Fig. 2

Intrinsically disease-resistant MN subpopulations mediate the reinnervation of vulnerable muscles after disease onset in rNLS8 mice. a The experimental approach used to investigate the identity of MNs that reinnervate the TA muscle during recovery in rNLS8 mice. The retrograde neuronal tracer AAV9-GFP was injected bilaterally in the TA of p4 mice to fluorescently label (in green) the pre-disease motor pool (denoted TA₁). Dox was then withdrawn for 6 wks. to activate hTDP-43ΔNLS expression, followed by 8 wks. Dox reintroduction for recovery, after which CTG-594 was injected bilaterally in the TA to fluorescently label (in red) the post-disease motor pool (denoted TA₂). Surviving local MNs would thus be labelled with both green and red fluorescence, whereas MNs from adjacent pools expanding their field to reinnervate the TA would be labelled with red fluorescence only. Below are illustrated potential outcomes for the experiment, including the interpretation of TA₂ MNs that were either exclusively co-labelled with GFP and CTB-594 or were labelled with CTB-594 alone. b Representative images of lumbar MNs co-labeled with AAV9-GFP and CTB-594 from rNLS8 and non-transgenic (nTg) mice at the endpoint of the experiment outlined in a. Yellow arrows mark MNs labelled with both AAV9-GFP and CTB-594 (i.e., surviving local MNs), while red arrows mark MNs labelled with CTB-594, only (i.e., MNs reinnervating from adjacent motor pools). Scale bar: 30 µm. c Quantification of the proportion of MNs labelled with CTB-594 only (i.e., MNs reinnervating from adjacent motor pools) or both AAV9-GFP and CTB-594 (i.e., surviving local MNs) in lumbar sections from rNLS8 and nTg mice at the endpoint of the experiment outlined in a. Three mice were examined per group, with 20–30 MNs scored per animal. T test, ***p = 0.0003