Molecular evolution of visual pigments

视觉色素被光激活触发了眼睛光感受器中感觉传导级联的第一步，最终导致神经信号到达大脑。视觉转导级联的第一个关键步骤中的变化，视觉色素激活，已知有助于脊椎动物视觉系统的重要方面，例如其在光强度变化方面的巨大动态范围，以及在感知的光的波长方面。然而，除了一些模型系统，视觉色素在自然界中的显着多样性还没有详细研究。 动物是如何适应极端昏暗光线条件下的视觉的？我的研究计划使用一种创新的方法来理解视觉色素功能的基本机制，通过研究生活在光照强度和可用光谱急剧减少的环境中的动物中发现的适应性变化： 1)夜行蛇在陆生脊椎动物中，蛇的视觉系统具有许多独特的特征，这些特征归因于它们的地下起源。游蛇科的蛇很迷人，因为它们中的许多都是白天活动的物种，具有全锥状视网膜，适应日光视觉，但也有适合昏暗光线视觉的黄昏和夜间物种。这些适应的分子基础知之甚少。我们将使用异源表达来研究适应昏暗视觉的各种蛇的视觉色素功能。这将与眼睛转录组测序相结合，然后进行进化计算分析，以确定积极选择下的视觉基因。这项研究不仅将导致第一个眼睛转录组报告的任何爬行动物，它也将与实验研究相结合的潜在分子机制，导致昏暗的光适应蛇。 2)潜水鲸鱼鲸类动物，如鲸鱼和海豚，对它们完全的水生生活方式具有显着的适应性。鲸目动物的视网膜主要由视杆细胞感光器控制，这将有助于在低光水平下增加视觉灵敏度。有迹象表明，这种专门化的昏暗光视觉也延伸到鲸目动物的视觉转导的分子机制，但这还有待详细研究。利用一些最近的基因组测序研究的鲸类动物，我们将功能特性的视觉色素从各种潜水鲸类动物使用光谱分析，以调查方面的视觉色素功能，可能与他们的水生生活方式。这项研究是令人兴奋的，因为它将是为数不多的关于鲸目动物分子适应的实验研究之一，使他们能够从陆地生活方式过渡到完全水生生活方式，这是进化史上最戏剧性的转变之一。

Visual pigment activation by light triggers the first step of the sensory transduction cascade in photoreceptors of the eye that ultimately results in a neural signal to the brain. Variation in this first critical step of the visual transduction cascade, visual pigment activation, is known to contribute to important aspects of the vertebrate visual system, such as its enormous dynamic range in terms of variation in light intensities, and in wavelengths of light perceived. However, aside from a few model systems, the remarkable diversity of visual pigments in nature has not been investigated in detail. How have animals adapted to vision under extreme dim light conditions? My research program uses an innovative approach to understanding fundamental mechanisms of visual pigment function by studying adaptive variation found in animals living in environments where the light intensities and available spectrum are dramatically reduced: 1) Nocturnal snakes. Among terrestrial vertebrates, the visual systems of snakes are known to possess many peculiar features that have been attributed to their subterranean origins. Colubrid snakes are fascinating in that many are diurnal species adapted to daylight vision with an all-cone retina, but there are also crepuscular and nocturnal species adapted for dim-light vision. The molecular basis of these adaptations are poorly understood. We will use heterologous expression to investigate visual pigment function in a diversity of snakes adapted for dim-light vision. This will be combined with eye transcriptome sequencing, followed by evolutionary computational analyses in order to identify visual genes under positive selection. This research will not only result in the first eye transcriptomes reported for any reptile, it will also be combined with experimental investigations into the underlying molecular mechanisms resulting in dim light adaptations in snakes. 2) Diving whales. Cetaceans such as whales and dolphins are known to possess remarkable adaptations to their fully aquatic lifestyle. The cetacean retina is dominated by rod photoreceptors, which would contribute to increased visual sensitivity at low light levels. There are hints that this specialization for dim light vision also extends to molecular mechanisms of visual transduction in cetaceans, but this has yet to be studied in detail. Taking advantage of a number of recent genome sequencing studies in cetaceans, we will functionally characterize visual pigments from a variety of diving cetaceans using spectroscopic assays, in order to investigate aspects of visual pigment function that may be related to their aquatic lifestyle. This research is exciting as it will be one of the few experimental studies of molecular adaptation in cetaceans that enabled their fascinating transition from terrestrial to fully aquatic lifestyles, one of the most dramatic transformations in evolutionary history.