in rodents and without considering the different follicular compartments.ResultsWe used RNA-seq technology to explore the sheep transcriptome during early ovarian follicular development in the two main compartments: oocytes and granulosa cells. We documented the differential expression of 3,015 genes during this phase and described the gene expression dynamic specific to these compartments. We showed that important steps occurred during primary/secondary transition in sheep. We also described the in vivo molecular course of a number of pathways. In oocytes, these pathways documented the chronology of the acquisition of meiotic competence, migration and cellular organization, while in granulosa cells they concerned adhesion, the formation of cytoplasmic projections and steroid synthesis. This study proposes the involvement in this process of several members of the integrin and BMP families. The expression of genes such as Kruppel-like factor 9 (KLF9) and BMP binding endothelial regulator (BMPER) was highlighted for the first time during early follicular development, and their proteins were also predicted to be involved in gene regulation. Finally, we selected a data set of 24 biomarkers that enabled the discrimination of early follicular stages and thus offer a molecular signature of early follicular growth. This set of biomarkers includes known genes such as SPO11 meiotic protein covalently bound to DSB (SPO11), bone morphogenetic protein 15 (BMP15) and WEE1 homolog 2 (S. pombe)(WEE2) which play critical roles in follicular development but other biomarkers are also likely to play significant roles in this process.ConclusionsTo our knowledge, this is the first in vivo spatio-temporal exploration of transcriptomes derived from early follicles in sheep.

Embryonic Poly(A)-Binding Protein Is Required During Early Stages of Mouse Oocyte Development for Chromatin Organization, Transcriptional Silencing, and Meiotic Competence.

During oocyte maturation, fertilization, and early embryo development until zygotic genome activation (ZGA), transcription is suppressed, and gene expression is dependent upon the timely activation of stored mRNAs. Embryonic poly(A)-binding protein (EPAB) is the predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos and is important for regulating translational activation of maternally stored mRNAs. EPAB is critical for early development because Epab(-/-) female mice do not produce mature eggs and are infertile. In this study, we further characterize morphological and molecular aspects of Epab(-/-) oocytes. We demonstrated that Epab(-/-) oocytes are smaller in size, contain peripheral germinal vesicles, and are loosely associated with cumulus cells. The chromatin reorganization of the surrounded nucleolus (SN) configuration and transcriptional silencing that normally occurs during oocyte growth does not occur in Epab(-/-) oocytes. Interestingly, microinjection of Epab mRNA into Epab(-/-) preantral follicle-enclosed oocytes rescues reorganization of chromatin and oocyte maturation to metaphase II. Overall, these results demonstrate an important role for EPAB during oocyte growth and the acquisition of meiotic competence.

Human cumulus-enclosed germinal vesicle oocytes from early antral follicles reveal heterogeneous cellular and molecular features associated with in vitro maturation capacity.

