Researchers have identified the first two core genes that regulate the amount of deep sleep and dreaming, a key development they believe will lead to the discovery of a network of related genes controlling sleep.
The study demonstrates in mice that a single gene controls the amount of non-REM (rapid eye movement) sleep, which includes deep sleep. A second gene controls the amount or need for REM sleep, associated with vivid dreaming. The findings provide a critical molecular entry point to explain how sleep works and to identify potential targets to better treat sleep disorders.
Previous research has identified genes that regulate the switch between wakefulness and sleep. But until this latest study in Nature, scientists have not known what mechanisms control the drive or need for non-REM sleep, nor the amount of REM sleep.
To find out, researchers used a forward-genetic approach in which they screened for sleep disorders in 8,000 mice using electroencephalogy (EEG) to monitor brain waves. They found two distinct pedigrees of note:
Sleepy - A mouse they called Sleepy had 50 percent more non-REM sleep than normal mice without any other obvious defects, caused by a mutation in the Salt-Inducible Kinase 3 Sik3 (Sik3) gene.
Dreamless - A mouse researchers called Dreamless was severely deficient in the amount of REM sleep, a stage of rest characterized by rapid eye movements and vivid dreams. This deficit was caused by a mutation in the Sodium Leak Channel Non-selective (Nalcn) gene.
Researchers introduced these same mutations into normal mice and saw their sleep behaviors change accordingly.
Normal sleep patterns include short durations of REM sleep surrounded by longer stretches of non-REM sleep and account for about a quarter of a night's rest in most young adults. Many forms of sleep disorder distort these patterns. Because the Sik3 and Nalcn genes have just been identified, no evidence yet exists to link them directly to known sleep disturbances in humans.
However, while the role and importance of REM sleep remains a point of debate, many scientists agree this stage of rest is involved in the formation of emotional memories and coping with negative experiences. Thus, a lack of REM sleep may contribute to conditions such as posttraumatic stress disorder (PTSD).