Expression, regulation, and function of progesterone receptors in bovine cumulus oocyte complexes during in vitro maturation

Progesterone (P4) exerts its effects by binding to specific genomic (nPR-A/B) and non-genomic (mPRalpha/beta, PGRMC1/2) receptors. P4 has a role in the regulation of the ovulatory cycle, but its participation in oocyte maturation in mammals has not yet been clarified. Therefore, the aim of the present study was to characterize the protein expression of P4 receptors (PRs) in bovine oocytes and cumulus cells during in vitro maturation (IVM) and to study the effect of P4 and its receptors on oocyte developmental competence. Cumulus-oocyte complexes (COCs) were subjected to IVM, in vitro fertilization, and in vitro culture. IVM was performed for 24 h in the presence or absence of P4, luteinizing hormone (LH), follicle-stimulating hormone (FSH), trilostane, promegestone (R5020), mifepristone (RU 486), or antibodies against mPRalpha or mPRbeta. Protein expression of PRs was studied by Western blotting and immunofluorescence. The results demonstrate the presence of both genomic and nongenomic PRs in bovine COCs. The dynamic changes observed in the protein expression of PRs following IVM or in response to supplementation with LH, FSH, or P4 suggest an important role during bovine oocyte maturation. Inhibition of P4 synthesis by cumulus cells or blocking of nPR and mPR alpha activity produced a decrease in bovine embryo development, indicating that P4 intracellular signaling is mediated by its interaction with nuclear and membrane PRs and is important for oocyte developmental competence.     

Cyclooxygenase-2 is expressed by cumulus cells during oocyte maturation in cattle.

Prostaglandins could be involved in various aspects of final differentiation of ovarian follicles. Prostaglandins are generated by the cyclooxygenase (cox) pathway. Until now, the expression pattern of isoforms cox-1 and cox-2 of cyclooxygenase in bovine cumulus-oocyte complexes (COCs) was unknown. Using immunodetection procedure, we demonstrated in the present study that cox-2 was expressed by cumulus cells during in vivo and in vitro maturation. Time course induction of cox-2 expression was investigated during in vitro maturation using Western blot analysis. Specific signal of cox-2 was markedly evidenced from 6 hr of culture and increased to reach a maximal level at 24 hr of culture. In vitro, cox-2 expression in COCs was associated with increased concentrations of PGE(2) and PGF(2alpha) in the maturation medium. In addition, the effects of culture conditions on cox-2 expression was considered using RT-PCR and Western-blot analysis. We demonstrated that the addition of 10 ng/ml of EGF to TCM199 clearly increased the expression level of cox-2 mRNA and protein. Higher levels of in vitro cox-2 expression was associated with greater rates of cumulus expansion and oocytes at metaphase II at 24 hr of culture. In conclusion, our present results suggest that cox-2 expression in cumulus cells may be involved in differentiation of COCs that occurs during oocyte maturation.     

Influence of hyaluronan accumulation during cumulus expansion on in vitro porcine oocyte maturation

During oocyte maturation, the cumulus-oocyte complexes (COCs) expand dramatically. This phenomenon, which is known as cumulus expansion, is the result of the synthesis and accumulation of hyaluronan in the extracellular space between cumulus cells. The purpose of this study was to investigate the effect of 6-diazo-5-oxo-l-norleucine (DON), an inhibitor of hyaluronan synthesis, on cumulus expansion during in vitro porcine oocyte maturation and hyaluronan accumulation within COCs. Further, this study aimed to examine the influence of hyaluronan accumulation within COCs on the rate of oocyte maturation. Cumulus expansion was observed during in vitro maturation. However, the addition of DON to the maturation medium significantly inhibited cumulus expansion. The total inhibition of hyaluronan accumulation within COCs was observed with the use of confocal microscopy. Moreover, a positive correlation between the area of cumulus expansion and the rate of oocyte maturation was observed. These results demonstrate that the hyaluronan accumulation within the COCs during oocyte maturation affects oocyte maturation. On the basis of these results, we propose that hyaluronan accumulation within the COCs during cumulus expansion is a necessary step in the porcine oocyte maturation process.     

