TY - JOUR T1 - Distinct and Separable Roles for Endogenous CRY1 and CRY2 within the Circadian Molecular Clockwork of the Suprachiasmatic Nucleus, as Revealed by the Fbxl3<sup>Afh</sup> Mutation JF - The Journal of Neuroscience JO - J. Neurosci. SP - 7145 LP - 7153 DO - 10.1523/JNEUROSCI.4950-12.2013 VL - 33 IS - 17 AU - Sneha N. Anand AU - Elizabeth S. Maywood AU - Johanna E. Chesham AU - Greg Joynson AU - Gareth T. Banks AU - Michael H. Hastings AU - Patrick M. Nolan Y1 - 2013/04/24 UR - http://www.jneurosci.org/content/33/17/7145.abstract N2 - The circadian clock of the suprachiasmatic nucleus (SCN) drives daily rhythms of behavior. Cryptochromes (CRYs) are powerful transcriptional repressors within the molecular negative feedback loops at the heart of the SCN clockwork, where they periodically suppress their own expression and that of clock-controlled genes. To determine the differential contributions of CRY1 and CRY2 within circadian timing in vivo, we exploited the N-ethyl-N-nitrosourea-induced afterhours mutant Fbxl3Afh to stabilize endogenous CRY. Importantly, this was conducted in CRY2- and CRY1-deficient mice to test each CRY in isolation. In both CRY-deficient backgrounds, circadian rhythms of wheel-running and SCN bioluminescence showed increased period length with increased Fbxl3Afh dosage. Although both CRY proteins slowed the clock, CRY1 was significantly more potent than CRY2, and in SCN slices, CRY1 but not CRY2 prolonged the interval of transcriptional suppression. Selective CRY-stabilization demonstrated that both CRYs are endogenous transcriptional repressors of clock-controlled genes, but again CRY1 was preeminent. Finally, although Cry1−/−;Cry2−/− mice were behaviorally arrhythmic, their SCN expressed short period (∼18 h) rhythms with variable stability. Fbxl3Afh/Afh had no effect on these CRY-independent rhythms, confirming its circadian action is mediated exclusively via CRYs. Thus, stabilization of both CRY1 and CRY2 are necessary and sufficient to explain circadian period lengthening by Fbxl3Afh/Afh. Both CRY proteins dose-dependently lengthen the intrinsic, high-frequency SCN rhythm, and CRY2 also attenuates the more potent period-lengthening effects of CRY1. Incorporation of CRY-mediated transcriptional feedback thus confers stability to intrinsic SCN oscillations, establishing periods between 18 and 29 h, as determined by selective contributions of CRY1 and CRY2. ER -