Low mitochondrial DNA and ATP contents contribute to the absence of birefringent spindle imaged with PolScope in in vitro matured human oocytes

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Abstract
Birefrigent meiotic spindle in live human oocytes can be visualized by the PolScope. This study investigated the relationship between birefrigent meiotic spindle and cytoplasmic mitochondrial DNA (mtDNA) and ATP contents in in vitro matured human oocytes. Oocytes at germinal vesicle stage were collected and cultured for 24–48 h with or without the metabolic inhibitor, carbonyl cyanide p-(tri-fluromethoxy) phenyl-hydrazone (FCCP). All in vitro matured oocytes were examined by PolScope for the presence of meiotic spindle, then the oocytes were used for either intracytoplasmic sperm injection or the measurement of mitochondrial quantity and ATP content. Meiotic spindles were observed in 51.3% (60/117) of the in vitro matured oocytes. Oocytes with detectable meiotic spindle contained significantly higher mtDNA copies (637 250 ± 237 606 versus 491 454 ± 153 406, P = 0.027) and ATP content (1.97 ± 0.38 versus 1.65 ± 0.32 pmol, P = 0.028) when compared with those without detectable meiotic spindle. However, in vitro matured oocytes showed a significantly reduced rate of positive meiotic spindle and a lower ATP content when cultured with FCCP. A lower incidence of normal fertilization and good quality embryos were observed if meiotic spindles were not detected. Low mtDNA and ATP content might contribute to the absence of birefringent spindle imaged with the PolScope in human in vitro matured oocytes.

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