Molecular evolution of vision and visual pigments

视觉和视觉色素的分子进化

• 批准号: RGPIN-2022-04107
• 负责人: Chang, Belinda
• 金额: $ 4.88万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751438
• 关键词: Molecular; evolution; vision; visual; pigments

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. Typical vertebrate retinas have two types of photoreceptors, cones for vision during the day, and rods for dim light. These photoreceptors are known to contain different components of the visual transduction cascade, including rod and cone visual pigments, which are thought to underlie some of the physiological differences between the two. Among vertebrates, reptiles possess some of the most diverse visual systems in known in nature, especially in terms of the photoreceptor composition of their retinas, with frequent losses of either of the two photoreceptor types. A longstanding theory postulated that this might be the result of unusual evolutionary transformations from one photoreceptor cell type into another, a process rare outside of reptiles. This was first discovered in nocturnal geckos, in which the rods are thought to have evolved from ancestral cones, retaining cone visual transduction genes. Our group has demonstrated that a similar evolutionary transformation has taken place, but in the opposite direction, in a strongly diurnal species of garter snake. Reptilian retinas appear to be capable of striking evolutionary transformations in terms of retinal composition, but the consequence of these differences in cellular context for the visual transduction machinery of the photoreceptor cell, including the visual pigments, is not well understood, and its origins remain shrouded in mystery. Reptilian visual systems represent a rare opportunity to study the origins and molecular consequences of these fascinating evolutionary photoreceptor transformations. My research program uses innovative evolutionary approaches, both experimental and computational, to understand fundamental mechanisms of visual pigment function by studying adaptive variation found in reptiles and other animals living in diverse environments where light intensities and available spectrum can be dramatically different. In this research proposal, we have three objectives. (1) We will experimentally investigate visual pigments from evolutionary transformed photoreceptors, comparing the functional shifts in snakes and geckos, and use mutagenesis approaches to determine if similar mechanisms underlie shifts in function in the two groups. (2) We will use a combination of sequencing, evolutionary analysis, and experimental assays of reconstructed ancestral squamate visual pigments to investigate the evolutionary origins of photoreceptor transformations in reptilian retinas. (3) Finally, my group has recently developed the first high-throughput assay of visual pigment activation, which allows us to rapidly screen thousands of mutations efficiently. We will use this to screen mutations in visual pigments, and better understand tradeoffs in different aspects of function.

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。典型的脊椎动物视网膜有两种类型的光感受器，白天用于视觉的视锥细胞和用于昏暗光线的视杆细胞。已知这些光感受器包含视觉转导级联的不同组分，包括视杆和视锥色素，这被认为是两者之间的一些生理差异的基础。在脊椎动物中，爬行动物拥有自然界中已知的一些最多样化的视觉系统，特别是在视网膜的光感受器组成方面，两种光感受器类型中的任何一种都经常丢失。一个长期存在的理论假设，这可能是从一种感光细胞类型到另一种感光细胞类型的不寻常进化转化的结果，这一过程在爬行动物之外很少见。这一点首先在夜行壁虎中发现，它们的视杆细胞被认为是从祖先的视锥细胞进化而来的，保留了视锥细胞的视觉转导基因。我们的研究小组已经证明，一个类似的进化转变已经发生，但在相反的方向，在一个强烈的昼夜活动的束带蛇物种。爬行动物视网膜似乎能够在视网膜组成方面发生惊人的进化转变，但这些差异在感光细胞（包括视色素）的视觉转导机制的细胞环境中的后果还没有得到很好的理解，其起源仍然笼罩在神秘之中。爬行动物的视觉系统代表了一个难得的机会来研究这些迷人的进化感光器转换的起源和分子后果。我的研究计划使用创新的进化方法，实验和计算，通过研究爬行动物和生活在不同环境中的其他动物中发现的适应性变化来了解视觉色素功能的基本机制，其中光强度和可用光谱可以显着不同。在这项研究计划中，我们有三个目标。(1)我们将通过实验研究来自进化转化的光感受器的视色素，比较蛇和壁虎的功能转变，并使用诱变方法来确定两组功能转变的基础机制是否相似。(2)我们将结合测序，进化分析和实验分析重建的祖先鳞状视色素，研究爬行动物视网膜光感受器转换的进化起源。(3)最后，我的团队最近开发了第一个高通量的视觉色素激活检测方法，使我们能够快速有效地筛选数千个突变。我们将用它来筛选视觉色素的突变，并更好地了解功能不同方面的权衡。