Fig. 2. Ultrastructure of synapses at CS,dlgm52 mutant, and rescueddlg neuromuscular junctions. a, Neuromuscular synapses formed by 1b and 1s boutons in CS larva.b, c, Synapses in adlgm52
mutant larva (b, 1b; c, 1s). d, Synapses of 1b and 1s boutons in a mutant rescued larva (dlg res.). Synapses (SY) are delimited by arrowheads; presynaptic dense bodies (active zone structures) are delimited by indicated arrows. Each synapse occurs in association with subsynaptic reticulum (SSR); synaptic vesicles (SV) are plentiful in all terminals. Note that densely stained synaptic membranes are much more extensive and synaptic vesicles are larger in dlgm52
mutant boutons than in control (CS and dlg res.) counterparts. Scale bar: (in d) a–d, 1.0 μm.e, f, Serial reconstructions of type 1b boutons from CS (e) and dlg(f) larvae to illustrate a major difference in synaptic structure. Boutons of dlg larvae have larger synaptic areas than controls (red regions); synapses are often confluent. The dense bars are shown in yellow. Scale bars, 1 μm. g, Histogram of the size of synaptic areas in CS (1b, 129 synapses, 15 boutons; 1s, 61 synapses, 15 boutons), dlgm52
(1b, 3 synapses, 3 boutons; 1s, 37 synapses, 10 boutons), and dlg res. (1b, 10 synapses, 2 boutons; 1s, 4 synapses, 2 boutons). The estimated CV is presented for each bouton type at the top of the corresponding bar.