Extraocular Vision in a Brittle Star Is Mediated by Chromatophore Movement in Response to Ambient Light
Extraocular Vision in a Brittle Star Is Mediated by Chromatophore Movement in Response to Ambient Light
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DOI：
10.1016/j.cub.2019.11.042
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发表时间：
2020-01-20
期刊：
影响因子：
9.2
通讯作者：
Ullrich-Lueter, Esther
中科院分区：
文献类型：
--
作者：
Sumner-Rooney, Lauren;Kirwan, John D.;Ullrich-Lueter, Esther
几乎所有的动物都能感觉到光，但只有那些有空间视觉的动物才能“看得见”。传统上，这仅限于拥有离散视觉器官(眼睛)的动物，但眼外视力可以促进没有眼睛的视力。棘皮动物构成了眼外视觉研究的焦点[1-7]，而脆弱的恒星文迪蛇(Ophiooma Wendtii)表现出对光的响应颜色变化和寻求庇护，成为人们感兴趣的关键物种[4，8，9]。文迪氏原虫和一个明显不受光线影响的同属植物--南美原虫都拥有广泛的r-视蛋白反应细胞网络，但其功能尚不清楚[4]。我们发现，虽然这两个物种都强烈厌恶光线，但文迪亚野生稻对需要空间视觉才能进行检测的刺激有定向，而南美野生稻则不是。然而，当生色团在骨架内收缩时，O.wendtii的反应就消失了。结合免疫组织化学、组织学和同步辐射显微断层扫描，我们在原位重建了光感受器的模型，并提取了估计的温氏原虫和南美原虫的角孔。根据这些模型得出的角度敏感度估计支持这样的假设，即色团构成了文迪氏原虫的一种筛选机制，提供了足够的分辨率来检测刺激。RNA测序(RNA-seq)在两个物种中发现了视蛋白候选者，包括多个r-opsins和转导途径成分，与免疫组织化学和对其他棘皮动物的研究一致[10，11]。最后，我们注意到两个物种在实验期间不同的身体姿势可能反映了信号整合的方面。这代表了迄今提出的眼外视觉最详细的机制之一，并与唯一另一个已证实的眼外视觉系统--也拥有色团的一些海胆的视觉系统--进行了有趣的相似之处[1]。
Almost all animals can sense light, but only those with spatial vision can "see.'' Conventionally, this was restricted to animals possessing discrete visual organs (eyes), but extraocular vision could facilitate vision without eyes. Echinoderms form the focus of extraocular vision research [1-7], and the brittle star Ophiocoma wendtii, which exhibits light-responsive color change and shelter seeking, became a key species of interest [4, 8, 9]. Both O. wendtii and an apparently light-indifferent congeneric, O. pumila, possess an extensive network of r-opsin-reactive cells, but its function remains unclear [4]. We show that, although both species are strongly light averse, O. wendtii orients to stimuli necessitating spatial vision for detection, but O. pumila does not. However, O. wendtii's response disappears when chromatophores are contracted within the skeleton. Combining immunohistochemistry, histology, and synchrotron microtomography, we reconstructed models of photoreceptors in situ and extracted estimated angular apertures for O. wendtii and O. pumila. Angular sensitivity estimates, derived from these models, support the hypothesis that chromatophores constitute a screening mechanism in O. wendtii, providing sufficient resolving power to detect the stimuli. RNA sequencing (RNA-seq) identified opsin candidates in both species, including multiple r-opsins and transduction pathway constituents, congruent with immunohistochemistry and studies of other echinoderms [10, 11]. Finally, we note that differing body postures between the two species during experiments may reflect aspect of signal integration. This represents one of the most detailed mechanisms for extraocular vision yet proposed and draws interesting parallels with the only other confirmed extraocular visual system, that of some sea urchins, which also possess chromatophores [1].