A new collection of inbred flies provides a tool for studying genetic control of sleep.
Sleep is vital for a healthy life, but some of us seem to get by with less snoozing than others. This individual variation isn’t unique to humans; fruit flies also show a variety of sleep patterns. These differences could potentially reveal more than just which flies are consistent cat-nappers—understanding the genetic basis of sleep variation could help pinpoint some of the molecular mechanisms that govern this essential and evolutionarily conserved process. In G3: Genes|Genomes|Genetics, Serrano Negron et al. describe a collection of inbred fly lines with extreme sleep behaviors that will serve as a useful tool for exploring such questions.
In a previous study, the authors had worked with flies from the Drosophila Genetic Reference Panel (DGRP), which is a large panel of inbred lines derived from a natural population. They chose the five longest-sleeping and five shortest-sleeping DGRP lines and allowed them to cross at random for 21 generations to produce an outbred population. They then used artificial selection to produce two long-sleeping and two short-sleeping populations.
In the new report, the authors created inbred lines from these long-sleeping and short-sleeping populations. Creating inbred lines is useful for gene editing studies because it reduces experimental noise caused by background genetic variation. To create lines of flies that sleep for either a very long or very short time, they mated one male and one female from one of the selected populations and then selected one male and one female from the progeny to propagate the line. They repeated this for 20 generations, eventually creating 39 inbred lines (19 long-sleeping lines and 20 short-sleeping lines), which were termed the Sleep Inbred Panel.
The duration of night sleep in the inbred lines ranged from just over an hour to nearly 11.5 hours, confirming that the extremes of the phenotypes had been maintained in the lines. The phenotypes were comparable to the selected parental populations, showing that the inbreeding process reduced genetic variability without drastically altering the sleep patterns. Interestingly, most of the variation between the new panel and the parental populations was due to short-sleeping inbred flies sleeping a little more than parental flies, which is likely because short sleep times made the flies less fit. Individual short-sleeping flies also showed more variation in how much they slept, likely for similar reasons.
By sequencing the genomes of flies in the panel, the authors identified a number of SNPs and other genomic variations associated with the sleep phenotypes, and they traced many of these variations back to the original DGRP lines. This resource can now be used to study the genetic underpinnings of sleep and may one day help shed light not only on ordinary differences between night owls and early birds but also on the causes of devastating sleep disorders.
The Sleep Inbred Panel, a Collection of Inbred Drosophila melanogaster with Extreme Long and Short Sleep Duration
Yazmin L. Serrano Negron, Nancy F. Hansen, Susan T. Harbison
G3: Genes, Genomes, Genetics September 2018 8: 2865-2873;