Molecular mechanisms of olfaction in mammals

描述（由申请人提供）：在哺乳动物中，挥发性气味是由鼻子嗅上皮（OE）中的嗅觉感觉神经元（OSNs）检测到的。在对气味做出反应时，osn将信号传递给大脑的嗅球（OB），后者再将信号传递给嗅觉皮层（OC）。前皮层将信息发送到与气味感知有关的其他大脑区域，以及气味对情绪和生理的影响。小鼠的气味检测由约1000种不同的气味受体（ORs）介导，每种气味受体由不同的嗅觉受体亚群表达。ORs以组合方式用于检测气味，从而允许对看似无限种类的气味进行区分。然而，我们最近在小鼠OE中发现了第二个由14个化学感觉受体组成的家族。编码这些受体的基因被称为“微量胺相关受体”（TAARs），存在于小鼠、人类和鱼类中，并且在鱼类和小鼠OE中都有发现。与or一样，单个小鼠TAAR在仅表达该受体的osn的独特亚群中表达，具有相同TAAR的osn分散在某些OE结构域内。这些发现表明，有多个osn亚群使用不同的TAARs而不是ORs来检测化学感觉刺激。筛选不同气味剂的TAARs发现了几种TAARs的配体，这些TAARs都是小挥发性胺。引人注目的是，至少有三种小鼠TAARs识别尿液中的胺。其中一个检测到一种与压力有关的化合物，而另外两个检测到男性和女性尿液中富含的化合物，其中一个据报道是一种信息素。TAAR家族的进化保守表明，该家族可能具有不同于ORs的化学感觉功能。到目前为止，为TAARs识别的配体暗示了一种与社会线索检测相关的功能。在本研究中，我们将进一步研究TAARs在小鼠中的作用。为了鉴定具有未知配体的TAARs识别的化合物，我们将筛选各种胺来激活单个TAARs。我们还将使用细胞系中表达的TAARs的钙成像来询问是否大多数或所有TAARs检测到小鼠尿液中的化合物，如果是，这些化合物在不同性别、年龄或遗传背景的小鼠尿液中的表现是否不同。然后，我们将研究TAAR信号如何在OB中表示。首先，我们将使用TAAR基因探针检查接收来自单个TAAR输入的肾小球的数量和位置。接下来，我们将使用与选定的TAARs共表达轴突报告者的小鼠来确定是否存在taar特异性肾小球。然后，我们将使用c-Fos检测个体TAAR肾小球对识别TAAR配体以及不同来源的小鼠尿液的反应。最后，我们将制备具有单个TAAR基因的跨神经元示踪剂共表达的小鼠，以研究TAAR信号在OC中的组织方式。项目的叙述

DESCRIPTION (provided by applicant): In mammals, volatile odorants are detected by olfactory sensory neurons (OSNs) in the olfactory epithelium (OE) of the nose. In response to odorants, OSNs transmit signals to the olfactory bulb (OB) of the brain, which relays signals to the olfactory cortex (OC). The OC sends information to yet other brain areas involved in odor perception and the emotional and physiological effects of odors. Odorant detection in mice is mediated by ~1000 different odorant receptors (ORs), each expressed by a different subset of OSNs. ORs are used in a combinatorial manner to detect odorants, thereby allowing discrimination of a seemingly unlimited variety of odorants. However, we recently identified a second family of fourteen chemosensory receptors in the mouse OE. Genes encoding these receptors, called `trace amine-associated receptors' (TAARs) are present in mouse, human, and fish, and are found in both fish and mouse OE. Like ORs, individual mouse TAARs are expressed in unique subsets of OSNs that express only that receptor, and OSNs with the same TAAR are dispersed within certain OE domains. These findings indicate that there are multiple subsets of OSNs that use different TAARs rather than ORs to detect chemosensory stimuli. Screening of TAARs with diverse odorants revealed ligands for several TAARs, all of which are small volatile amines. Strikingly, at least three mouse TAARs recognize amines found in urine. One detects a compound linked to stress while the other two detect compounds enriched in male versus female urine, one reportedly a pheromone. The evolutionary conservation of the TAAR family suggests that this family may have a chemosensory function distinct from ORs. Ligands identified for TAARs thus far hint at a function associated with the detection of social cues. In the proposed studies, we will further investigate the roles played by TAARs in the mouse. To identify compounds recognized by TAARs with unknown ligands, we will screen a wide variety of amines for activation of individual TAARs. We will also use calcium imaging of TAARs expressed in a cell line to ask whether most or all TAARs detect compounds in mouse urine and, if so, whether those compounds are differentially represented in the urine of mice of different genders, ages, or genetic backgrounds. We will then examine how TAAR signals are represented in the OB. First, we will use TAAR gene probes to examine to number and positions of glomeruli that receive input from individual TAARs. Next, we will use mice coexpressing axonal reporters with selected TAARs to determine whether or not there are TAAR-specific glomeruli. Then, we will use c-Fos to examine the responses of individual TAAR glomeruli to identified TAAR ligands as well as to mouse urine from different sources. Finally, we will prepare mice that coexpress a transneuronal tracer with single TAAR genes to investigate how TAAR signals are organized in the OC.Project Narrative The mechanisms that the brain uses to perceive the world around us and to learn and remember are unknown. We will investigate the mechanisms that underlie the sense of smell to gain insight into these questions.