Cytoplasmic factors influence mitochondrial reorganization and resumption of cleavage during culture of early mouse embryos

The mitochondrial distribution pattern has been monitored innormally cleaving and developmentally arrested preimplan tatlonmouse embryos in vitro and compared with the distribution foundimmediately after flushing from the oviduct in vivo. Mitochondriain normally cleaving embryos in vitro and in vivo were foundto be homogeneously distributed throughout the cytoplasm ofthe blastomeres during interphase. In developmentally arrestedembryos in vitro the mitochondrla became progressively aggregatedand localized in the perinuclear region and the area of thecytocortex immediately adjacent to the plasma membrane. Injectionof G₂ cell cyde cytoplasmic factor(s) from a cycling 2-cellembryo into an arrested embryo resulted in the re-initiationof normal deavage. Concomitant with the re-initiation of cleavage,a re-distribution of the aggregated mitochondria to the pattern,associated with normally cycling embryos, was observed. Specificmitochondrial translocatiofts to the mitotic spindle were observedduring deavage. The results have shown that observation of themltochoiidrial distribution using the vital stain Rhodamlne123, provides an accurate and reliable prediction of an embryo'sability to proceed through the next cleavage stage and developin vitro and suggests that the specific association of mitochondriawith the mitotic spindle is a prerequisite for normal deavage.