Dynamin 2 regulates actin-mediated spindle migration in mouse oocytes

Background information: During meiosis, a bipolar spindle forms in the central cytoplasm of an oocyte and then moves to the cortex to extrude the first polar body. This is dependent on the regulation of actin and actin-related molecules. Dynamin 2, a large guanosine triphosphatases (GTPase) known to regulate clathrin-mediated endocytosis, is involved in actin recruitment and actin-based vesicle mobility. In this study, we investigated the role of Dynamin 2 in oocyte meiosis. Results: Dynamin 2 was localised at the cortex and around the spindles of oocytes. Disrupting Dynamin 2 activity by RNAi or an inhibitor resulted in polar body extrusion failure. Using time-lapse microscopy to monitor aberrant oocyte cytokinesis, the chromosomes were first separated, but then re-joined. Actin expression in oocytes was decreased; and actin cap formation was disrupted, which was confirmed by the disappearance of cortical-granule-free domains. In addition, live cell imaging showed that spindle migration had failed and that spindles were arrested centrally in oocytes. This may have been due to the Dynamin-binding protein Profilin and actin-related protein 2/3 (ARP2/3) complexes, which exhibited dispersed signals after disrupting Dynamin 2 activity. Conclusions: Thus, our results indicate that Dynamin 2 regulates spindle migration and polar body extrusion during mouse oocyte meiosis through an actin-based pathway.