Membrane traffic during cell locomotion.

The key role played by a polarised endocytic cycle in extending the front of a eukaryotic cell is now becoming established. Highlights that have occurred during the past year include the visualisation of vesicles fusing with the advancing edge of Physarum, directly leading to extensions of the cell; furthermore, the fusion of vesicles at the leading edge in plant pollen tubes appears to be controlled by a small GTPase, Rop 1, which is a plant homologue of the mammalian Rac. In animal cells, Rac appears to help determine where exocytosis occurs on the surface of a polarised cell. These and other observations illuminate how the endocytic cycle assists the locomotory process in animal cells.