Background Nicotinic and muscarinic acetylcholine receptors likely evolved in the cnidarian-bilaterian common ancestor. Both receptor families are best known for their role at chemical synapses in bilaterian animals, but they also have described roles as non-neuronal signaling receptors within the bilaterians. It is not clear when either of the functions for nicotinic or muscarinic receptors evolved. Previous studies in cnidarians suggest that acetylcholine's neuronal role existed prior to the cnidarian-bilaterian divergence, but did not address potential non-neuronal functions. To determine the origins of neuronal and non-neuronal functions of nicotinic acetylcholine receptors, we investigated the phylogenetic position of cnidarian acetylcholine receptors, characterized the spatiotemporal expression patterns of nicotinic receptors in N. vectensis, and compared pharmacological studies in N. vectensis to the previous work in other cnidarians. Results Consistent with described activity in other cnidarians, treatment with acetylcholine-induced tentacular contractions in the cnidarian sea anemone N. vectensis. Phylogenetic analysis suggests that the N. vectensis genome encodes 26 nicotinic (nAChRs) and no muscarinic (mAChRs) acetylcholine receptors and that nAChRs independently radiated in cnidarian and bilaterian linages. The namesake nAChR agonist, nicotine, induced tentacular contractions similar to those observed with acetylcholine, and the nAChR antagonist mecamylamine suppressed tentacular contractions induced by both acetylcholine and nicotine. This indicated that tentacle contractions are in fact mediated by nAChRs. Nicotine also induced the contraction of radial muscles, which contract as part of the peristaltic waves that propagate along the oral-aboral axis of the trunk. Radial contractions and peristaltic waves were suppressed by mecamylamine. The ability of nicotine to mimic acetylcholine responses, and of mecamylamine to suppress acetylcholine and nicotine-induced contractions, supports a neuronal function for acetylcholine in cnidarians. Examination of the spatiotemporal expression of N. vectensis nAChRs (NvnAChRs) during development and in juvenile polyps identified that NvnAChRs are expressed in neurons, muscles, gonads, and large domains known to be consistent with a role in developmental patterning. These patterns are consistent with nAChRs functioning in both a neuronal and non-neuronal capacity in N. vectensis. Conclusion Our data suggest that nAChR receptors functioned at chemical synapses in N. vectensis to regulate tentacle contraction. Similar responses to acetylcholine are well documented in cnidarians, suggesting that the neuronal function represents an ancestral role for nAChRs. Expression patterns of nAChRs are consistent with both neuronal and non-neuronal roles for acetylcholine in cnidarians. Together, these observations suggest that both neuronal and non-neuronal functions for the ancestral nAChRs were present in the cnidarian-bilaterian common ancestor. Thus, both roles described in bilaterian species likely arose at or near the base of nAChR evolution.

中文翻译：

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Nematostella vectensis 中 nAChR 的表征支持刺胞动物-双侧动物共同祖先中的神经元和非神经元作用。

背景烟碱型和毒蕈碱型乙酰胆碱受体可能在刺胞动物-双侧动物共同祖先中进化。这两个受体家族最出名的是它们在双侧动物化学突触中的作用，但它们也将作用描述为双侧动物内的非神经元信号受体。目前尚不清楚烟碱或毒蕈碱受体的功能是何时进化的。先前对刺胞动物的研究表明，乙酰胆碱的神经元作用在刺胞动物-双侧动物分化之前就存在，但并未解决潜在的非神经元功能。为了确定烟碱型乙酰胆碱受体的神经元和非神经元功能的起源，我们研究了刺胞动物乙酰胆碱受体的系统发育位置，表征了烟碱型受体在 N 中的时空表达模式。vectensis，并将 N. vectensis 的药理学研究与之前在其他刺胞动物中的工作进行了比较。结果与在其他刺胞动物中描述的活动一致，用乙酰胆碱诱导的刺胞海葵 N. vectensis 的触手收缩进行治疗。系统发育分析表明，N. vectensis 基因组编码 26 种烟碱型 (nAChRs) 而没有毒蕈碱型 (mAChRs) 乙酰胆碱受体，并且 nAChRs 在刺胞动物和双侧动物系中独立辐射。同名的 nAChR 激动剂尼古丁诱导的触手收缩与用乙酰胆碱观察到的相似，而 nAChR 拮抗剂美加明抑制了乙酰胆碱和尼古丁诱导的触手收缩。这表明触手收缩实际上是由 nAChRs 介导的。尼古丁还引起桡侧肌肉收缩，作为沿躯干口-口轴传播的蠕动波的一部分收缩。美卡拉明抑制了径向收缩和蠕动波。尼古丁模拟乙酰胆碱反应的能力，以及美加明抑制乙酰胆碱和尼古丁诱导的收缩的能力，支持了刺胞动物中乙酰胆碱的神经元功能。检查 N. vectensis nAChRs (NvnAChRs) 在发育过程和幼年息肉中的时空表达，发现 NvnAChRs 在神经元、肌肉、性腺和已知与发育模式中的作用一致的大域中表达。这些模式与 nAChRs 在 N. vectensis 的神经元和非神经元能力中发挥作用是一致的。结论 我们的数据表明 nAChR 受体在 N. vectensis 调节触手收缩。对乙酰胆碱的类似反应在刺胞动物中得到充分证明，这表明神经元功能代表了 nAChR 的祖先作用。nAChRs 的表达模式与乙酰胆碱在刺胞动物中的神经元和非神经元作用一致。总之，这些观察结果表明，祖先 nAChR 的神经元和非神经元功能都存在于刺胞 - 双侧共同祖先中。因此，在双侧动物物种中描述的这两种角色都可能出现在 nAChR 进化的基础处或附近。nAChRs 的表达模式与乙酰胆碱在刺胞动物中的神经元和非神经元作用一致。总之，这些观察结果表明，祖先 nAChR 的神经元和非神经元功能都存在于刺胞 - 双侧共同祖先中。因此，在双侧动物物种中描述的这两种角色都可能出现在 nAChR 进化的基础处或附近。nAChRs 的表达模式与乙酰胆碱在刺胞动物中的神经元和非神经元作用一致。总之，这些观察结果表明，祖先 nAChR 的神经元和非神经元功能都存在于刺胞 - 双侧共同祖先中。因此，在双侧动物物种中描述的这两种角色都可能出现在 nAChR 进化的基础处或附近。