Presynaptic expression of Tollo rescues NMJ undergrowth in Tollo mutants. (A–K) Representative confocal images of NMJ3 in larvae of indicated genotypes labeled with FITC–anti-HRP. (L) Quantification of bouton numbers at NMJ3 in larvae of genotypes shown. Neuronal expression of Tollo in wild-type larvae (c155/+; UAS-Tollo/+) leads to an increase in bouton number (D and L) compared with control larvae (A–C and L). Bouton number is restored to wild-type levels in Tollo mutant larvae (G, J, and L) by neuronal expression of Tollo (e.g., c155/+; UAS-Tollo/+; Tollo⁵⁵⁹⁷/Tollo¹⁴⁵; H, K, and L). Expression of Tollo in the muscle neither increases bouton number in wild-type larvae nor restores bouton number in Tollo mutant larvae (L). Error bars indicate SEM. ***, P < 0.001; n.s., not statistically significant. n ≥ 15. Bar, 20 µm.