FIG 3. Organized PER2 expression in the SCN.
Assessment of luciferase bioluminescence in acute brain slices of the SCN from PER2∷LUC mice using unconstrained cluster analysis [53]. The analysis reveals a wave of oscillatory activity within the SCN, with expression of PER2 (as assessed by the bioluminescence signal of the LUC reporter gene) spreading through the nucleus. This pattern of serial activation of PER2 can be visualized as a “map” of distinct SCN subregions, defined here solely by the spatiotemporal distribution of the bioluminescent signal, without any underlying assumptions being specified by the experimenter. (A) The color coded ‘map’ indicates the location of each cluster in the slice. Note the substantial symmetry between the left and right sides of the SCN. (B) The time series graph displays the mean brightness for each distinct cluster over time [53]. Such a finding reveals that circadian oscillation is characterized by a stable daily cycle of gene expression involving orderly serial activation of specific SCN subregions, followed by a silent interval [53]. Time series for clusters in the map that cannot be discerned from scatter of light are not shown. Figure provided by the authors. Adapted, with permission, from [53].