Figure 4.

Postsynaptic axon response to stimulation is unaffected by mitochondrial health. A, Schematic of the neural circuit in a sensory neuromast of the pLL. Apical stereocilia on HCs are deflected by water movement and signal through ribbon synapses to afferent (postsynaptic) axons. Support cells surround HCs. B, C, actr10^nl15 mutants have fewer sensory HCs as assayed by Myosin VIIa immunolabeling. D, D', HC and synapse number is rescued by expressing RFP-tagged Actr10 in HCs (HC rescue) using the Tg(myo6b:mRFP-actr10)^y610 transgenic. Ribeye: presynapse; MAGUK: postsynapse. E–G, GCaMP6s expression in an axon terminal of a WT (E), actr10^nl15 mutant (F), and actr10^nl15 mutant with HC rescue (G) at 5 dpf. E'–G', Shown are spatial patterns of GCaMP6s signal increases in afferent terminals during stimulation. GCaMP6s signals are colorized according to the dF/F₀ heat maps and are superimposed onto a prestimulus baseline GCaMP6s image. H, H', The average change in GCaMP6s fluorescence intensity on stimulation, shown in plots (H) and quantification (H': WT: 73.26 ± 10.62; actr10^nl15: 1.53 ± 0.76; actr10^nl15+HC rescue: 43 ± 7.78), revealed a reduction in actr10^nl15 mutants with and without HC rescue (ANOVA). Black dotted lines represent SEM. I, J, Actr10 rescue in axons using mosaic expression of the 5kbneurod:mRFP-actr10 transgene (axon rescue) in the background of the Tg(myo6b:mRFP-actr10 ^y610 transgenic (HC rescue). K, Rescuing Actr10 in neurons does not rescue postsynaptic axonal activity based on average GCaMP6s fluorescence (t test). WT: 50.90 ± 8.45; WT+HC rescue: 54.52 ± 16.0; actr10^nl15: 20.69 ± 5.37; actr10^nl15+HC rescue: 26.65 ± 4.45. Sample sizes indicated on graph. Scale bar: 10 µm. All data are mean ± SEM.