Gene Expression in Bovine Oocytes and Cumulus Cells After Meiotic Inhibition with the Cyclin-Dependent Kinase Inhibitor Butyrolactone I

Relative transcript abundance in porcine cumulus cells collected from different sized follicles

Crosstalk between the oocyte and surrounding cumulus cells (CCs) is essential for the production of competent oocytes. Previous studies have analysed the relative transcript abundance in oocytes derived from small (SF: <3 mm diameter)- and medium-sized (MF: 3-6 mm diameter) follicles to determine the potential use of SF-derived oocytes in assisted reproductive technologies (ART). The aim of this study was to examine the relative transcript abundance of CCs obtained from cumulus-oocyte complexes (COCs) derived from SF and MF. Nine genes were selected according to their importance for developmental competence: AT-rich interaction domain 1B (ARID1B), bone morphogenic protein receptor 2 (BMPR2), CD44, follicle-stimulating hormone receptor (FSHR), follistatin (FST), inhibin beta-A (INHBA), luteinizing hormone receptor (LHR), nuclear receptor subfamily 2 group F member 6 (NR2F6) and vascular endothelial growth factor A (VEGFA). The expression of these genes was analysed by RT-qPCR. The results pointed to significant differences in five genes, and the relative transcript abundance of SF-derived CCs was lower in the case of INHBA, but higher in FSHR, FST, LHR and NR2F6 compared with MF-derived CCs. We provide information of gene activity in the porcine CCs from different sized follicles, thus improving our understanding of oocyte biology and providing new markers that identify viable and competent oocytes.

Effect of Rolipram on in vitro maturation, gene expression and embryonic development in bovines

ABSTRACT The aim of this work was to evaluate the effect of the Rolipram during the maturation of bovine oocytes and gene expression of embryos produced in vitro. Bovine ovaries were collected in slaughterhouse. The COCs were selected and divided into 5 groups: Control 0 time; Control: IVM for 24 hours; Rolipram treatments with IVM blocking for 24 hours in maturation medium containing (100, 150 and 200µM). After 24 hours all groups were reseated in IVM for another 24 hours. Subsequently COCs were subjected to the same IVM system and fertilized, being checked for cleavage post fertilization and for blastocyst. In addition, performed expression of the following genes: Mater, BMP15 and Bax. No difference was found in gene expression. Of oocytes evaluated shortly after follicular aspiration, 79.00% were in GV, GVBD, MI, while 13.40%, were in MII and 7.60%, D/NI. Significant difference was observed in different concentrations (T100, T200 and T150µM) in oocytes that have reached the MII phase compared to control treatments (P= 0.003). Differences were observed in cleavage rate (P< 0.05) between T150 and T200 when compared to the C/24 Group. A high difference was observed on blastocyst rate (P< 0.001) among treatments compared to the control group.

Dynamic changes in the global transcriptome of bovine germinal vesicle oocytes after vitrification followed by in vitro maturation

This study was conducted to investigate the effect of vitrification on the dynamics of the global transcriptome in bovine germinal vesicle (GV) oocytes and their in vitro-derived metaphase II (MII) oocytes. The GV oocytes were vitrified using the open-pulled straw method. After warming, GV oocytes and the resulting MII-stage oocytes were cultured in vitro for 2h and 24h respectively and were then collected. The fresh GV oocytes and their in vitro-derived MII oocytes were used as controls. Then, each pool (fresh GV, n=3; vitrified GV, n=4; fresh MII, n=1 and MII derived from vitrified GV, n=2) from the different stages was used for mRNA transcriptome sequencing. The results showed that the in vitro maturation rates of GV oocytes were significantly decreased (32.36% vs 53.14%) after vitrification. Bovine GV oocyte vitrification leads to 12 significantly upregulated and 19 downregulated genes. After culturing in vitro, the vitrification-derived MII oocytes showed 47 significantly upregulated and six downregulated genes when compared with those from fresh GV oocytes. Based on molecular function-gene ontology terms analysis and the Kyoto encyclopaedia of genes (KEGG) pathway database, the differentially expressed genes were associated with the pathways of cell differentiation and mitosis, transcription regulation, regulation of actin cytoskeleton, apoptosis and so on, which potentially result in the lower in vitro development of GV bovine oocytes.

