Institute of Life Sciences, Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing 210096, China.
Institute of Life Sciences, Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing 210096, China; Co-innovation Center of Neuroregeneration, Nantong University, Nantong, China.
Curr Biol. 2017 Dec 4;27(23):3616-3625.e5. doi: 10.1016/j.cub.2017.10.052. Epub 2017 Nov 22.
The timing of sleep is tightly governed by the circadian clock, which contains a negative transcriptional feedback loop and synchronizes the physiology and behavior of most animals to daily environmental oscillations. However, how the circadian clock determines the timing of sleep is largely unclear. In vertebrates and invertebrates, the status of sleep and wakefulness is modulated by the electrical activity of pacemaker neurons that are circadian regulated and suppressed by inhibitory GABAergic inputs. Here, we showed that Drosophila GABA receptors undergo rhythmic degradation in arousal-promoting large ventral lateral neurons (lLNvs) and their expression level in lLNvs displays a daily oscillation. We also demonstrated that the E3 ligase Fbxl4 promotes GABA receptor ubiquitination and degradation and revealed that the transcription of fbxl4 in lLNvs is CLOCK dependent. Finally, we demonstrated that Fbxl4 regulates the timing of sleep through rhythmically reducing GABA sensitivity to modulate the excitability of lLNvs. Our study uncovered a critical molecular linkage between the circadian clock and the electrical activity of pacemaker neurons and demonstrated that CLOCK-dependent Fbxl4 expression rhythmically downregulates GABA receptor level to increase the activity of pacemaker neurons and promote wakefulness.
睡眠的时间由生物钟严格控制，生物钟包含一个负转录反馈回路，使大多数动物的生理和行为与日常环境波动同步。然而，生物钟如何确定睡眠的时间在很大程度上还不清楚。在脊椎动物和无脊椎动物中，睡眠和觉醒的状态是由起搏神经元的电活动调节的，起搏神经元的电活动受节律调节，并被抑制性 GABA 能输入所抑制。在这里，我们发现果蝇 GABA 受体在促进觉醒的大型腹外侧神经元（lLNvs）中呈现节律性降解，并且其在 lLNvs 中的表达水平呈每日振荡。我们还证明，E3 连接酶 Fbxl4 促进 GABA 受体的泛素化和降解，并揭示了 lLNvs 中 fbxl4 的转录依赖于 CLOCK。最后，我们证明 Fbxl4 通过节律性降低 GABA 敏感性来调节睡眠的时间，从而调节 lLNvs 的兴奋性。我们的研究揭示了生物钟和起搏神经元电活动之间的关键分子联系，并证明 CLOCK 依赖性 Fbxl4 表达节律性地下调 GABA 受体水平，增加起搏神经元的活动，促进觉醒。
