Mitochondrial Calcium uniporters are essential for meiotic progression in mouse oocytes by controlling Ca2+ entry.

OBJECTIVES: The alteration of bioenergetics by oocytes in response to the demands of various biological processes plays a critical role in maintaining normal cellular physiology. However, little is known about the association between energy sensing and energy production with energy-dependent cellular processes like meiosis. MATERIALS AND METHODS: We demonstrated that cell cycle-dependent mitochondrial Ca2+ connects energy sensing to mitochondrial activity in meiosis progression within mouse oocytes. Further, we established a model in mouse oocytes using siRNA knockdowns that target mitochondrial calcium uniporters (MCUs) in order to inhibit mitochondrial Ca2+ concentrations. RESULTS: Decreased numbers of oocytes successfully progressed to the germinal vesicle stage and extruded the first polar body during in vitro culture after inhibition, while spindle checkpoint-dependent meiosis was also delayed. Mitochondrial Ca2+ levels changed, and this was followed by altered mitochondrial masses and ATP levels within oocytes during the entirety of meiosis progression. Abnormal mitochondrial Ca2+ concentrations in oocytes then hindered meiotic progress and activated AMP-activated protein kinase (AMPK) signalling that is associated with gene expression. CONCLUSIONS: These data provide new insight into the protective role that MCU-dependent mitochondrial Ca2+ signalling plays in meiotic progress, in addition to demonstrating a new mechanism of mitochondrial energy regulation by AMPK signalling that influences meiotic maturation.

Cryopreservation of Porcine Embryos: Recent Updates and Progress.

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Cytokeratin distribution and expression during the maturation of mouse germinal vesicle oocytes after vitrification.

Cytokeratin (CK) is a type of the cytoskeleton that increases cell stabilization during oocyte maturation. This study was conducted to investigate the effect of vitrification on the distribution and expression of CK during mouse oocyte maturation. Germinal vesicle (GV) oocytes were randomly allocated into three groups: (1) untreated (fresh), (2) exposed to vitrification solution (VS) without being plunged into liquid nitrogen (CPA exposure), or (3) vitrified using the open-pulled straw (OPS) method (vitrification). The oocytes were then incubated for 0 h, 6h (metaphase I (MI) stage), and 10h (metaphase II (MII) stage). The CK distribution in the oocytes at the GV, MI, and MII stages was observed by immunofluorescence, and the expression at the MII stage oocytes derived from vitrified GV oocytes was detected by Western blotting. The CK distribution in the GV oocytes (88.5%) displayed a cortical pattern in the fresh group, whereas a granular pattern was mainly found at the MI (86.7%) and MII (93.5%) stages. In the CPA exposure group, 90.3% of the GV oocytes were observed to display the cortical pattern, and 69.2% of the MI oocytes and 92.9% of the MII oocytes showed the granular pattern. In the vitrification group, most oocytes (GV, 88.9%; MI, 100%; MII, 93.3%) exhibited the cortical pattern. The CK fluorescence intensities of the MII stage oocytes in both the fresh (59.27) and CPA exposure (60.05) group were significantly higher than that of the vitrification (26.53) group (p<0.05). Western blotting showed that the CK expression in the MII oocytes derived from vitrified GV oocytes was significantly lower (p<0.05) than in the control. In conclusion, OPS vitrification affects the normal CK distribution pattern during oocyte maturation and results in decreased CK expression in MII oocytes derived from vitrified GV oocytes.