Regulation Of Oocyte Maturation Research Articles

Fibronectin 1 supports oocyte in vitro maturation in pigs

Oocyte in vitro maturation (IVM) based on the follicular fluid (FF) environment can exploit untapped resources, however, what FF factors regulate oocyte maturation remains unclear. This work demonstrated that serum and FF significantly promoted oocyte polar body extrusion (PBE) and subsequent embryo development, and FF was especially effective. Fibronectin 1 (FN1) was predicted as one potential candidate to regulate oocyte maturation by proteomics. FN1 transcription obviously decreased, and the protein expression significantly increased and migrated to plasma membrane or even outside during oocyte IVM. Treatment with 10 ng/mL FN1 significantly improved oocyte PBE rate. FN1 significantly upregulated the percentage of regular spindle morphology, downregulated the γ-H2AX level, decreased the levels of ROS and apoptosis, and increased GSH and mitochondrion contents by ameliorating the expression of corresponding genes. Moreover, FN1 significantly increased the p-PI3K level to enhance the activation of PI3K signaling pathway. In conclusion, this study discovers and confirms that FN1 is one factor in FF that significantly enhances oocyte maturation, and the underlying mechanism is that FN1 ameliorates oocyte nuclear and cytoplasmic maturation by promoting the activation of PI3K signaling pathway.

Oocyte and cumulus cell cooperativity and metabolic plasticity under the direction of oocyte paracrine factors.

Mammalian oocytes develop and mature in a mutually dependent relationship with surrounding cumulus cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble paracrine oocyte-secreted factors (OSFs). We characterized the molecular mechanisms by which two model OSFs, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Exposure to these OSFs during mouse oocyte maturation in vitro altered the proteomic and multispectral autofluorescence profiles of both the oocyte and cumulus cells. In oocytes, cumulin significantly upregulated proteins involved in nuclear function. In cumulus cells, both OSFs elicited marked upregulation of a variety of metabolic processes (mostly anabolic), including lipid, nucleotide, and carbohydrate metabolism, whereas mitochondrial metabolic processes were downregulated. The mitochondrial changes were validated by functional assays confirming altered mitochondrial morphology, respiration, and content while maintaining ATP homeostasis. Collectively, these data demonstrate that cumulin and BMP15 remodel cumulus cell metabolism, instructing them to upregulate their anabolic metabolic processes, while routine cellular functions are minimized in the oocyte during maturation, in preparation for ensuing embryonic development.NEW & NOTEWORTHY Oocyte-secreted factors (OSFs) promote oocyte and cumulus cell cooperativity by altering the molecular composition of both cell types. OSFs downregulate protein catabolic processes and upregulate processes associated with DNA binding, translation, and ribosome assembly in oocytes. In cumulus cells, OSFs alter mitochondrial number, morphology, and function, and enhance metabolic plasticity by upregulating anabolic pathways. Hence, the oocyte via OSFs, instructs cumulus cells to increase metabolic processes on its behalf, thereby subduing oocyte metabolism.

Global crotonylome identifies EP300-regulated ANXA2 crotonylation in cumulus cells as a regulator of oocyte maturation

Lysine crotonylation (Kcr), a newly discovered post-translational modification, played a crucial role in physiology and disease progression. However, the roles of crotonylation in oocyte meiotic resumption remain elusive. As abnormal cumulus cell development will cause oocyte maturation arrest and female infertility, we report that cumulus cells surrounding human meiotic arrested oocytes showed significantly lower crotonylation, which was associated with decreased EP300 expression and blocked cumulus cell expansion. In cultured human cumulus cells, exogenous crotonylation or EP300 activator promoted cell proliferation and reduced cell apoptosis, whereas EP300 knockdown induced the opposite effect. Transcriptome profiling analysis in human cumulus cells indicated that functions of crotonylation were associated with activation of epidermal growth factor receptor (EGFR) pathway. Importantly, we characterized the Kcr proteomics landscape in cumulus cells by LC-MS/MS analysis, and identified that annexin A2 (ANXA2) was crotonylated in cumulus cells in an EP300-dependent manner. Crotonylation of ANXA2 enhanced the ANXA2-EGFR binding, and then activated the EGFR pathway to affect cumulus cell proliferation and apoptosis. Using mouse oocytes IVM model and EP300 knockout mice, we further confirmed that crotonylation alteration in cumulus cells affected the oocyte maturation. Together, our results indicated that EP300-mediated crotonylation is important for cumulus cells functions and oocyte maturation.

