Figure 2: Selective mutant GARS expression in motor neurons induces progressive muscle denervation in a proximo–distal gradient.
(a–e) NMJs of third instar larvae expressing GARS in motor neurons (OK371-GAL4) were visualized by staining for the postsynaptic marker discs large 1 (dlg1). Arrows indicate the NMJ on muscle 24, which is missing in the vast majority of GARS_G240R and GARS_G526R animals. Scale bar, 50 μm. (f) No differences in motor neuron numbers were found between control and GARS larvae; one-way analysis of variance (ANOVA) with Bonferroni correction; P=0.88; N=21–33. (g) Quantification of the percentage of animals with muscle 24 innervated; χ2-Test; ***P<1 × 10−8; N=26. (h) Muscle 24 innervation in OK371-GAL4>2 × GARS_G240R larvae at different developmental stages (L2: second instar and L3: third instar). N=51, 42 and 30 NMJs; Mann–Whitney U-test; ***P<0.005 versus L2. (i) The effect of motor neuron-selective expression of GARS transgenes on synapse length on muscles 21, 8, 4 and 1/9 was quantified and plotted as the percentage change from 2 × GARS_WT. Muscles 8 and 21 are both innervated by the SNa motor nerve, whereas muscles 4 and 1/9 are innervated by the ISN motor nerve. Phenotypic strength ranged from G240R>G526R>E71G, and for all mutants, the phenotypic severity showed a proximo–distal gradient, with distal muscle (8 and 1/9) more severely affected than proximal ones (21 and 4); one-way ANOVA with Bonferroni correction; *P<0.05, **P<0.01, ***P<0.00005; N=12–14. Error bars represent s.e.m.
