Abstract
The cleavage-furrow tip adjacent to the actomyosin contractile ring is believed to be the predominant site for plasma-membrane insertion through exocyst-tethered vesicles during cytokinesis. Here we found that most secretory vesicles are delivered by myosin-V on linear actin cables in fission yeast cytokinesis. Surprisingly, by tracking individual exocytic and endocytic events, we found that vesicles with new membrane are deposited to the cleavage furrow relatively evenly during contractile-ring constriction, but the rim of the cleavage furrow is the main site for endocytosis. Fusion of vesicles with the plasma membrane requires vesicle tethers. Our data suggest that the transport particle protein II (TRAPP-II) complex and Rab11 GTPase Ypt3 help to tether secretory vesicles or tubulovesicular structures along the cleavage furrow while the exocyst tethers vesicles at the rim of the division plane. We conclude that the exocyst and TRAPP-II complex have distinct localizations at the division site, but both are important for membrane expansion and exocytosis during cytokinesis.
Highlights
Cytokinesis partitions a mother cell into two daughter cells following chromosome segregation
A significant amount of new plasma membrane is needed at the cleavage furrow during cytokinesis in many cell types
By tracking individual vesicles with high spatiotemporal resolution and using electron microscopy, we found that new membrane is deposited relatively evenly along the cleavage furrow in fission yeast, while the rim of the division plane is the predominant site for endocytosis
Summary
Cytokinesis partitions a mother cell into two daughter cells following chromosome segregation. Once vesicles approach the target membrane, a series of reactions trigger the vesicle-membrane fusion: tethering, docking, priming, SNARE complex assembly, and fusion [11]. The pairing between v-SNARE on the vesicle and tSNARE on the plasma membrane provides the force for the vesicle-membrane fusion [14,15]. On the other hand, branched actin filaments nucleated by the Arp2/3 complex provide the force for membrane invagination during clathrin-mediated endocytosis [16,17,18]. Given that endocytosis removes membrane from the plasma membrane, it is intriguing that cytokinesis is inhibited or delayed when endocytosis is blocked by drug treatment or in endocytic mutants [19,20,21]. Close investigation of exocytic and endocytic events during cytokinesis is of great interest
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