Are oocyte size, chromatin remodelling, transcriptional activity and mitochondrial distribution in human immature oocytes from early antral follicles retrieved for in vitro maturation (IVM) associated with the acquisition of meiotic competence? Oocyte size, chromatin compaction, cessation of RNA synthesis and mitochondria rearrangement around the nucleus are associated with the oocyte's potential to resume meiosis in vitro. Information on oocyte features that confer meiotic competence in human mainly derives from germinal vesicle (GV) oocytes that failed to resume meiosis following an hCG trigger after ovulation induction cycles. Characterization of cumulus-enclosed GV oocytes from small antral follicles prior to IVM provides knowledge on the initial oocyte status and suggests culture requirements in order to promote oocyte competence in vitro. Prospective collection of 107 oocytes immediately after retrieval (before IVM) and of 293 GV oocytes that had failed to resume meiosis (after IVM). Human oocytes were collected from women with polycystic ovary syndrome (PCOS), receiving in total 450 IU of highly purified-hMG for IVM treatment (patients) or who donated oocytes for IVM research (donors). Oocytes at GV-stage were retrieved from follicles <10 mm (range 2-10 mm) diameter, before IVM (oocytes at retrieval) or those that failed to mature after IVM (meiotically incompetent). Oocytes were allocated for either mitochondrial staining, by incubating in mitotracker red and then fixed; or for nascent RNA staining, which was assessed by fluorescent labelling (Click-iT(®) RNA Assay). In every case, oocyte diameter was recorded and chromatin was stained after oocyte fixation. GV-stage oocytes were analysed by confocal laser-scanning microscopy and their characteristics were compared and related to their meiotic competence. Analysis of oocytes at the immature GV-stage revealed that oocytes at retrieval were significantly larger than those that failed to resume meiosis after IVM (112.7 versus 109.6 µm, P < 0.0001). Oocytes assessed at retrieval showed that 50.6% had a condensed chromatin configuration (perinucleolar chromatin rim) and were consistently transcriptionally silent. This rate matched maturation rates in our current in vitro culture system (49%). However, oocytes that had not reinitiated meiosis after 30 h IVM demonstrated, apart of being smaller in diameter, significantly higher rates of dispersed or intermediate chromatin (P = 0.005). Analysis of mitochondrial distribution revealed that many oocytes at retrieval displayed mitochondrial internalization towards the nucleus (12/30) or a perinuclear mitochondrial distribution (6/30). These mitochondrial patterns were observed more rarely in GV incompetent oocytes following 30 h IVM (16/98 and 1/98, respectively). Most of the analyses involved the use of invasive techniques. Hence, despite the fact that these data deliver essential information on the intrinsic oocyte maturational and developmental status, a direct match with embryological outcomes could not be established. The evidence described here can aid in tailoring IVM systems in order to promote completion of nuclear and cytoplasmic maturation of unexpanded cumulus-oocyte complexes. This study was supported by research grants by the Institute for the Promotion of Innovation by Science and Technology in Flanders, project numbers IWT 130327 and 110680; the Fund for Research Flanders, project number FWO G.0343.13, the Belgian Foundation Against Cancer (HOPE project) and COOK Medical. None of the authors has any competing interest to declare.

Cytoplasm replacement following germinal vesicle transfer restores meiotic maturation and spindle assembly in meiotically arrested oocytes

Both the cytoplasmic and nuclear compartments are essential for the acquisition of meiotic competence. This study assessed the role of the cytoplasm in meiosis resumption in meiotically arrested oocytes at the germinal vesicle (GV) stage. Mouse oocytes at GV stage were meiotically arrested with 3-isobutyl-1-methylxanthine (IBMX). GV transfer was performed between IBMX-treated and non-treated (control) mouse oocytes, and between control mouse and human GV oocytes. Extrusion of first polar body (PB) was examined as an indication of nuclear maturation. Meiotic spindle assembly and chromosome alignment were examined by immunostaining. Results indicated that oocytes arrested with IBMX for 24 and 48 h exhibited reduced ability for meiotic maturation and for extruding the first PB when compared with controls (P < 0.01). IBMX-treated oocytes reconstituted with cytoplasm, but not GV, of control oocytes restored the assembly of meiotic spindle and meiotic maturation. Mouse oocytes reconstituted with GV of human oocytes underwent meiosis similar to that observed in mice, but not humans. Additionally, human oocytes reconstituted by mouse GV underwent meiosis similar to that observed in humans, but not mice. These findings suggest that cytoplasm replacement by GV transfer could represent a potential therapeutic option for women who do not produce mature oocytes during IVF.

Androgens promote the acquisition of maturation competence in bovine oocytes.

Recent studies in mice suggest that androgens are important for normal follicle development. However, there have been few reports concerning the action of androgens in the growth of oocytes from large animals. The purpose of this study was to determine the roles of androgens in bovine oocyte growth in vitro. Oocyte-granulosa cell complexes (OGCs) collected from 0.4−0.7 mm early antral follicles were cultured for 14 days with 17β-estradiol (E2) and a non-aromatizable androgen, dihydrotestosterone (DHT). We also examined the ability of an androgen receptor (AR) inhibitor, hydroxyflutamide, to antagonize the effect of androgens on the oocytes. During growth culture, the OGC structures collapsed in the medium with DHT alone, while in the presence of E2, the OGC structures were maintained. In the medium with both androgens and E2, the mean diameter of oocytes was increased from 95 μm to around 120 μm, larger than those grown with E2 alone (115 μm). Also in the maturation culture, oocytes grown with androgens (A4 or DHT) and E2 showed higher percentages of metaphase II oocytes (63% or 69%, respectively) than those grown with E2 alone (32%). Moreover, these maturation rates were decreased by hydroxyflutamide in a dose-dependent manner. Immunostaining showed that ARs were expressed in oocytes and granulosa cells in early antral follicles, and the nuclei of granulosa cells showed intense AR expression. In conclusion, although E2 supports the OGC structure, additional androgens promote oocyte growth and their acquisition of meiotic competence via AR during in vitro growth culture.

