TRAFFIC OF DYNAMIN WITHIN INDIVIDUAL DROSOPHILA SYNAPTIC BOUTONS RELATIVE TO COMPARTMENT-SPECIFIC MARKERS

Presynaptic terminals contain several specialized compartments, which have been described by electron microscopy. We show in an identified D rosophila neuromuscular synapse that several of these compartments-syn aptic vesicle clusters, presynaptic plasma membrane, presynaptic cytos ol, and axonal cytoskeleton-labeled by specific reagents may be resolv ed from one another by laser scanning confocal microscopy. Using a pan el of compartment-specific markers and Drosophila shibire(ts1) mutants to trap an intermediate stage in synaptic vesicle recycling, we have examined the localization and redistribution of dynamin within single synaptic varicosities at the larval neuromuscular junction, Our result s suggest that dynamin is not a freely diffusible molecule in resting nerve terminals; rather, it appears localized to synaptic sites by ass ociation with yet uncharacterized presynaptic components. In shi(ts1) nerve terminals depleted of synaptic vesicles, dynamin is quantitative ly redistributed to the plasma membrane. It is not, however, distribut ed uniformly over presynaptic plasmalemma; instead, fluorescence image s show ''hot spots'' of dynamin on th plasma membrane of vesicle-deple ted nerve terminals. We suggest that these dynamin-rich domains may ma rk the active zones for synaptic vesicle endocytosis first described a t the frog neuromuscular junction.