Fig. 4.

Innervation of cutaneous targets is not maintained in type III Nrg1^–/– mouse embryos during late embryogenesis. (A) Hindlimb sections of WT (a-d) or type III Nrg1^–/– (e-h) embryos were labeled for TrkA. At E12.5, TrkA⁺ axons innervated the proximal hindlimb epithelium in WT (a) and type III Nrg1^–/– (e) embryos, but axons appeared disorganized in mutants. TrkA⁺ axon innervation was reduced in mutants at E14.5 (f), E16.5 (g) and E18.5 (h). Scale bar: 50 μm. (B) Quantification of TrkA⁺ nerve endings within the hindlimb upper dermis and epidermis (n≥2 embryos per genotype). (C) Immunoblot of TrkA expression in hindlimb epithelium from WT or type III Nrg1^–/– embryos at E14.5 and E18.5. β-tubulin was used as a lysate loading control. TrkA band intensity is shown relative to WT (n≥3 embryos per genotype). Mean ± s.e.m. ^*, P<0.05; ^**, P<0.01 (ANOVA with post-hoc Fisher’s PLSD test).