Transcriptome analysis of Schizothorax oconnori (Cypriniformes: Cyprinidae) oocytes: The role of K+ in promoting yolk globule fusion and regulating oocyte maturation.

Schizothorax oconnori (S. oconnori) is an economically important fish in Tibet. Oocyte maturation is a physiological process that is of great significance to reproduction and seed production in S. oconnori, yet little is currently known regarding the molecular mechanisms of oocyte development in this species. To identify candidate genes involved in reproduction of female fish, a combination of PacBio and Illumina HiSeq technologies was employed to provide deep coverage of the oocyte transcriptome. Transcriptome analysis revealed several candidate genes that are potentially involved in the regulation of oocyte maturation in S. oconnori, including GIRK1, CHRM3, NPY2R, GABRA3, GnRH3, mGluR1α, GPER1, GDF9, HSP90, and ESR2. Genes that are significantly expressed during oocyte maturation mainly contribute to the GPCR signaling pathway and the estrogen signaling pathway. Neurotransmitter (Ach, NPY, and GABA) and peptide hormone (GnRH3) binding to G protein-coupled receptors (GPCRs) frees G-protein βγ subunits to interact with the G protein-gated inward rectifier K+ channel 1 (GIRK1). This process helps release K+ from granulosa cells to maturing oocytes, allowing yolk globule fusion. This mechanism may play an important role in oocyte maturation in S. oconnori. In conclusion, this study provides a valuable basis for deciphering the reproductive system in S. oconnori during the oocyte maturation process.

The ERβ-cAMP signaling pathway regulates estradiol-induced ovine oocyte meiotic arrest

Although 17β-estradiol (E2) and its receptors (ERs) are reported to play important roles in regulating oocyte maturation, the specific mechanism remains unclear. First, we performed immunohistochemistry analyses to determine the expression of the ERα and ERβ proteins in ovine ovarian tissue. Second, E2 (0.5 ng/mL and 1 μg/mL) were added to pre-IVM medium for 0 h, 1 h and 2 h. The effects of E2 (0.5 ng/mL and 1 μg/mL) on cyclic adenosine monophosphate (cAMP) level in cumulus-oocyte complexes (COCs) and on oocyte meiotic progression were evaluated by ELISA and DAPI staining respectively. Third, the effects of E2 on the gene and protein expression of ERα and ERβ in COCs were investigated by Western blotting and real-time PCR. Afterward, ERβ and cAMP regulators were added to the 2-h pretreatment medium with or without E2 (0.5 ng/mL) to explore the possible interactions among E2, cAMP and ERβ. The results showed that both ERα and ERβ proteins were expressed in ovine cumulus layers and oocytes. E2 significantly increased intra-COC cAMP levels, maintained oocyte meiotic arrest, and promoted ERβ transcript and protein expression. E2 treatment increased the cAMP concentration, which was enhanced by ERβ agonist treatment and remarkably attenuated by ERβ inhibitor treatment. Forskolin plus IBMX treatment increased ERβ protein expression in COCs (P < 0.05), and this was attenuated by Rp-cAMP treatment. In conclusion, E2 (0.5 ng/mL) increased intra-COC cAMP levels by promoting ERβ expression, thereby maintaining oocyte meiotic arrest. cAMP in COCs has a positive feedback effect on ERβ expression, which provides a novel explanation for the positive role of E2 in regulating ovine follicle development and oocyte maturation.

