Cytoplasmic streaming induced by intracytoplasmic spindle translocation contributes to developmental competence through mitochondrial distribution in mouse oocytes

To evaluate the developmental competency of mouse metaphase II oocytes and the pattern of mitochondrial positioning through cytoplasmic streaming in mouse metaphase II oocytes.We observed cytoplasmic streaming as movement indicated by fluorescently stained mitochondria using a newly developed method in which the spindle is translocated to the opposite site of the oocyte. This method is termed as intracytoplasmic spindle translocation (ICST).University research laboratory.Female B6D2F1 mice.None.Fresh oocytes, postovulatory-aged oocytes, and oocytes treated with cytochalasin B were classified based on the presence of cytoplasmic streaming induced by ICST. The pattern of redistributed mitochondria and developmental competence caused by parthenogenetic activation were evaluated in oocytes with or without cytoplasmic streaming.Induced cytoplasmic streaming occurred in 84% of the fresh oocytes but not in the postovulatory-aged oocytes and the oocytes treated with cytochalasin B. Abnormal mitochondrial aggregation was observed in oocytes in which cytoplasmic streaming was not induced. Furthermore, the developmental competence was significantly lower in oocytes without cytoplasmic streaming.Cytoplasmic streaming induced by ICST contributes to developmental competence through the redistribution of mitochondria and may be a valuable criterion for predicting early developmental competence in mouse oocytes.