(A) Expression of full length cDNAs of mouse CELF2 or CELF4 with mCherry tag in C. elegans touch neurons significantly rescues the unc-75 axon regrowth defect. Normalized PLM axon regrowth 24 hr post axotomy, N = 14–28. Based on mCherry fluorescence the CELF2 and CELF4 transgenes are expressed at similar levels (not shown). (B) Celf2 transcript levels in DRG neurons decrease during postnatal development, whereas Celf4 levels increase. Expression was normalized to P1, and mouse β-Actin was used as internal reference. Statistics, One-way ANOVA followed by Bonferroni's Multiple Comparison Post Test. N = 4–6. (C) Expression of Celf2 transcripts in DRG of 2 month old mice is significantly enhanced 3 days after sciatic nerve injury. Ratio of the crushed side to the uncrushed side within the same animal is plotted. Statistics, Student’s t-Test. (D) Mutation of Celf2 impairs axon regeneration in DRG PV+ neurons. Confocal images of longitudinal sciatic nerve sections distal to the lesion, stained with anti-SCG10 (green) at 3 days post crush. tdTomato expression is from Rosa26-lox-STOP-lox-tdTomato and marks neurons in which Cre was active. Enlarged images of the boxed areas are shown on the right; white dashed line marks the lesion site. Scale bar: 0.5 mm. (E) Quantitation of SCG10 intensity in tdTomato positive axons at different distances from the lesion site, normalized to SCG10 intensity proximal to the lesion. 6 control and 5 mutant animals were analyzed. Statistics, One-way ANOVA followed by Bonferroni's multiple comparison post test.