280 EFFECTS OF HOT SEASON ON BOVINE OOCYTE QUALITY: HOW TO BYPASS THE POOR OOCYTE QUALITY DURING THIS SEASON?

Many authors attribute the decline of reproductive activity in summer to the heat stress, a multifactorial problem in which hyperthermia affects cellular function in various tissues of the female reproductive tract (Hansen et al. 2001; De Rensis et al. 2003). In particular, the combination of high temperatures and high humidity for a long period causes a reduced blood flow to uterus, oviducts, and ovaries, leading to a rise in the concentration of the degradation products of cellular activity. Therefore, the aim of this work was to elucidate the negative effect of the hot season on bovine oocyte quality and evaluate the influence of different factors on the acquisition of meiotic competence. In particular, meiotic competence of bovine oocytes recovered from animals housed at 44°28′00″ N, 11°26′00″ E during spring (March, 4–13°C) and summer (June, 16–27°C) was evaluated. Likewise, in summer the effect of an antioxidant, myo-inositol, the use of serum replacement (SR), and the use of oocytes recovered from cycling heifers (16–18 months) as compared to cows (&gt;24 months) were tested. A total of 1346 abattoir-derived oocytes, equally divided for different experimental groups (over 6 replicates), were in vitro matured in TCM 199 supplemented with EGF (25 ng mL–1), IGF1 (100 ng mL–1), ITS supplement, pFSH-LH (0.1 IU each), and 10% FBS. Myoinositol was added at a concentration of 0, 15, 30, and 50 mM, while 10% SR was used alternatively to FBS. At the end of maturation period (20–22 h), oocytes were denuded and stained with 10 μg mL–1 of Hoechst 33342 at room temperature in the dark. After 15 min they were mounted on glass slides for evaluation of nuclear status using a Nikon Eclipse E400 microscope equipped with fluorescence filters. Nuclear configurations were classified as (a) germinal vesicle (GV), (b) germinal vesicle breakdown (GVBD), (c) metaphase I (M-I), (d) metaphase II (M-II), and (e) degenerated (DEG). Data are expressed as mean ± s.e.m. and were analysed by ANOVA (IBM SPSS Statistics) considering significance at P &lt; 0.05. Oocyte quality of summer oocytes was significantly lower than spring counterparts as result of a higher rate of DEG (8.2 ± 0.6 v. 0.7 ± 0.6) and GV (5.4 ± 0.3 v. 0.4 ± 0.4, respectively; P &lt; 0.05). Myo-inositol supplementation in IVM medium did not significantly affect either oocyte quality or meiotic competence in the hot season, such as the use of SR. When the oocytes were collected from cycling heifers ovaries during summer, the recovery rate of COC/ovary was significantly higher as compared to cows (4.5 v. 2.0), and a lower rate of DEG (1.8 ± 0.2; 8.2 ± 0.6) and GVBD (0.9 ± 0.6; 6.1 ± 0.3) was found (P &lt; 0.05), even if the rate of GV (22.4 ± 0.1 v. 5.4 ± 0.3) was higher (P &lt; 0.05) compared with cow. In conclusion, the hot season negatively affects oocyte quality, myo-inositol does not affect nuclear maturation, and SR can be used alternatively to FBS. The lower age of oocyte donor positively influenced the number of recoverable oocyte and degeneration rate.

The TRIM-NHL protein LIN-41 and the OMA RNA-binding proteins antagonistically control the prophase-to-metaphase transition and growth of Caenorhabditis elegans oocytes.

In many animals, oocytes enter meiosis early in their development but arrest in meiotic prophase I. Oocyte growth, which occurs during this arrest period, enables the acquisition of meiotic competence and the capacity to produce healthy progeny. Meiotic resumption, or meiotic maturation, involves the transition to metaphase I (M phase) and is regulated by intercellular signaling and cyclin-dependent kinase activation. Premature meiotic maturation would be predicted to diminish fertility as the timing of this event, which normally occurs after oocyte growth is complete, is crucial. In the accompanying article in this issue, we identify the highly conserved TRIM-NHL protein LIN-41 as a translational repressor that copurifies with OMA-1 and OMA-2, RNA-binding proteins redundantly required for normal oocyte growth and meiotic maturation. In this article, we show that LIN-41 enables the production of high-quality oocytes and plays an essential role in controlling and coordinating oocyte growth and meiotic maturation. lin-41 null mutants display a striking defect that is specific to oogenesis: pachytene-stage cells cellularize prematurely and fail to progress to diplotene. Instead, these cells activate CDK-1, enter M phase, assemble spindles, and attempt to segregate chromosomes. Translational derepression of the CDK-1 activator CDC-25.3 appears to contribute to premature M-phase entry in lin-41 mutant oocytes. Genetic and phenotypic analyses indicate that LIN-41 and OMA-1/2 exhibit an antagonistic relationship, and we suggest that translational regulation by these proteins could be important for controlling and coordinating oocyte growth and meiotic maturation.

