Figure 3. Nrg1 intracellular signaling is sufficient to promote axonal growth in vitro.

(A) Representative images and drawings of control and Nrg1-overexpressing cultured neurons. The neurons were transfected to express either Nrg1-FL-GFP or Nrg1-ICD-GFP and co-cultured with control neurons. The cells were fixed at DIV4. Scale bar, 50 μm. (B) Schematic representation of the structure of Nrg1-FL: on the left in its full conformation (also named Nrg1-FL), which includes an epithelial growth factor domain, a transmembrane domain (TM), a cysteine-rich domain, and an NLS; on the right, the intracellular Nrg1 (Nrg1-ICD). (C) Quantification of the axonal length of Nrg1-expressing neurons shown in fold change as compared to the control. Ctrl: n = 96; Nrg1-FL–overexpressing neurons: n = 55; Nrg1-ICD–overexpressing neurons: n = 60, out of three independent neuronal cultures. One-way ANOVA and post hoc with Turkey’s test, ***P < 0.001. Average ± SEM. (D) Graph showing the quantification of axonal branch density control and Nrg1-FL– and Nrg1-ICD–expressing neurons. Ctrl: n = 78, Nrg1-FL–overexpressing neurons: n = 55; Nrg1-ICD–overexpressing neurons: n = 60, all of them out of three independent neuronal cultures. One-way ANOVA and post hoc with Tukey’s test. Ctrl versus Nrg1-FL, P = 0.27; Ctrl versus Nrg1-ICD, P = 0.94. ns, not significant. Average ± SEM.