The switch from cAMP-independent to cAMP-dependent arrest of meiotic prophase is associated with coordinated GPR3 and CDK1 expression in mouse oocytes

miR-155-5p improves oocyte maturation in porcine cumulus cells through connexin 43-mediated regulation of MPF activity

In this study, we aimed to investigate the effect of the expression of miR-155-5p and its target genes on oocyte maturation. We analyzed the expression of miR-155-5p and its target genes in cumulus cells and oocytes using quantitative real-time reverse-transcription polymerase chain reaction. Using carboxyfluorescein, porcine cumulus cells were transfected with mimics and inhibitors of ssc-miR-155-5p to induce in vitro maturation, and subsequently, cumulus expansion, oocyte maturation, and cleavage rate were measured. We found that miR-155-5p expression in cumulus cells at the metaphase II stage was significantly higher than that at the germinal vesicle (GV) stage, whereas Cx43 expression was significantly lower than that at the GV stage (P < 0.05). Compared with those in the negative control group, the cumulus diffusion area of cumulus oocyte complexes; oocyte maturation rate; cleavage rate; HAS2, PTGS2, CD44, PTX3, and TNFAIP6 expression in cumulus cells; and GDF9, BMP15, CyclinB1, and CDK1 expression in oocytes were significantly increased in the miR-155-5p mimics group (P < 0.05), whereas the mRNA and protein expression of CX43 were significantly decreased (P < 0.05). Compared with that in the negative control group, the protein expression of CyclinB1 and p-CDK1 (Thr14, Tyr15) in the miR-155-5p mimics group was significantly increased (P < 0.05). These results suggest that miR-155-5p regulates maturation promoting factor activity by targeting Cx43, which improves the in vitro maturation and cleavage rate of porcine oocytes.

Rare variants in GPR3 in POI patients: a case series with review of literature

BACKGROUND

Premature ovarian insufficiency (POI) is a highly heterogeneous disease, and up to 25% of the cases can be explained by genetic causes. G protein-coupled receptor 3 (GPR3) plays an important role in oocyte arrest, and Gpr3-deficient mice exhibited POI-like phenotypes.

CASE PRESENTATION

We identified two heterozygous missense variants of GPR3: NM_005281: c.C973T (p.R325C) and c.G772A (p.A258T) in two sporadic Han Chinese POI cases through whole exome sequencing and genetic analysis. The two patients were diagnosed as POI in their late 20s, presenting elevated serum levels of follicle stimulating hormone and secondary amenorrhea. Both variants are very rare in the population databases of ExAC, gnomAD and PGG.Han. The affected amino acids are conserved across species and the mutated amino acids are predicted deleterious with bioinformatics prediction tools and the protein three-dimensional structure analysis.

CONCLUSIONS

It is the first report of rare GPR3 variants associated with POI women, providing an important piece of evidence for GPR3 as a candidate gene which should be screened in POI. This finding suggested the necessity of including GPR3 in etiology study and genetic counseling of POI patients.

Meiotic Cell Cycle Progression in Mouse Oocytes: Role of Cyclins

All eukaryotic cells, including oocytes, utilize an engine called cyclin-dependent kinase (Cdk) to drive the cell cycle. Cdks are activated by a co-factor called cyclin, which regulates their activity. The key Cdk-cyclin complex that regulates the oocyte cell cycle is known as Cdk1-cyclin B1. Recent studies have elucidated the roles of other cyclins, such as B2, B3, A2, and O, in oocyte cell cycle regulation. This review aims to discuss the recently discovered roles of various cyclins in mouse oocyte cell cycle regulation in accordance with the sequential progression of the cell cycle. In addition, this review addresses the translation and degradation of cyclins to modulate the activity of Cdks. Overall, the literature indicates that each cyclin performs unique and redundant functions at various stages of the cell cycle, while their expression and degradation are tightly regulated. Taken together, this review provides new insights into the regulatory role and function of cyclins in oocyte cell cycle progression.

Comparative Transcriptome Analysis Reveals the Process of Ovarian Development and Nutrition Metabolism in Chinese Mitten Crab, Eriocheir Sinensis

Ovarian development is a key physiological process that holds great significance in the reproduction of the Chinese mitten crab (Eriocheir sinensis), which is an economically important crab species for aquaculture. However, there is limited knowledge for the regulatory mechanisms of ovarian development. To study the molecular mechanisms of its ovarian development, transcriptome analysis was performed in the ovary and hepatopancreas of E. sinensis during ovarian stages I (oogonium proliferation), II (endogenous vitellogenesis), and III (exogenous vitellogenesis). The results showed that 5,520 and 226 genes were differentially expressed in the ovary and hepatopancreas, respectively. For KEGG enrichment analysis, the differentially expressed genes in the ovary were significantly clustered in phototransduction-fly, phagosome, and ECM-receptor interaction. Significantly enriched pathways in the hepatopancreas included fatty acid biosynthesis, fatty acid metabolism, and riboflavin metabolism. Further analysis showed that 25 genes and several pathways were mainly involved in oogenesis, including the ubiquitin-proteasome pathway, cyclic AMP-protein kinase A signaling pathway, and mitogen-activated protein kinase signaling pathway. Twenty-five candidate genes involved in vitellogenesis and endocrine regulation were identified, such as vitellogenin, vitellogenin receptor, estrogen sulfotransferase, ecdysone receptor, prostaglandin reductase 1, hematopoietic prostaglandin D synthase and juvenile hormone acid O-methyltransferase. Fifty-six genes related to nutritional metabolism were identified, such as fatty acid synthase, long-chain-fatty-acid-CoA ligase 4, 1-acyl-sn-glycerol-3-phosphate acyltransferase 4, fatty acid-binding protein, and glycerol-3-phosphate acyltransferase 1. These results highlight the genes involved in ovarian development and nutrition deposition, which enhance our understanding of the regulatory pathways and physiological processes of crustacean ovarian development.

