Light-driven molecular rhythms in the SCN of Cry1-/-Cry2-/- mice. Temporal mRNA profiles of Per2 (A), Per1 (B), Bmal1 (C) and PK2 (D) in Cry1-/-Cry2-/- mice under 12L:12D (LD) or two days constant darkness (2DD). Each value represents the mean ± SEM of 3–4 animals. Two-way ANOVA with Bonferroni's posthoc analysis was used to test for significant interactions between expression across time of sampling and under different lighting conditions (LD vs 2DD). p < 0.0001 (Per2), p < 0.002 (Per1), p < 0.0001 (Bmal1) and p < 0.0001 (PK2). (E) Light pulse-induced PK2 mRNA in Cry1-/-Cry2-/- mice. PK2 mRNA was measured one and two hours after brief light pulse at ZT14 (shaded bar). Black bar represents dark controls that did not receive light pulse. Each value represents the mean ± SEM of 5–6 animals. Two-way ANOVA indicates a significant difference in PK2 expression between light and dark treatment (p < 0.05), however, the PK2 induction is not significantly different between the two timepoints (1 hr vs 2 hr). (F) Locomotor behavioural rhythms of wild type (left) and Cry1-/-Cry2-/- mice (right) in response to 6 hour advance of light/dark cycle. Open and filled bars indicate light and dark periods, respectively. Black arrow indicates the day of 6 hour advance shift (6hrA). Numbers above and below the actograms represent timescale in zeitgeber time (ZT) for LD and 6hrA. (G) Rapid adjustment of PK2 rhythm in Cry1-/-Cry2-/- mice to 6 hour advance (6hrA). PK2 mRNA was quantitated in the SCN of wildtype and Cry1-/-Cry2-/- mice under LD (shaded) or 6hrA (black). Each value represents the mean ± SEM of 3–4 animals. Three-way ANOVA with Bonferroni's post hoc analysis indicates a significant interaction between light/dark cycle (LD vs 6hrA), timepoint (ZT4 vs ZT16) and genotype (wildtype vs Cry1-/-Cry2-/- mice), p < 0.001. Two-way ANOVA with Bonferroni's post hoc analysis show that there is significant difference in wildtype PK2 expression level between LD and 6hrA, (ZT4, ***p < 0.001; ZT16, **p < 0.01), but not in Cry1-/-Cry2-/- mice (ZT4, p = 1.000; ZT16, p = 1.000).