Impact of oocyte-secreted factors on its developmental competence in buffalo

Identification and molecular characterization of genes modulating progression of an oocyte from M-I to M-II in rat ovary

BACKGROUND

To achieve oocyte competence for successful fertilization, bidirectional communication between oocyte and granulosa cells is crucial. The acquisition of meiotic competency in oocyte is facilitated by various regulatory genes however, expression pattern of these genes is not well documented during meiotic transition from Metaphase-I to Metaphase-II stage. Therefore, the present research analyzed the expression pattern of regulatory genes that are involved in the transition from M-I to M-II stages in rat oocyte.

METHODS

The analysis of the data was conducted by applying an array of bioinformatic tools. The investigation of gene group interactions was carried out by employing the STRING database, which relies on co-expression information. The gene ontology (GO) analysis was performed utilizing the comparative GO database. Functional annotation for GO and pathway enrichment analysis were performed for genes involved in networking. The GO obtained through computational simulations was subsequently validated using quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis.

RESULTS

The findings of our study suggest that there is a distinct gene expression pattern in both the oocyte and granulosa cells. This pattern indicates that oocyte-secreted factors, such as BMP15 and GDF9, play a crucial role in regulating the progression of the meiotic cell cycle from the M-I to M-II stages. We have also examined the level of mRNA expression of genes including CYP11A1, CYP19A1, and STAR, which are crucial for the steroidogenesis.

CONCLUSIONS

It is fascinating to observe that the oscillatory pattern of specific key genes may hold significance in the process of in vitro oocyte maturation, specifically during the transition from the M-I to M-II stage. It might be useful for determining biomarker genes and potential pathways that play a role in attaining oocyte competency, thereby aiding in the assessment of oocyte quality for the purpose of achieving successful fertilization.

Advances in Oocyte Maturation In Vivo and In Vitro in Mammals

The quality and maturation of an oocyte not only play decisive roles in fertilization and embryo success, but also have long-term impacts on the later growth and development of the fetus. Female fertility declines with age, reflecting a decline in oocyte quantity. However, the meiosis of oocytes involves a complex and orderly regulatory process whose mechanisms have not yet been fully elucidated. This review therefore mainly focuses on the regulation mechanism of oocyte maturation, including folliculogenesis, oogenesis, and the interactions between granulosa cells and oocytes, plus in vitro technology and nuclear/cytoplasm maturation in oocytes. Additionally, we have reviewed advances made in the single-cell mRNA sequencing technology related to oocyte maturation in order to improve our understanding of the mechanism of oocyte maturation and to provide a theoretical basis for subsequent research into oocyte maturation.

Intercellular communication in the cumulus-oocyte complex during folliculogenesis: A review

During folliculogenesis, the oocyte and surrounding cumulus cells form an ensemble called the cumulus-oocyte complex (COC). Due to their interdependence, research on the COC has been a hot issue in the past few decades. A growing body of literature has revealed that intercellular communication is critical in determining oocyte quality and ovulation. This review provides an update on the current knowledge of COC intercellular communication, morphology, and functions. Transzonal projections (TZPs) and gap junctions are the most described structures of the COC. They provide basic metabolic and nutrient support, and abundant molecules for signaling pathways and regulations. Oocyte-secreted factors (OSFs) such as growth differentiation factor 9 and bone morphogenetic protein 15 have been linked with follicular homeostasis, suggesting that the communications are bidirectional. Using advanced techniques, new evidence has highlighted the existence of other structures that participate in intercellular communication. Extracellular vesicles can carry transcripts and signaling molecules. Microvilli on the oocyte can induce the formation of TZPs and secrete OSFs. Cell membrane fusion between the oocyte and cumulus cells can lead to sharing of cytoplasm, in a way making the COC a true whole. These findings give us new insights into related reproductive diseases like polycystic ovary syndrome and primary ovarian insufficiency and how to improve the outcomes of assisted reproduction.

Bone morphogenetic protein 15 supplementation enhances cumulus expansion, nuclear maturation and progesterone production of in vitro-matured bovine cumulus-oocyte complexes

In vitro embryo production (IVP) efficiency is reduced when compared to in vivo. The basic knowledge of bovine in vitro oocyte maturation (IVM) mechanisms provides support to improve in vitro embryo production yields. The present study assessed the effects of bone morphogenetic protein 15 (BMP15), fibroblast growth factor 16 (FGF16) and their combined action on cumulus cells (CC) expansion, oocyte and CC DNA fragmentation, oocyte nuclear maturation, energetic metabolism and progesterone production in bovine IVM. Cumulus-oocyte complexes (COC) were matured in control or supplemented media containing BMP15 (100 ng/ml), FGF16 (10 ng/ml) or BMP15 combined with FGF16; and assessed at 0 and 22 hr of IVM. BMP15 alone or its association with FGF16 enhanced cumulus expansion. BMP15 decreased DNA fragmentation in both CC and oocytes, and improved oocyte nuclear maturation rate. In addition, BMP15 increased CC progesterone production, an effect not previously reported. The present study reinforces previous data pointing to a beneficial influence of BMP15 during IVM, while providing novel evidence that the underlying mechanisms involve increased progesterone production.