Comparative proteomics elucidates the dynamics of ovarian development in the Chinese mitten crab Eriocheir sinensis

Ovarian development is a complex physiological process for crustacean reproduction that is divided into the oogonium proliferation stage, endogenous vitellogenic stage, exogenous vitellogenic stage, and oocyte maturation stage. Proteomics analysis offers a feasible approach to reveal the proteins involved in the complex physiological processes of any organism. Therefore, this study performed a comparative proteomics analysis of the ovary and hepatopancreas at three key ovarian stages, including stages I (oogonium proliferation), II (endogenous vitellogenesis) and IV (exogenous vitellogenesis), of the Chinese mitten crab Eriocheir sinensis using a label-free quantitative approach. The results showed that a total of 2,224 proteins were identified, and some key proteins related to ovarian development and nutrition metabolism were differentially expressed. The 26 key proteins were mainly involved in the ubiquitin/proteasome pathway (UPP), cyclic AMP-protein kinase A (cAMP-PKA) signaling pathway, and mitogen-activated protein kinase (MAPK) signaling pathway during oogenesis. Fifteen differentially abundant proteins (DAPs) were found to participate in vitellogenesis and oocyte development, such as vitelline membrane outer layer protein 1 homolog, vitellogenin, vitellogenin receptor, heat shock 70 kDa protein cognate 3 and farnesyl pyrophosphate synthase. Forty-seven DAPs related to nutrition metabolism were identified, including the protein digestion, fatty acid metabolism, prostaglandin metabolism, lipid digestion and transportation, i.e. short-chain specific acyl-CoA dehydrogenase, acyl-CoA desaturase, fatty acid-binding protein, long-chain fatty acid CoA ligase 4, and hematopoietic prostaglandin D synthase. These results not only indicate proteins involved in ovarian development and nutrient deposition but also enhance the understanding of the regulatory pathways and physiological processes of crustacean ovarian development.

Di (2-ethylhexyl) phthalate impairs primordial follicle assembly by increasing PDE3A expression in oocytes

It is known that Di (2-ethylhexyl) phthalate (DEHP) may impact mammalian reproduction and that in females one target of the drug's action is follicle assembly. Here we revisited the phthalate's action on the ovary and from bioinformatics analyses of the transcriptome performed on newborn mouse ovaries exposed in vitro to DEHP, up-regulation of PDE3A, as one of the most important alterations caused by DEHP on early folliculogenesis, was identified. We obtained some evidence suggesting that the decrease of cAMP level in oocytes and the parallel decrease of PKA expression, consequent on the PDE3A increase, were a major cause of the reduction of follicle assembly in the DEHP-exposed ovaries. In fact, Pde3a RNAi on cultured ovaries reducing cAMP and PKA decrease counteracted the primordial follicle assembly impairment caused by the compound. Moreover, RNAi normalized the level of Kit, Nobox, Figla mRNA and GDF9, BMP15, CX37, γH2AX proteins in oocytes, and KitL transcripts in granulosa cells as well as their proliferation rate altered by DEHP exposure. Taken together, these results identify PDE3A as a new critical target of the deleterious effects of DEHP on early oogenesis in mammals and highlight cAMP-dependent pathways as major regulators of oocyte and granulosa cell activities crucial for follicle assembly. Moreover, we suggest that the level of intracellular cAMP in the oocytes may be an important determinant for their capability to repair DNA lesions caused by DNA damaging compounds including DEHP.

