Fig. 3

Neuregulin-1 type 1 (NRG1-I) overexpression (OE) in Schwann cells triggers neuropathic symptoms. a Genetic constructs for mice overexpressing Nrg1-Iß1 (upper panel) and Nrg1-IIIß1 (lower panel) isoforms after Cre-mediated recombination, respectively. The constructs are composed of an eGFP-stop cassette, flanked by loxP sites following the murine Nrg1-Iß1 or Nrg1-IIIß1 cDNA fused to an HA tag, respectively. The transgene expression is driven by a beta actin promoter. b Western blot of sciatic nerve lysates from 4-month-old wild-type, CMT1A, CMT1A-NRG1cKO, and NRG1-I OE mice with N-terminal NRG1 antibody (SC393006) shows expression of the cleaved (CL) N-terminal fragment of NRG1 protein in CMT1A mice and in NRG1-I OE mice (next to full-length [FL] NRG1, ns: not Schwann cell specific; for full blots, see Supplementary Figure 5). c Rotarod analysis of 3-month-old mice on 4 consecutive days (control n = 10, NRG1-I OE n = 4, two-way analysis of variance). d Hind limb grip strength test of 3-month-old mice (control n = 10, NRG1-I OE n = 4; Student’s T test). e Nerve conduction velocity (NCV, right panel) and compound muscle action potential (CMAP, left panel) in 4-month-old mice (CMAP: control n = 12, NRG1-I OE n = 7, NCV: control n = 7, NRG1-I OE n = 6, Student’s T test). f Representative light microscopic images of sciatic nerve cross-sections of 4-month-old NRG1-I OE and respective control mice (left panels, scale bar: 10 µm). Quantification of the number of myelinated axons per sciatic nerve cross-section (right panel, control n = 8, NRG1-I OE n = 6, Student’s T test). g Representative electron micrographs of sciatic nerve cross-sections of 4-month-old NRG1-I OE (middle panel) and control mice (left panel, scale bars 2.5 µm), demonstrating hypermyelination of small to mid-caliber axons (arrows). Quantification of g-ratio (right panel, control n = 5, NRG1-I OE n = 4, Student’s T test). h Scatter blots of quantified myelin sheath thickness (g-ratio, data from g) plotted against the axon diameter. i Electron micrograph of aberrant Schwann cell protrusions in a femoral nerve of an 11-month-old NRG1-I OE mouse (scale bar 2 µm). j Electron micrograph of an onion bulb-like structure (right) from i (scale bar 2 µm). Arrows in blow up in i and j demarcate the basal lamina, which identifies a Schwann cell as such. k Quantification of onion bulb structures per cross section area (15,740 µm²) in sciatic nerves of 4-month-old NRG1-I OE (n = 4) mice compared to controls (n = 4; Student’s T test). Source data are provided as a source data file. All respective p values are depicted as a range of significance with *p < 0.05; **p < 0.01