The role of proliferative, pro-, and anti-inflammatory endothelial factors in the regulation of oocyte maturation in the treatment of infertility

The role of proliferative, pro-, and anti-inflammatory endothelial factors in the regulation of oocyte maturation in the treatment of infertility

LSM14B coordinates protein component expression in the P-body and controls oocyte maturation

The generation of mature and healthy oocytes is the most critical event in the entire female reproductive process, and the mechanisms regulating this process remain to be studied. Here, we demonstrate that Smith-like (LSM) family member 14B (LSM14B) regulates oocyte maturation, and the loss of LSM14B in mouse ovaries leads to abnormal oocyte MII arrest and female infertility. Next, we find the aberrant transcriptional activation, indicated by abnormal non-surrounded nucleolus and surrounded nucleolus oocyte proportions, and abnormal chromosome assembly and segregation in Lsm14b-deficient mouse oocytes. The global transcriptome analysis suggests that many transcripts involved in cytoplasmic processing body (P-body) function are altered in Lsm14b-deficient mouse oocytes. Deletion of Lsm14b results in the expression and/or localization changes of P-body components (such as LSM14A, DCP1A, and 4E-T). Notably, DDX6, a key component of the P-body, is downregulated and accumulates in the nuclei in Lsm14b-deficient mouse oocytes. Taken together, our data suggest that LSM14B links mouse oocyte maturation to female fertility through the regulation of the P-body.

Effects of microcystin-LR on mammalian ovaries

The ovaries play critical roles in regulating oocyte maturation and sex steroid hormone production and thus are critical for female reproduction. Ovarian function relies on hormone receptors and signaling pathways, making the ovaries potential targets for environmental factors, such as microcystins (MCs). MCs are a diverse group of cyanobacterial toxins generally found in eutrophic water or algal blooms. Here, we review relevant research on the associations between MC exposure and ovarian dysfunction, including their effects on ovarian morphology, folliculogenesis, steroid production, oxidative stress, endoplasmic reticulum stress, apoptosis, autophagy, and fertility. This review covers the most recent in vitro and in vivo studies in mammals. We also discuss important gaps in the literature. Overall, current evidence indicates that MC exposure causes impairments in ovarian function, but further studies are needed to elucidate the mechanisms through which MCs affect ovarian function and other female endocrine functions.

Serotonin Transporter Activity in Mouse Oocytes Is a Positive Indicator of Follicular Growth and Oocyte Maturity.

Serotonin (5-hydroxytryptamine, 5-HT) is known to be a regulator of oocyte maturation in a large number of animal species. In maturing mammalian oocytes, the accumulation of exogenous, maternal serotonin occurs due to the activity of the membrane transporter SERT. In this work, we investigated how SERT activity in oocytes correlates with indicators of follicular selection and oocyte maturity. An immunohistochemical study showed that the difference in the 5-HT intake activity in oocytes does not correlate with the marker of apoptosis in follicular cells, but positively correlates with markers of follicular growth, such as granulosa proliferation and follicle size. Functional analysis of oocytes at different stages of maturation showed that the expression and activity of SERT increases with oocyte maturation. An in vivo experiment on administration of the selective serotonin reuptake inhibitor fluoxetine (20 mg/kg) for 7 days showed a significant decrease in the content of serotonin in both growing GV-oocytes and ovulated mature MII-oocytes. The data obtained clearly indicate that the mechanism of specific membrane transport of serotonin normally ensures the accumulation of serotonin in maturing oocytes, and can be considered as a promising positive marker of their mature status.

