Tick Tock: How ‘Clock’ Genes Control Our Circadian Rhythm

Scientists can now simultaneously monitor in real-time the switching on and off of circadian ‘clock’ genes and their effects on mouse behavior.

AsianScientist (Jul. 4, 2016) – Researchers from Hokkaido University in Japan have developed an imaging technique that allows them to monitor the expression of ‘clock’ genes in multiple tissues in moving, fully conscious mice. Their findings are published in Nature Communications.

‘Clock’ genes turn on and off in rhythmic patterns throughout the body to regulate physiological conditions and behavior. The expression pattern of these genes, especially in tissues outside the brain, is still poorly understood because scientists lack sufficient means to simultaneously monitor gene rhythms in specific tissues in freely moving subjects.

To track the movement of the mice, the researchers attached scintillators, which are materials that fluoresce when excited, to the backs and heads of the mice. They developed a software program that was able to detect the 3D position of the scintillators in the freely moving mice based on images received from two separate cameras placed in the mouse cage.

Next, they used bioluminescence to monitor the expression of per1—which is known to be important for maintaining circadian rhythms—in the transgenic mice. This technique has previously been used to monitor gene expression in fully anesthetized mice; anesthesia, however, is believed to affect the expression of ‘clock’ genes.

The team also developed a set of algorithms that allowed them to identify the intensity of the bioluminescent signals from target tissues, such as the right and left ears, despite the movement of the mice.

The fluorescence signal from the scintillators (white arrow heads) and bioluminescent signals from the target areas were acquired by cameras. The dotted line shows the shape of the mouse body. Credit: Toshiyuki Hamada, Hokkaido University
The fluorescence signal from the scintillators (white arrow heads) and bioluminescent signals from the target areas were acquired by cameras. The dotted line shows the shape of the mouse body. Credit: Toshiyuki Hamada, Hokkaido University

“Using the present system, we observed robust circadian rhythmicity in per1 expression at six different areas in the bodies of freely moving mice,” the researchers reported.

Per1 expression was at its peak in all six areas at the onset of mouse daily activity. When the researchers artificially shifted the hours of night and day for the mice, such as might happen when shifting time zones, per1’s rhythmic expression became desynchronized for one day in the different areas and then synchronized again.

While further improvements are still required, the new monitoring technique could be widely applied to many areas of biomedical research, as well as in applications beyond medicine, the researchers said.


The article can be found at: Hamada et al. (2016) In vivo Imaging of Clock Gene Expression in Multiple Tissues of Freely Moving Mice.

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Source: Hokkaido University.
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