Relative importance of phosphatidylinositol-3 kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK3/1) signaling during maturational steroid-induced meiotic G2-M1 transition in zebrafish oocytes

Endocrine-Disruptive Effects of Adenylate Cyclase Activator Forskolin: In Vitro and In Vivo Evidence

Forskolin (FSK) is a potent adenylate cyclase activator and may display endocrine-disruptive effects via the disruption of steroidogenesis. Here, we tested this hypothesis by use of the in vitro H295R steroidogenesis assay and the in vivo long-term medaka (Oryzias latipes) exposure assay. The results from the H295R assay demonstrated that the transcriptional levels of a series of genes involved in steroidogenesis, including HSD3B2, CYP11A, CYP11B2, CYP17, CYP19, and CYP21, were remarkably up-regulated. Meanwhile, the productions of estrogens (17β-estradiol (17β-E2) and estrone (E1)) and progestins (progesterone (PGT) and 17-hydroxyprogesterone (17-HPT)) were significantly increased, and those of androgens (androstenedione (ADD) and testosterone (TTR)) were significantly inhibited. After waterborne exposure of medaka to FSK for 100 days, the gene expressions of HMGR, HSD17B1, CYP17B, CYP19A, and CYP21A were significantly enhanced in the gonads of male medaka. 17β-E2 was remarkably induced, although without statistical significance. In addition, the biomarker genes for estrogenicity, including VTG-I, VTG-II, CHG-H, and CHG-L, were significantly induced in male medaka livers. Pathological damage to their gonads was further identified. Therefore, the results demonstrated that FSK modulates the transcriptions of steroidogenesis genes and alters hormone levels in vitro and in vivo, which is a mark of endocrine disruption in organisms.

Investigation on the potential adverse outcome pathway of the sensitive endpoint for nephrotoxicity induced by gardenia yellow based on an integrated strategy using bioinformatics analysis and in vitro testing validation

To explore the potential the adverse outcome pathway of Gardenia Yellow (GY)-induced sensitive endpoint for nephrotoxicity, an integrated strategy was applied in the present study. Using bioinformatic analysis, based on the constructed Protein-protein interaction networks, Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis on the core target network were performed to illustrate the potential gene targets and signal pathways. Then, the most enriched pathway was validated with Cell counting kit-8 assays and Western blot analysis in embryonic kidney epithelial 293 cell models. According to the findings, GY may interact with 321 targets related to the endpoint. The five targets on the top ranking in the PPI network were STAT3, SRC, HRAS, AKT1, EP300. Among them, PI3K/Akt was the most enriched pathway. In vitro testing showed that GY exerted a proliferative effect on the cell variability in a dose-dependent manner. GY at concentration of 1000 μg/ml and stimulation for 30 min can significantly enhance the expression of phosphorylated Akt. Thus, after the quantitative weight of evidence evaluation, Akt phosphorylation induced PI3K/Akt activation was speculated as a molecular initiating event leading to a proliferative and inflammatory response in renal tubular epithelial cells.

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.

Role of phosphoinositide 3-kinase/ protein kinase B/ phosphatase and tensin homologue (PI3K/AKT/PTEN) pathway inhibitors during in vitro maturation of mammalian oocytes on in vitro embryo production: A systematic review

Modulation of phosphoinositide 3-kinase/protein kinase B/phosphatase and tensin homologue (PI3K/AKT/PTEN) pathway in mammals yields mixed results. A deep understanding of its regulation can be a powerful tool for better in vitro blastocyst production. This systematic review aims to map the evidence of PI3K/AKT/PTEN pathway modulation during in vitro maturation (IVM), to assess its effects on meiosis resumption and nuclear maturation progression of mammalian oocytes, and their impacts on embryo development and quality. A total of 1058 articles were screened in three databases, and 22 articles were included. Fifty-two IVM assessments were identified, among which 11 evaluated blastocyst yield. Three PI3K inhibitors (3-methyladenine, Wortmannin, and LY294002) and one AKT inhibitor (SH6) were investigated. The impact of this pathway modulation on meiosis resumption in swines and murines was not well established, depending on the inhibitor used, concentration, and media supplementation, while in bovines, resumption seems to be independent of PI3K/AKT/PTEN pathway. However, progression to metaphase II (MII) is highly controlled by this pathway on both bovines and swines. Studies that focused on the inhibition reversibility showed that the removal of the modulator produced MII rates similar to the control group. Experiments that aimed to temporarily block meiosis resumption or reduce PI3K activity resulted in blastocyst production equal to or even higher than control groups. Altogether, these data indicate the paramount potential of this pathway as a possible strategy to improve overall in vitro embryo production efficiency, by synchronizing both nuclear and cytoplasmic maturation.

Inhibition of Oocyte Maturation by Malathion and Structurally Related Chemicals in Zebrafish (Danio rerio) After In Vitro and In Vivo Exposure

Oogenesis is the process by which a primary oocyte develops into a fertilizable oocyte, making it critical to successful reproduction in fish. In zebrafish (Danio rerio), there are five stages of oogenesis. During the final step (oocyte maturation), the maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (MIH) activates the membrane progestin receptor, inducing germinal vesicle breakdown. Using in vitro assays, it has been shown that anthropogenic stressors can dysregulate MIH-induced oocyte maturation. However, it is unknown whether the in vitro assay is predictive of reproductive performance after in vivo exposure. We demonstrate that a known inhibitor of oocyte maturation, malathion, and a structurally related chemical, dimethoate, inhibit oocyte maturation. However, malaoxon and omethoate, which are metabolites of malathion and dimethoate, did not inhibit oocyte maturation. Malathion and dimethoate inhibited maturation to a similar magnitude when oocytes were exposed for 4 h in vitro or 10 days in vivo, suggesting that the in vitro zebrafish oocyte maturation assay might be predictive of alterations to reproductive performance. However, when adult zebrafish were exposed to malathion for 21 days, there was no alteration in fecundity or fertility in comparison with control fish. Our study supports the oocyte maturation assay as being predictive of the success of in vitro oocyte maturation after in vivo exposure, but it remains unclear whether inhibition of MIH-induced oocyte maturation in vitro correlates to decreases in reproductive performance. Environ Toxicol Chem 2022;41:1381-1389. © 2022 SETAC.