Acquisition of meiotic competence in porcine secondary follicles following long-term culture

Acquisition of meiotic competence in porcine secondary follicles following long-term culture

Steroid hormones promote bovine oocyte growth and connection with granulosa cells

Many approaches have been investigated for growing oocytes in vitro in mammals. To support oocyte growth in vitro, the culture systems must meet certain conditions for maintaining connections between oocytes and surrounding granulosa cells. The aims of this study were to determine the effects of combinations of 17β-estradiol (E2) and androstenedione (A4) on in vitro growth of bovine oocytes and to determine the number of connections between the oocyte and granulosa cells. Oocyte–granulosa cell complexes (OGCs) collected from early antral follicles (0.4−0.7 mm in diameter) were cultured for 14 days in a medium with different concentrations of E2 and A4, either alone or in combinations. We then assessed the number of transzonal projections (TZPs), which extend from granulosa cells through the zona pellucida to the oolemma. During in vitro growth culture, OGC structures were maintained in the medium with steroid hormones. The mean diameter of oocytes grown in the medium with both E2 and A4 was increased from 95.8 μm to around 120 μm, larger than oocytes grown without steroid hormones (109.9 μm) and similar in size to in vivo fully grown oocytes (119.4 μm) from 4- to 6-mm antral follicles. In subsequent in vitro maturation culture (22 hours), 30% (12 of 40) and 34% (14 of 41) of oocytes grown with E2 or A4 alone, respectively, matured to metaphase II; meanwhile, oocytes grown with a combination of E2 and A4 matured to metaphase II at a high rate (58%, 23 of 40). Growing oocytes isolated from early antral follicles had many uniformly distributed TZPs throughout the zona pellucida. After 14 days of culture, there was a significant decrease in the number of TZPs in oocytes grown without steroid hormones, whereas the number of TZPs was maintained in oocytes grown with steroid hormones. In particular, oocytes grown with E2 alone or with a combination of E2 and A4 had numbers of TZPs similar to oocytes before growth culture. In conclusion, a combination of E2 and A4 maintained the connections between oocytes and granulosa cells during in vitro growth culture of bovine oocytes for 14 days, resulting in the complete oocyte growth and the acquisition of meiotic competence in more than half the oocytes.

Cytoplasmic Anchoring of cAMP-Dependent Protein Kinase (PKA) by A-Kinase Anchor Proteins (AKAPs) Is Required for Meiotic Arrest of Porcine Full-Grown and Growing Oocytes1

Mammalian growing oocytes (GOs) lack the ability to resume meiosis, although the molecular mechanism of this limitation is not fully understood. We previously hypothesized that the meiotic incompetence of porcine GOs was attributed to complex spatial-temporal regulation of cAMP-dependent protein kinase (PKA) by A-kinase anchor proteins (AKAPs), but found that AKAP1 is not involved in the meiotic incompetence of porcine GOs. In the present study, we cloned porcine cDNAs of AKAP5 and AKAP7alpha, and found that inhibiting the expression of these AKAPs induced PKA translocation into the nucleus and promoted meiotic resumption of porcine GOs without affecting the total PKA activity of GOs, whereas overexpressing these AKAPs had no effect. Because AKAPs regulate PKA localization through binding with regulatory subunits of PKA (PKA-Rs), PKA-R binding with AKAPs was inhibited by AKAP-binding inhibition peptides or PKA-R expression inhibition by antisense RNAs. We found that the expression inhibition and binding inhibition of PRKAR1A, an isoform of mammalian PKA-R, promoted meiotic resumption of porcine GOs, whereas these inhibitions of PRKAR2A, another PKA-R isoform, had no effect. In contrast, the expression inhibition and binding inhibition of PRKAR2A had higher effects than those of PRKAR1A on meiotic resumption of porcine full-grown oocytes. These results suggest that cytoplasmic anchoring of PKA by AKAPs is required for meiotic arrest of oocytes and that the PKA-R isoform working for the maintenance of meiotic arrest changed from PRKAR1A to PRKAR2A during the acquisition of meiotic competence.

