Molecular cloning and hormonal control in the ovary of connexin 31.5 mRNA and correlation with the appearance of oocyte maturational competence in red seabream

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.

Inhibition of medaka ovulation by gap junction blockers due to its disrupting effect on the transcriptional process of LH-induced Mmp15 expression

Using medaka, we found that in vitro follicle ovulation, but not germinal vesicle breakdown, was inhibited by three gap junction blockers, carbenoxolone, mefloquine, and flufenamic acid. The blockers specifically inhibited follicular expression of matrix metalloproteinase-15 mRNA and the protein (mmp15/Mmp15), a protease indispensable for medaka ovulation, indicating that gap junctional communication may be required for successful ovulation and mmp15/Mmp15 expression. Further experiments using carbenoxolone as the representative of the gap junction blockers showed that expression of nuclear progestin receptor (Pgr), a transcription factor required for mmp15 expression, was not affected by carbenoxolone treatment, but the formation of phosphorylated Pgr was considerably suppressed. Carbenoxolone treatment caused a decrease in the Pgr binding to the promoter region of mmp15. mRNA expression of cyclin-dependent protein kinase-9 (cdk9) and cyclin I (ccni), whose translation products are demonstrated to be involved in Pgr phosphorylation in the medaka ovulating follicles, was suppressed by carbenoxolone treatment. Transcripts of connexin 34.5 (cx34.5) and connexin 35.4 (cx35.4) were dominantly expressed in the follicle cells of ovulating follicles. The results indicate that gap junctional communication plays an important role in medaka ovulation.

Ovarian function of the trout preovulatory ovary: new insights from recent gene expression studies

During the preovulatory period the follicle-enclosed oocyte progressively acquires maturational and developmental competence. In addition, the follicle is also preparing for the release of the oocyte from the follicle at ovulation. Using real-time PCR and cDNA microarrays we have investigated the molecular mechanisms of oocyte competence acquisition and ovulation in rainbow trout (Oncorhynchus mykiss) by monitoring gene expression in the preovulatory ovary. These studies have demonstrated that many molecular events related to maturational competence and developmental competence acquisition, and ovulation occur concomitantly in the preovulatory ovarian follicle. Oocyte maturational competence acquisition is associated with a decrease of estrogen synthesis and signaling capacities. We also observed a differential expression of genes encoding for igfs and related binding protein, members of the TGF beta superfamily, proteins involved in ion and water transport, bone morphogenetic proteins, and cathepsins. In addition, our observation of a strong up-regulation, prior to ovulation, of genes encoding for proteins putatively involved in proteolysis, inflammation, coagulation, vasodilatation, and angiogenesis further supports the hypothesis comparing ovulation with an inflammatory-like reaction. Together, our results suggest that a finely tuned cross-talk exists between oocyte and follicular layers and between the ovulatory process and the oocyte maturational and developmental competence acquisition processes.

Identification of new participants in the rainbow trout (Oncorhynchus mykiss) oocyte maturation and ovulation processes using cDNA microarrays

BACKGROUND

The hormonal control of oocyte maturation and ovulation as well as the molecular mechanisms of nuclear maturation have been thoroughly studied in fish. In contrast, the other molecular events occurring in the ovary during post-vitellogenesis have received far less attention.

METHODS

Nylon microarrays displaying 9152 rainbow trout cDNAs were hybridized using RNA samples originating from ovarian tissue collected during late vitellogenesis, post-vitellogenesis and oocyte maturation. Differentially expressed genes were identified using a statistical analysis. A supervised clustering analysis was performed using only differentially expressed genes in order to identify gene clusters exhibiting similar expression profiles. In addition, specific genes were selected and their preovulatory ovarian expression was analyzed using real-time PCR.

RESULTS

From the statistical analysis, 310 differentially expressed genes were identified. Among those genes, 90 were up-regulated at the time of oocyte maturation while 220 exhibited an opposite pattern. After clustering analysis, 90 clones belonging to 3 gene clusters exhibiting the most remarkable expression patterns were kept for further analysis. Using real-time PCR analysis, we observed a strong up-regulation of ion and water transport genes such as aquaporin 4 (aqp4) and pendrin (slc26). In addition, a dramatic up-regulation of vasotocin (avt) gene was observed. Furthermore, angiotensin-converting-enzyme 2 (ace2), coagulation factor V (cf5), adam 22, and the chemokine cxcl14 genes exhibited a sharp up-regulation at the time of oocyte maturation. Finally, ovarian aromatase (cyp19a1) exhibited a dramatic down-regulation over the post-vitellogenic period while a down-regulation of Cytidine monophosphate-N-acetylneuraminic acid hydroxylase (cmah) was observed at the time of oocyte maturation.

CONCLUSION

We showed the over or under expression of more that 300 genes, most of them being previously unstudied or unknown in the fish preovulatory ovary. Our data confirmed the down-regulation of estrogen synthesis genes during the preovulatory period. In addition, the strong up-regulation of aqp4 and slc26 genes prior to ovulation suggests their participation in the oocyte hydration process occurring at that time. Furthermore, among the most up-regulated clones, several genes such as cxcl14, ace2, adam22, cf5 have pro-inflammatory, vasodilatory, proteolytics and coagulatory functions. The identity and expression patterns of those genes support the theory comparing ovulation to an inflammatory-like reaction.

Molecular cloning and expression of connexin 32.3 cDNA in the ovary from the red seabream (Pagrus major)

This study examined connexin (Cx) gene activity in relation to oocyte maturation in the red seabream (Pagrus major) ovary. Mixed primers for the polymerase chain reaction (PCR) were designed based on the high sequence homology of selected regions of known Cx genes. PCR-amplified cDNA fragments generated by 3' and 5' rapid amplication of cDNA ends (RACE) were combined to generate full-length cDNA sequences. The 1212-bp cDNA has an open reading frame encoding 282 amino acids, with a molecular mass of 32.3 kDa (red seabream Cx32.3). Hydropathy plots of red seabream Cx32.3 show the four typical major hydrophobic and four major hydrophilic regions of Cx proteins. Typical Cx consensus sequences are observed in the first and second extracellular loops. The ovarian follicles of matured female seabream were incubated in the presence of 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP, 10 ng/ml), gonadotropin (GtH)-I (300 ng/ml) and GtH-II (300 ng/ml). Northern blot analysis of poly(A)(+) RNA extracted from the ovarian follicles were hybridized with red seabream Cx32.3 and beta-actin probes. The transcription level of PmCx32.3 in the presence of DHP, PmGtH-I and PmGtH-II was significantly higher than in the control.