The rhythmic changes in our behavior and metabolism are controlled by an inner clock, the circadian clock, which is regulated by the daily light and dark cycles. Disruption of the circadian rhythm can lead to sleep disorders, depression and even cancer. A set of genes controls this body clock. It has been difficult to study these genes in people, but now Japanese researchers found “clock” genes in hair follicles and showed that human behavior can change the rhythmic expression of these genes.
The daily 24-hour cycle of day and night affects our behavior and physiology and that of almost all species of animals. The circadian rhythm in our behavior is not just a response to the earth turning, generating light-dark cycles, but it is due to a biological clock. The internal clock can be reset and changed, but may become defective with certain lifestyles or aging. The master controls for this clock are embedded in nerve cells at the bottom of our brains, called the suprachiasmatic nuclei. Many genes are involved in the clock’s mechanism and they are also found in non-brain tissue such as liver and lung. The function of these genes is to synchronize our external and internal environments. Studies in the mouse have suggested that about 10 percent of the body’s non-cycling genes are regulated by the circadian clock according (Cell  109:307).
Hair clock genes
Japanese researchers searched for a non-invasive method to study clock genes in people. They plucked hairs from scalps and beards and looked for the clock genes in the hair follicles at the end of the plucked hairs. The researchers found that the circadian clock genes became activated about an hour before waking. The earliest risers also had the earliest peak in gene activity. After establishing their methodology, the researchers examined the clock genes in hair follicles from rotating shift workers. Previous studies have linked various health disorders in shift workers to disorders of the circadian clock rhythm. The Japanese researchers found a shift in the expression of the clock genes, but it lagged a few hours behind the new change in the working hours. They concluded that one week of shift work was not enough for the circadian clock genes to adjust to the change in lifestyle. The researchers suggest that additional studies on clock genes might be able to help optimize the schedules of shift workers.
Importance of circadian rhythm
The importance of circadian clock genes is illustrated by an experiment in mice, generated to lack one of these genes. These mice aged faster than their normal counterparts, had organ shrinkage, had hair loss, used their running wheel at odd times, and lived only half as long as normal mice (Kondratov, R.V.). Evidence from studies in mice and humans also suggests that cancer may be a circadian rhythm-related disorder, because the circadian clock genes are disrupted in various cancers. Further studies may tell us how factors, other than light, may reset or improve the functioning of our cycling clock genes.
Akashi, M. et al. Noninvasive method for assessing the human circadian clock using hair follicle cells. Proceedings of the National Academy of Sciences (2010) 107: 15643
Kondratov, R.V. et al. Early aging and age-related pathologies in mice deficient in BMAL1, the core component of the circadian clock. Genes & Development (2006) 20: 1868