Dormivigilia

Instead of focusing on a Journal of Neuroscience piece this week, I am going to highlight a paper published in a recent PNAS that I presented in journal club today. The study was undertaken by a group of fellow sleep researchers at Wash U in St. Louis who are experts in Drosophila sleep and subsequently how changes to their direct genetic and physical environment profoundly affects their sleep. Now, the first question that you may have is how is sleep in such a tiny model organism measured as the use of EEG/EMG implants for the recording and analysis of sleep in these creatures would be near impossible. The answer is infrared sensor technology with very strict temporal resolution, such that there are very specific criteria for the amount of activity and the amount of quiescence that constitutes wake and sleep. So, in this study, the researchers manipulated levels of the gene foraging which encodes for a critical signaling protein (protein kinase G) and foraging-like behaviors in Drosophila. In fact, the gene encoding for protein kinase G is well conserved across many mammalian and nonmammalian species and similarly encodes for many overt physiological and behavioral processes related to feeding, sleeping, and learning. Conveniently enough, these three phenotypes (feeding, sleeping, and learning) were simultaneously investigated in this study to determine if changes in these behavioral and physiological processes are under direct influence of levels of foraging gene expression. To accomplish this, they used two types of test flies. “Rover” flies had high levels of foraging expression and phenotypically traveled greater distances between food patches, performed quite well on short-term memory tasks, and had more sleep over a 24 hr period compared with other fly lines. “Sitters,” on the other hand, had low levels of foraging expression, traveled shorter distances between food patches, performed well on long-term memory tasks, and had more waking across a 24 hrs period. Through the utility of these two different fly lines bred from parents as well as other transgenic lines that had regionally-specific high (or low) levels of foraging via the GAL4/UAS technique or RNA interference, the researchers found that resistance to sleep loss is largely dependent on levels of foraging gene expression. Thus, sleep loss achieved through physical means (cage shaking) or environmental means (starvation) was never recovered in rovers or flies with temporally high levels of foraging, but was in sitters or flies with temporally low levels of foraging. There is a trade-off, however, in that rovers performed worse on short-term memory tasks under conditions of starvation compared with sitters. Starvation also reduced mortality in rovers too. More details on these findings and others can be found here. The take home message of this study though is that the highly pleiotropic nature of  genes like foraging doesn’t allow some “versions” to be highly propagated throughout a population compared with others because there are often life-determining trade-offs. From a translational aspect, while it would seem advantageous for some people (namely military personnel and king crab fisherman) to work long hours in harsh environments with little access at times to food, the cognitive performance (and life expectancy) of these individuals may be compromised.

Donlea J, Leahy A, Thimgan MS, Suzuki Y, Hughson BN, Sokolowski MB, & Shaw PJ (2012). foraging alters resilience/vulnerability to sleep disruption and starvation in Drosophila. Proceedings of the National Academy of Sciences of the United States of America, 109 (7), 2613-8 PMID: 22308351