Identification and Characterization of C-Mos in Pearl Mussel Hyriopsis cumingii and Its Role in Gonadal Development

C-Mos, a proto-oncogene, regulates oocyte maturation by activating the classical MAPK pathway in cells. To examine the function of C-Mos in Hyriopsis cumingii, C-Mos was identified in this study. The full-length cDNA of C-Mos was 2213 bp, including 144 bp in the 5′ UTR, 923 bp in 3′ the UTR, and 1146 bp in the open reading frame (ORF) region. During early gonad development, the expression of C-Mos from 4 to 6 months of age in H. cumingii was significantly higher than that in other months, with the highest expression in 6-month-old H. cumingii, suggesting that C-Mos may be involved in early gonadal development in H. cumingii. Clear hybridization signals were found by in situ hybridization in the oocytes, oocyte nucleus and oogonium, and a small number of hybridization signals were found in the follicular wall of the male gonads. In addition, the C-Mos RNA interference (RNAi) assay results showed that the knockdown of C-Mos caused a down-regulation of ERK and P90rsk. In summary, these results indicate that C-Mos has a crucial part to play in gonadal development in H. cumingii.

Progesterone and Androstenedione Are Important Follicular Fluid Factors Regulating Porcine Oocyte Maturation Quality.

Oocytes matured in vitro are useful for assisted human and farm animal reproduction. However, the quality of in vitro matured oocytes is usually lower than that of in vivo matured oocytes, possibly due to the absence of some important signal regulators in vitro. In this study, untargeted metabolomics was used to detect the changes in the metabolites in the follicular fluid (FF) during in vivo pig oocyte maturation and in the culture medium during in vitro maturation. Our results showed that the total metabolite changing profile of the in vivo FF was different from that of the in vitro maturation medium, but the levels of 23 differentially expressed metabolites (DEMs) changed by following the same trend during both in vivo and in vitro pig oocyte maturation. These 23 metabolites may be important regulators of porcine oocyte maturation. We found that progesterone and androstenedione, two factors in the ovarian steroidogenesis pathway enriched from the DEMs, were upregulated in the FF during in vivo pig oocyte maturation. The levels of these two factors were 31 and 20 fold, respectively, and they were higher in the FF than in the culture medium at the oocyte mature stage. The supplementation of progesterone and androstenedione during in vitro maturation significantly improved the pig oocyte maturation rate and subsequent embryo developmental competence. Our finding suggests that a metabolic abnormality during in vitro pig oocyte maturation affects the quality of the matured oocytes. This study identified some important metabolites that regulate oocyte maturation and their developmental potential, which will be helpful to improve assisted animal and human reproduction.

Selective Destabilization of Transcripts by mRNA Decapping Regulates Oocyte Maturation and Innate Immunity Gene Expression during Ageing in C. elegans.

Removal of the 5' cap structure of RNAs (termed decapping) is a pivotal event in the life of cytoplasmic mRNAs mainly catalyzed by a conserved holoenzyme, composed of the catalytic subunit DCP2 and its essential cofactor DCP1. While decapping was initially considered merely a step in the general 5'-3' mRNA decay, recent data suggest a great degree of selectivity that plays an active role in the post-transcriptional control of gene expression, and regulates multiple biological functions. Studies in Caenorhabditis elegans have shown that old age is accompanied by the accumulation of decapping factors in cytoplasmic RNA granules, and loss of decapping activity shortens the lifespan. However, the link between decapping and ageing remains elusive. Here, we present a comparative microarray study that was aimed to uncover the differences in the transcriptome of mid-aged dcap-1/DCP1 mutant and wild-type nematodes. Our data indicate that DCAP-1 mediates the silencing of spermatogenic genes during late oogenesis, and suppresses the aberrant uprise of immunity gene expression during ageing. The latter is achieved by destabilizing the mRNA that encodes the transcription factor PQM-1 and impairing its nuclear translocation. Failure to exert decapping-mediated control on PQM-1 has a negative impact on the lifespan, but mitigates the toxic effects of polyglutamine expression that are involved in human disease.

