The fruit fly Drosophila melanogaster, like most organisms, exhibits increased sleep amount and depth in young compared to mature animals. While the fly has emerged as a powerful model for studying sleep during development, qualitative behavioral features of sleep ontogeny and its genetic control are poorly understood. Here we find that, in addition to increased sleep time and intensity, young flies sleep with less place preference than mature adults, and, like mammals, exhibit more motor twitches during sleep. In addition, we show that ontogenetic changes in sleep amount, twitch, and place preference are preserved across sleep mutants with lesions in distinct molecular pathways. Our results demonstrate that sleep ontogeny is characterized by multifaceted behavioral changes, including quantitative and qualitative alterations to sleep as animals mature. Further, the preservation of sleep ontogenetic changes despite mutations that alter sleep time suggests independent genetic control mechanisms for sleep maturation.

Across species, sleep in young animals is critical for normal brain maturation. The molecular determinants of early life sleep remain unknown. Through an RNAi-based screen, we identified a gene, pdm3, required for sleep maturation in Drosophila. Pdm3, a transcription factor, coordinates an early developmental program that prepares the brain to later execute high levels of juvenile adult sleep. PDM3 controls the wiring of wake-promoting dopaminergic (DA) neurites to a sleep-promoting region, and loss of PDM3 prematurely increases DA inhibition of the sleep center, abolishing the juvenile sleep state. RNA-Seq/ChIP-Seq and a subsequent modifier screen reveal that pdm3 represses expression of the synaptogenesis gene Msp300 to establish the appropriate window for DA innervation. These studies define the molecular cues governing sleep behavioral and circuit development, and suggest sleep disorders may be of neurodevelopmental origin.

Sleep disruptions are among the most commonly reported symptoms across neurodevelopmental disorders (NDDs), but mechanisms linking brain development to normal sleep are largely unknown. From a Drosophila screen of human NDD-associated risk genes, we identified the chromatin remodeler Imitation SWItch/SNF (ISWI) to be required for adult fly sleep. Loss of ISWI also results in disrupted circadian rhythms, memory, and social behavior, but ISWI acts in different cells and during distinct developmental times to affect each of these adult behaviors. Specifically, ISWI expression in type I neuroblasts is required for both adult sleep and formation of a learning-associated brain region. Expression in flies of the human ISWI homologs SMARCA1 and SMARCA5 differentially rescues adult phenotypes, while de novo SMARCA5 patient variants fail to rescue sleep. We propose that sleep deficits are a primary phenotype of early developmental origin in NDDs and point toward chromatin remodeling machinery as critical for sleep circuit formation.

Sleep disruptions are among the most commonly-reported symptoms across neurodevelopmental disorders (NDDs), but mechanisms linking brain development to normal sleep are largely unknown. From a Drosophila screen of human NDD-associated risk genes, we identified the chromatin remodeler Imitation SWItch/SNF (ISWI) to be required for adult fly sleep. Loss of ISWI also results in disrupted circadian rhythms, memory, and social behavior, but ISWI acts in different cells and during distinct developmental times to affect each of these adult behaviors. Specifically, ISWI expression in type I neuroblasts is required for both adult sleep and formation of a learning-associated brain region. Expression in flies of the human ISWI homologs SMARCA1 and SMARCA5 differentially rescue adult phenotypes. We propose that sleep deficits are a primary phenotype of early developmental origin in NDDs, and point towards chromatin remodeling machinery as critical for sleep circuit formation.

Introduction Sleep is commonly disrupted in patients with neurodevelopmental disorders (NDDs). Despite strong clinical associations between disrupted sleep and other NDD symptoms, we lack an understanding of how these are pathophysiologically related. Drosophila melanogaster exhibit essential characteristics of human sleep and have well-defined neural circuits underlying learning and social behaviors. This represents an ideal system to investigate the mechanistic interaction between disrupted sleep and other behavioral dysfunctions in NDDs. Methods We performed a reverse genetic RNAi-based screen targeting Drosophila homologs of human genes within NDD-associated risk loci. Pan-neuronal knockdown of risk genes was achieved using the Gal4-UAS system. Results Pan-neuronal knockdown of ISWI led to dramatic deficits in sleep and circadian arrhythmicity in the adult fly. Across species, ISWI and its homologs are ATP-dependent chromatin remodelers that regulate gene expression important for neural differentiation. We found that depleting ISWI also leads to memory and social deficits. ISWI functions during dissociable temporal windows of pre-adult development and in different circuits to establish different adult behaviors. The sleep phenotype associated with ISWI knockdown mapped to a specific population of cells. RNA-Seq of developing brains during the window important for sleep deficits revealed significant transcriptional changes in genes associated with nervous system development, suggesting ISWI acts in the development of sleep regulatory circuits. Finally, mutations in the human homologs of ISWI, SMARCA1/5, have been implicated in NDDs. Expressing either SMARCA1/5 in the setting of ISWI knockdown differentially rescued adult deficits. Conclusion Identification of ISWI provides a platform for unraveling pleiotropic behavioral effects from an NDD risk gene. Sleep, circadian rhythms, memory, and social behaviors are affected by ISWI knockdown, and map to different developmental periods and circuits. In addition, SMARCA1/5 differentially rescue adult behaviors, suggesting NDD-causing mutations in these genes may affect different behaviors. Current work aims to determine how human mutations in SMARCA1/5 affect behaviors. Support This work was supported by NIH K08 NS090461 (MSK) and T32 HL007953 (NNG), Hearst Foundation Fellowship 2018 (NNG), Burroughs Welcome Career Award for Medical Scientists, March of Dimes Basil O’Connor Scholar Award, and Sloan Research Fellowship (MSK).