Coculturing denuded oocytes during the in vitro maturation of bovine cumulus oocyte complexes exerts a synergistic effect on embryo development

The present study examined the effect of coculturing cumulus oocyte complexes (COCs) and denuded oocytes (DOs) during in vitro maturation (IVM) on nuclear and cytoplasmic maturation, zona pellucida (ZP) hardening, the pattern of fertilization and glutathione peroxidase 1 (GPX1) gene expression in the oocyte. Furthermore, the rate of embryonic development and the quality of blastocysts were examined for both COCs and DOs. Three IVM conditions were studied: 1) the coculture of 12 COCs and 60 DOs, 2) COC control with 12 COCs, and 3) DO control with 60 DOs. The IVM was performed in a 120-μl droplet of TCM199-based IVM medium. Following IVM, in vitro fertilization (IVF) and in vitro culture (IVC) were conducted separately for the COCs and DOs (DO coculture) from the IVM coculture group. Coculturing COCs and DOs increased the percentage of oocytes reaching the blastocyst stage and the total number of cells per blastocyst in both the COC coculture (44.4 ± 8.6 vs 26.7 ± 9.7%, P < 0.01, and 137.9 ± 24.9 vs 121.7 ± 21.1, P < 0.05) and the DO coculture (20.5 ± 5.0 vs 11.1 ± 2.5%, P < 0.01, and 121.9 ± 27.5 vs 112.3 ± 33.2, P < 0.05) compared to their respective control groups. The synergistic effects of coculturing were detected as increased nuclear and cytoplasmic maturation, the prevention of ZP hardening, increased monospermic fertilization and increased expression of GPX1 in the oocytes in response to endogenous oocyte-secreted factors. In conclusion, coculturing COCs and DOs may be an effective culture system for both intact COCs and immature DOs.     

Supplementation with vascular endothelial growth factor during in vitro maturation of porcine cumulus oocyte complexes and subsequent developmental competence after in vitro fertilization

The aim of the present study was to investigate whether the effects of vascular endothelial growth factor (VEGF) on porcine cumulus oocyte complexes (COCs) and subsequent blastocyst formation following in vitro fertilization are attributable to improved fertilization and cytoplasmic maturation. Porcine COCs were cultured for 42 h in TCM199 medium with 5 ng/mL human recombinant VEGF, and the resultant metaphase II oocytes were fertilized in vitro. COCs without VEGF supplementation served controls. Supplementation with VEGF during in vitro maturation (IVM) significantly (P < 0.05) improved the blastocyst formation rate and total cell number (46.7 ± 3.1% and 82.8 ± 6.7, respectively) compared with controls (32.5 ± 3.4% and 64.1 ± 5.6, respectively). On day 2, the percentage of four-cell stage embryos was significantly higher in the VEGF-matured group (49.1 ± 2.7%) than in the control (33.1 ± 5.8%), and the percentage of two-cell stage embryos was significantly higher in the control group (10.4 ± 1.4%) than in the VEGF-matured group (6.6 ± 0.9%). At 10 h after the onset of in vitro fertilization (IVF), oocytes with two pronuclei were considered as monospermically or normally fertilized, and oocytes with more than two pronuclei were considered as polyspermically fertilized. Monospermy was significantly higher in VEGF-matured oocytes (47.2 ± 4.3%) than in the control (20.0 ± 2.4%), and polyspermy and sperm penetration per oocyte were significantly higher in the control group (54.4 ± 3.8% and 2.3 ± 0.1, respectively) than in the VEGF-matured oocytes (43.9 ± 3.6% and 1.8 ± 0.1, respectively). Supplementation with VEGF during IVM significantly (P < 0.05) improved male pronuclear formation as compared with the control (91.1 ± 1.9 vs 74.4 ± 3.8%). Type III cortical granule distribution in oocytes was more common in VEGF-matured oocytes (78.0%) than in the control (52.1%). These results suggest that VEGF supplementation during IVM enhanced the developmental potential of porcine IVF embryos through higher male pronuclear formation and higher monospermic fertilization rates as a consequence of improved cytoplasmic maturation.     

