Activation of myosin V–based motility and F-actin–dependent network formation of endoplasmic reticulum during mitosis

It is widely believed that microtubule- and F-actin–based transport of cytoplasmic organelles and membrane fusion is down-regulated during mitosis. Here we show that during the transition of Xenopus egg extracts from interphase to metaphase myosin V–driven movement of small globular vesicles along F-actin is strongly inhibited. In contrast, the movement of ER and ER network formation on F-actin is up-regulated in metaphase extracts. Our data demonstrate that myosin V–driven motility of distinct organelles is differently controlled during the cell cycle and suggest an active role of F-actin in partitioning, positioning, and membrane fusion of the ER during cell division.