The brominated flame retardant, TBCO, impairs oocyte maturation in zebrafish (Danio rerio)

The brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), has been shown to decrease fecundity in Japanese medaka (Oryzias latipes) and there is indirect evidence from analysis of the transcriptome and proteome that this effect might be due to impaired oogenesis. An assay for disruption of oocyte maturation by chemical stressors has not been developed in Japanese medaka. Thus, using zebrafish (Danio rerio) as a model, objectives of the present study were to determine whether exposure to TBCO has effects on maturation of oocytes and to investigate potential mechanisms. Sexually mature female zebrafish were given a diet of 35.3 or 628.8 μg TBCO / g food for 14 days after which, stage IV oocytes were isolated to assess maturation in response to maturation inducing hormone. To explore potential molecular mechanisms, abundances of mRNAs of a suite of genes that regulate oocyte maturation were quantified by use of quantitative real-time PCR, and abundances of microRNAs were determined by use of miRNAseq. Ex vivo maturation of oocytes from fish exposed to TBCO was significantly less than maturation of oocytes from control fish. The percentage of oocytes which matured from control fish and those exposed to low and high TBCO were 89, 71, and 67%, respectively. Among the suite of genes known to regulate oocyte maturation, mRNA abundance of insulin like growth factor-3 was decreased by 1.64- and 3.44-fold in stage IV oocytes from females given the low and high concentrations of TBCO, respectively, compared to the control group. Abundances of microRNAs regulating the expression of proteins that regulate oocyte maturation, including processes related to insulin-like growth factor, were significantly different in stage IV oocytes from fish exposed to TBCO. Overall, results of this study indicated that impaired oocyte maturation might be a mechanism of reduced reproductive performance in TBCO-exposed fish. Results also suggested that effects of TBCO on oocyte maturation might be due to molecular perturbations on insulin-like growth factor signaling and expression of microRNAs.

Abnormal PIWI-interacting RNA profile and its association with the deformed extracellular matrix of oocytes from recurrent oocyte maturation arrest patients

OBJECTIVE

To depict the PIWI-interacting RNA (piRNA) profile in oocytes from patients with recurrent oocyte maturation arrest (ROMA) and explore the piRNA candidates associated with the disease.

DESIGN

An observational study.

SETTING

Academic research unit.

PATIENT(S)

Sixteen ROMA patients who provided 140 immature oocytes that arrested at metaphase I, and 146 control patients who provided 420 oocytes for in vitro culture that were collected at the stages of germinal vesicle (GV), metaphase I (MI), and MII.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Expression profiles of piRNA and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) validating data of piR-hsa-17139 and its target genes.

RESULT(S)

After the piRNA profile was established using piRNA sequencing and hierarchical clustering, the target genes of the piRNA were predicted by bioinformatics databases and matched with mRNA sequencing data. The piRNA expression profiles showed a greater quantity of differentially expressed piRNAs in the older-stage oocytes compared with the early-stage oocytes. The piRNA and mRNA sequencing data indicated that the most affected genes were mainly concentrated in the extracellular matrix (ECM) pathway. Based on the comparison of the piRNA and mRNA sequencing data, four differentially expressed piRNAs were associated with modulation of those ECM pathway genes. The qRT-PCR validation confirmed that piR-hsa-17139 was the only up-regulated piRNA, and its target ECM genes were suppressed in ROMA oocytes. The expression level of piR-hsa-17139 declined slightly while the expression of its target ECM genes plunged dramatically during the development of normal oocytes.

CONCLUSION(S)

As the important genome monitors in gametogenesis, abnormally expressed piRNAs may affect the expression of ECM modulating genes, which subsequently contributes to ROMA.

PI3K inhibitor reduces in vitro maturation and developmental competence of porcine oocytes

The phosphatidylinositol -3- kinase (PI3K) signaling pathway is critical for the cell proliferation, apoptosis, metabolism, DNA repair and protein synthesis. Significant effort has focused on elucidating the relationship between PI3K signaling pathway and other nuclear signal transducers; However, little is known about the connection between PI3K signaling pathway and porcine oocyte meiotic maturation. In this study, we investigated the function of PI3K signaling pathway in porcine oocytes. PI3K signaling pathway was important during oocyte maturation. Furthermore, the PI3K signaling pathway inhibitor LY-294002 blocked porcine oocyte maturation, reducing the percentage of oocytes that first polar body (PBI) extrusion. LY-294002 also decreased the expression of oocyte proliferation-related gene PCNA and reduced the mRNA and protein levels of PI3K. What's more, LY-294002 also decreased other maturation-related genes that are predominantly expressed duringporcine oocyte maturation, including bone morphogenetic protein 15 (BPM15), growth differentiation factor 9 (GDF9), cell division cycle protein 2 (CDC2), phosphatase and tensin homolog (PTEN), CyclinB1, MOS and Akt. LY-294002 treatment decreased the developmental potential of blastocysts following parthenogenetic activation, increased the level of cell apoptosis and reduced the level of cell-cycle. This study revealed that inhibiting the PI3K signaling pathway could reduce in vitro maturation and developmental competence of porcine oocytes, probably by reducing cell cycle arrest and proliferation, promoting the oocyte apoptosis, and altering the expression of other maternal genes.