Researchers identify genes that influence sleep and dreaming

Research Summary
Saurab Faruque
Research Assistant

In a study published in Nature, scientists used mice to investigate the genes that are important in sleep.

Until now, researchers have used fruit flies to study genes that control sleep and circadian rhythms. Fruit flies, when awake, are constantly active and moving. But they are still for an extended period of time when asleep. So, researchers can monitor fruit flies’ sleep by monitoring their activities. By altering various genes in a large number of fruit flies and then monitoring their sleep, researchers can detect and isolate flies that have abnormal sleep and compare their genes to those of a normal fruit fly. This allows researchers to identify the genes that are important for sleep because alterations in those genes will cause unusual patterns of sleep. Fruit flies are, however, pretty different from people. It’s not clear which of the discoveries from fly research are relevant for understanding human sleep and sleep disorders.

In humans, unlike fruit flies, sleep is monitored by electroencephalogram (EEG), which monitors our brain activity by using electrodes placed on the scalp. There are specific patterns in this brain activity that indicate sleep and the stages of sleep. The most important distinction between sleep stages is between rapid eye movement (REM) and non-REM sleep. REM sleep is the stage of sleep when we are usually dreaming. Research shows that REM sleep is very important for learning and memory.

The new study used mice instead of fruit flies. As in the previous fruit fly studies, the researchers altered genes in a large number of mice, and then screened for sleep problems. Instead of monitoring movement or activity, the researchers used EEG to monitor sleep in the mice. Mice are evolutionarily closer to humans than fruit flies, and mouse sleep stages as measured with EEG are similar to human sleep stages. This, combined with the large number of mice used and the length of time over which they were studied, makes this project an important step toward understanding human sleep.

Two specific genes were identified, which when altered, resulted in irregular sleep in mice. The first was found in mice that slept much more than normal mice and was called the Sik3 gene. The researchers discovered a gene alteration that caused the Sik3 gene to remain on and this caused the effected mice to sleep much more than normal. The second gene, the Nalcn gene, was found in mice that spent much less time in REM sleep than normal mice. The researchers discovered that this gene increased the activity of brain cells that inhibit REM sleep, which caused the mice to have much less REM sleep than normal.

Identifying genes that are involved in human sleep is important to understanding typical and disordered sleep. Because there are thousands of genes in the human body, it is an enormous task for researchers to tease apart which genes are related to sleep. And, each sleep-related gene may contribute to sleep in a different way. For example, a recent study revealed variations in genes between early-risers and night-owls. Although the details of the Sik3 and Nalcn genes identified by this study aren’t fully understood yet, exploring the regulation of sleep in mice is a step towards uncovering its mysteries in humans.