褪黑素抑制小鼠卵母细胞的体外成熟

目的:探讨褪黑素(MT)对小鼠卵母细胞的体外成熟的影响.方法:通过卵母细胞自发、次黄嘌呤(HX)阻滞和激素诱导成熟三种体外培养模型研究了褪黑素(MT)对小鼠卵母细胞体外成熟的影响.结果:①0.1 g/L、0.02g/L、0.004 g/L及0.0008 g/L浓度的MT均能显著抑制小鼠卵丘卵母细胞复合体(CEOs)自发成熟过程中第一极体(PB1)的释放(P＜0.01);②动力曲线分析表明,MT对自发成熟的CEOs的GVBD和PB1有显著的推后作用,与对照组相比,处理组的GVBD和PB1分别被推后8～10 h和3～4 h;③0.1 g/L和0.02 g/L两有效浓度的MT还能显著抑制促性腺激素(FSH)诱导的HX阻滞的CEOsGVBD的发生(P＜0.05),对PB1的排出虽有一定的抑制作用,但没有统计学意义;④MT和次黄嘌呤(HX)对CEOs的自发成熟有协同抑制作用(P＜0.01),但在裸卵(DO)自发成熟的阻滞中没有协同效应.结论:MT是调节哺乳动物卵母细胞成熟的重要激素之一,其作用机制可能是通过卵丘细胞实现的.     

Effect of vitrification on meiotic maturation and expression of genes in immature goat cumulus oocyte complexes

The aim of the study was to evaluate meiotic maturation, and expression of genes coding for oocyte secreted factors (GDF9, BMP15, TGFBR1, and BPR2) and apoptosis (BCL2, BAX and P53) after vitrification of immature goat cumulus oocyte complexes (COCs) and in vitro maturation. COCs were vitrified in a solution containing ethylene glycol, dimethyl sulfoxide and sucrose using either a conventional straw (CS), open pulled straw (OPS), cryoloop (CL), hemistraw (HS) or cryotop (CT). Freshly collected COCs (Control), COCs exposed to vitrification and dilution solutions without cryopreservation (EC) and vitrified-warmed COCs were matured in vitro for 27h. The viability of vitrified-warmed COCs 2 h post warming and in vitro maturation was similar for CL, HS and CT. The proportion of oocytes that extruded a 1st polar body and reached TI/MII was significantly higher with CT and HS followed by CL, OPS and CS. Gene expression of GDF9, BMP15, BMPR2, BAX and P53 were comparable to control levels for OPS, CL, HS and CT. The gene expression pattern in CS vitrified COCs was by contrast changed in that GDF9, BMP15, TGFBR1 and BAX were up regulated and BMPR2, BCL2 and P53 down regulated. In conclusion immature goat COCs vitrified using CT and HS showed that viability, maturation rates and expression of genes coding for oocyte secreted factors and apoptosis were similar to non-vitrified controls.     

Specificity of epidermal growth factor action on maturation of the murine oocyte and cumulus oophorus in vitro

Experiments were carried out to determine the specificity of growth factor action on maturation of the oocyte-cumulus cell complex in vitro. Cumulus cell-enclosed oocytes (CEO) from primed mice were maintained in meiotic arrest in vitro with hypoxanthine (HX) and treated with one of ten different growth-promoting factors. The percentage of germinal vesicle breakdown (GVB) in the HX controls ranged from 44 to 64.7% after 21-22 h. Oocytes responded to treatment with growth-promoting factors in one of three ways: (1) no response; (2) low response; or (3) high response. The nonresponding groups included transforming growth factor-beta, platelet-derived growth factor, bombesin, sodium orthovanadate, nerve growth factor, and insulin-like growth factors I and II, each of which had no statistically significant effect on GVB. Insulin and fibroblast growth factor were members of the low response group and stimulated increases in GVB of 21.2 24.9%. Epidermal growth factor (EGF) was the only factor that produced a high frequency of maturation in the CEO; 100% of the arrested CEO were stimulated to undergo GVB in response to EGF treatment (a 51% increase over controls). No interaction was observed when EGF was tested with follicle-stimulating hormone (FSH) on hormone-induced GVB. When tested for an action on cumulus cell expansion, EGF was the only growth-promoting factor that triggered this response and did so more effectively than FSH. Heparin suppressed cumulus expansion in both EGF- and FSH-treated CEO, but did not prevent GVB stimulated by either hormone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the culture medium composition on cattle oocyte maturation and embryogenesisin vitro

