Drosophila HyperkineticMutants Have Reduced Sleep and Impaired Memory

In mammals, sleep is thought to be important for health, cognition, and memory. Fruit flies share most features of mammalian sleep, and a recent study found that Drosophila lines carrying loss-of-function mutations in Shaker (Sh) are short sleeping, suggesting that the Sh current plays a major role in regulating daily sleep amount. The Sh current is potentiated by a beta modulatory subunit coded by Hyperkinetic (Hk). Here, we demonstrate that severe loss-of-function mutations of Hk reduce sleep and do so primarily by affecting the Sh current. Moreover, we prove, using a transgenic approach, that a wild-type copy of Hk is sufficient to restore normal sleep. Furthermore, we show that short-sleeping Hk mutant lines have a memory deficit, whereas flies carrying a weaker hypomorphic Hk allele have normal sleep and normal memory. By comparing six short-sleeping Sh lines with two normal sleeping ones, we also found that only alleles that reduce sleep also impair memory. These data identify a gene, Hk, which is necessary to maintain normal sleep, and provide genetic evidence that short sleep and poor memory are linked.