Mitochondrial aggregation patterns and activity in human oocytes and preimplantation embryos

Mitochondria play a vital role in the metabolism of energy-containing compo unds in the oocyte cytoplasm to provide adenosine trisphosphate for fertili zation and preimplantation embryo development. In this study, ratiometric c onfocal microscopy with the mitochondrion-specific membrane potential-sensi tive fluorescence dye JC-l (5,5 ' ,6,6 ' -tetrachloro-1,1 ' ,3,3 ' -tetraet hylbenzimidazolyl-carbocyanine iodine) was used to measure the activity of mitochondria in human oocytes and developing preimplantation embryos. Mitoc hondria in oocytes and embryos were characterized by distinct localized agg regation patterns. These patterns however did not determine localized regio ns of heterogeneity in mitochondrial activity. Mitochondrial activity was a nalysed during oocyte maturation and after fertilization. The activity of m itochondria in fresh metaphase II oocytes was negatively correlated with ma ternal age. This trend continued when the activity of developing embryos wa s analysed. Mitochondrial activity was strongly correlated with the rate of embryo development on day 3 after fertilization, but not on day 2, Partial regression analysis showed that the rate of cleavage of preimplantation em bryos was more highly correlated,vith embryo mitochondrial activity than ma ternal age. These data suggest that the efficiency of mitochondrial respira tion in oocytes and preimplantation embryos is closely correlated with the programmed rate of embryo development, and suggest that maternal age furthe r influences this factor. The loss of mitochondrial activity in oocytes obt ained from ageing couples may therefore contribute to lower embryo developm ent and pregnancy rates observed during cycles of IVF.