ER takes a faster track

During mitosis, the movement of membrane-bound organelles within a cell is generally believed to slow down so that organelles can partition accurately into daughter cells. Using a new procedure for studying Xenopus oocyte extracts, Wöllert et al. now report on page 571 that the picture is more complicated.

Previous studies have focused primarily on microtubule-based organelle motility, whereas the new work examined F-actin–based movement. The authors used extracts from interphase or metaphase-arrested oocytes, and developed an in vitro procedure to produce stable three-dimensional microtubule-free F-actin networks from the extracts. Motion analysis shows that the movement of ER membranes and globular vesicles on F-actin is differentially regulated throughout the cell cycle. During mitosis, the ER speeds up while globular vesicles slow down. Myosin V is responsible for ER transport in this system, and the motor appears...