The origin of bilateral symmetry, a major transition in animal evolution, coincided with the evolution of organized nervous systems that show regionalization along major body axes. Studies of Xenacoelomorpha, the likely outgroup lineage to all other animals with bilateral symmetry, can inform the evolutionary history of animal nervous systems. Here, we characterized the neural anatomy of the acoel Hofstenia miamia. Our analysis of transcriptomic data uncovered orthologues of enzymes for all major neurotransmitter synthesis pathways. Expression patterns of these enzymes revealed the presence of a nerve net and an anterior condensation of neural cells. The anterior condensation was layered, containing several cell types with distinct molecular identities organized in spatially distinct territories. Using these anterior cell types and structures as landmarks, we obtained a detailed timeline for regeneration of the H. miamia nervous system, showing that the anterior condensation is restored by eight days after amputation. Our work detailing neural anatomy in H. miamia will enable mechanistic studies of neural cell type diversity and regeneration and provide insight into the evolution of these processes.

中文翻译：

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acoel Hofstenia miamia 的神经结构和再生

双侧对称的起源是动物进化的一个主要转变，与有组织的神经系统的进化相吻合，这些神经系统显示出沿主要身体轴的区域化。对 Xenacoelomorpha 的研究，可能是所有其他双侧对称动物的外群谱系，可以为动物神经系统的进化史提供信息。在这里，我们描述了 acoel Hofstenia miamia 的神经解剖结构。我们对转录组数据的分析揭示了所有主要神经递质合成途径的酶的直系同源物。这些酶的表达模式揭示了神经网络的存在和神经细胞的前部凝聚。前浓缩是分层的，包含在空间不同的区域中组织的具有不同分子身份的几种细胞类型。使用这些前部细胞类型和结构作为地标，我们获得了迈阿密嗜血杆菌神经系统再生的详细时间表，表明前部凝结在截肢后 8 天恢复。我们详细介绍迈阿密嗜血杆菌神经解剖学的工作将使神经细胞类型多样性和再生的机制研究成为可能，并提供对这些过程进化的深入了解。