The gustatory system allows animals to assess the nutritive value and safety of foods prior to ingestion. The first step in gustation is the interaction of taste stimuli with one or more specific sensory receptors, that are generally believed to be present on the apical surface of the taste receptor cells. However, this assertion is rarely tested. We recently identified OTOP1 as a proton channel and showed that it is required for taste response to acids (sour) and ammonium. Here we examined the cellular and subcellular localization of OTOP1 by tagging the endogenous OTOP1 protein with an N-terminal HA epitope (HA-OTOP1). Using both male and female HA-OTOP1 mice and high-resolution imaging, we show that OTOP1 is strictly localized to the apical tips of taste cells throughout the tongue and oral cavity. Interestingly, immunoreactivity is observed in the actin-rich taste pore above the tight junctions defined by Zonula Occludens-1 (ZO-1) and also immediately below these junctions. Surprisingly, OTOP1 immunoreactivity is not restricted to Type III taste receptor cells (TRCs) that mediate sour taste but is also observed in glia-like Type I TRCs proposed to perform housekeeping functions, a result that is corroborated by scRNA-seq data. The apical localization of OTOP1 supports the contention that OTOP1 functions as a taste receptor and suggests that OTOP1 may be accessible to orally available compounds that could act as taste modifiers.Significance Statement It is generally accepted that humans and other vertebrates can detect five basic tastes, each mediated by a unique receptor. Recently the receptor for sour taste was identified as the proton channel OTOP1. Here we show that OTOP1 is expressed at the apical surface of taste receptors cells, consistent with a sensory function. Surprisingly, OTOP1 is not restricted to Type III taste cells that detect sour tastes but is also expressed by glia-like taste cells, where it may play a role in removing excess protons. These results provide insight and tools applicable to understanding the contribution of OTOP1 to cell physiology and pathology in other contexts where the channel is expressed such as in the vestibular system.

中文翻译：

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小鼠基因组编辑的表位标记显示，质子通道 OTOP1 位于顶端，不限于 III 型“酸”味觉受体细胞。


味觉系统允许动物在摄入前评估食物的营养价值和安全性。味觉的第一步是味觉刺激与一个或多个特定感觉受体的相互作用，这些受体通常被认为存在于味觉受体细胞的顶端表面。然而，这种说法很少受到检验。我们最近将 OTOP1 确定为质子通道，并表明它是对酸（酸）和铵的味觉反应所必需的。在这里，我们通过用 N 末端 HA 表位 （HA-OTOP1） 标记内源性 OTOP1 蛋白来检查 OTOP1 的细胞和亚细胞定位。使用雄性和雌性 HA-OTOP1 小鼠和高分辨率成像，我们表明 OTOP1 严格定位于整个舌和口腔的味觉细胞的顶端。有趣的是，在闭塞带 1 （ZO-1） 定义的紧密连接上方以及这些连接正下方的富含肌动蛋白的味道孔中观察到免疫反应性。令人惊讶的是，OTOP1 免疫反应性不仅限于介导酸味的 III 型味觉受体细胞 （TRC），而且在被认为执行看家功能的神经胶质样 I 型 TRC 中也观察到，这一结果得到了 scRNA-seq 数据的证实。OTOP1 的顶端定位支持 OTOP1 作为味觉受体发挥作用的论点，并表明 OTOP1 可能被可作为味觉调节剂的口服化合物所接近。意义声明 人们普遍认为，人类和其他脊椎动物可以检测到五种基本味觉，每种味觉都由一种独特的受体介导。最近，酸味受体被确定为质子通道 OTOP1。 在这里，我们表明 OTOP1 在味觉受体细胞的顶端表面表达，与感觉功能一致。令人惊讶的是，OTOP1 不仅限于检测酸味的 III 型味觉细胞，还由神经胶质样味觉细胞表达，它可能在去除多余的质子方面发挥作用。这些结果提供了适用于理解 OTOP1 在通道表达的其他环境中（例如前庭系统）对细胞生理学和病理学的贡献的见解和工具。