We studied the capacity of the cattle oocyte for the resumption of meiosis and the achievement of metaphase II in various protein-free culture media (DMEM, TCM-199, Ham’s F-10, and Ham’s F-12) and the pattern of influence of the estrous serum on thein vitro development of fertilized cattle oocytes, with special reference to the time of its addition to the synthetic oviduct fluid containing BSA. In the first experimental series, it was shown that the highest number of oocytes (76.1%) resumed meiosis in DMEM medium. Meiosis was not resumed in Ham’s F-12. Intermediate results were obtained for TCM-199 (55.1%), which is commonly used for the maturation of cattle oocytesin vitro and for Ham’s F-10 (51.7%). The oocytes reached metaphase II in DMEM at a higher rate (45.3%) than in TCM-199 or Ham’s F-10 (29.4 and 8.6%, respectively). In the second experimental series, the estrous serum was added to the culture medium within 20 h (control) or 42 h (experiment) after the beginning of fertilization. The estrous serum did not inhibit the first cleavage division (the percentage of cleaving embryos did not differ reliably: 32.7 and 37.9%, respectively). However, a later serum addition to the culture medium (within 42 h after the beginning of fertilization) reliably increased the percentage of embryos that reached the blastocyst stage (6.5% in the control and 17.8% in the experiment) and the hatched blastocyst stage (2 and 9.2%, respectively).     

Role of cumulus cells for rat oocyte maturation and metabolism

Oocytes collected from immature PMSG-treated rats on the morning of proestrus were allowed to mature in culture either surrounded by their cumulus cells or after denudation. It was found that the time course of oocyte nuclear maturation was similar whether the cumulus cells were present or not. The oxygen consumption of noncultured oocytes was 0.12 nl/hr/oocyte and increased by 40% after four to eight hours in culture with intact cumulus. Respiration of oocytes cultured without cumulus remained constant throughout the culture, except for a transient decrease after four hours. It is concluted that the cumulus cells do not affect the spontaneous nuclear maturation in vitro, but that the metabolism in oocytes cultured with intact cumulus is different from that of cultured denuded oocytes. Furthermore, it appears that the rise in oocyte oxygen consumption is not a prerequisite for nucler maturation.     

Ultrastructure of in-vitro oocyte maturation in cattle

Cumulus-oocyte complexes were collected from cows at an abattoir by aspiration from small (1-6 mm) antral follicles. After different periods of culture the complexes were processed for electron microscopy. Cumulus expansion occurred at 12-18 h of culture and concomitantly enlargement of cumulus cell projections in the perivitelline space was seen. At 48 h the innermost cumulus cells flattened and adhered tightly to the zona pellucida. In the oocyte the following changes occurred: at 0-3 h of culture the perivitelline space developed; at 3-12 h disconnection of the junctions between cumulus cell projections and the oolemma, and the concomitant breakdown of the nucleus was observed; at 12-18 h the mitochondria moved from a peripheral location to a more even spatial distribution and the Golgi complexes decreased in size; at approximately 18 h the smooth endoplasmic reticulum formed large aggregates surrounded by mitochondria; at 18-21 h the first polar body was abstricted; at 24-40 h the cortical granules spread; at 30-40 h the polar body degenerated in some specimens; at 40-48 h the perivitelline space decreased in size; and at 48 h one oocyte was in the process of fragmentation. It is concluded that nuclear and cytoplasmic oocyte maturation is simulated in vitro. However, certain deviations were noticed compared to in-vivo maturation.     

