Actin-associated proteins at the presynaptic actin core. (A) Live imaging of the branched actin nucleator Arp2/3, visualized via Arp3::GFP (cyan), shows decoration of spot-like and linear F-actin assemblies labeled with Lifeact::Halo (magenta). See also Video 2. (B) Linear actin nucleator formin/Dia::GFP (cyan) decorates actin cables (magenta), in addition to its punctate distribution throughout the NMJ (see also Video 3). (C) Diffuse cytosolic GFP (cyan) shows no specific enrichment or colocalization with presynaptic actin assemblies (magenta); see also Video 4. (D) Distribution of the NMII light chain subunit Sqh::GFP at the NMJ in live larvae expressing Lifeact::Halo in neurons. The inner yellow line denotes the Lifeact::Halo-positive neuronal region; the outer yellow line denotes a 2 µm dilation defining the postsynaptic region. See also Video 5. Scale bars—2 µm. See Table S1 for detailed genotypes.