Melanin-Concentrating Hormone: Ancestral Role in Feeding & Sleep Regulation

描述（由申请人提供）：在哺乳动物中，黑色素浓缩激素（melanin- concentration hormone, hMCH）是摄食行为、能量稳态和睡眠的关键调节因子。MCH于1983年首次在鲑鱼中被发现是一种诱导皮肤变亮的肽（sMCH）。然而，尽管在不同鱼类中进行了大量研究，但没有发现sMCH对摄食的明显影响。去年，我们在斑马鱼和其他四种硬骨鱼中发现了两个MCH基因：mch1和mch2。虽然mch1与鲑鱼的sMCH完全相似，但mch2基因和mch2肽与哺乳动物的hMCH具有相同的基因组结构、合成和高度同源性。与哺乳动物的hMCH一样，斑马鱼的MCH2在不同的下丘脑神经元群体中表达，并在禁食时上调，这表明在脊椎动物中MCH2/hMCH的调节和功能是守恒的。然而，虽然哺乳动物下丘脑含有数千个MCH细胞，但斑马鱼幼虫和成年大脑分别含有50个和150个MCH神经元的更紧凑的网络。由于在果蝇和秀丽隐杆线虫等非脊椎动物模型中没有发现MCH，因此mch2的发现为我们在简单的可调节遗传模型斑马鱼中探索MCH功能提供了独特的机会。我们提出的第一个具体目标是表征MCH2神经回路，并将其活动与行为状态联系起来。为此，我们将(i)分析MCH2神经元的身份和快速神经递质表型，（ii）研究它们的树突和连接，以及（iii）在不同行为条件下用钙成像法精确监测它们的活动模式。由于进食和睡眠行为在时间上是排他的，因此跟踪MCH神经元整体的放电模式来区分潜在的进食相关和睡眠相关亚群是至关重要的。在第二个具体目标中，我们将精确地研究MCH2对行为的影响。为此，我们将使用经典的遗传方法和最先进的mch2电路的光遗传操作。我们将首先(i)研究MCH2肽和回路如何调节食物摄入、生长和体重。此外，（ii）使用一种新型的多行为跟踪系统，我们将分析与能量不平衡、食物搜索和消费相关的大量行为，如探索、焦虑、攻击性、贪食行为与慢食行为，以及食物的享乐主义影响。最后，我们将通过分析正常睡眠、诱导睡眠和睡眠剥夺后的睡眠结构来研究MCH在睡眠-觉醒调节中的祖先作用。总之，斑马鱼作为一种透明的脊椎动物提供了一种独特的情况，可以对小而完整的神经网络进行非侵入性观察和操作。它将为我们理解相同的下丘脑回路如何计时和调节在时间和功能上如此不同的行为带来重大见解。

DESCRIPTION (provided by applicant): In mammals, melanin-concentrating hormone (hMCH) is a key regulator of feeding behavior, energy homeostasis, and sleep. MCH was first identified in salmon in 1983 as a peptide (sMCH) that induced skin lightening. Despite numerous studies in different fish species, however, no clear effect on feeding was shown for sMCH. Last year, we found, in zebrafish and four other teleost fishes, two MCH genes: mch1 and mch2. Whereas mch1 perfectly resembles salmon sMCH, the mch2 gene and MCH2 peptide share genomic structure, synteny, and high homology with mammalian hMCH. Zebrafish MCH2, like mammalian hMCH, is expressed in a distinct population of hypothalamic neurons and is up-regulated upon fasting, suggesting a conservation of MCH2/hMCH regulation and function across vertebrates. However, while mammalian hypothalamus harbors thousands of MCH cells, zebrafish larval and adult brains contain more compact networks of 50 and 150 MCH neurons respectively. As MCH is not found in non-vertebrate models like Drosophila and C. elegans, the discovery of mch2 offers us a unique opportunity to explore MCH function in a simple amenable genetic model, the zebrafish. We propose in a first specific aim to characterize the MCH2 neurocircuit and to relate its activity to behavioral states. To do so, we will (i) analyze MCH2 neurons identity and fast neurotransmitter phenotype, (ii) study their arborization and connections, and (iii) precisely monitor their pattern of activity with a calcium-imaging assay in different behavioral conditions. As feeding and sleep behaviors are exclusive in their timing, it is critical to follow the firing patterns of the totality of the MCH neurons to distinguish potential feeding- related and sleep-on subpopulations. In the second specific aim, we will precisely investigate the behavioral influence(s) of MCH2. To do so we will use both a classic genetic approach and state-of-the-art optogenetic manipulation of the mch2 circuit. We will first (i) study how the MCH2 peptide and circuit regulate food intake, growth, and body weight. Further, (ii) using a novel multi-behavioral tracking system we will analyze a large spectrum of behaviors associated with energy unbalance, food search and consumption, such as exploration, anxiety, aggressiveness, bulimic like behaviors versus slow eating, and the hedonistic influence of food. Finally, (iii) we will investigate the ancestral role for MCH in sleep- wake regulation by analyzing the sleep architecture during normal sleep, induced sleep, and after sleep deprivation. In conclusion, zebrafish offers a unique situation as a transparent vertebrate to perform non-invasive observation and manipulation of small but complete neuronal networks. It will bring major insight to our understanding of how a same hypothalamic circuit times and regulates behaviors so distinct in their timing and their functions.