Histology and metabonomics reveal the toxic effects of kresoxim-methyl on adult zebrafish

Studies have shown that kresoxim-methyl (KM) and other strobilurin fungicides have toxic effects on aquatic organisms. However, the potential deleterious effects of kresoxim-methyl (KM) on adult zebrafish regarding the ecological risk of environmental concentration remain unclear. Here, the histology and untargeted metabonomics was used to investigate the adverse effect on female zebrafish after exposure to KM at environmental concentration, aquatic life benchmark and one-half LC50 of adult zebrafish. Results demonstrated KM affected zebrafish liver, ovary and intestine development, blurred the boundary between hepatocytes or caused hepatic vacuoles, increased the percentage of perinucleolar oocyte and cortical alveolus oocyte, decreased intestinal goblet cells and disturbed villus and wall integrity after 21 d exposure. Metabonomics showed different concentrations of KM simultaneously influenced the metabolites annotated to vitamin digestion and absorption, serotonergic synapse, retinol metabolism, ovarian steroidogenesis and arachidonic acid (AA) metabolism in zebrafish liver. Results showed the decreased triglyceride and cholesterol levels, as well as the metabolic alterations in amino acid, lipid, vitamin and retinol metabolism caused by KM, might disturb the energy supply for normal liver development and oocyte maturation. In addition, KM altered the transcription of Tdo2a, Tdo2b, Ido1, Cxcl8b, Cyp7a, Cyp11a, Cyp11b, Cyp17a, Cyp19a, Hsd3β, Hsd17β, Pla2, Ptgs2a and Ptgs2b, the level of TG, TC, MDA, IFN, IL6 and Ca2+, and the activity of CAT, SOD Ca2+-ATPase in zebrafish liver. Moreover, cytoscape analysis suggested the disturbed AA metabolism caused by KM, might interconnect multiple metabolic pathways to share implicated function in the regulation of oocyte maturation and immune response. Current study brought us closer to an incremental understanding of the toxic mechanism of KM on adult zebrafish, indicated there was crosstalk among different regulatory pathways to regulate the metabolic disorders and biologically hazardous effects induced by KM.

HDAC1 in the Ovarian Granulosa Cells of Tan Sheep Improves Cumulus Cell Expansion and Oocyte Maturation Independently of the EGF-like Growth Factors.

Simple SummaryThis study aimed to explore the possible role of histone deacetylase 1 (HDAC1), an epigenetic modifying enzyme, in the improvement of oocyte maturation recovered from the Tan sheep of China. We supplemented a specific inhibitor of HDAC1 to in vitro-cultured cumulus oocyte complexes (COCs). The results showed that the cumulus cell expansion and oocyte maturation ratio were impaired, while the production of the epidermal growth factor (EGF) was only slightly changed, despite the fact that the pan-acetylation levels of the histones were significantly elevated. This study implies that HDAC1 may participate in the maturation of oocytes in Tan sheep independently of the classic gonadotrophin-induction pathway.Previous studies have shown that some of the histone deacetylases (HDACs) play diverse roles in the regulation of ovarian somatic cell development, oocyte maturation and early embryonic development in different species including sheep. This study aimed to clarify whether HDAC1 also played pivotal roles in regulating oocyte maturation in Tan sheep. The results showed that HDAC1 was expressed in the nuclei of both the granulosa cells and oocytes of the growing follicles in the Tan sheep’s ovaries. However, the level of HDAC1 was unaffected by luteinizing hormone (LH) induction in cultured granulosa cells. Meanwhile, the specific inhibition of HDAC1 using pyroxamide did not induce significant changes in the expression levels of EGF-like growth factors in vitro, whereas both the cumulus expansion and oocyte maturation of the cultured cumulus oocyte complexes (COCs) were significantly inhibited by pyroxamide. Additionally, the numbers of histone acetylation sites (H4K5, H4K12, H3K14 and H3K9) in ovarian granulosa cells were significantly increased. In conclusion, a constant expression of HDAC1 in the growing follicles of Tan sheep may be pivotal for supporting oocyte growth and maturation, although its action may not be closely correlated with LH induction, nor does it directly affect the expression of the EGF-like factors. Our study implies that there may exist diverse functions of the respective HDACs in modulating female reproduction in sheep.

