Inhibition of calcineurin by FK506 stimulates germinal vesicle breakdown of mouse oocytes in hypoxanthine-supplemented medium

Proteomic Exploration of Porcine Oocytes During Meiotic Maturation in vitro Using an Accurate TMT-Based Quantitative Approach

The dynamic changes in protein expression are well known to be required for oocyte meiotic maturation. Although proteomic analysis has been performed in porcine oocytes during in vitro maturation, there is still no full data because of the technical limitations at that time. Here, a novel tandem mass tag (TMT)-based quantitative approach was used to compare the proteomic profiles of porcine immature and in vitro mature oocytes. The results of our study showed that there were 763 proteins considered with significant difference−450 over-expressed and 313 under-expressed proteins. The GO and KEGG analyses revealed multiple regulatory mechanisms of oocyte nuclear and cytoplasmic maturation such as spindle and chromosome configurations, cytoskeletal reconstruction, epigenetic modifications, energy metabolism, signal transduction and others. In addition, 12 proteins identified with high-confidence peptide and related to oocyte maturation were quantified by a parallel reaction monitoring technique to validate the reliability of TMT results. In conclusion, we provided a detailed proteomics dataset to enrich the understanding of molecular characteristics underlying porcine oocyte maturation in vitro.

Identification of calcineurin as a predictor of oocyte quality and fertilization competence based on microarray data

OBJECTIVE

The aim of our study was to detect a biomarker for selection of competent oocytes with acceptable fertilization potential. Calcium ion fluctuation play the most critical role of modulating intercellular signaling pathways in oocyte maturation, egg activation and the egg-to-embryo transition. Since, the stimulatory action of calcium ion is mediated by binding to certain proteins, the calcium/calmodulin-binding genes (CBGs), as the main calcium binding group, was analyzed in detail.

METHODS

In this work, bioinformatics analysis was conducted on the CBGs of human cumulus cells (CCs) to elucidate a reliable biomarker for fertile oocyte selection. Calcineurin (CaN) or protein phosphatase 3 (PPP3) was selected which consists of a catalytic subunit A with PPP3CA (Aα), PPP3CB (Aβ), and PPP3CC (Aγ) isoforms and a regulatory subunit B. Whereas CaN A regulates calcium ion function, our study gives insights to probable role of related isoforms within human oogenesis process. The presence of CaN A in CCs surrounding growing and mature oocytes was confirmed by western blotting and the expression patterns of related isoforms were examined by reverse transcription-quantitative PCR (RT-qPCR).

RESULTS

Our results indicated the increased expression of the catalytic subunit of CaN protein in the CCs of metaphase (M) II oocytes. The expression level of PPP3CB was significantly elevated in CCs of fertile MII compared with those in the germinal vesicle (GV), MI and unfertilized MII oocytes (P ≤ 0.05).

CONCLUSION

Elevated level of PPP3CB isoform in the CCs of fertile MII oocyte could be a reliable indication of oocyte fertilization potential. However, further researches are required to introduce CaN Aβ as an appropriate biomarker for oocyte selection in assisted reproduction technique (ART) programs.

Increased transcriptome variation and localised DNA methylation changes in oocytes from aged mice revealed by parallel single-cell analysis

Advancing maternal age causes a progressive reduction in fertility. The decline in developmental competence of the oocyte with age is likely to be a consequence of multiple contributory factors. Loss of epigenetic quality of the oocyte could impair early developmental events or programme adverse outcomes in offspring that manifest only later in life. Here, we undertake joint profiling of the transcriptome and DNA methylome of individual oocytes from reproductively young and old mice undergoing natural ovulation. We find reduced complexity as well as increased variance in the transcriptome of oocytes from aged females. This transcriptome heterogeneity is reflected in the identification of discrete sub-populations. Oocytes with a transcriptome characteristic of immature chromatin configuration (NSN) clustered into two groups: one with reduced developmental competence, as indicated by lower expression of maternal effect genes, and one with a young-like transcriptome. Oocytes from older females had on average reduced CpG methylation, but the characteristic bimodal methylation landscape of the oocyte was preserved. Germline differentially methylated regions of imprinted genes were appropriately methylated irrespective of age. For the majority of differentially expressed transcripts, the absence of correlated methylation changes suggests a post-transcriptional basis for most age-related effects on the transcriptome. However, we did find differences in gene body methylation at which there were corresponding changes in gene expression, indicating age-related effects on transcription that translate into methylation differences. Interestingly, oocytes varied in expression and methylation of these genes, which could contribute to variable competence of oocytes or penetrance of maternal age-related phenotypes in offspring.