Soluble signals mediate PGC-1α1-associated motor neuron recruitment. A) Motor neuron recruitment in response to overexpression of PGC-1α1 at day 6 using standard flow (from muscle to motor neuron compartment) and reverse flow (from motor neuron to muscle compartment) on days 4 and 5. Data are presented as mean ± SEM relative to control for n = 3 experiments with 2–3 devices per condition of each experiment. B) Expression by RT-qPCR of interleukin 15 (IL-15), neurturin (NRTN) and nerve growth factor (NGF), relative to controls from myotubes overexpressing PGC-1α1 or PGC-1α4. Data are presented as mean ± SEM from n = 3 experiments. Statistical significance was determined using a one-way ANOVA with Bonferroni's post-hoc test, (***) p < 0.001, (**) p < 0.01, (*) p < 0.05. C–F) Factors secreted from myotubes in response to overexpression of PGC-1α1, PGC-1α4 and GFP. Concentration of C) glial derived neurotrophic factor (GDNF), D) interleukin 15 (IL-15), E) neurturin (NRTN), and F) nerve growth factor (NGF) within myotube cell culture medium was determined using a ProSeek assay. Data is presented as mean ± SEM from n = 3 experiments. Statistical significance was determined using a one-way ANOVA with Bonferroni's post-hoc test, (*) p < 0.05.