Trol is required for formation of postsynaptic structures and glutamate receptor localization at postsynaptic sites. (A–F) Electron micrographs of wild-type (A, C, and E) and trol^null mutant (B, D, and F) tissues are presented. In trol^null mutants, the cell surface of muscle is located closer to the basement membrane (arrowheads in B) than in the wild type (A). Mutations in trol caused small SSRs (D) and abnormally enlarged pockets in the postsynaptic region apposed to active zones (asterisks in D and F). The structure of T bar appeared normal in the trol^null mutant (arrowheads in E and F). Arrowheads in A indicate the cell surface of the muscle. An asterisk in E indicates the normal postsynaptic area apposed to the active zone. (G–I) Morphometric analyses of type Ib boutons showed that the SSR area was decreased (G), and the number of enlarged pockets increased (H) in trol^null mutants. On the other hand, the number of synaptic vesicles was not altered in trol^null mutants (I). To count the number of synaptic vesicles, we selected those within 250 nm of the active zones. Error bars represent SEM (n = 15; *, P < 0.0001). (J–L) Synaptic regions of wild-type (J) and trol^null mutants (K) were stained with the antibodies against active zone marker BRP and GluRIIA. (J) BRP and GluRIIA clusters were located on apposed membranes at the synaptic boutons in wild-type larvae. (K) In trol^null mutants, the levels of GluRIIA, but not BRP, were dramatically decreased compared with those of wild-type animals. (L) Bar graphs show the mean staining intensity for GluRIIA and BRP at the NMJ. Error bars represent SEM (n = 20; **, P < 0.001). Bars: (A, B, E, and F) 500 nm; (C and D) 1.5 µm; (J and K) 15 µm. AZ, active zone.