The Science of IVM

Oocyte in vitro maturation (IVM) makes use of oocytes from patients that have received minimal or no gonadotrophin stimulation. Whilst this brings many advantages to patients, this typically means oocytes are collected from small-medium sized (4-12 mm) antral follicles. These oocytes are under-developed, and yet removal of these from the follicle and culture in vitro leads to spontaneous oocyte meiotic maturation, without the benefit of the physiological signals that naturally induce oocyte maturation at ovulation. Using animals models, over the past decade seminal advances have been made in our understanding of the fundamental mechanisms regulating oocyte maturation in vivo. Most IVM systems, as practised clinically today, typically do not recapitulate these key cellular processes, possibly accounting for the lower efficiency of IVM compared to IVF. A key objective of modern approaches to IVM is to restore in vitro, as far as possible, the natural processes that occur during oocyte maturation in vivo. One strategy to achieve this in IVM is to: 1) prevent spontaneous meiotic resumption at oocyte collection using phosphodiesterase inhibitors, then 2) artificially maintain or elevate cumulus-oocyte complex (COC) cAMP levels, and finally to 3) induce oocyte meiotic resumption using EGF-like peptides. This typically requires the use of biphasic or 2-step IVM systems. One such biphasic IVM system is called capacitation-IVM (CAPA-IVM), as the oocyte is “capacitated” for development in vitro. CAPA-IVM uses the follicle’s natural oocyte meiotic inhibitor, c-type natriuretic peptide (CNP), in the pre-IVM phase, and amphiregulin as the oocyte meiotic inducer in the second IVM phase. Such biphasic-IVM systems typically lead to subsequent improvements in embryo yield compared to standard IVM, and indeed this is the case for CAPA-IVM. Several pilot RCTs and a large RCT of CAPA-IVM vs conventional IVF have been completed, and CAPA-IVM is now practiced in a few centres globally and is commencing in Sydney. The development and clinical application of modern IVM systems, built on decades of animal scientific research, is a bench-to-bedside success story of biomedical research. IVM is now a viable minimally invasive procedure for the treatment of infertility and for fertility preservation in female cancer patients.

Histone Methyltransferase SETD2 Is Required for Porcine Early Embryonic Development.

Simple SummaryNormal early embryonic development is important for ensuring sow fertility. Low quality of in vitro production embryos severely limits extensive application of porcine embryo engineering technologies in animal agriculture and the biomedicine field. Histone H3K36 methyltransferase SETD2 reportedly regulates oocyte maturation and preimplantation embryonic development in mice. However, the specific substrate and function of SETD2 in porcine early embryonic development remains unclear. Here, we show that SETD2 preferentially catalyzes H3K36me3 in porcine early embryos. SETD2 knockdown severely impeded blastocyst cavitation and perturbed normal allocation of inner cell mass and trophectoderm. SETD2 knockdown caused the apoptosis of cells within blastocysts. Therefore, SETD2 is essential for porcine early embryonic development. These findings provide a better understanding of porcine early embryonic development and lay a potential basis for improving the quality of porcine in vitro production embryos.SET domain-containing 2 (SETD2) is a methyltransferase that can catalyze the di- and tri-methylation of lysine 36 on histone H3 (H3K36me2/me3). SETD2 frequently mediates H3K36me3 modification to regulate both oocyte maturation and preimplantation embryonic development in mice. However, the specific substrate and function of SETD2 in porcine early embryonic development are still unclear. In this study, SETD2 preferentially catalyzed H3K36me3 to regulate porcine early embryonic development. SETD2 mRNA is dynamically expressed during early embryonic development. Functional studies using an RNA interference (RNAi) approach revealed that the expression levels of SETD2 mRNA were effectively knocked down by siRNA microinjection. Immunofluorescence analysis indicated that SETD2 knockdown (KD) did not affect H3K36me2 modification but significantly reduced H3K36me3 levels, suggesting a preferential H3K36me3 recognition of SETD2 in porcine embryos. Furthermore, SETD2 KD significantly reduced blastocyst rate and disrupted allocation between inner cell mass (ICM) and trophectoderm (TE) lineage. The expression levels of key genes important for specification of the first two lineages apparently decreased in SETD2 KD blastocysts. SETD2 KD markedly increased the apoptotic percentage of cells within embryos and altered the expression of pro- and anti-apoptotic genes. Therefore, our data indicate that SETD2 is essential for porcine early embryonic development.

