(A,B) qRT-PCR analysis of ddb2 (A) and 6–4 photolyase (B) mRNA expression in PAC-2 (ZF) and EPA (PA) cells during a 60-hour period in DD following exposure to a short UV-C pulse (20 J/m²). (C) qRT-PCR analysis in zebrafish and cavefish cells treated with 6 mM N-acetylcysteine (NAC) or vehicle (Ctrl), at 24 hours and 36 hours following a short UV-C pulse (20 J/m²). On the y-axes are plotted the fold induction (± s.d.) of expression with respect to samples subjected to identical treatment but maintained under DD. Times are indicated on the x-axes. Statistical analysis results (Student’s t-test (unpaired, two tailed)) are represented by asterisks (***p<0.001, **p<0.01, *p<0.05) and reported in S1 Table. (D) Bioluminescence analysis of PAC-2 (blue trace) and EPA (orange trace) cells transfected with the E2F/D-box_ddb2-Luc reporter, maintained in constant darkness following exposure to a short UV-C light pulse (20 J/m²). (E,F) Comparable bioluminescence analysis of PAC-2 (blue trace) and EPA (orange trace) cells transfected with the ddb2-Luc reporter, maintained in constant darkness following exposure to a short UV-C pulse (20 J/m²). Grey traces in panels E and F represent control (Ctrl) transfected PAC-2 and EPA cells, respectively, that were not treated with UV-C. Each experiment was performed a minimum of three times.