Abstract. The follicle is a unique micro-environment within which the oocyte can develop and mature to a fertilisable gamete. The aim of this study was to investigate the ability of a panel of follicular parameters, including intrafollicular steroid and metabolomic profiles and theca, granulosa and cumulus cell candidate gene mRNA abundance, to predict the potential of bovine oocytes to develop to the blastocyst stage in vitro. Individual follicles were dissected from abattoir ovaries, carefully ruptured under a stereomicroscope and the oocyte was recovered and individually processed through in vitro maturation, fertilisation and culture. The mean (AE s.e.m.) follicular concentrations of testosterone (62.8 AE 4.8 ng mL ) were not different (P . 0.05) between oocytes that formed (competent) or failed to form (incompetent) blastocysts. Principal-component analysis of the quantified aqueous metabolites in follicular fluid showed differences between oocytes that formed blastocysts and oocytes that degenerated; L-alanine, glycine and L-glutamate were positively correlated and urea was negatively correlated with blastocyst formation. Follicular fluid associated with competent oocytes was significantly lower in palmitic acid (P ¼ 0.023) and total fatty acids (P ¼ 0.031) and significantly higher in linolenic acid (P ¼ 0.036) than follicular fluid from incompetent oocytes. Significantly higher (P , 0.05) transcript abundance of LHCGR in granulosa cells, ESR1 and VCAN in thecal cells and TNFAIP6 in cumulus cells was associated with competent compared with incompetent oocytes.

Abstract. The aim of this study was to develop an in-straw dilution method suitable for 1-step bovine embryo transfer of vitrified embryos using the Cryotop vitrification-straw dilution (CVSD) method. The development of embryos vitrified using the CVSD method was compared with those of embryos cryopreserved using in-straw vitrificationdilution (ISVD) and conventional slow freezing, outside dilution of straw (SFODS) methods. In Experiment 1, in vitroproduced (IVP) embryos cryopreserved using the CVSD method were diluted, warmed and exposed to the dilution solution at various times. When vitrified IVP embryos were exposed to the dilution solution for 30 min after warming, the rates of embryos developing to the hatched blastocyst stage after 72 h of culture (62.0-72.5%) were significantly lower (P<0.05) than those of embryos exposed to the solution for 5 and 10 min (82.4-94.3%), irrespective of supplementation with 0.3 M sucrose in the dilution solution. In Experiment 2, the rate of embryos developing to the hatching blastocyst stage after 48 h of culture in IVP embryos cryopreserved using the SFODS method (75.0%) was significantly (P<0.05) lower than those of embryos cryopreserved using the CVSD and ISVD methods (93.2 and 97.3%, respectively). In Experiment 3, when in vivo-produced embryos that had been cryopreserved using the CVSD, ISVD and SFODS methods and fresh embryos were transferred to recipient animals, no significant differences were observed in the conception and delivery rates among groups. In Experiment 4, when IVP embryos derived from oocytes collected by ovum pick-up that had been cryopreserved using the CVSD and ISVD methods and fresh embryos were transferred to recipient animals, no significant differences were observed in the conception rates among groups. Our results indicate that this simplified regimen of warming and diluting Cryotop-vitrified embryos may enable 1-step bovine embryo transfer without the requirement of a microscope or other laboratory equipment. Key words: Bovine, Conception rate, Cryotop, Embryo transfer, Vitrification (J. Reprod. Dev. 57: [437][438][439][440][441][442][443] 2011) ince the first successful cryopreservation of bovine embryos [1], cryopreservation of bovine embryos has been widely used commercially. A recent worldwide inventory revealed that more than 250,000 bovine in vivo-produced embryos have been used for embryo transfer (ET) after freezing and thawing [2]. However, the pregnancy rate of frozen-thawed embryos is slightly lower than that of fresh embryos [3]. And the pregnancy rate of frozen-thawed in vitro-produced (IVP) embryos is also significantly lower than that of fresh IVP embryos. Therefore, it is necessary to develop an embryo cryopreservation method to obtain higher conception rates. Recent reports have confirmed that vitrification of embryos, especially IVP embryos, is at least as efficient as conventional slow freezing [4][5][6][7]. Vitrification reduces the time commitment and equipment expense associated with cryopreservation compared with con...

Abstract. Mitochondrial bioenergetics in mammalian oocytes has not been sufficiently characterized. In this study, the function of oxidative phosphorylation (OXPHOS), a major pathway in mitochondria, was investigated in individual bovine oocytes by monitoring oxygen consumption using modified scanning electrochemical microscopy (SECM). At the germinal vesicle (GV) stage, 65% of basal respiration was used for mitochondrial respiration, which was inhibited by complex IV inhibitor. Around 63% of mitochondrial respiration was coupled to ATP synthesis, as determined by sensitivity to an ATP synthase inhibitor, and the remaining 37% was attributed to proton leak. In contrast, 50% and 43% of mitochondrial respiration were used for ATP synthesis in in vivo-and in vitro-derived metaphase II (MII)-stage oocytes, respectively. ATP-linked respiration, in both in vivo-and in vitro-derived MII-stage oocytes, was significantly lower than in GV-stage oocytes, suggesting that OXPHOS in bovine oocytes is more active at the GV stage compared with the MII stage. Interestingly, basal respiration in in vitro-derived MII oocytes was significantly higher than for in vivo-derived oocytes, reflecting an increase in proton leak. Next, we assessed respiration in MII oocytes cultured for 8 h. The aged oocytes had a significantly reduced maximum respiratory capacity, which was stimulated by a mitochondrial uncoupler, and reduced ATP-linked respiration compared with non-aged oocytes. However, the aging-related phenomenon could be prevented by caffeine treatment. We conclude that OXPHOS in bovine oocytes varies in the transition from GV to MII stage, in vitro maturation and the aging process. This approach will be particularly useful for analyzing mitochondrial bioenergetics in individual mammalian oocytes. Key words: Bovine, Mitochondrial function, Oocyte, Oxidative phosphorylation, Oxygen consumption (J. Reprod. Dev. 58: [636][637][638][639][640][641] 2012) M itochondria play fundamental roles in the cell, and mitochondrial dysfunction has been linked with several pathologies, including infertility and developmental failure. Although they share general characteristics, mitochondria can have distinct features based on inner membrane invaginations and matrix structures. Depending on their cell type and functional status, mitochondria present an extensive range of morphologies, are functionally heterogeneous [1], and vary in number [2]. Oxidative phosphorylation (OXPHOS), the process that couples substrate oxidation to ATP synthesis, is the major and best-known metabolic function of mitochondria. During OXPHOS, electrons are transferred from nutrients to reducing equivalents (e.g., NADH), then to electron carriers, and finally to oxygen. Such electron transfer is mediated by oxido-reductive reactions of the tricarboxylic acid cycle in the mitochondrial matrix and by electron transport in the inner mitochondrial membrane. The energy harvested during these oxido-reductive reactions is stored in a proton gradient across the inner mitochondrial ...

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