Sarcoma-180 tumor affects the quality of oocytes in mice

Numerous factors can affect the quality of oocytes; however, the effects of cancer on the quality of oocytes and the underlying mechanisms remain unclear. In the present study, the effects of the sarcoma-180 (S-180) cell line on the quality of oocytes were investigated using S-180 tumor-bearing mice. In total, 42 female C57BL/6J mice were randomly divided into the tumor-bearing group and the control group, with 21 mice per group. The weight of the mice and ovaries were recorded, and blood glucose, serum insulin, lipopolysaccharide, triglyceride (TG) and total cholesterol (TC) levels were analyzed using the corresponding detection kits. Hematoxylin and eosin staining was performed to observe the pathological changes of the ovarian tissue, and reverse transcription-quantitative PCR (RT-qPCR) was used to analyze the expression levels of meiosis arrest female 1 (MARF1), SUMO-specific protease 7 (SENP7), aralkylamine N-acetyltransferase (AANAT), cell division cycle 25B and glycine-rich protein 3. The results of the present study revealed that the number of oocytes in the two groups of mice was similar; however, the number of abnormal oocytes was increased in the tumor-bearing group. The serum levels of TG and TC were significantly elevated in the tumor-bearing group compared with in the control group (P<0.01). Additionally, RT-qPCR analysis demonstrated that the expression levels of SENP7 were downregulated, while the expression levels of MARF1 and AANAT were upregulated in the ovaries of the tumor-bearing group compared with in the control group (P<0.01). In conclusion, the findings of the present study suggested that cancer may affect the reproductive system of mice and decrease the quality of oocytes by regulating the expression levels of reproduction-associated genes. These results provided novel insights into the reproductive ability of patients with cancer.

Transcriptome sequencing revealed that knocking down FOXL2 affected cell proliferation, the cell cycle, and DNA replication in chicken pre-ovulatory follicle cells

Forkhead box L2 (FOXL2) is a single-exon gene encoding a forkhead transcription factor, which is mainly expressed in the ovary, eyelids and the pituitary gland. FOXL2 plays an essential role in ovarian development. To reveal the effects of FOXL2 on the biological process and gene expression of ovarian granulosa cells (GCs), we established stable FOXL2-knockdown GCs and then analysed them using transcriptome sequencing. It was observed that knocking down FOXL2 affected the biological processes of cell proliferation, DNA replication, and apoptosis and affected cell cycle progression. FOXL2 knockdown promoted cell proliferation and DNA replication, decreased cell apoptosis, and promoted mitosis. In addition, by comparing the transcriptome after FOXL2 knockdown, we found a series of DEGs (differentially expressed genes) and related pathways. These results indicated that, through mediating these genes and pathways, the FOXL2 might induce the cell proliferation, cycle, and DNA replication, and play a key role during ovarian development and maintenance.

High cGMP and low PDE3A activity are associated with oocyte meiotic incompetence

Resumption of meiosis in mammalian oocytes, defined as oocyte maturation, is stimulated by luteinizing hormone (LH). Fully grown oocytes can also mature spontaneously, upon their release from the ovarian follicle. However, growing oocytes fail to resume meiosis in vitro and the mechanism underlying their meiotic incompetence is unknown. It is commonly accepted that a drop in intraoocyte cyclic guanosine monophosphate (cGMP) resulting in the elevated activity of the oocyte-specific PDE3A leads to a decrease in cAMP content, essential for reinitiation of meiosis. We explored the regulation of these cyclic nucleotides and their degrading PDE3A in growing oocytes. Our research addressed the LH-induced rather than spontaneous oocyte maturation. We examined 16-21 as compared to 25-day-old, PMSG-primed rats, treated with the LH analog, hCG. The effect of LH was also examined ex vivo, in isolated ovarian follicles. We found that hCG failed to induce oocyte maturation and ovulation in the younger animals and that ovulation-associated genes were not upregulated in response to this gonadotropin. Furthemore, the drop of intraoocyte cGMP and cAMP observed in fully grown oocytes upon exposure of the ovary to LH, was not detected in growing oocytes. Interestingly, whereas the global expression of PDE3A in growing and fully grown oocytes is similar, a significantly lower activity of this enzyme was determined in growing oocytes. Our findings show that meiotic incompetence is associated with a relatively high oocyte cGMP concentration and a low activity of PDE3A, which in follicle-enclosed oocytes may represent the failure of the somatic follicle cells to respond to LH.

Cyclin B2 is required for progression through meiosis in mouse oocytes

Cyclins associate with cyclin-dependent serine/threonine kinase 1 (CDK1) to generate the M phase-promoting factor (MPF) activity essential for progression through mitosis and meiosis. Although cyclin B1 (CCNB1) is required for embryo development, previous studies concluded that CCNB2 is dispensable for cell cycle progression. Given previous findings of high Ccnb2 mRNA translation rates in prophase-arrested oocytes, we re-evaluated the role of this cyclin during meiosis. Ccnb2-/- oocytes underwent delayed germinal vesicle breakdown and showed defects during the metaphase-to-anaphase transition. This defective maturation was associated with compromised Ccnb1 and Moloney sarcoma oncogene (Mos) mRNA translation, delayed spindle assembly and increased errors in chromosome segregation. Given these defects, a significant percentage of oocytes failed to complete meiosis I because the spindle assembly checkpoint remained active and anaphase-promoting complex/cyclosome function was inhibited. In vivo, CCNB2 depletion caused ovulation of immature oocytes, premature ovarian failure, and compromised female fecundity. These findings demonstrate that CCNB2 is required to assemble sufficient pre-MPF for timely meiosis re-entry and progression. Although endogenous cyclins cannot compensate, overexpression of CCNB1/2 rescues the meiotic phenotypes, indicating similar molecular properties but divergent modes of regulation of these cyclins.