Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St. Louis, MO, USA.
Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal General Hospital, Montréal, Québec, Canada.
J Biol Rhythms. 2019 Apr;34(2):131-143. doi: 10.1177/0748730419830845. Epub 2019 Feb 25.
The circadian clock is an evolutionarily conserved mechanism that generates the rhythmic expression of downstream genes. The core circadian clock drives the expression of clock-controlled genes, which in turn play critical roles in carrying out many rhythmic physiological processes. Nevertheless, the molecular mechanisms by which clock output genes orchestrate rhythmic signals from the brain to peripheral tissues are largely unknown. Here we explored the role of one rhythmic gene, Achilles, in regulating the rhythmic transcriptome in the fly head. Achilles is a clock-controlled gene in Drosophila that encodes a putative RNA-binding protein. Achilles expression is found in neurons throughout the fly brain using fluorescence in situ hybridization (FISH), and legacy data suggest it is not expressed in core clock neurons. Together, these observations argue against a role for Achilles in regulating the core clock. To assess its impact on circadian mRNA rhythms, we performed RNA sequencing (RNAseq) to compare the rhythmic transcriptomes of control flies and those with diminished Achilles expression in all neurons. Consistent with previous studies, we observe dramatic upregulation of immune response genes upon knock-down of Achilles. Furthermore, many circadian mRNAs lose their rhythmicity in Achilles knock-down flies, suggesting that a subset of the rhythmic transcriptome is regulated either directly or indirectly by Achilles. These Achilles-mediated rhythms are observed in genes involved in immune function and in neuronal signaling, including Prosap, Nemy and Jhl-21. A comparison of RNAseq data from control flies reveals that only 42.7% of clock-controlled genes in the fly brain are rhythmic in both males and females. As mRNA rhythms of core clock genes are largely invariant between the sexes, this observation suggests that sex-specific mechanisms are an important, and heretofore under-appreciated, regulator of the rhythmic transcriptome.
生物钟是一种进化上保守的机制，它产生下游基因的节律表达。核心生物钟驱动时钟控制基因的表达，这些基因反过来在执行许多节律生理过程中起着关键作用。然而，时钟输出基因协调来自大脑到外周组织的节律信号的分子机制在很大程度上是未知的。在这里，我们探索了一个节律基因 Achilles 在调节果蝇头部节律转录组中的作用。Achilles 是果蝇中一种时钟控制基因，编码一种假定的 RNA 结合蛋白。使用荧光原位杂交 (FISH) 在果蝇大脑中的神经元中发现 Achilles 的表达，并且遗留数据表明它不在核心时钟神经元中表达。这些观察结果一起表明 Achilles 不在调节核心时钟中发挥作用。为了评估它对 circadian mRNA 节律的影响，我们进行了 RNA 测序 (RNAseq)，比较了对照果蝇和所有神经元中 Achilles 表达减少的果蝇的节律转录组。与先前的研究一致，我们观察到 Achilles 敲低后免疫反应基因的显著上调。此外，许多 circadian mRNAs 在 Achilles 敲低果蝇中失去了节律性，这表明一部分节律转录组直接或间接地受到 Achilles 的调节。这些 Achilles 介导的节律在参与免疫功能和神经元信号传导的基因中观察到，包括 Prosap、Nemy 和 Jhl-21。对对照果蝇的 RNAseq 数据的比较表明，在果蝇大脑中，只有 42.7%的时钟控制基因在雄性和雌性中都是节律性的。由于核心时钟基因的 mRNA 节律在两性之间基本不变，这一观察结果表明性别特异性机制是节律转录组的一个重要且迄今未被充分认识的调节因子。
