Trish Goodwin, PhD
Department of Biology
(October 5, 2015)
MicroRNAs in Drosophila Sleep
As anyone who has experienced jet lag can attest, the body can go without sleep for only so long. Eventually you crash and sleep for 12 or more hours in one night. What signals your body to do this? Dr. Goodwin is examining the molecular processes behind this “rebound sleep,” or the body’s method of regaining balance in the sleep/wake cycle. In her talk, she discussed her work with Drosophila (fruit flies), looking for particular spots in the genetic code necessary for controlling how and when we sleep.
Sleep is a highly conserved behavior that is essential for brain function, but the molecular machinery that controls sleep is poorly understood. Changes in sleep/wake status are accompanied by changes in gene expression. One mechanism that may control these changes is microRNA-mediated suppression of mRNA translation. MicroRNAs (miRs) are small, 22 nucleotide-long non-coding RNAs that bind to the 3’ UTRs of mRNAs and prevent their translation. Studies of sleep in mammals and circadian behavior in Drosophila suggest that miRs play a role in sleep and circadian clock output, but the role of miRs in sleep has not been studied systematically. Our research seeks to identify and characterize miRs that regulate sleep by employing miR sponges to inhibit specific miRs in the Drosophila genome. Sponges contain tandem repeats of miR target sequence, which prevent miRs from binding to their endogenous targets. To identify the maximum number of miRs that affect sleep, we have initially expressed sponges ubiquitously using TubulinGal4 and have begun screening these flies for changes in baseline sleep and sleep homeostasis. Sleep homeostasis is the ability to detect low levels of sleep and subsequently produce a compensatory increase in sleep (called “rebound sleep”). Out of 81 miRs screened thus far, we have identified 32 miRs that affect sleep. We found that the majority of miR sponges with effects on sleep cause decreases in sleep (n=23), while a minority of sponges cause increases in sleep (n=7). We have also identified 4 miRs that regulate the sleep homeostat (i.e. rebound sleep). Half of these affect rebound sleep specifically, while the other half affect both baseline and rebound sleep. Additionally, we investigated whether changes in sleep can cause changes in miR expression in Drosophila. We used nCounter miRNA expression assays (Nanostring Tech.) to compare miR expression after: (1) normal nighttime sleep, (2) 12 hours of nighttime sleep deprivation, (3) normal daytime waking, and (4) 12 hours of rebound sleep following nighttime sleep deprivation. We identified 16 miRs that undergo significant changes in expression with time of day or sleep deprivation (2-Way ANOVA). Of these 16 miRs, nine were found to have effects on sleep when we inhibited their function using sponges, four miRs had no change in sleep after inhibition, and three are undergoing testing. Future experiments will employ cell-type specific Gal4s and temporally restricted sponge expression (using Gal80ts) to determine where miRs function and whether they function in adults or during development to regulate sleep.