Comparisons between two different conditions were assessed using the two-tailed Student’s t test. If the normality test failed, the Mann-Whitney test was performed. Experiments with three or more experimental groups were compared using one-way ANOVA with either a post hoc Dunnett’s or Tukey’s multi-comparison test, as appropriate. Toe survival was tested using log rank analysis. The data are expressed as mean ± SEM. p values less than 0.05 were considered to indicate statistical significance (*p < 0.05, **p < 0.01, ***p ≤ 0.001). Analyses were performed using Prism software version 6 (Graph Pad).