Long noncoding RNA 2193 regulates meiosis through global epigenetic modification and cytoskeleton organization in pig oocytes

Long noncoding RNAs (lncRNAs) regulate a variety of physiological and pathological processes. However, the biological function of lncRNAs in mammalian germ cells remains largely unexplored. Here we identified one novel lncRNA (lncRNA2193) from single-cell RNA sequencing performed on porcine oocytes and investigated its function in oocyte meiosis. During in vitro maturation (IVM), from germinal vesicle (GV, 0 hr), GV breakdown (GVBD, 24 hr), to metaphase II stage (MII, 44 hr), the transcriptional abundance of lncRNA2193 remained stable and high. LncRNA2193 interference by small interfering RNA microinjection into porcine GV oocytes could significantly inhibit rates of GVBD and the first polar body extrusion, but enhance the rates of oocytes with a nuclear abnormality. Moreover, lncRNA2193 knockdown disturbed cytoskeletal organization (F-actin and spindle), and decreased DNA 5-methylcytosine (5mC) and histone trimethylation (H3K4me3, H3K9me3, H3K27me3, and H3K36me3) levels. The lncRNA2193 downregulation induced a decrease of 5mC level could be partially due to the reduction of DNA methyltransferase 3A and 3B, and the elevation of 5mC-hydroxylase ten-11 translocation 2 (TET2). After parthenogenetic activation of MII oocytes, parthenotes exhibited higher fragmentation but lower cleavage rates in the lncRNA2193 downregulated group. However, lncRNA2193 interference performed on mature MII oocytes and parthenotes at 1-cell stage did not affect the cleavage and blasctocyst rates of pathenotes. Taken together, lncRNA2193 plays an important role in porcine oocyte maturation, providing more insights for relevant investigations on mammalian germ cells.

Effect of roscovitine on developmental competence of small follicle-derived buffalo oocytes

Background & objectives:

The lower recovery of competent oocytes in buffalo species limits the commercialization of in vitro embryo production technology in field condition. In this context, pre-maturation of small follicle (SF)-derived oocytes with meiotic inhibition may be a promising alternative to obtain more number of competent oocytes. Thus, the present study was conducted with an objective to enhance the developmental potential of less competent SF-derived buffalo oocytes.

Methods:

All the visible follicles (used for aspiration) from buffalo ovaries were divided into two categories: large follicle (LF) (follicles having diameter ≥6 mm) and SF (follicles of diameter <6 mm). The competence of LF and SF oocytes was observed in terms of brilliant cresyl blue (BCB) staining, cleavage rate, blastocyst rate and relative gene expression of oocyte and blastocyst competence markers. Thereafter, less competent SF oocytes were treated with 0, 12.5, 25, 50 and 100 mM doses of roscovitine (cyclin-dependent kinase inhibitor) to enhance their developmental potential.

Results:

Based on parameters studied, LF oocytes were found to be more competent than SF oocytes. Pre-maturation incubation of SF oocytes with roscovitine reversibly arrested oocyte maturation for 24 h to ensure the proper maturation of less competent oocytes. A significantly higher number of BCB-positive oocytes were noted in roscovitine-treated group than SF group. Cleavage and blastocyst rates were also higher in roscovitine-treated group. The relative messenger RNA expression of oocyte (GDF9, BMP15, GREM1, EGFR, PTGS2 and HAS2) as well as blastocyst (INF-τ, GLUT1 and POU5F1) competence markers was significantly greater in roscovitine-treated group relative to SF group. Again, on comparison with LF group, these parameters depicted a lower value in the treatment group.

Interpretation & conclusions:

The findings of this study has revealed that pre-maturation incubation of SF-derived oocytes with 25 μM roscovitine can improve its developmental competence and thus can be utilized to get maximum number of competent oocytes for better commercialization of in vitro embryo production technology in buffalo.

Expression Analysis of the Prolific Candidate Genes, BMPR1B, BMP15, and GDF9 in Small Tail Han Ewes with Three Fecundity (FecB Gene) Genotypes

Simple Summary

As important prolific candidate genes, BMPR1B, BMP15, and GDF9 may affect the lambing performance of sheep. Therefore, regarding the three FecB genotypes of Small Tail Han (STH) sheep (FecB BB, FecB B+, and FecB ++), this study explored the gene expression characteristics of different tissues using reverse transcription PCR (RT-PCR) and real-time quantitative PCR (qPCR). The results showed that BMPR1B, BMP15, and GDF9 expression differed between the selected tissues, with all being highly expressed in the ovaries. Further analysis indicated that there was no significant difference in BMPR1B expression among the three FecB genotypes, but both GDF9 and BMP15 had the highest expression in FecB B+. As for other non-ovarian tissues, expression also varied. This study is relevant to understanding the high prolificacy of the STH breed.

Abstract

The expression characteristics of the prolific candidate genes, BMPR1B, BMP15, and GDF9, in the major visceral organs and hypothalamic–pituitary–gonadal (HPG) axis tissues of three FecB genotypes (FecB BB, FecB B+, and FecB ++) were explored in STH ewes using RT-PCR and qPCR. The results were as follows, BMPR1B was expressed in all FecB BB genotype (Han BB) tissues, and GDF9 was expressed in all selected tissues, but BMP15 was specifically expressed in the ovaries. Further study of ovarian expression indicated that there was no difference in BMPR1B expression between genotypes, but the FecB B+ genotype (Han B+) had greater expression of GDF9 and BMP15 than Han BB and FecB ++ genotype (Han ++) (p < 0.05, p < 0.01). BMP15 expression was lower in the ovaries of Han BB than in Han ++ sheep, but the reverse was shown for GDF9. The gene expression in non-ovarian tissues was also different between genotypes. Therefore, we consider that the three genes have an important function in ovine follicular development and maturation. This is the first systematic analysis of the tissue expression pattern of BMPR1B, BMP15, and GDF9 genes in STH sheep of the three FecB genotypes. These results contribute to the understanding of the molecular regulatory mechanism for ovine reproduction.