Abstract

Acoel flatworms possess epidermal sensory-receptor cells on their body surfaces and exhibit behavioral repertoires such as geotaxis and phototaxis. Acoel epidermal sensory receptors should be mechanical and/or chemical receptors; however, the mechanisms of their sensory reception have not been elucidated. We examined the three-dimensional relationship between epidermal sensory receptors and their innervation in an acoel flatworm, Praesagittifera naikaiensis. The distribution of the sensory receptors was different between the ventral and dorsal sides of worms. The nervous system was mainly composed of a peripheral nerve net, an anterior brain, and three pairs of longitudinal nerve cords. The nerve net was located closer to the body surface than the brain and the nerve cords. The sensory receptors have neural connections with the nerve net in the entire body of worms. We identified five homologs of polycystic kidney disease (PKD): PKD1-1, PKD1-2, PKD1-3, PKD1-4, and, PKD2, from the P. naikaiensis genome. All of these PKD genes were implied to be expressed in the epidermal sensory receptors of P. naikaiensis. PKD1-1 and PKD2 were dispersed across the entire body of worms. PKD1-2, PKD1-3, and PKD1-4 were expressed in the anterior region of worms. PKD1-4 was also expressed around the mouth opening. Our results indicated that P. naikaiensis possessed several types of epidermal sensory receptors to convert various environmental stimuli into electrical signals via the PKD channels and transmit the signals to afferent nerve and/or effector cells.

中文翻译：

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无腔扁虫 (Praesagittifera naikaiensis) 假定表皮感觉受体的结构

摘要

Acoel 扁虫的体表具有表皮感觉感受器细胞，并表现出趋地性和趋光性等行为特征。 Acoel表皮感觉受体应该是机械和/或化学受体；然而，它们的感觉接收机制尚未阐明。我们研究了无腔扁虫Praesagittifera naikaiensis的表皮感觉受体及其神经支配之间的三维关系。蠕虫腹侧和背侧感觉感受器的分布不同。神经系统主要由周围神经网、前脑和三对纵向神经索组成。神经网比大脑和神经索更靠近身体表面。感觉受体与蠕虫全身的神经网络有神经联系。我们从P. naikaiensis基因组中鉴定出多囊肾病 ( PKD ) 的五个同源物：PKD1-1、PKD1-2、PKD1-3、PKD1-4和PKD2。所有这些PKD基因都被暗示在P. naikaiensis的表皮感觉受体中表达。PKD1-1和PKD2分散在蠕虫的整个身体中。PKD1-2、PKD1-3和PKD1-4在线虫的前部区域表达。PKD1-4也在张口周围表达。我们的研究结果表明，内开P. naikaiensis拥有多种类型的表皮感觉受体，可以通过 PKD 通道将各种环境刺激转化为电信号，并将信号传输到传入神经和/或效应细胞。