Figure 3

Circadian-phase estimation using hair follicle cells. The human circadian phase can be determined by using the hair follicle cells attached to the scalp or facial hair roots by real-time PCR. The hair should be sampled more than three times per day. At each sampling time point, the quantification of clock gene expression requires more than 200 ng of total RNA. For Japanese subjects, 1–10 strands of hair need to be collected. The Per3, Nr1d1 and Nr1d2 genes exhibit circadian fluctuations in transcription with good reproducibility. We previously reported that the intervals among the peak expression times of these three genes were constantly maintained with only small interindividual variation. From the expression levels of Per3, Nr1d1 and Nr1d2 at more than three different time points, the peak times are determined by a cosine curve fitted with the least-squares method. Circadian misalignment can be evaluated by making a comparison between the mathematically estimated peak times and the lifestyle time schedules of the subjects (in particular, waking times on weekdays/workdays). A full color version of this figure is available at the Hypertension Research journal online.