How CRY1 Controls The Body Clock

Specially designed knockout rescue mice have helped us understand how the circadian rhythm is regulated.

AsianScientist (Jan. 4, 2017) – Using next-generation mammalian genetics, researchers have pinpointed the key parts of the CRY1 protein that affect the length of the circadian period in mice. Their results have been published in Molecular Cell.

Circadian rhythms are physiological changes at the cellular levels in almost all plants and animals that follow a 24-hour cycle. They are guided by internal biological clocks and are affected by many internal genetics factors, which in turn can influence behavior. Circadian rhythms are best studied in vivo as opposed to cell cultures, since behavior can only be studied in live animals.

However, creating knock-in and knock-out mice is a laborious, time-consuming and costly process. Researchers led by Professor Hiroki Ueda at the RIKEN Quantitative Biology Center have now succeeded in efficiently creating gene knockout (KO) mice without backcrossing or breeding. Their technique can begin with KO embryonic stem cells, insert rescue genes, and then analyze the behavior of the mouse when it matures—all within a single generation.

The group used this new KO-rescue technique to better understand cryptochromes, proteins associated with physiological functions that are controlled by environmental light. While cryptochromes are related to circadian rhythms in both plants and animals, their exact physiological roles appear quite different. In mammals, the cryptochrome gene CRY1 is essential for a normal circadian rhythm, but its exact role in regulating the length of circadian periods remains unclear.

Guided by mass spectrometry-based identification of specific sites on CRY1, and a comprehensive analysis of all CRY1 mutants at each site, Ueda and his team identified more than ten areas in the gene that affect the period of the circadian clock in cultured cells. They then selected 17 CRY1 mutations and added each mutant CRY1 into different mouse embryonic stem cells that lacked all cryptochrome genes. When the mice grew up, they then analyzed their activity patterns.

“Mice without these genes lack a circadian rhythm,” explains first author Dr. Koji Ode. “By adding the Cry1 gene back in these mice, we were able to rescue the circadian rhythm. Most interestingly, the lengths of the restored circadian periods depended on nature of the mutations.”

The article can be found at: Ode et al. (2016) Knockout-Rescue Embryonic Stem Cell-Derived Mouse Reveals Circadian-Period Control by Quality and Quantity of CRY1.


Source: RIKEN; Photo: Shutterstock.
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