Figure 2.
Distinct dismantling processes of presynaptic and postsynaptic elimination. Postsynaptic components become diffuse and eventually degraded, whereas SVs aggregate and presynaptic membrane retracts. A–D, Representative images of NMJ 4 from abdominal segment A3 of a third-instar larva (A), 6 h APF pupa (B), 7 h APF pupa (C), and 9 h APF pupa (D). NMJ synapses were triply labeled by anti-Dlg (green), anti-Syt (magenta), and Texas Red-labeled anti-HRP (red). Anti-Dlg detects the postsynaptic scaffold protein Dlg; anti-Syt labels SVs and anti-HRP labels the presynaptic membrane. A1–A4, A typical NMJ 4 terminal with beads-on-a-string boutons in a third-instar larva. B1–B4, Postsynaptic Dlg staining is diffused, whereas filopodia-like structures indicated by arrows in B3 are formed at 6 h APF. Anti-Syt staining shows larger aggregates compared with the discrete punctate staining seen at the larval NMJ (compare B2, A2). The arrows in B2 and B3 indicate Syt-positive signals overlapping with filopodia-like structures. C1–C4, Postsynaptic Dlg is more diffused at 7 h APF and the number of filopodia-like structures has dramatically decreased compared with that at 6 h APF. D1–D4, Anti-DLG staining has almost disappeared by 9 h APF, whereas synaptic vesicles labeled by anti-Syt staining and presynaptic membrane labeled by anti-HRP staining are further aggregated and retracted to form a few large boutons. Scale bar, 10 μm. E, F, Statistical results of synaptic area positive for anti-Syt staining from third-instar larvae to 9 h APF pupae (E) and the number of filopodial structures detected by anti-HRP staining during synapse elimination (F). The number of animals analyzed is indicated. “ns” denotes no significant difference; **p < 0.05; ***p < 0.001. Error bars indicate SEM.