Developmental Genetics of Serotonin Neuron Subtypes in Brain Reward Circuits

描述（由申请人提供）：5-羟色胺（5-羟色胺，5HT）产生的神经元和5-羟色胺神经传递与一系列人类疾病有关，从精神和情绪障碍，如药物寻求行为、药物成瘾和病理性焦虑，到儿童发育障碍，如自闭症、胎儿酒精综合征和婴儿猝死综合征。每种疾病的临床特征不同，提示血清素神经元功能的异质性。然而，能够识别生理上相关的5HT神经元亚型的分子标记，可能解释这种异质性和不同的疾病易感性，是未知的。因此，缺乏获得5HT神经元特定亚群的遗传途径进行实验研究的手段。虽然成熟的5HT神经元亚型的标记物还很缺乏，但是，目前的标记物（转录因子）可以分解血清素能祖细胞的亚群。这种祖细胞标记，如果与后代神经元相关联，可能会定义成熟5HT神经元的生理相关亚群；这是因为决定神经元最终命运和功能的发育程序通常是由它们的亲本祖细胞之间差异表达的转录因子的作用启动的。因此，即使没有能够区分成熟5HT神经元亚型的标记物，也可以通过鉴定其组成遗传亚系来构建血清素能系统的分子框架。在这里，我们首次提出建立这样一个框架，通过创建一个鼠菱形体(r)定义的血清素能亚谱系的分子命运图。我们将扩展我们最近开发的交叉和减法遗传命运定位范式，以便直接和同时可视化来自不同菱形体的5HT神经元的发育。每个成熟的5HT神经元亚型，由其先前的斜形球(r)特异性遗传谱定义，将分析其在脑干中缝和中缝外核中的解剖位置。随后将分析细胞形态、神经化学特征和轴突投影。我们有转基因，根据所采用的组合，应该允许我们单独解决来自r1， r2, r3， r5或r6- r8的5HT神经元。我们还建议产生能够从r7/8衍生的5HT神经元中分离r6-的转基因。从由此产生的分子命运图中，应该有可能提取有关人类中可能具有特定疾病相关性的5HT神经元亚群的信息。这项工作是创新的，可能会产生重大影响，因为它有可能重新定义一个关键的神经系统-血清素能系统-并提供一套试剂，最终将允许控制体内离散的5HT电路的活性，作为评估其在发育，行为和/或认知中的作用的手段。5-羟色胺（5-羟色胺，5-HT）神经传递以及5-羟色胺能神经元的异常与许多人类疾病有关，从精神疾病、情绪、药物成瘾到儿童发育障碍，如自闭症和婴儿猝死综合征。每种疾病的临床特征不同，提示血清素神经元功能的异质性，然而这种异质性和不同疾病易感性的分子基础在很大程度上是未知的。为了填补这一知识空白，我们建议构建5HT系统的第一个分子框架，该框架具有遗传定义的谱系作为其组成元素，应该具有生理和临床相关性；此外，所产生的结果和遗传工具应该会产生重大影响，因为它首次提供了一种获得5 -羟色胺能神经元亚群的遗传途径，以评估它们在行为、认知和/或发育中的精确作用。

DESCRIPTION (provided by applicant): Serotonin (5-hydroxytryptamine, 5HT)-producing neurons and serotonin neurotransmission are implicated in a spectrum of human disorders ranging from psychiatric disorders of mind and mood such as drug seeking behavior, drug addiction, and pathological anxiety, to childhood developmental disorders such as autism, fetal alcohol syndrome, and the sudden infant death syndrome. Each disorder differs in clinical feature, suggesting heterogeneity in serotonin neuron function. Yet, molecular markers capable of identifying physiologically relevant 5HT neuron subtypes, which might explain this heterogeneity and differential disease susceptibility, are unknown. Consequently lacking, in addition, are means to gain genetic access to specific subsets of 5HT neurons for experimental study. While markers of mature 5HT neuron subtypes are wanting, at hand, however, are markers (transcription factors) that resolve subsets of serotonergic progenitor cells. Such progenitor cell markers, if linked to progeny neurons, would likely define physiologically relevant subgroupings of mature 5HT neurons; this is because developmental programs that define the ultimate fate and function of neurons are often set in motion by the action of transcription factors differentially expressed among their parent progenitor cells. Thus, even in the absence of markers capable of distinguishing mature 5HT neuron subtypes, a molecular framework for the serotonergic system can be constructed through identification of its constituent genetic sublineages. Here we propose to build, for the first time, such a framework, by creating a molecular fate map of rhombomere(r)-defined serotonergic sublineages in mice. We will extend our recently developed paradigm of intersectional and subtractive genetic fate mapping in order to visualize directly and simultaneously the development of 5HT neurons arising from different rhombomeres. Each mature 5HT neuron subtype, defined by its antecedent rhombomere (r)-specific genetic profile, will be analyzed for anatomical position within the brainstem raphe and extra-raphe nuclei. Analyses of cellular morphology, neurochemical profile, and axonal projections will follow. We have transgenics that, depending on the employed combination, should allow us to separately resolve 5HT neurons derived from r1, r2, r3, r5, or r6- r8. We also propose to generate transgenics capable of resolving r6- from r7/8-derived 5HT neurons. From the resultant molecular fate maps, it should be possible to extract information about subsets of 5HT neurons that in humans are likely to have specific disease relevance. This work is innovative and likely of major impact because it has the potential to redefine a critical neural system - the serotonergic system - and to provide a set of reagents that ultimately will permit controlling the activity of discrete 5HT circuits in vivo as a means to assess their roles in development, behavior, and/or cognition. Abnormalities in serotonin (5-hydroxytryptamine, 5-HT) neurotransmission as well as serotonergic neurons are implicated in numerous human disorders ranging from psychiatric disorders of mind, mood, and drug addiction to childhood developmental disorders such as autism and the sudden infant death syndrome. Each disorder differs in clinical feature suggesting heterogeneity in serotonin neuron function, yet the molecular underpinnings of such heterogeneity and differential disease susceptibility are largely unknown. Towards filling this knowledge gap, here we propose to construct the first molecular framework for the 5HT system that, having genetically-defined lineages as its component elements, should have physiological and clinical relevance; moreover, the generated results and genetic tools should have major impact by providing, for the first time, a means to gain genetic access to subgroups of serotonergic neurons to assess their precise roles in behavior, cognition, and/or development.