QRT-PCR: Gene expression determined by real-time PCR on P0 and P0 TrkA mutant mouse lumbar DRG. TrkA and Ube2e3 (ubiquitin-conjugating enzyme E2E 3) were used as controls. Data (means ± SEM) were calculated by the delta-CT method  on three independent experimental replicates. The arithmetic means of the expression levels of two genes (Polr2j, Ddx48) whose expression do not change in the course of development and in TrkA-/- DRG were used to normalize the expression levels. Data were analyzed using the Mann Whitney U-test (*P < 0.05). ND: Not detected.