Mitochondrial reorganization during resumption of arrested meiosis in the mouse oocyte

Correlated nuclear and cytoplasmic reorganizations during the 14 hr of reactivated meiosis in vivo and in vitro were examined in the laboratory mouse. Observations of living oocytes by differential interference contrast microscopy, and by fluorescent microscopy with nontoxic mitochondrial and DNA-specific probes, enabled us to determine that the major cytoplasmic reorganization involved two mitochondrial translocations associated with two stages of nuclear maturation. These observations were confirmed at the fine structural level by parallel transmission electron microscopy. Mitochondria translocate to the perinuclear region during formation of the first metaphase spindle and subsequently disperse during abstriction of the first polar body. Determinations of frequency of maturation in more than 2,900 normal oocytes, and in more than 1,100 oocytes in which germinal vesicle breakdown was reversibly inhibited, indicated that mitochondrial redistributions are a normal and probably necessary feature of reactivated meiosis in the laboratory mouse. We suggest that these two rapid translocations serve to concentrate mitochondria for localized activities that require elevated levels of adenosine triphosphate.