Sleep is under homeostatic control, whereby increasing wakefulness generates sleep need and triggers sleep drive. However, the molecular and cellular pathways by which sleep need is encoded are poorly understood. In addition, the mechanisms underlying both how and when sleep need is transformed to sleep drive are unknown. Here, using ex vivo and in vivo imaging, we show in Drosophila that astroglial Ca 2+ signaling increases with sleep need. We demonstrate that this signaling is dependent on a specific L-type Ca 2+ channel and is required for homeostatic sleep rebound. Thermogenetically increasing Ca 2+ in astrocytes induces persistent sleep behavior, and we exploit this phenotype to conduct a genetic screen for genes required for the homeostatic regulation of sleep. From this large-scale screen, we identify TyrRII, a monoaminergic receptor required in astrocytes for sleep homeostasis. TyrRII levels rise following sleep deprivation in a Ca 2+ -dependent manner, promoting further increases in astrocytic Ca 2+ and resulting in a positive-feedback loop. These data suggest that TyrRII acts as a gate to enable the transformation of sleep need to sleep drive at the appropriate time. Moreover, our findings suggest that astrocytes then transmit this sleep need to the R5 sleep drive circuit, by upregulation and release of the interleukin-1 analog Spätzle. These findings define astroglial Ca 2+ signaling mechanisms encoding sleep need and reveal dynamic properties of the sleep homeostatic control system.

The attachment of a sugar to a hydrophobic polyisoprenyl carrier is the first step for all extracellular glycosylation processes. The enzymes that perform these reactions, polyisoprenyl-glycosyltransferases (PI-GTs) include dolichol phosphate mannose synthase (DPMS), which generates the mannose donor for glycosylation in the endoplasmic reticulum. Here we report the 3.0Å resolution crystal structure of GtrB, a glucose-specific PI-GT from Synechocystis, showing a tetramer in which each protomer contributes two helices to a membrane-spanning bundle. The active site is 15 Å from the membrane, raising the question of how water-soluble and membrane-embedded substrates are brought into apposition for catalysis. A conserved juxtamembrane domain harbours disease mutations, which compromised activity in GtrB in vitro and in human DPM1 tested in zebrafish. We hypothesize a role of this domain in shielding the polyisoprenyl-phosphate for transport to the active site. Our results reveal the basis of PI-GT function, and provide a potential molecular explanation for DPM1-related disease.

Main The function of WAKE is conserved in mammalsWe previously identified the clock-output molecule WIDE AWAKE (WAKE) from a forward genetic screen in Drosophila 4 . WAKE modulates the activity of arousalpromoting clock neurons at night, in order to promote sleep onset and quality 4,5 . The mammalian proteome contains a single ortholog, mWAKE (also named ANKFN1/Nmf9), with 56% sequence similarity and which is enriched in the core region of the master circadian pacemaker suprachiasmatic nucleus (SCN) 4,6 ( Fig. 1a, Extended Data Fig. 1a). To investigate whether the function of WAKE is conserved in mice, we generated a putative null allele of mWAKE (mWAKE (-) ) by CRISPR/Cas9 insertion of 8 base pairs (containing a stop codon and generating a downstream frameshift) in exon 4, which is predicted to be in all splice isoforms of mWAKE ( Fig. 1b). As expected, mWAKE expression, as assessed by quantitative PCR and in situ hybridization (ISH), was markedly reduced in mWAKE (-/-) mice, likely due to nonsense-mediated decay (Fig. 1c, 1d). Given mWAKE expression in the SCN, we first examined locomotor circadian rhythms and found that mWAKE (-/-) mice exhibit a mild but non-significant decrease in circadian period length (Extended Data Fig. 1b, 1c). These results are similar to findings from fly wake mutants and mice bearing the Nmf9 mutation (a previously identified ENU-generated allele of mWAKE) 4,6 .Because we previously demonstrated that WAKE mediates circadian regulation of sleep timing and quality in fruit flies 4,5 , we next assessed sleep in mWAKE (-/-) mice via electroencephalography (EEG). Under light:dark (L:D) conditions, there was no difference in the amount of wakefulness, non-rapid eye movement (NREM), or REM sleep between mWAKE (-/-) mutants and wild-type (WT) littermate controls (Extended Data Fig. 1d). In constant darkness (D:D), there is a modest main effect of genotype on wakefulness (P<0.05) and NREM sleep (P<0.05), and a mild but significant decrease in REM sleep in mWAKE (-/-) mutants (Fig. 1e). Although the amount of wakefulness did not appreciably differ in mWAKE (-/-) mutants compared to controls, there was a change in the distribution of wakefulness at night; mutants spent more daily time in prolonged wake bouts, and some mutants exhibited dramatically long bouts of wakefulness (Extended Data Fig. 1e, 1f).

