![]() Per2 knockout) because the degradation rate of Per2 is higher and its rate of accumulation is slower than Per1. Per1 knockout) is longer than the period length observed at a greater concentration of Per1 (e.g. Period length at a greater concentration of Per2 (e.g. ( D) Our hypothesis on the factors that determine endogenous period length. ( C) Model of short period-associated Per1 and long period-associated Per2 proteins. ( B) Degradation curve (a) and half-lives (b) of Per2(WT), Per2(FASPS), and Per1 are plotted against time. The F and P-values from the Tukey’s test are shown in Supplemental Table S5. P-values were calculated using one-way ANOVA and Tukey’s post hoc tests. These data include outliers, but not dishes for which oscillation was not determined. ( A) Data from all rescued Per2 knockout ES cells are shown. The P-value was calculated using the Mann Whitney U test. ( F) Comparison of the period length calculated by autocorrelation analysis in individual (a) lines and (b) genotypes. ( E) Detrend/baseline oscillation of ES cells rescued with Per2 or Per1 coding region. ( D) Rescue constructs containing Per2 or Per1 coding region. ( D–F) Comparison of rescue with Per2 and Per1 coding regions. ( C) Rate of oscillation period identification (a) and comparison of period length (b). Data without coding region were generated using two lines (n = 2, 2 lines * 2 conditions, twice). Data with Per2 coding region were generated using one cell line (n = 2, twice). Results of analysis of two independent experiments are shown. ( B) Detrend/baseline oscillation of ES cells rescued with or without Per2 coding region. ( A) Rescue constructs with or without Per2 coding region. ( A–C) Comparison of Per2 knockout cells rescued with and without Per2 coding region. The presence of the coding regions, not the promoters, seems to be important in the difference between Per1 and Per2. The F and P-values from the Tukey’s test are shown in Supplemental Table S4. The light intensity was approximately 0.01 Lux at the trough and approximately 5.4 Lux at the peak at the centre bottom of the cage. The red line shows the concordance of environmental and behavioural periods. We performed both chi-square periodograms for a duration of 2 weeks and one with a final week for each environmental period. ( F) Behavioural period (the circadian period of locomotor activity) determined by chi-square periodogram and environmental period (the period of the light cycle) under gradually changing light with period of 22 h to 27 h for (a) 2 weeks (b) final 1 week. ( E) Pattern of gradually changing light level programmed in this experiment. We used 1/100 current so that mice would not sense the light as constant. ( D) Light intensity (lux) measured by luminance meter on the floor of the rack just below the LED at each light level (0–255) with (a) normal and (b) 1/100 electric current. ( C) Block diagram of LED control device. ( B) Components of 12-LED–based lighting system: (a) main unit, (b) infrared sensor and LED, (c) interface. ( A) Number and genotype of mice used in this experiment. Under conditions of gradually changing light, both Per1 (−/−) and Per2 (−/−) mice were entrained to a broader range of period length than WT mice. These results suggest that the rigid circadian rhythm maintained through the cooperation of Per1-Per2 could negatively impact modern society, in which the use of artificial lighting is ubiquitous, and result in circadian disorders, including delirium. In conclusion, short period-associated protein Per1 and long period-associated Per2 cooperated to rigidly confine the circadian period to "circa" 24-h. Upon introduction of the Per1 coding region in this system, we saw period shortening. To analyse Per1-Per2 cooperative roles at the cell culture level, we established a Per2 knockout-rescue system, which can detect period shortening in a familial advanced sleep phase syndrome (FASPS) mutant. Under gradually changing light in the absence of phase shift with different periods, both Per1((-/-)) and Per2((-/-)) mice were entrained to a broader range of period length than wild-type mice. We then established a light-emitting diode-based lighting system that can generate any pattern of light intensity. Under constant light conditions, the period length of Per1 and Per2 knockout mice depended on the copy number ratio of Per1:Per2. In this study, we identified a new role of Per1-Per2 cooperation, and its mechanism, using our new experimental methods. Period circadian clock (Per) genes Per1 and Per2 have essential roles in circadian oscillation. ![]()
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