The Xenopus oocyte and the Human Embryonic Kidney (HEK) 293 cell expression systems are frequently used for functional characterization (deorphanization) of insect odorant receptors (ORs). However, the inherent characteristics of these heterologous systems differ in several aspects, which raises the question of whether the two systems provide comparable results, and how well the results correspond to the responses obtained from olfactory sensory neurons in vivo. Five candidate pheromone receptors were previously identified in the primitive moth Eriocrania semipurpurella (Esem) and their responses were characterized in HEK cells. We re-examined the responses of these five EsemORs in Xenopus oocytes. We showed that in both systems, EsemOR1 specifically responded to the plant volatile β-caryophyllene. EsemOR3 responded stronger to the pheromone component (S,Z)-6-nonen-2-ol than to its enantiomer (R,Z)-6-nonen-2-ol, the second pheromone component. However, EsemOR3 also responded secondarily to the plant volatile β-caryophyllene in the oocyte system, but not in the HEK cell system. EsemOR4 was unresponsive in the HEK cells, but responded primarily to (R,Z)-6-nonen-2-ol followed by (S,Z)-6-nonen-2-ol in the oocytes, representing a discovery of a new pheromone receptor in this species. EsemOR5 was broadly tuned in both systems, but the rank order among the most active pheromone compounds and antagonists was different. EsemOR6 showed no response to any compound in either system. We compared the results obtained in the two different heterologous systems with the activity previously recorded in vivo, and performed in situ hybridization to localize the expression of these OR genes in the antennae. In spite of similar results overall, differences in OR responses between heterologous expression systems suggest that conclusions about the function of individual ORs may differ depending on the system used for deorphanization.

中文翻译：

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蛾（Eriocrania semipurpurella）蛾的气味受体的功能表征：非洲爪蟾卵母细胞和HEK细胞系统的结果比较。

非洲爪蟾卵母细胞和人类胚胎肾（HEK）293细胞表达系统经常用于昆虫气味受体（OR）的功能表征（去甲壳化）。但是，这些异源系统的固有特性在几个方面有所不同，这引发了一个问题，即这两个系统是否提供可比较的结果，以及该结果与体内嗅觉感觉神经元的响应程度相对应。以前在原始飞蛾半紫pur（Esem）中鉴定了五个候选信息素受体，并在HEK细胞中表征了它们的反应。我们重新检查了非洲爪蟾卵母细胞中这五个EsemOR的反应。我们表明，在两个系统中，EsemOR1都对植物的挥发性β-石竹烯有特异性应答。EsemOR3对信息素组分（S，Z）-6-壬烯-2-醇的反应要强于其对映异构体（R，Z）-6-壬烯-2-醇（第二信息素组分）。然而，EsemOR3在卵母细胞系统中对植物的挥发性β-叶绿素酶也具有第二反应，而在HEK细胞系统中则没有。EsemOR4在HEK细胞中无反应，但主要对卵母细胞中的（R，Z）-6-壬烯-2-醇产生响应，然后对（S，Z）-6-壬烯-2-醇产生响应，这表明发现了一个新的该物种的信息素受体。EsemOR5在这两个系统中均进行了广泛的调优，但最活跃的信息素化合物和拮抗剂之间的等级顺序是不同的。EsemOR6在两个系统中均未显示对任何化合物的反应。我们将在两个不同的异源系统中获得的结果与之前在体内记录的活性进行了比较，并进行原位杂交以定位这些OR基因在触角中的表达。尽管总体上具有相似的结果，但异源表达系统之间的OR响应差异表明，有关单个OR的功能的结论可能会有所不同，具体取决于用于去孤儿化的系统。