Functions and species differences of softpalate taste buds in mammals

在软腭味蕾（SP）中，几乎所有表达ip3r3的细胞（96.7%）都表达Gustducin，而在真菌状（FF）和环形（CV）乳头中，Gustducin阳性细胞分别占42.4%和60.1%。为了证实gustducin在SP的味觉传导中的广泛作用，我们电生理记录了gustducin- ko小鼠三条主要味觉神经的反应，并比较了这些神经的反应特性。与大鼠的免疫组化结果一致，gustducin-KO小鼠的大浅表岩神经（GSP）对甜味和苦味刺激的神经反应明显降低。与GSP相比，鼓室索神经（CT）和舌咽神经（GL）分别对甜味和苦味刺激的反应减弱。小鼠gustducin和IP3R3免疫组化结果显示，SP中91.1%的IP3R3表达细胞呈gustducin阳性。这些结果进一步表明，味觉传导素参与味觉信号通路的不同细胞系，取决于味觉细胞的分化。采用原位杂交和免疫组织化学方法检测小鼠胚胎中味蕾基底细胞标记物Shh、Proxi和Mashi的表达情况，探讨其胚胎发育情况。从Shh在前舌区（E1 2.5）和软腭区（E14.5）的点状表达开始，Proxi就与Shh共表达，这表明胚胎味蕾基底细胞和Shh表达点具有共同的特征。在两个区域中，Mashi的表达比Shh和Proxi的表达晚约2天。在Mashi表达开始之前，神经到达表达Shh的上皮。这些结果表明，味蕾基底细胞的分化始于神经独立。采用免疫组织化学和原位杂交技术对CT与GSP交叉再生大鼠和小鼠的味蕾再生情况进行了分析。结果表明，不同神经供应的SP和FF再生后，gustducin和IP3R3的共表达不依赖于神经，而依赖于上皮。这一结果表明，交叉再生后仍然存在相同的功能差异。少

Gustducin was expressed in almost all (96.7%) IP3R3-expressing cells in taste buds of the soft palate (SP),whereas gustducin-positive cells were 42.4% and 60.1 % of IP3R3-expressing cells in the fungiform (FF) and circumvalate (CV) papillae, respectively. To confirm the broad role of gustducin in the taste transduction on the SP, responses from three major gustatory nerves in gustducin-KO mice were recorded electrophysiologically and the response properties were compared among the nerves. In consistent with the immunohistochemical results in the rat, nerve responses to both sweet and bitter stimuli were markedly reduced in the greater superficial petrosal nerve (GSP) of gustducin-KO mice. In contrast to the GSP, the chorda tympani nerve (CT) and the glossopharngeal nerve (GL) showed reduced responses to sweet and bitter stimuli, respectively. Immunohistochemistry of gustducin and IP3R3 in mice showed that 91.1% of IP3R3-expressing cells in the SP was gustducin positive. These results d … More emonstrate that gustducin is involved in the different lines of the taste-signaling pathway depending on the taste cell differentiation.To examine the embryonic development of the basal cells, the expression of the basal cell markers of taste buds (Shh, Proxi and Mashi) was determined in the mouse embryo by in situ hybridization and immunohistochemistry. Proxi was co-expressed with Shh from the beginning of Shh expression in a punctate pattern on the anterior tongue (E1 2.5) and soft palatal region (E14.5),suggesting that the basal cells of taste buds and Shh-expressing spots in embryos share common features. Mashi expression lagged behind the expression of Shh and Proxi by approximately 2 days in both regions. Nerves reached the epithelium expressing Shh slightly before the onset of Mashi expression. These results suggest that the differentiation of the basal cells in the taste bud starts nerve-independently.We analyzed regenerated taste buds induced by cross-regeneration of CT and GSP in rats and mice using immunohistochemistry and in situ hybridization. The results showed that the gustducin and IP3R3 co-expression between in the SP and FF after the regeneration with the different nerve supply were not depend on the nerve but on the epithelium. This result suggests that the same functional difference still remain after the cross-regeneration. Less