Post-fusion structural changes and their roles in exocytosis and endocytosis of dense-core vesicles.

ABSTRACT: Vesicle fusion with the plasma membrane generates an ?-shaped membrane profile. Its pore is thought to dilate until flattening (full-collapse), followed by classical endocytosis to retrieve vesicles. Alternatively, the pore may close (kiss-and-run), but the triggering mechanisms and its endocytic roles remain poorly understood. Here, using confocal and stimulated emission depletion microscopy imaging of dense-core vesicles, we find that fusion-generated ?-profiles may enlarge or shrink while maintaining vesicular membrane proteins. Closure of fusion-generated ?-profiles, which produces various sizes of vesicles, is the dominant mechanism mediating rapid and slow endocytosis within ~1-30 s. Strong calcium influx triggers dynamin-mediated closure. Weak calcium influx does not promote closure, but facilitates the merging of ?-profiles with the plasma membrane via shrinking rather than full-collapse. These results establish a model, termed ?-exo-endocytosis, in which the fusion-generated ?-profile may shrink to merge with the plasma membrane, change in size or change in size then close in response to calcium, which is the main mechanism to retrieve dense-core vesicles.

SUBMITTER: Chiang HC 

PROVIDER: S-EPMC4267856 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature