Abstract
A major challenge in modern physiology is to integrate molecular mechanisms with tissue level organization. Studies of circadian clock gene function have relied heavily on behavioral phenotypes of knockout mice, with little attention to system-level interactions. We therefore studied clock function at the level of individual cells, using bioluminescence imaging of PER2::LUC expression in tissue explant or dissociated cell cultures from Per1-, Cry1-, Cry2-, Bmal1-, and Clock-deficient mice. Similar lengthening of circadian period was observed in Cry2-deficient cells, explants, and behavior. However, behavior did not predict the cellular and tissue level phenotypes of other genetic perturbations. In particular, Per1 and Cry1 were required for persistent circadian rhythmicity in single cells, but oscillator network interactions uniquely present in the suprachiasmatic nucleus, the master neuronal circadian pacemaker, were able to compensate for Per1 or Cry1 deficiency, preserving sustained rhythmicity in SCN slices and in behavior. We are currently analyzing data from Bmal1- and Clock-deficient cells. By examining effects of genetic perturbations at the level of single cells and tissues, we have demonstrated that cellular interactions are in fact essential to the operation of the circadian clock. [J Physiol Sci. 2008;58 Suppl:S12]