MicroRNA21 inhibition affects porcine oocyte maturation and alters protein expression critical for metabolic pathway function.

MicroRNA21 (MIR21) abundance in porcine oocytes and cumulus cells increases during in vitro maturation. The mechanism by which MIR21 regulates oocyte maturation and the effect on the developmental competence of subsequent embryos remains unclear. The objective of this study was to assess the function of MIR21 during porcine oocyte maturation and its effect on embryonic development. Treatment with peptide nucleic acid MIR21 inhibitor (MIR21-PNA), designed to specifically bind to and prevent MIR21 activity during in vitro oocyte maturation, decreased cumulus cell expansion, and the oocyte ability to achieve metaphase II maturation stage when compared to control groups. Following parthenogenetic activation, the cleavage rate at 48 h in the MIR21-PNA group was decreased (p ≤ 0.03) relative to the control groups. Additionally, liquid chromatography-mass spectrometry (LC-MS/MS) of oocyte and cumulus cell total protein following MIR21-PNA treatment during in vitro maturation identified changes in signaling pathways with primary involvement of glucose metabolism (GM) pathways. Furthermore, there was no difference (p = 0.21) in oocyte maturation of control and MIR21-PNA treated oocytes when cultured in pyruvate lacking medium. Finally, MIR21-PNA treatment decreased (p = 0.04) glutathione and increased (p = 0.07) reactive oxygen species production in the oocyte. These data suggest that MIR21 influences porcine oocyte maturation by regulating GM pathways in the cumulus-oocyte complex.

The role of Kisspeptin signaling in Oocyte maturation.

Kisspeptins (KPs) secreted from the hypothalamic KP neurons act on KP receptors (KPRs) in gonadotropin (GPN) releasing hormone (GnRH) neurons to produce GnRH. GnRH acts on pituitary gonadotrophs to induce secretion of GPNs, namely follicle stimulating hormone (FSH) and luteinizing hormone (LH), which are essential for ovarian follicle development, oocyte maturation and ovulation. Thus, hypothalamic KPs regulate oocyte maturation indirectly through GPNs. KPs and KPRs are also expressed in the ovarian follicles across species. Recent studies demonstrated that intraovarian KPs also act directly on the KPRs expressed in oocytes to promote oocyte maturation and ovulation. In this review article, we have summarized published reports on the role of hypothalamic and ovarian KP-signaling in oocyte maturation. Gonadal steroid hormones regulate KP secretion from hypothalamic KP neurons, which in turn induces GPN secretion from the hypothalamic-pituitary (HP) axis. On the other hand, GPNs secreted from the HP axis act on the granulosa cells (GCs) and upregulate the expression of ovarian KPs. While KPs are expressed predominantly in the GCs, the KPRs are in the oocytes. Expression of KPs in the ovaries increases with the progression of the estrous cycle and peaks during the preovulatory GPN surge. Intrafollicular KP levels in the ovaries rise with the advancement of developmental stages. Moreover, loss of KPRs in oocytes in mice leads to failure of oocyte maturation and ovulation similar to that of premature ovarian insufficiency (POI). These findings suggest that GC-derived KPs may act on the KPRs in oocytes during their preovulatory maturation. In addition to the intraovarian role of KP-signaling in oocyte maturation, in vivo, a direct role of KP has been identified during in vitro maturation of sheep, porcine, and rat oocytes. KP-stimulation of rat oocytes, in vitro, resulted in Ca2+ release and activation of the mitogen-activated protein kinase, extracellular signal-regulated kinase 1 and 2. In vitro treatment of rat or porcine oocytes with KPs upregulated messenger RNA levels of the factors that favor oocyte maturation. In clinical trials, human KP-54 has also been administered successfully to patients undergoing assisted reproductive technologies (ARTs) for increasing oocyte maturation. Exogenous KPs can induce GPN secretion from hypothalamus; however, the possibility of direct KP action on the oocytes cannot be excluded. Understanding the direct in vivo and in vitro roles of KP-signaling in oocyte maturation will help in developing novel KP-based ARTs.