The relationship between cumulus cell-oocyte coupling,oocyte meiotic maturation,and cumulus expansion

The timing of the reduction of cumulus cell-oocyte coupling was correlated with oocyte meiotic maturation and the expansion (mucification) of the cumulus oophorus using immature mice treated with gonadotropins. Three hours after the injection of an ovulatory dose of human chorionic gonadotropin (hCG), more than 90% of the oocytes isolated from large Graafian follicles had undergone germinal vesicle breakdown, indicating that oocyte meiotic maturation had been initiated. However, no cumulus expansion or reduction of intercellular coupling was detected at this time. By 6 hr after hCG injection, the index of oocyte-cumulus cell coupling was still not less than that found in oocyte-cumulus cell complexes isolated from control mice not receiving hCG. Cumulus expansion at 6 hr post-hCG was limited to the outer cumulus cells while those adjacent to the oocyte were still tightly packed. Cumulus expansion appeared complete by 9 hr after hCG injection and the cumulus cell-oocyte coupling index was greatly reduced. These results show that oocyte meiotic maturation in the mouse is not initiated by a reduction in cumulus cell-oocyte coupling or by cumulus expansion. However, the results suggest that the reduction of intercellular coupling in vivo may be a result of cumulus expansion.     

Studies of the role of steroid hormone in the regulation of oocyte maturation in cattle

Background  

The objective of this study was to investigate whether the steroid hormone(s) secreted from cumulus-oocyte complexes (COCs) is a prerequisite for bovine oocyte maturation and cumulus expansion using aminoglutethimide (AGT), a P450 cholesterol side-chain cleavage inhibitor.     

Dynamic changes of estradiol and progesterone concentrations during in vitro oocyte maturation in cattle

Two culture techniques, an open system using 1.0-ml medium and a covered system using 50-mul droplets of medium covered by paraffin oil, used for in vitro bovine follicular oocyte maturation were compared. Estradiol-17beta (E2) was added to Ham's F-10 medium together with other supplementations. In the absence of oocytes, E2 concentration remained unchanged in the 1.0-ml open system, but it decreased gradually in the 50-mul covered system. In the presence of oocytes, E2 increased significantly in the 1.0-ml open system, but this increase could not be detected in the 50-mul covered system. Progesterone (P4) concentration increased in both systems, but it was much higher in the 1.0-ml culture than in the 50-mul culture. The two culture systems allowed an identical nuclear oocyte maturation rate of 88.6 vs 87.0%, a sperm penetration rate of 54.3 vs 59.6%, and a polyspermy rate of 6.8 vs 11.6% for 1.0-ml and 50-mul systems, respectively. The cleavage rate, however, differed significantly (78.3 vs 41.7% for 1.0-ml and 50-mul systems, respectively). It is concluded that diffusion of steroids into the paraffin oil occurs and may affect the cleavage rate but not the maturation or penetration rate.     

Quantitative inhibitory influence of porcine cumulus cells upon the maturation of pig and cattle oocytes in vitro

Porcine cumulus oocyte complexes (COCs) were cultured together in 10-microliters droplets of culture medium. When 10 COCs were cultured for 24 h, germinal vesicle breakdown (GVBD) occurred in 81% of them. When more COCs (20 or 40) were put into the same volume of medium the frequency of GVBD gradually decreased. This inhibition was not observed in denuded oocytes. The process of GVBD was adversely influenced when 10 COCs were cultured in cumulus-preconditioned medium. It is concluded that porcine cumulus cells produced a factor inhibiting GVBD. After removing the inhibitory block and extensive washing, GVBD of arrested oocytes was significantly accelerated. The addition of LH or heparin only partially overcame the inhibitory action. This factor produced by porcine cumulus cells negatively influenced maturation of bovine oocytes; however, a similar effect was not demonstrated in the mouse. Our results suggest that a high concentration of porcine cumulus cells exerts a quantitative inhibitory effect upon GVBD of porcine and cattle oocytes cultured in vitro.