Molecular mechanisms of olfaction in mammals

描述(申请人提供)：在哺乳动物中，挥发性气味是由鼻子嗅觉上皮(OE)中的嗅觉神经元(OSN)检测到的。作为对气味的反应，嗅觉神经元将信号传输到大脑的嗅球(OB)，后者将信号传递到嗅皮层(OC)。OC将信息发送到与气味感知以及气味的情绪和生理影响有关的其他大脑区域。小鼠的气味识别是由大约1000个不同的气味受体(ORs)介导的，每个ORs都由不同的OSNs亚集表达。有机化合物以一种组合的方式用于检测气味，从而允许区分似乎无限种类的气味。然而，我们最近在小鼠的OE中发现了第二个家族的14个化学感受器。编码这些受体的基因被称为“示踪胺相关受体”(TAAR)，存在于小鼠、人和鱼中，在鱼和小鼠的OE中也发现了这种受体。与ORs一样，单独的小鼠TAAR在仅表达该受体的OSNs的独特子集中表达，具有相同TAAR的OSNs分散在某些OE结构域中。这些发现表明，有多个OSNs的子集使用不同的TAAR而不是ORs来检测化学感觉刺激。对含有不同气味的TAAR的筛选显示，几种TAAR的配体都是小挥发性胺。令人惊讶的是，至少有三个老鼠TAAR识别尿液中的胺。一种检测到一种与压力有关的化合物，而另外两种检测到男性和女性尿液中富含的化合物，其中一种据说是信息素。TAAR家族的进化保守性提示该家族可能具有不同于ORS的化学感觉功能。到目前为止，为TAAR识别的配体暗示了一种与社会线索检测相关的功能。在拟议的研究中，我们将进一步研究TAAR在小鼠中所起的作用。为了识别具有未知配体的TAAR识别的化合物，我们将筛选各种胺来激活单个TAAR。我们还将使用细胞系中表达的TAAR的钙成像来询问大多数或所有TAAR是否在小鼠尿液中检测到化合物，如果是的话，这些化合物是否在不同性别、年龄或遗传背景的小鼠的尿液中有不同的表达。然后我们将研究TAAR信号在OB中是如何表示的。首先，我们将使用TAAR基因探针来检测接受单个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TAAR共表达轴突报告基因的小鼠来确定是否存在TAAR特异的肾小球。然后，我们将使用c-Fos来检测单个TAAR肾小球对已识别的TAAR配体以及对不同来源的小鼠尿液的反应。最后，我们将准备与单个TAAR基因共表达跨神经元示踪剂的小鼠，以研究TAAR信号在OC.项目叙述中是如何组织的 大脑用来感知周围世界以及学习和记忆的机制是未知的。我们将研究嗅觉背后的机制，以深入了解这些问题。

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.