A branched pathway model for the attenuation of synaptic growth signals by endosomal traffic. (A) Model depicting how Nwk and SNX16 may drive tubulation-based sorting of synaptic growth receptors from the signal-permissive early endosome to the recycling endosome, where signaling (indicated by yellow starbursts) is attenuated. In the absence of Nwk or Nwk–SNX16 interactions, receptors are retained in the early endosome. In the absence of SNX16, receptors are down-regulated by internalization into the endosomal lumen. (B) Representative confocal images of Cpx-stained NMJs from hrs^D28/Df(exel6277) and Snx16^PB, hrs^D28/Snx16^Δ1, Df(exel6277) larvae and quantification of the mean bouton number. (C) Overexpression of SNX16^3A increases MVB number. Electron micrographs of type 1b boutons from SNX16-GFP and SNX16^3A-GFP–expressing larvae and quantification of MVB structures. Error bars are means ± SEM, and the number of samples averaged in each measurement is indicated at the base of each bar. *, P < 0.05; **, P < 0.01; ***, P < 0.005. Bars: (B) 10 µm; (C) 200 nm.