SummaryOxytocin is a neuropeptide important for maternal physiology and childcare, including parturition and milk ejection during nursing. Suckling triggers oxytocin release, but other sensory cues- specifically infant cries- can elevate oxytocin levels in new human mothers, indicating that cries can activate hypothalamic oxytocin neurons. Here we describe a neural circuit routing auditory information about infant vocalizations to the oxytocin system of the mouse brain. We performed in vivo electrophysiological recordings and photometry from identified oxytocin neurons in awake maternal mice presented with pup calls. We found that oxytocin neurons responded to pup vocalizations via input from the posterior intralaminar thalamus, and repetitive thalamic stimulation induced lasting disinhibition of oxytocin neurons. Suppression of this pathway impaired maternal behavior and playing pup calls led to central oxytocin release in vivo. This circuit provides a mechanism for transforming acoustic input into hormonal output to ensure modulation of brain state required for successful parenting.

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Oxytocin is a neuropeptide important for maternal physiology and childcare, including parturition and milk ejection during nursing1-8. Suckling triggers oxytocin release, but other sensory cues- specifically infant cries- can elevate oxytocin levels in new human mothers9-11 indicating that cries can activate hypothalamic oxytocin neurons. Here we describe a neural circuit routing auditory information about infant vocalizations to mouse oxytocin neurons. We performed in vivo electrophysiological recordings and photometry from identified oxytocin neurons in awake maternal mice presented with pup calls. We found that oxytocin neurons responded to pup vocalizations, but not pure tones, via input from the posterior intralaminar thalamus, and repetitive thalamic stimulation induced lasting disinhibition of oxytocin neurons. This circuit gates central oxytocin release and maternal behavior in response to calls, providing a mechanism for the integration of sensory cues from the offspring in maternal endocrine networks to ensure modulation of brain state for successful parenting.

SUMMARYSleep is under homeostatic control, whereby increasing wakefulness generates sleep need and triggers sleep drive. However, the molecular and cellular pathways by which sleep need is encoded are poorly understood. In addition, the mechanisms underlying both how and when sleep need is transformed to sleep drive are unknown. Here, using ex vivo and in vivo imaging, we show in Drosophila that astroglial Ca2+ signaling increases with sleep need. We demonstrate that this signaling is dependent on a specific L-type Ca2+ channel and is required for homeostatic sleep rebound. Thermogenetically increasing Ca2+ in astrocytes induces persistent sleep behavior, and we exploit this phenotype to conduct a genetic screen for genes required for the homeostatic regulation of sleep. From this large-scale screen, we identify TyrRII, a monoaminergic receptor required in astrocytes for sleep homeostasis. TyrRII levels rise following sleep deprivation in a Ca2+-dependent manner, promoting further increases in astrocytic Ca2+ and resulting in a positive-feedback loop. These data suggest that TyrRII acts as a gate to enable the transformation of sleep need to sleep drive at the appropriate time. Moreover, our findings suggest that astrocytes then transmit this sleep need to the R5 sleep drive circuit, by upregulation and release of the interleukin-1 analog Spätzle. These findings define astroglial Ca2+ signaling mechanisms encoding sleep need and reveal dynamic properties of the sleep homeostatic control system.