Glucocorticoid Receptor-regulated gene transcription in the epigenetic embedding of neural stress responses: towards a mechanistic understanding of ch

下丘脑-垂体-肾上腺(HPA)轴是机体对外界应激源做出生理反应的主要调节因子，在脊椎动物中高度保守。作为对生物应激源的反应，下丘脑产生促肾上腺皮质激素释放激素(CRH)，刺激脑下垂体释放促肾上腺皮质激素(ACTH)，从而导致肾上腺/肾间腺释放皮质醇。在大脑中，皮质醇是糖皮质激素受体(GR)转录因子NR3C1的配体，它调节神经内分泌和神经活动调节基因的表达。为了确保应激诱导的HPA轴活动依赖于外部应激源的持续，皮质醇结合的NR3C1通过抑制CRH和ACTH的转录而对HPA轴施加负反馈。如果不能通过转录抑制或NR3C1突变提供这种反馈，就会导致持续的HPA轴激活、高皮质醇血症和糖皮质激素抵抗--所有这些都是抑郁症的特征。在有儿童期虐待和抑郁症病史的自杀者的大脑中，NR3C1基因表现出高度甲基化和转录降低[1]。在有抑郁行为的啮齿类动物的大脑中也发现了类似的变化，这些啮齿动物的抑郁行为是由于早期剥夺了母亲的照顾[2]。此外，NR3C1的遗传失活会导致Chrousos综合征，这是一种以慢性疲劳、高皮质醇血症、严重焦虑和抑郁为特征的遗传性疾病。虽然这些发现暗示NR3C1活性的丧失是抑郁症发病机制中的一个因果步骤，但NR3C1功能降低的下游表观基因组和转录后果仍不清楚。为了严格研究表观基因组在调节抑郁行为中的作用[3]，我们目前正在斑马鱼的神经甲基组中确定NR3C1信号的靶标，斑马鱼是一种高度易驯化的模型生物，用于神经系统发育和疾病的遗传和表观遗传分析。斑马鱼NR3C1的突变导致HPA轴过度激活、皮质醇升高和纯合成年人的抑郁行为[4]，为Chrousos综合症和其他抑郁障碍提供了一个有效的模型。拟议的博士项目将推进我们正在进行的研究，通过比较成年野生型和NR3C1突变鱼的神经转录来识别对NR3C1反应的mRNAs，然后使用尖端生物信息学技术将这些转录数据与我们新出现的表观基因组数据相结合。我们以前采用这种综合方法来阐明斑马鱼神经元规范的表观遗传调控[5]，它将允许特定的NR3C1相关表观基因组信号与NR3C1对大脑内靶基因转录的功能影响联系起来。利用原位杂交，NR3C1调节的基因将被归类为共表达组，以了解NR3C1功能丧失如何通过改变神经基因转录模式促进抑郁症。因此，该项目将通过使用湿实验室技术和新的生物信息学工具的组合，识别促进对应激源的行为反应的转录调控模块。参考：[1]McGowan PO等人。(2009)。自然神经病。12：342-348。[2]Weaver IC等人。(2004)。自然神经病。7：847-854。[3]《坎利夫VT》(2015)电线系统。比奥尔。地中海医院。7：52-71。[4]L等人。(2012年)。摩尔。精神病学18：681-691。[5]哈里森先生等人。(2011)。BMC基因组学12：24。

The Hypothalamo-Pituitary-Adrenal (HPA) axis is the body's main regulator of physiological responses to external stressors and is highly conserved within vertebrates. In response to a biological stressor, the hypothalamus produces Corticotrophin Releasing Hormone (CRH), stimulating the pituitary to release Adrenocorticotrophic Hormone (ACTH), which causes the adrenal/interrenal glands to release cortisol. In the brain, cortisol is a ligand for the Glucocorticoid Receptor (GR) transcription factor, NR3C1, which regulates expression of neuroendocrine and neural activity-regulated genes. In order to ensure that stress-induced HPA axis activity depends on the persistence of an external stressor, cortisol-bound NR3C1 exerts negative feedback on the HPA axis by repressing transcription of CRH and ACTH. Failure to provide this feedback, by transcriptional inhibition or mutation of NR3C1, causes sustained HPA axis activation, hypercortisolaemia and glucocorticoid resistance - all of which are characteristics of depression. In the brains of suicide completers with histories of childhood abuse and depression, the NR3C1 gene exhibits both hypermethylation and reduced transcription [1]. Similar changes are found in the brains of rodents with depressive behaviours caused by early life deprivation of maternal care [2]. Moreover, genetic inactivation of NR3C1 causes Chrousos Syndrome, a genetic disorder characterised by chronic fatigue, hypercortisolaemia, profound anxiety and depression. While these findings imply that loss of NR3C1 activity is a causal step in the pathogenesis of depression, the downstream epigenomic and transcriptional consequences of reduced NR3C1 function remain unknown. In order to investigate rigorously the role of the epigenome in the regulation of depressive behaviours [3], we are currently identifying the targets of NR3C1 signalling within the neural methylome of the zebrafish, a highly tractable model organism for genetic and epigenetic analysis of development and disorders of the nervous system. Mutation of zebrafish nr3c1 causes hyperactivation of the HPA axis, hypercortsolaemia and depressive behaviours in homozygous adults [4], providing a valid model for Chrousos Syndrome and other depressive disorders. The proposed PhD project will take forward our ongoing research by comparing the neural transcriptomes of adult wild-type and nr3c1 mutant fish to identify Nr3c1-responsive mRNAs, and then integrating this transcriptomic data with our emerging epigenomic data using cutting-edge bioinformatics techniques. This integrative approach, which we previously adopted to elucidate the epigenetic regulation of neuronal specification in zebrafish [5], will allow specific Nr3c1-associated epigenomic signals to be linked to the functional impacts of Nr3c1 on target gene transcription within the brain. Using in situ hybridization, Nr3c1-regulated genes will be classified into synexpression groups to understand how loss of nr3c1 function promotes depression through changes to patterns of neural gene transcription. The project will thus identify transcriptional regulatory modules that facilitate behavioural responses to stressors, through use of a combination of wet lab techniques and novel bioinformatics tools.References: [1] McGowan PO et al. (2009). Nature Neurosci. 12: 342-348.[2] Weaver IC et al. (2004). Nature Neurosci. 7: 847-854. [3] Cunliffe VT (2015). WIRES Syst. Biol. Med. 7: 52-71.[4] Ziv L et al. (2012). Mol. Psychiatry 18: 681-691.[5] Harrison MR et al. (2011). BMC Genomics 12: 24.