In taste buds, Type I cells represent the majority of cells (50–60%) and primarily have a glial-like function in taste buds. However, recent studies suggest that they have additional sensory and signaling functions including amiloride-sensitive salt transduction, oxytocin modulation of taste, and substance P mediated GABA release. Nonetheless, the overall function of Type I cells in transduction and signaling remains unclear, primarily because of the lack of a reliable reporter for this cell type. GAD65 expression is specific to Type I taste cells and GAD65 has been used as a Cre driver to study Type I cells in salt taste transduction. To test the specificity of transgene-driven expression, we crossed GAD65Cre mice with floxed tdTomato and Channelrhodopsin (ChR2) lines and examined the progeny with immunochemistry, chorda tympani recording, and calcium imaging. We report that while many tdTomato+ taste cells express NTPDase2, a specific marker of Type I cells, we see some expression of tdTomato in both Gustducin and SNAP25-positive taste cells. We also see ChR2 in cells just outside the fungiform taste buds. Chorda tympani recordings in the GAD65Cre/ChR2 mice show large responses to blue light. Furthermore, several isolated tdTomato-positive taste cells responded to KCl depolarization with increases in intracellular calcium, indicating the presence of voltage-gated calcium channels. Taken together, these data suggest that GAD65Cre mice drive expression in multiple taste cell types and thus cannot be considered a reliable reporter of Type I cell function.

中文翻译：

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GAD65Cre 驱动多种味觉细胞类型中的报告基因表达

在味蕾中，I 型细胞占大多数细胞 (50-60%)，并且在味蕾中主要具有神经胶质样功能。然而，最近的研究表明它们具有额外的感觉和信号传导功能，包括阿米洛利敏感的盐转导、催产素味觉调节和 P 物质介导的 GABA 释放。尽管如此，I 型细胞在转导和信号传导方面的整体功能仍不清楚，主要是因为缺乏针对该细胞类型的可靠报告基因。GAD65 表达对 I 型味觉细胞具有特异性，GAD65 已被用作 Cre 驱动程序来研究 I 型细胞的盐味转导。为了测试转基因驱动表达的特异性，我们将 GAD65Cre 小鼠与 floxed tdTomato 和视紫红质通道 (ChR2) 系杂交，并通过免疫化学、鼓索记录和钙成像检查后代。我们报告说，虽然许多 tdTomato+ 味觉细胞表达 NTPDase2（I 型细胞的特定标记），但我们在 Gustducin 和 SNAP25 阳性味觉细胞中发现 tdTomato 的一些表达。我们还在菌状味蕾外部的细胞中发现了 ChR2。GAD65Cre/ChR2 小鼠的鼓弦记录显示出对蓝光的强烈反应。此外，一些分离的 tdTomato 阳性味觉细胞对 KCl 去极化做出反应，细胞内钙含量增加，表明电压门控钙通道的存在。总而言之，这些数据表明 GAD65Cre 小鼠在多种味觉细胞类型中驱动表达，因此不能被视为 I 型细胞功能的可靠报告者。