Actin filaments: key players in the control of asymmetric divisions in mouse oocytes

Redistribution of mitochondria leads to bursts of ATP production during spontaneous mouse oocyte maturation

During mammalian oocyte maturation there are marked changes in the distribution of mitochondria that supply the majority of the cellular ATP. Such redistribution of mitochondria is critical for oocyte quality, as oocytes with a poor developmental potential display aberrant mitochondrial distribution and lower ATP levels. Here we have investigated the dynamics of mitochondrial ATP production throughout spontaneous mouse oocyte maturation, using live measurements of cytosolic and mitochondrial ATP levels. We have observed three distinct increases in cytosolic ATP levels temporally associated with discrete events of oocyte maturation. These changes in cytosolic ATP levels are mirrored by changes in mitochondrial ATP levels, suggesting that mitochondrial ATP production is stimulated during oocyte maturation. Strikingly, these changes in ATP levels correlate with the distribution of mitochondria undergoing translocation to the peri-nuclear region and aggregation into clusters. Mitochondrial clustering during oocyte maturation was concomitant with the formation of long cortical microfilaments and could be disrupted by cytochalasin B treatment. Furthermore, the ATP production bursts observed during oocyte maturation were also inhibited by cytochalasin B suggesting that mitochondrial ATP production is stimulated during oocyte maturation by microfilament-driven, sub-cellular targeting of mitochondria. J. Cell. Physiol. 224: 672–680, 2010. © 2010 Wiley-Liss, Inc.

Dynamic modulation of cytoskeleton during in vitro maturation in human oocytes

OBJECTIVE

To investigate the role of cytoskeleton in several important dynamic events during in vitro maturation of human oocytes.

STUDY DESIGN

Human germinal vesicle stage oocytes were divided randomly into control and study groups. After cultured for 24 hours, chromatin state and position, spindle formation and migration, cortical granules, and mitochondria distribution were evaluated.

RESULTS

In colchicine group, spindles did not form. Cortical granules migrated to the cortex but mitochondria maintained the peripheral distribution pattern in most of the oocytes. In cytochalasin B group, the migration of spindle and chromosomes to the cortex was prohibited. Microfilaments disruption influenced cortical granules migration but not redistribution of mitochondria.

CONCLUSION

Meiosis progression could not go beyond metaphase I stage when microtubule or microfilament polymerization was prohibited in human oocytes. The migration of cortical granules to the cortex and redistribution of mitochondria to the inner cytoplasm were mediated by microfilaments and microtubules, respectively.