Calcineurin expression and localisation during porcine oocyte growth and meiotic maturation

The processes of oocyte growth, acquisition of meiotic competence and meiotic maturation are regulated by a large number of molecules. One of them could be calcineurin consisting of catalytic subunit A (Aα, Aβ, Aγ isoforms) and regulatory subunit B (B1, B2 isoforms). Calcineurin is involved in the meiotic maturation of oocytes in invertebrates or in lower vertebrates. In the mammalian oocytes, the possible role of calcineurin in the regulation of oocyte meiosis has not been clarified to date. In this study, to investigate the role of calcineurin during porcine oocyte growth, acquisition of meiotic competence and meiotic maturation, we analysed the expression and localisation of calcineurin subunits and the mRNA expression of calcineurin isoforms. Calcineurin was expressed in growing porcine oocytes, in fully grown oocytes and during their in vitro meiotic maturation. We found both subunits of calcineurin. Calcineurin A and calcineurin B were localised mainly in the cortex in all porcine oocytes. The changes in the intracellular localisation of separate calcineurin subunits during meiotic maturation were determined. We detected mRNA for calcineurin isoforms Aβ, Aγ, B2 in oocytes and mRNA for calcineurin isoforms Aβ, Aγ, B1, and B2 in cumular cells. To our knowledge, this is the first confirmation of calcineurin presence in porcine oocytes.

Two-Cell Embryo Developmental Block Is Due to Lack of Cytoplasmic Lattices in Mouse Antral NSN Oocytes.

In most mammals, the antral compartment of the ovary contains two different kinds of oocytes, SN and NSN (Surrounded Nucleolus and Not Surrounded Nucleolus), whose main differentiating characteristic lies in their acquisition of developmental competence: still inexplicably only the SN (70% of the antral oocytes population) are able to develop to the blastocyst stage while the NSN arrest at the two-cell stage. Taking advantage of proteomics and microscopy techniques, we analyzed both SN and NSN oocytes, showing for the first time that NSN-derived embryo inability to develop to the blastocyst stage is due to the under-regulation of some maternal proteins together with a lack of cytoplasmic lattices (CPLs). Additionally, we analyzed the lipid droplets content, showing that NSN oocyte cytoplasm contains a significantly higher amount of lipid droplets than SN. The proteomic profile of 600 antral oocytes (300 SN and 300 NSN) showed up-regulation of 6 proteins in SN and 23 in NSN; in particular, when compared to SN oocytes, NSN showed a significant down-regulation of the proteins MATER and FILIA. MATER is the main constituent of the Subcortical Maternal Complex and it is considered one of the factors responsible for the acquisition of meiotic competence. In fact, it is already known that Matertm/tm oocytes, without any distinction based on chromatin organization, do not have cytoplasmic lattices and are not able to progress beyond the two-cell stage. Based on our proteomic results, we speculated that the Matertm/tm antral population should be composed mostly of NSN oocytes. To test this hypothesis, we analyzed Matertm/tm antral oocytes showing that 84% of these oocytes are of the NSN type. To confirm this data, we performed Transmission Electron Microscopy analysis on SN and NSN oocytes, revealing that NSN contain no or very few cytoplasmic lattices as compared to SN. For this reason, the absence of CPLs can be considered a NSN-specific molecular morphology feature. MATER has also been correlated with the anti-apoptotic pathway, so the accumulation of lipid droplets in Mater null oocytes could be related to apoptotic activity. Through the morphometric analysis of lipid droplet content, we demonstrated that NSN oocytes contain a significantly higher amount of lipid droplets than SN. This is further evidence of the role played by CPLs in the resumption of meiosis and of lipid droplets being good candidate markers for oocyte developmental competence. Our results provide the first molecular evidence that accounts for NSN-derived embryo's inability to progress beyond the two-cell stage and, thus, for some of the naturally occurring pre-implantation losses in mammals. These data will also give basic knowledge about the function of the miniature, wonderfully organized laboratory of molecular biology that is the oocyte.