Cone-like rhodopsin expressed in the all-cone retina of the colubrid pine snake as a potential adaptation to diurnality
Cone-like rhodopsin expressed in the all-cone retina of the colubrid pine snake as a potential adaptation to diurnality
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DOI：
10.1242/jeb.156430
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发表时间：
2017-07-01
影响因子：
2.8
通讯作者：
Chang, Belinda S. W.
中科院分区：
文献类型：
--
作者：
Bhattacharyya, Nihar;Darren, Benedict;Chang, Belinda S. W.
游蛇科是最大和最多样化的蛇类，其视觉系统反映了这种多样性，包括各种视网膜感光组织。Walls提出的嬗变理论假设光感受器可以在鳞状细胞的细胞类型之间进行进化转换，但很少有研究验证这一理论。最近，在一种昼夜活动的束带蛇（Thamnophis）中发现了全锥视网膜中的变形和杆状机制的证据，似乎视紫红质基因至少可能在游蛇中广泛存在。然而，支持超越视紫红质基因存在的嬗变的功能证据仍然很少。我们研究了另一种游蛇的全锥视网膜，Pituophis melanoleucus，被认为比Thamnophis更隐秘/穴居。我们发现黑色素原细胞在眼内表达两种视锥细胞视蛋白（SWS 1，LWS）和视紫红质（RH 1）。免疫组织化学定位视紫红质的光感受器的外段在所有的视锥视网膜的蛇和所有的视蛋白基因产生功能性视色素时，在体外表达。与其他研究一致，我们发现P. melanoleucus视紫红质是非常蓝移的。令人惊讶的是，P. melanoleucus视紫红质与羟胺反应，这是一种典型的视锥细胞视蛋白特性。这些结果支持了黑条拟步行蛇的含视紫红质的光感受器是从杆状祖先进化嬗变的产物的观点，并表明这种现象可能在游蛇中广泛存在。我们推测，嬗变可能是一种适应昼夜，更明亮的光视觉，这可能会导致增加光谱灵敏度和色彩的歧视与潜在的色觉。
Colubridae is the largest and most diverse family of snakes, with visual systems that reflect this diversity, encompassing a variety of retinal photoreceptor organizations. The transmutation theory proposed by Walls postulates that photoreceptors could evolutionarily transition between cell types in squamates, but few studies have tested this theory. Recently, evidence for transmutation and rod-like machinery in an all-cone retina has been identified in a diurnal garter snake (Thamnophis), and it appears that the rhodopsin gene at least may be widespread among colubrid snakes. However, functional evidence supporting transmutation beyond the existence of the rhodopsin gene remains rare. We examined the all-cone retina of another colubrid, Pituophis melanoleucus, thought to be more secretive/burrowing than Thamnophis. We found that P. melanoleucus expresses two cone opsins (SWS1, LWS) and rhodopsin (RH1) within the eye. Immunohistochemistry localized rhodopsin to the outer segment of photoreceptors in the all-cone retina of the snake and all opsin genes produced functional visual pigments when expressed in vitro. Consistent with other studies, we found that P. melanoleucus rhodopsin is extremely blue-shifted. Surprisingly, P. melanoleucus rhodopsin reacted with hydroxylamine, a typical cone opsin characteristic. These results support the idea that the rhodopsin-containing photoreceptors of P. melanoleucus are the products of evolutionary transmutation from rod ancestors, and suggest that this phenomenon may be widespread in colubrid snakes. We hypothesize that transmutation may be an adaptation for diurnal, brighter-light vision, which could result in increased spectral sensitivity and chromatic discrimination with the potential for colour vision.