Reorganization of Sleep by Temperature in Drosophila Requires Light, the Homeostat, and the Circadian Clock.

Increasing ambient temperature reorganizes the Drosophila sleep pattern in a way similar to the human response to heat, increasing daytime sleep while decreasing nighttime sleep. Mutation of core circadian genes blocks the immediate increase in daytime sleep, but not the heat-stimulated decrease in nighttime sleep, when animals are in a light:dark cycle. The ability of per(01) flies to increase daytime sleep in light:dark can be rescued by expression of PER in either LNv or DN1p clock cells and does not require rescue of locomotor rhythms. Prolonged heat exposure engages the homeostat to maintain daytime sleep in the face of nighttime sleep loss. In constant darkness, all genotypes show an immediate decrease in sleep in response to temperature shift during the subjective day, implying that the absence of light input uncovers a clock-independent pro-arousal effect of increased temperature. Interestingly, the effects of temperature on nighttime sleep are blunted in constant darkness and in cry(OUT) mutants in light:dark, suggesting that they are dependent on the presence of light the previous day. In contrast, flies of all genotypes kept in constant light sleep more at all times of day in response to high temperature, indicating that the presence of light can invert the normal nighttime response to increased temperature. The effect of temperature on sleep thus reflects coordinated regulation by light, the homeostat, and components of the clock, allowing animals to reorganize sleep patterns in response to high temperature with rough preservation of the total amount of sleep.

PDF cells are a GABA-responsive wake-promoting component of the Drosophila sleep circuit.

Daily sleep cycles in humans are driven by a complex circuit within which GABAergic sleep-promoting neurons oppose arousal. Drosophila sleep has recently been shown to be controlled by GABA, which acts on unknown cells expressing the Rdl GABAA receptor. We identify here the relevant Rdl-containing cells as PDF-expressing small and large ventral lateral neurons (LNvs) of the circadian clock. LNv activity regulates total sleep as well as the rate of sleep onset; both large and small LNvs are part of the sleep circuit. Flies mutant for pdf or its receptor are hypersomnolent, and PDF acts on the LNvs themselves to control sleep. These features of the Drosophila sleep circuit, GABAergic control of onset and maintenance as well as peptidergic control of arousal, support the idea that features of sleep-circuit architecture as well as the mechanisms governing the behavioral transitions between sleep and wake are conserved between mammals and insects.

Modulation of GABAA receptor desensitization uncouples sleep onset and maintenance in Drosophila.

Many lines of evidence indicate that GABA and GABA(A) receptors make important contributions to human sleep regulation. Pharmacological manipulation of these receptors has differential effects on sleep onset and sleep maintenance insomnia. Here we show that sleep is regulated by GABA in Drosophila and that a mutant GABA(A) receptor, Rdl(A302S), specifically decreases sleep latency. The drug carbamazepine (CBZ) has the opposite effect on sleep; it increases sleep latency as well as decreasing sleep. Behavioral and physiological experiments indicated that Rdl(A302S) mutant flies are resistant to the effects of CBZ on sleep latency and that mutant RDL(A302S) channels are resistant to the effects of CBZ on desensitization, respectively. These results suggest that this biophysical property of the channel, specifically channel desensitization, underlies the regulation of sleep latency in flies. These experiments uncouple the regulation of sleep latency from that of sleep duration and suggest that the kinetics of GABA(A) receptor signaling dictate sleep latency.

The Drosophila ARC homolog regulates behavioral responses to starvation.

The gene encoding dARC1, one of three Drosophila homologs of mammalian activity-regulated cytoskeleton-associated protein (ARC), is upregulated in both seizure and muscular hypercontraction mutants. In this study we generate a null mutant for dArc1 and show that this gene is not involved in synaptic plasticity at the larval neuromuscular junction or in formation or decay of short-term memory of courtship conditioning, but rather is a modifier of stress-induced behavior. dARC1 is expressed in a number of neurosecretory cells and mutants are starvation-resistant, exhibiting an increased time of survival in the absence of food. Starvation resistance is likely due to the fact that dArc1 mutants lack the normal hyperlocomotor response to starvation, which is almost universal in the animal kingdom. dARC1 acts in insulin-producing neurons of the pars intercerebralis to control this behavior, but does not appear to be a general regulator of insulin signaling. This suggests that there are multiple modes of communication between the pars and the ring gland that control starvation-induced behavioral responses.

Identification of alternative splicing regulators by RNA interference in Drosophila.

Alternative splicing is thought to be regulated by nonspliceosomal RNA binding proteins that modulate the association of core components of the spliceosome with the pre-mRNA. Although the majority of metazoan genes encode pre-mRNAs that are alternatively spliced, remarkably few splicing regulators are currently known. Here, we used RNA interference to examine the role of >70% of the Drosophila RNA-binding proteins in regulating alternative splicing. We identified 47 proteins as splicing regulators, 26 of which have not previously been implicated in alternative splicing. Many of the regulators we identified are nonspliceosomal RNA-binding proteins. However, our screen unexpectedly revealed that altering the concentration of certain core components of the spliceosome specifically modulates alternative splicing. These results significantly expand the number of known splicing regulators and reveal an extraordinary richness in the mechanisms that regulate alternative splicing.