A Secreted Ig-Domain Protein Required in Both Astrocytes and Neurons for Regulation of Drosophila Night Sleep

Summary Endogenous rhythmic behaviors are evolutionarily conserved and essential for life. In mammalian and invertebrate models, well-characterized neuronal circuits and evolutionarily conserved mechanisms regulate circadian behavior and sleep [ 1 , 2 , 3 , 4 ]. In Drosophila, neuronal populations located in multiple brain regions mediate arousal, sleep drive, and homeostasis (reviewed in [ 3 , 5 , 6 , 7 ]). Similar to mammals [ 8 ], there is also evidence that fly glial cells modulate the neuronal circuits controlling rhythmic behaviors, including sleep [ 1 ]. Here, we describe a novel gene (CG14141; aka Nkt) that is required for normal sleep. NKT is a 162-amino-acid protein with a single IgC2 immunoglobulin (Ig) domain and a high-quality signal peptide [ 9 ], and we show evidence that it is secreted, similar to its C. elegans ortholog (OIG-4) [ 10 ]. We demonstrate that Nkt-null flies or those with selective knockdown in either neurons or glia have decreased and fragmented night sleep, indicative of a non-redundant requirement in both cell types. We show that Nkt is required in fly astrocytes and in a specific set of wake-promoting neurons—the mushroom body (MB) α’β’ cells that link sleep to memory consolidation [ 11 ]. Importantly, Nkt gene expression is required in the adult nervous system for normal sleep, consistent with a physiological rather than developmental function for the Ig-domain protein.