The trochozoan excitatory peptide (EP) and its ortholog, the arthropod CCHamide, are neuropeptides that are only investigated in very few animal species. Previous studies on different trochozoan species focused on their physiological effect in adult specimens, demonstrating a myo-excitatory effect, often on tissues of the digestive system. The function of EP in the planktonic larvae of trochozoans has not yet been studied. We surveyed transcriptomes from species of various spiralian (Orthonectida, Nemertea, Brachiopoda, Entoprocta, Rotifera) and ecdysozoan taxa (Tardigrada, Onychophora, Priapulida, Loricifera, Nematomorpha) to investigate the evolution of EPs/CCHamides in protostomes. We found that the EPs of several pilidiophoran nemerteans show a characteristic difference in their C-terminus. Deorphanization of a pilidiophoran EP receptor showed, that the two splice variants of the nemertean Lineus longissimus EP activate a single receptor. We investigated the expression of EP in L. longissimus larvae and juveniles with customized antibodies and found that EP positive nerves in larvae project from the apical organ to the ciliary band and that EP is expressed more broadly in juveniles in the neuropil and the prominent longitudinal nerve cords. While exposing juvenile L. longissimus specimens to synthetic excitatory peptides did not show any obvious effect, exposure of larvae to either of the two EPs increased the beat frequency of their locomotory cilia and shifted their vertical swimming distribution in a water column upwards. Our results show that EP/CCHamide peptides are broadly conserved in protostomes. We show that the EP increases the ciliary beat frequency of L. longissimus larvae, which shifts their vertical distribution in a water column upwards. Endogenous EP may be released at the ciliary band from the projections of apical organ EP positive neurons to regulate ciliary beating. This locomotory function of EP in L. longissimus larvae stands in contrast to the repeated association of EP/CCHamides with its myo-excitatory effect in adult trochozoans and the general association with the digestive system in many protostomes.

中文翻译：

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一种纽虫兴奋性肽/CCHamide 调节长线虫幼虫的纤毛游泳

trochozoan 兴奋性肽 (EP) 及其直系同源物节肢动物 CCHamide 是仅在极少数动物物种中研究的神经肽。以前对不同带虫物种的研究集中在它们对成年标本的生理作用上，证明了一种肌肉兴奋作用，通常对消化系统的组织产生作用。尚未研究 EP 在轮虫浮游幼虫中的功能。我们调查了来自各种螺旋动物（Orthonectida、Nemertea、Brachiopoda、Entoprocta、Rotifera）和蜕皮动物类群（Tardigrada、Onychophora、Priapulida、Loricifera、Nematomorpha）物种的转录组，以研究 EPs/CCHamides 在原生动物中的进化。我们发现，几种纤毛虫的 EP 在其 C 端显示出特征性差异。pilidophoran EP 受体的去孤儿化表明，纽虫 Lineus longissimus EP 的两个剪接变体激活单个受体。我们用定制的抗体研究了 EP 在 L. longissimus 幼虫和幼虫中的表达，发现幼虫中 EP 阳性神经从顶端器官投射到睫状带，并且 EP 在幼虫的神经纤维和突出的纵向神经中表达更广泛线。虽然将幼年 L. longissimus 标本暴露于合成的兴奋性肽没有显示出任何明显的效果，但将幼虫暴露于两种 EP 中的任何一种都会增加它们的运动纤毛的节拍频率，并使它们在水柱中的垂直游泳分布向上移动。我们的结果表明 EP/CCHamide 肽在原生动物中广泛保守。我们表明 EP 增加了 L. longissimus 幼虫的纤毛跳动频率，这将它们在水柱中的垂直分布向上移动。内源性 EP 可以在睫状带从顶端器官 EP 阳性神经元的投射中释放出来，以调节睫状体跳动。EP 在 L. longissimus 幼虫中的这种运动功能与 EP/CCHamides 的反复关联与其在成年轮虫中的肌兴奋作用以及与许多原生动物中的消化系统的一般关联形成鲜明对比。