Temporal expression pattern of steroid-metabolizing enzymes in bovine COC during in vitro maturation employing different gonadotropin concentrations

Steroid hormones are regulators in the fine-tuned process of follicular development. During final maturation in vivo a switch from oestradiol (E2) to progesterone (P4) dominance within the follicle is well-described. This change is accompanied by the resumption of meiosis and results in the maturation of the oocyte. It also suggests the important role of these hormones. However, present in vitro maturation (IVM) systems do not completely mimic the in vivo situation, resulting in oocytes of reduced quality. Aim of the study was to determine the temporal pattern of steroid hormone concentrations in the IVM medium of bovine cumulus-oocyte-complexes (COC) at defined time points. The influence of different gonadotropin supplementations during IVM on oocyte maturation, as well as the molecular quality of the oocytes and their corresponding cumulus cells was investigated. COCs were obtained from abattoir-derived ovaries and matured in medium added with different compounds of gonadotropins (eCG/hCG; FSH/LH, each at 0.05 IU or 0.01 IU; only FSH; without gonadotropins) employing a standard protocol without oil overlay. In experiment 1, medium, oocytes and cumulus cells were collected at different time points (0 h [control], 4 h, 8 h, 12 h, 16 h, 20 h, 24 h) after IVM in just eCG/hCG-supplemented medium. In experiment 2, medium, oocytes and cumulus cells were collected at 0 h (control) and after 24 h of IVM with all above-named supplements. The E2 concentration remained similar during IVM whereas P4 concentration increased during experiment 1. No significant changes could be determined after the addition of different gonadotropins (experiment 2). These results suggest that during IVM the temporal pattern of E2 and P4 did not correspond with the pattern during final maturation in vivo. RT-qPCR was used to assess the relative abundance of developmentally important genes in oocytes (BMP15; GDF9; ZAR1; PGR; PGRMC1/2; G6PD; StAR; ESR1/2; SULT1E1; STS; SOAT) and cumulus cells (ESR1/2; FSHR; LHCGR; CYP19A1; HSD3B1; PGR; PGRMC1/2; SULT1E1; STS; SOAT) at all collection points in both experiments. Most transcripts follow a time-regulated mRNA expression pattern during the entire in vitro maturation period. In addition, the expression of the analyzed transcripts was not influenced by the different gonadotropin supplementations during the IVM period. In all, this underlines that present conditions of IVM do not reflect the in vivo situation and require further optimisation.

Effects of meiotic inhibitors and gonadotrophins on porcine oocytes in vitro maturation, fertilization and development

This study evaluated the effect of three reversible meiotic inhibitors (MINs) and their interaction with gonadotrophins (Gns) on the meiotic maturation and developmental competence of porcine oocytes. In experiment 1, the oocytes were matured for 22 hr in the presence or absence of dbcAMP (1 mM), cycloheximide (7 μM) or cilostamide (20 μM) with or without Gns, and for an additional 22 hr in the absence of MINs and Gns. At 22 hr of maturation, regardless of the presence of Gns, a higher proportion (p < .001) of oocytes cultured in the presence of MINs were effectively arrested at the germinal vesicle stage compared with the oocytes cultured without MINs. At 44 hr of maturation, the proportion of oocytes that reached MII was higher (p < .05) in groups with Gns compared with groups without Gns. In experiment 2, oocytes that were matured as in experiment 1 were inseminated and cultured for 7 days to evaluate fertilization parameters and blastocyst formation. Only oocytes from the dbcAMP + Gns group had higher (p < .05) efficiency of fertilization compared with the other treatment groups. The presence of dbcAMP during maturation also increased (p < .05) blastocyst formation and efficiency of blastocyst formation in both the presence and absence of Gns. These results indicate that the interaction of Gns with the tested MINs improved meiotic progression. In addition, regardless of supplementation with Gns, the presence of dbcAMP during the first maturation period increased and even doubled the capacity of oocytes to develop to the blastocyst stage.

Meiosis progression and donor age affect expression profile of DNA repair genes in bovine oocytes

Several genetic and physiological factors increase the risk of DNA damage in mammalian oocytes. Two critical events are: (i) meiosis progression, from maturation to fertilization, due to extensive chromatin remodelling during genome decondensation; and (ii) aging, which is associated with a progressive oxidative stress. In this work, we studied the transcriptional patterns of three genes, RAD51, APEX-1 and MLH1, involved in DNA repair mechanisms. The analyses were performed by real-time quantitative PCR (RT-qPCR) in immature and in vitro matured oocytes collected from 17 ± 3-month-old heifers and 94 ± 20-month-old cows. Batches of 30-50 oocytes for each group (three replicates) were collected from ovarian follicles of slaughtered animals. The oocytes were freed from cumulus cells at the time of follicle removal, or after in vitro maturation (IVM) carried out in M199 supplemented with 10% fetal calf serum, 10 IU luteinising hormone (LH)/ml, 0.1 IU follicle-stimulating hormone (FSH)/ml and 1 μg 17β-oestradiol/ml. Total RNA was extracted by Trizol method. The expression of bovine GAPDH gene was used as the internal standard, while primers for bovine RAD51, APEX-1 and MLH1 genes were designed from DNA sequences retrieved from GenBank. Results obtained indicate a clear up-regulation of RAD51, APEX-1 and MLH1 genes after IVM, ranging between two- and four-fold compared with germinal vesicle (GV) oocytes. However, only RAD51 showed a significant transcript increase between the immature oocytes collected from young or old individuals. This finding highlights RAD51 as a candidate gene marker for discriminating bovine immature oocytes in relation to the donor age.