Circadian systems biology revealed by mPer2 real-time reporting

Abstract

Many physiological and behavioral systems are controlled by an internal self-sustained molecular oscillating mechanism with a periodicity of approximately 24 hours, known as the biological clock. This self-sustaining clock exists in animals, plants and even in bacteria and adjusted by the alternating of the day and night of the earth``s cycle. This biological rhythms that persist under constant conditions and has a periodicity of - 1 day is called "circadian"(cirda "around"; dian, "day"). This clock system have the cell-autonomous, genetically-based biological propertues with which to respond appropriately to daily changes in environmental stimuli, the most important of which is the light-dark cycle. To understand most remarkable feature of clock gene; circadian oscillation, we made mPer2 real time reporting system by making mPer2:luciferase functional knock-in mice and identified a noncanonical E-box enhancer sequence in the 5``-UTR of the mPer2 gene and used this sequence to drive the circadian expression of luciferase in transgenic mice. mPer2:luciferase functional knock-in mice showed persistent oscillation of bioluminescence with ca. 24 hours of period. Behavior analysis of mPer2:luciferase mouse showed normal behavior compare to same littermate wild type mouse. We demonstrate that the E-box enhancer: luciferase transgenic line and the mPer2: Luciferase knock-in line allow us to monitor in real-time the transcriptional and translational profiles, respectively, of the mPer2 gene in explanted SCN and peripheral tissues. SCN and peripheral tissues showed robust and self-sustained sustained circadian rhythms of mPer2 expression with only slight damping in static explant cultures for up to 20 days. Furthermore, in SCN-lesioned knock-in animals, a persistent circadian oscillation in bioluminescence in peripheral tissues was obserbed, yet from tissue to tissue within each animal and among animals there is a loss of phase coordination. Contrary to previous studies...