Data analysis

All data were analyzed by using a Prism5 (Graphpad, San Diego CA) or SPSS (IBM, Chicago IL) software, and expressed as mean ± standard error mean (SEM). Significance was calculated by using one variable comparison analyses (1-way ANOVA) with Tukey’s post hoc test, and multiple comparison analyses (2-way ANOVA) with Bonferroni post hoc test. If data were not normally distributed, then Mann-Whitney test and Kruskal-Wallis with Dunn’s test were employed. Significance is presented by * (WT.Tc vs. WT), & (PARP1-/-.Tc vs. PARP1-/-), and # (WT.Tc vs. PARP1-/-.Tc), and annotated as follows: *,&,#p<0.05, **,&&,##p<0.01, ***,&&&,###p<0.001).