Humans have always woken up at sunrise, and gone to sleep at sunset. This phenomenon can be explained culturally, but is yet to be fully understood biologically.
Wendy Chen from the David Proper laboratory at the California Institute of Technology, USA has made a step forward in our understanding of this topic in her recent study published in Neuron, which investigates the brain-specific Prok2 protein. It was already known that Prok2 was involved in sleep regulation, but the details were not clear.
Chen genetically engineered zebrafish to either overexpress Prok2, or to express a mutated version. She found that both kinds of engineered fish had abnormal sleep-wake cycles compared to normal zebrafish. Specifically, she found that Prok2 overexpression led to more sleep during the daytime, and an increase in the sleep-promoting protein galanin. However, all effects were determined by light exposure rather than pre-existing circadian rhythms.
This suggests that the effects of the Prok2 protein on sleep are regulated by light, and that the correct amount of this protein is necessary for effective sleep-wake cycle regulation.
The result has provided some insight into the importance of limiting light exposure when it comes to getting a good nights sleep. However, further investigation into the direct link between light and Prok2 are still required, as well as future human studies.