Regulation of oocyte maturation: Role of conserved ERK signaling.

During oogenesis, oocytes arrest at meiotic prophase I to acquire competencies for resuming meiosis, fertilization, and early embryonic development. Following this arrested period, oocytes resume meiosis in response to species-specific hormones, a process known as oocyte maturation, that precedes ovulation and fertilization. Involvement of endocrine and autocrine/paracrine factors and signaling events during maintenance of prophase I arrest, and resumption of meiosis is an area of active research. Studies in vertebrate and invertebrate model organisms have delineated the molecular determinants and signaling pathways that regulate oocyte maturation. Cell cycle regulators, such as cyclin-dependent kinase (CDK1), polo-like kinase (PLK1), Wee1/Myt1 kinase, and the phosphatase CDC25 play conserved roles during meiotic resumption. Extracellular signal-regulated kinase (ERK), on the other hand, while activated during oocyte maturation in all species, regulates both species-specific, as well as conserved events among different organisms. In this review, we synthesize the general signaling mechanisms and focus on conserved and distinct functions of ERK signaling pathway during oocyte maturation in mammals, non-mammalian vertebrates, and invertebrates such as Drosophila and Caenorhabditis elegans.

NAT10 Maintains OGA mRNA Stability Through ac4C Modification in Regulating Oocyte Maturation.

In vitro maturation (IVM) refers to the process of developing immature oocytes into the mature in vitro under the microenvironment analogous to follicle fluid. It is an important technique for patients with polycystic ovary syndrome and, especially, those young patients with the need of fertility preservation. However, as the mechanisms of oocyte maturation have not been fully understood yet, the cultivation efficiency of IVM is not satisfactory. It was confirmed in our previous study that oocyte maturation was impaired after N-acetyltransferase 10 (NAT10) knockdown (KD). In the present study, we further explored the transcriptome alteration of NAT10-depleted oocytes and found that O-GlcNAcase(OGA) was an important target gene for NAT10-mediated ac4C modification in oocyte maturation. NAT10 might regulate OGA stability and expression by suppressing its degradation. To find out whether the influence of NAT10-mediated ac4C on oocyte maturation was mediated by OGA, we further explored the role of OGA in IVM. After knocking down OGA of oocytes, oocyte maturation was inhibited. In addition, as oocytes matured, OGA expression increased and, conversely, O-linked N-acetylglucosamine (O-GlcNAc) level decreased. On the basis of NAT10 KD transcriptome and OGA KD transcriptome data, NAT10-mediated ac4C modification of OGA might play a role through G protein–coupled receptors, molecular transduction, nucleosome DNA binding, and other mechanisms in oocyte maturation. Rsph6a, Gm7788, Gm41780, Trpc7, Gm29036, and Gm47144 were potential downstream genes. In conclusion, NAT10 maintained the stability of OGA transcript by ac4C modification on it, thus positively regulating IVM. Moreover, our study revealed the regulation mechanisms of oocytes maturation and provided reference for improving IVM outcomes. At the same time, the interaction between mRNA ac4C modification and protein O-GlcNAc modification was found for the first time, which enriched the regulation network of oocyte maturation.