五彩斑斓！蝴蝶早期颜色处理的视觉神经回路 | Cell Press 青促会评述

作为世界领先的全科学领域学术出版社，细胞出版社特与“中国科学院青年创新促进会”合作开设“青促会述评”专栏，以期增进学术互动，促进国际交流。

2022年第十四期（总第98期）专栏文章，由中国科学院动物研究所助理研究员 郭浩，就Current Biology中的论文发表述评。

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▲图1 柑橘凤蝶复眼视觉神经和突触连接模式图。A：复眼薄板结构图。虚线标记区域为论文重点研究的8个cartridges（a-h），每个cartridge包含9个光感受器（R1-R9）和4个薄板单极细胞（L1-L4）。B: 9个光感受器和4个薄板单极细胞组成的神经束。C：单个光感受器和薄板单极细胞三维重构图。箭头表示轴突末端。D和E：突触连接。箭头表示突触前位点。

▲图2 光感受器和薄板单极细胞的反应特性。（A) 模拟化的光感受器和薄板单极细胞光谱反应。（B）L1-L3的光谱反应的叠加。左边小图：根据小眼类型的叠加；右边小图：根据细胞类型的叠加。（C）电生理记录细胞反应（灰色）与模拟细胞反应（红色）的对比。（D）薄板单极细胞去极化反应。

在模式动物中，连接组技术已经成为标准的神经生物学研究方法。在以往的连接组研究中，视觉系统是热门的研究对象。近年来，结合连接组学、神经环路和行为生理学，科学家对果蝇视觉神经节早期波长处理的神经生物学机制进行了深入的研究。然而，与访花昆虫相比，黑腹果蝇（Drosophila melanogaster）的颜色视觉能力有限。例如，柑橘凤蝶（Papilio xuthus）有6类感受不同波长的光感受器。每个小眼包含9个光感受器，这些感受器组合成三种固定的模式，因此昆虫复眼是由大量感受三种光谱的小眼组成。在行为上，花椒凤蝶可以感受到从紫外到红色光谱中1 nm波长的差异，比人类更精确。那么，这种精确性的神经元基础是什么? 这样的系统是如何进化的? 回答这些问题需要对相关神经回路进行比较研究。在本研究中，我们利用连接组技术分析了柑橘凤蝶第一视神经节薄板组成单元之间的相互作用。薄板由cartridges组成，每个cartridges通常包含来自单个小眼的9个光感受器轴突和4个二级神经元。通过此分析，我们在柑橘凤蝶的薄板中发现了丰富的光感受器之间的连接，而这种现象在黑腹果蝇的薄板中没有发现。同样，我们也发现了相邻cartridges之间的连接，特别是在接收不同光谱信息输入的cartridges之间。另外，突触连接的线性求和模型很好地解释了光感受器和二级神经元的光谱敏感性。

Connectomics has become a standard neuroscience methodology in a few model animals, with the visual system being a popular target of study. Combining connectomics with circuit and behavioral physiology, recent studies on the color vision of the fruit fly Drosophila melanogaster have focused on the mechanisms underlying early wavelength processing in the optic ganglia. However, the color vision capabilities of D. melanogaster are limited, compared with many flower-visiting insects. For example, a butterfly Papilio xuthus has six spectral classes of photoreceptors. Each ommatidium contains nine photoreceptors in one of three fixed combinations, making the eye an array of three spectrally distinct ommatidia types. Behaviorally, P. xuthus can detect 1 nm differences in light wavelength across the spectrum from ultraviolet to red, outperforming humans. What is the neuronal basis of such precise color vision? How does such a system evolve? Addressing these questions requires comparative studies at the circuit level. Here, we performed a connectome analysis in the first optic ganglion, the lamina, of P. xuthus. The lamina comprises cartridges, each typically containing nine photoreceptor axons from a single ommatidium and 4 second-order neurons. We found abundant inter-photoreceptor connections, which are absent in the lamina of D. melanogaster. We also identified connections between neighboring cartridges, particularly those receiving inputs from spectrally distinct ommatidia. The linear summation of synaptic connections well explains the spectral sensitivity of photoreceptors and second-order neurons in the lamina.

郭浩，博士，中国科学院动物研究所行为生理与神经遗传学课题组助理研究员，中国科学院生物互作卓越创新中心青年人才。主要从事昆虫神经生物学和行为学研究，重点关注昆虫与植物互作的化学生态学原理。目前在Journal of Neuroscience、PLoS Genetics、Insect Biochemistry and Molecular bIology 和 Pest Management Science等神经生物学和分子生物学主流期刊上发表SCI论文18篇。现担任Frontiers in Physiology 等杂志编委。

Hao Guo, Ph.D., is currently working as an assistant professor in the Group of Behavioral Physiology and Neurogenetics, Institute of Zoology, Chinese Academy of Sciences and an adjunct AP in the CAS Center for Excellence in Biotic Interactions, the University of Chinese Academy of Sciences. His major research interests include insect neurobiology and ethology, with a particular focus on the chemical ecological mechanism underlying the intricacy and complication of insect-plant interactions. He has authored 18 SCI papers published in top-tier journals, such as Journal of Neuroscience, PLoS Genetics, Insect Biochemistry and Molecular Biology, and Pest Management Science, etc. He is currently serving on the editorial board of Frontiers in Physiology Journal.

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