Reproduction Abstracts

Introduction: Mitochondria are abundant in fully-grown mammalian oocytes with a unique spherical morphology, but the manner in which the behavior of mitochondria is controlled is not well understood. We explored the spatiotemporal control of mitochondrial morphology by mitochondrial fusion and fission mechanisms and the functional impact of that control on meiotic division, using mouse oocytes.

Materials and methods: Immature oocytes were collected from the ovaries of CD1 female mice. Oocytes were microinjected with mRNAs encoding mitochondrial fusion and fission proteins, i.e. Mfn1, Mfn2, Opa1, and Drp1. Oocytes were matured in vitro for 16 h. Mitochondria were labeled with green fluorescence protein and the subcellular distribution of mitochondria during meiotic division wass examined using confocal microscopy. To investigate the colocalization of mitochondria with endoplasmic reticulum (ER) or chromosomes, mCherry-tagged ER and histone H2B were expressed in oocytes respectively.

Results and discussion: Overexpression of Mfn1 or Mfn2 causes marked mitochondrial aggregation, particularly in the perinuclear region during meiotic progression. This aggregation occurs because of the contact between mitochondrial outer membranes, but not of the interconnected tubules. Tracking of mitochondria with chromosomes or ER throughout the first meiotic division demonstrates that Mfn-promoted mitochondrial aggregation disturbs the spatiotemporal dynamic of the ER and chromosomes. Our findings suggest that organelle dynamics are coordinately controlled during meiotic division, and an imbalance of mitochondrial fusion/fission leads to disorganization of the organelle compartments.