Vesicles modulate an actin network for asymmetric spindle positioning.

Actin networks drive many essential cellular processes, including cell migration, cytokinesis and tissue morphogenesis. However, how cells organize and regulate dynamic actin networks that consist of long, unbranched actin filaments is only poorly understood. This study in mouse oocytes reveals that cells can use vesicles as adaptable, motorized network nodes to regulate the dynamics and density of intracellular actin networks. In particular, Rab11a-positive vesicles drive the network dynamics in a myosin-Vb-dependent manner, and modulate the network density by sequestering and clustering the network's actin nucleators. We also report a simple way by which networks of different densities can be generated, namely by adjusting the number and volume of vesicles in the cell. This vesicle-based mechanism of actin network modulation is essential for asymmetric positioning of the meiotic spindle in mouse oocytes, a vital step in the development of a fertilizable egg in mammals.