I would like to get the current novel insight about the life science.

The active time of each animal species is evolutionally set to accommodate their lifestyle and survival strategy, which is restricted in the morning and evening in the case of Drosophila. The brain functions at the activity peaks must be subsequently upregulated at the neural circuit or synaptic level, latter of which has been demonstrated by the circadian synaptic plasticity in the clock neurons. However, the biological significance of the circadian synaptic plasticity and its regulation remain elusive. Here we report that the circadian synaptic plasticity in the visual circuit controls the duration of the activity peak in Drosophila. An ortholog of BDNF receptor, Kek2 that regulates presynaptic size is oscillatory expressed in the visual circuit at the activity peak time. Kek2 expression was induced by the upstream signaling via NO-dependent cGMP pathway. Knockdown of kek2 in the visual circuit results in the low arousal state in the phototactic behavioral assay at the activity peak time, but persistence of awake state, indicating that Kek2 is required for maintaining arousal and terminating awake state. Thus, the synaptic circadian plasticity mediated by Kek2 controls the quality and duration of the awake state, suggesting the organismal activity setting through the circadian synaptic plasticity.