Figure 7.

Endocytic intermediates are affected in Rab5 mutant presynaptic terminals. Ultrastructure of presynaptic terminals of wild-type (A–D), w; UAS-Rab5S43N/+; elav-GAL4/+ (E), and w; UAS-Rab5/+; elav-GAL4/+ third instar larvae (F). (A and E) Solid arrowheads indicate endocytic intermediates with an average diameter of 70 nm. (B–D) Electron micrographs corresponding to serial sections from a wild-type synapse showing cisternal (black arrows) and tubular (white arrows) endosomal structures. Bars, 100 nm. Cisternal structures are frequently detected in serial sections spanning 500 nm–1 μm, but are not present in each of the sections through the synapse. In Rab5S43N-expressing terminals (E), an accumulation of the 70-nm vesicles was observed (solid arrowhead). In Rab5-overexpressing terminals (F), tubules (white arrows), cisternae (black arrow), and multivesicular bodies (white arrowheads) were found in each section throughout the synapse, indicating an expansion of the endosomal compartment. No major change was observed in other synaptic features neither in Rab5S43N nor in Rab5 overexpressing terminals including the number and structure of the T-bars, the number of docked vesicles defined as vesicles touching the plasma membrane at the T-bar (WT: 1.31 ± 0.24, n = 17; Rab5S43N: 1.67 ± 0.20, n = 30; Rab5: 1.29 ± 0.22, n = 14; GFP-Rab: 1.22 ± 0.18, n = 10), the overall appearance of the presynaptic terminal and the subsynaptic reticulum postsynaptically.