Figure 1.

Biased innervation at the neuromuscular junction (NMJ) elicits distinct target-specific homeostatic adaptations. (A) Schematic of a motor neuron innervating both muscle 6 and 7 at the Drosophila larval NMJ. Biased innervation is achieved by overexpressing the cell adhesion factor FasII specifically on muscle 6 using H94-Gal4 (M6 >FasII: w; UAS-FasII/+; H94-Gal4/+). Red outlines highlight the likely synaptic compartment in which the adaptation occurs. (B) Representative images of muscle 6/7 neuromuscular junctions (NMJs) immunostained with antibodies that recognize the neuronal membrane (Horshradish Peroxidase; HRP) and synaptic vesicles (Synapsin; SYN) in wild type (w¹¹¹⁸) and M6 >FasII. Note that while boutons labeled by SYN puncta are roughly equally split between muscles 6 and 7 in wild type, M6 >FasII causes biased innervation on muscle 6 at the expense of muscle 7. (C) Representative electrophysiological traces of recordings from muscles 7 and 6 in wild type and M6 >FasII NMJs. Note that while EPSP amplitudes are similar across all muscles, miniature excitatory postsynaptic potentials (mEPSPs) are increased only on muscle 7 of M6 >FasII. (D) Quantification of bouton number, EPSP amplitude, mEPSP amplitude, quantal content, and quantal content normalized per bouton on muscle 7 in M6 >FasII. All values are normalized to the values at wild type muscle 7. Enhanced mEPSP amplitude (shaded bar) implies reduced quantal content and no change in quanta released per bouton. (E) Quantification of all values in (D) on muscle 6 of M6 >FasII normalized to wild type muscle 6 values. Note that the estimated quantal content per bouton (shaded bar) is significantly reduced. Error bars indicate ±SEM (n ≥ 16; one-way ANOVA; Supplementary Table S2). **p < 0.01; ***p < 0.001; ****p < 0.0001; ns, not significant.