A genetic screen for sleep and circadian mutants reveals mechanisms underlying regulation of sleep in Drosophila.

Study Objectives: In order to characterize the genetic mechanisms underlying sleep, we have carried out a large-scale screen in Drosophila to identify short-sleeping mutants. The objectives of this study were as follows: (1) characterize the phenotypes of the shortest-sleeping mutants; (2) examine whether changes in arousal threshold or sleep homeostasis underlie short-sleeping phenotypes; (3) clone a gene affected in one of the shortest sleepers; and (4) investigate whether circadian mutants can be identified using light:dark (L:D) locomotor data obtained for studying sleep behavior.

Design: Locomotor activity was measured using the Drosophila Activity Monitoring System in a 12:12 L:D cycle.

Setting: Drosophila research laboratory.

Participants: Adult flies from the 2nd chromosome Zuker collection, which contain mutations in most of the nonessential genes on the Drosophila 2nd chromosome.

Measurements And Results: Our analysis of sleep characteristics suggests that daily activity (but not waking activity) correlates with daily sleep time and that defects in sleep maintenance are more common than defects in sleep initiation. Our shortest sleepers have intact or increased sleep rebound following sleep deprivation but show reduced thresholds for arousal. Molecular analysis of one of the short-sleeping lines indicates that it is a novel allele of a dopamine transporter (DAT). Finally, we describe a novel approach for identifying circadian mutants using L:D data.

Conclusions: Our data suggest that most short-sleeping mutant phenotypes in Drosophila are characterized by an inability to stay asleep, most likely because of a reduced arousal threshold.