Research Press Release | July 31, 2015
|Key Points||・Optical fiber used to successfully measure long-term gene expression in the brain simultaneously with spontaneous movements in unrestrained mice.
・Three clock gene1 expression rhythms have the same phase relationship but slightly delayed phases compared to those in culture conditions.
・Clock gene expression of the suprachiasmatic nucleus2 in free movements shows two types of rhythms with different periods, that of approximately twenty-four hours and of several hours.
|Overview||Biological functions, such as sleep and wakefulness, have rhythms of approximately twenty-four hours (circadian rhythms), and in mammals, the center for these rhythms is located in the suprachiasmatic nucleus of the hypothalamus (the biological clock). Circadian rhythms are regarded to be generated by a molecular feedback loop3 where multiple clock genes and their proteins products are involved. While recent progress in gene manipulation techniques of firefly luciferase reporters enabled us to investigate the expression patterns of clock genes in real time, long-term measurement of gene expression in the deep brain area was still impossible in unanesthetized, unrestrained animals. This research has developed a system that enabled to measure bioluminescence4 by using an optical fiber without interfering movements of animals. With this system, we have succeeded in performing real-time measurement of three types of clock gene expression for at least three consecutive weeks from the suprachiasmatic nucleus simultaneously with spontaneous movement in freely moving mice.
As a result, we verified that the in vivo expression of these clock genes shows a circadian rhythm, and for the first time in the world we demonstrated that clock gene expression also has a short-term rhythm with a period of several hours (ultradian rhythm). We also found that the circadian rhythm seen under culture conditions is two to three hours phase-advanced compared to the circadian rhythm seen in vivo. The present study, by making it possible to capture dynamic changes of gene expression in specific regions in the brain, presents a new research standard for analyzing gene expression in vivo at high time resolution without anesthesia or restraints.
This research was supported by a grant-in-aid from the Creation of Innovation Centers for Advanced Interdisciplinary Research Areas Program of the Ministry of Education, Culture, Sports, Science, and Technology.
1 Clock Genes:
A group of genes considered necessary for generating the approximately twenty-four-hour circadian rhythm.
2 Suprachiasmatic Nucleus:
A collection of neurons located above the optic chiasm where the optic nerves cross at the base of the brain. This is the center of the biological clock in mammals.
3 Molecular Feedback Loop:
Proteins created by the transcription and translation of clock genes suppress their own transcription, so that an approximately twenty-four hour rhythm occurs for protein synthesis. This is thought to be the molecular mechanism that generates circadian rhythm.
4 Highly sensitive luminescence measuring system:
A measurement system that can perform real-time monitoring of targeted gene transcription activity using the luminescence reaction by which fireflies glow.
Coordinating Office, Future Drug Discovery and Medical Care Innovation Project, Hokkaido University
Publicity liaison: Ms. Wada
|Publications||Circadian and ultradian rhythms of clock gene expression in the suprachiasmatic nucleus of freely moving mice, Scientific Reports (2015.7.21)|