Sleep is regulated by homeostatic sleep drive and the circadian clock. While tremendous progress has been made in elucidating the molecular components of the core circadian oscillator, the output mechanisms by which this robust oscillator generates rhythmic sleep behavior remain poorly understood. At the cellular level, growing evidence suggests that subcircuits in the master circadian pacemaker suprachiasmatic nucleus (SCN) in mammals and in the clock network in Drosophila regulate distinct aspects of sleep. Thus, to identify novel molecules regulating the circadian timing of sleep, we conducted a large-scale screen of mouse SCN-enriched genes in Drosophila. Here, we show that Tob (Transducer of ERB-B2) regulates the timing of sleep onset at night in female fruit flies. Knockdown of Tob pan-neuronally, either constitutively or conditionally, advances sleep onset at night. We show that Tob is specifically required in "evening neurons" (the LNds and the fifth s-LNv) of the clock network for proper timing of sleep onset. Tob levels cycle in a clock-dependent manner in these neurons. Silencing of these "evening" clock neurons results in an advanced sleep onset at night, similar to that seen with Tob knockdown. Finally, sharp intracellular recordings demonstrate that the amplitude and kinetics of LNd postsynaptic potentials (PSPs) cycle between day and night, and this cycling is attenuated with Tob knockdown in these cells. Our data suggest that Tob acts as a clock output molecule in a subset of clock neurons to potentiate their activity in the evening and enable the proper timing of sleep onset at night.

睡眠由稳态睡眠驱动和生物钟调节。尽管在阐明核心昼夜节律振荡器的分子成分方面已经取得了巨大进展，但这种强大的振荡器产生节律性睡眠行为的输出机制仍然知之甚少。在细胞水平上，越来越多的证据表明，哺乳动物的主昼夜节律起搏器视交叉上核（SCN）和果蝇的时钟网络中的子电路调节睡眠的不同方面。因此，为了识别调节睡眠昼夜节律的新分子，我们对果蝇中富含小鼠 SCN 的基因进行了大规模筛选。在这里，我们证明 Tob（ERB-B2 传感器）调节雌性果蝇夜间入睡的时间。 Tob 全神经元的敲低，无论是组成性的还是条件性的，都会促进夜间入睡。我们表明，为了正确确定睡眠开始时间，时钟网络的“夜间神经元”（LNds 和第五个 s-LNv）特别需要 Tob。 Tob 水平在这些神经元中以时钟依赖性方式循环。这些“夜间”时钟神经元的沉默会导致夜间提前入睡，类似于 Tob 敲低的情况。最后，清晰的细胞内记录表明，LNd 突触后电位 (PSP) 的振幅和动力学在白天和夜间之间循环，并且这种循环随着这些细胞中 Tob 的敲低而减弱。我们的数据表明，Tob 在时钟神经元子集中充当时钟输出分子，以增强它们在晚上的活动并确保夜间入睡的正确时间。