We examined the relationships between chronotype or social jetlag and clock gene expression. Twenty-four young men [Chronotype: morningness, n = 8; intermediate, n = 8, eveningness, n = 8], aged 27 ± 2 years old (mean ± SE), completed two trials in a randomized order: (1) a Friday trial and (2) a Monday trial. In both trials, hair follicle cells were collected to evaluate the expression of clock genes over a 24-hour period at 4-hour intervals. There was a significant main effect of time on the expression of NR1D1, NR1D2, and PER3 (P < 0.001) in the morningness group, but not in the eveningness group. Changes in the peak time of expression of NR1D1 (r = 0.434, P = 0.034), NR1D2 (r = 0.481, P = 0.017), and PER3 (r = 0.457, P = 0.025) from the Friday to Monday trials were positively correlated with social jetlag (SJL) time. Our findings indicate that there was no change in the patterns of clock gene expression between workdays and the day after the holiday in the morningness group, and that SJL time influences the peak time of clock gene expression, moving it from the early to late workday, after a holiday.
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