Molecular evolution of visual pigments

由光激活的视觉色素触发了眼睛光感受器感觉转导的第一步，最终导致神经信号到达大脑。众所周知，视觉转导级联的第一个关键步骤--视觉色素激活的变化有助于脊椎动物视觉系统的重要方面，如其在光强度和所感知的光波长方面的巨大动态范围。然而，除了几个模型系统之外，自然界中视觉色素的显著多样性还没有得到详细的研究。动物如何在极端昏暗的光线条件下适应视觉？我的研究项目使用了一种创新的方法来了解视觉色素功能的基本机制，方法是研究生活在光线强度和可用光谱急剧减少的环境中的动物的适应性变化：*1)夜间活动的蛇。在陆生脊椎动物中，蛇的视觉系统被认为具有许多独特的特征，这些特征被归因于它们的地下起源。游蛇之所以令人着迷，是因为许多蛇是白天活动的物种，具有全视锥视网膜，但也有黄昏和夜间活动的物种，适应昏暗的视觉。这些适应的分子基础还知之甚少。我们将使用异源表达来研究适应弱光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，随后进行进化计算分析，以识别正选择下的视觉基因。这项研究不仅将产生报道的所有爬行动物的第一个眼睛转录本，还将与导致蛇类适应暗光的潜在分子机制的实验研究相结合。潜水鲸。众所周知，鲸鱼和海豚等鲸目动物对其完全水生的生活方式具有非凡的适应能力。鲸目动物的视网膜由杆状感光器主导，这将有助于提高在弱光下的视觉敏感度。有迹象表明，这种弱光视觉的专门化也延伸到鲸目动物视觉传导的分子机制，但这还有待详细研究。利用最近的鲸目动物基因组测序研究，我们将使用光谱分析对各种潜水鲸目动物的视觉色素进行功能表征，以研究可能与它们的水生生活方式有关的视觉色素功能。这项研究是令人兴奋的，因为它将是少数几个关于鲸目动物分子适应的实验研究之一，使它们能够从陆地生活方式迷人地转变为完全水生生活方式，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.**