Specialization in the Visual System: Designing Different Optics for Different Roles

你能想象在几乎完全黑暗的情况下看到紫外线、天空中的偏振模式甚至你周围的环境是什么感觉吗？这些是许多动物都具有的惊人的视觉能力，我们只能想象世界是如何出现在它们面前的。在所有脊椎动物中，这种显著的特化都源于眼睛后部的视网膜如何吸收光线。在视网膜中有两种类型的光敏感细胞，即视杆细胞和视锥细胞。这两种细胞执行不同的任务;例如，杆细胞负责低光水平视觉，而锥细胞提供颜色和偏振光敏感性。视网膜工作方式最有趣的方面之一是视杆细胞和视锥细胞的不同微观特性如何决定这些细胞执行的不同任务。本研究的主要目的是详细了解视杆细胞和视锥细胞的不同结构和不同的物理性质如何影响它们在视网膜中的不同作用。我建议使用几种互补的方法，如X射线散射，光学吸收和激光镊子来研究不同的性质，如膜结构，视杆细胞和视锥细胞的膜流动性和偏振光吸收率。我的研究计划将实现以下目标。我将研究吸收光的杆和锥部分的膜堆叠的分层结构。使用一种新的对齐技术来定向细胞进行X射线散射，我将在这两种细胞类型之间进行第一次比较研究，分析结果以提供关于为什么杆细胞和锥细胞在灵敏度和反应速度方面存在差异的新信息。2.我将测量和比较光吸收色素如何在视杆细胞和视锥细胞的细胞膜内旋转。我将再次使用这些结果来将这些光感受器的微观物理特性与它们在视网膜中的不同作用联系起来。3.我将确定偏振光是如何在不同的波长吸收在每一个锥类型从偏振敏感物种（银鲑）。我将使用新的对齐技术来改变细胞的方向，因为它们实际上存在于眼睛中。这将是该方向上的第一次详细的吸光度测量。这些结果将回答单个光感受器如何向大脑提供光的偏振信息的具体问题。这一部分将构成该项目的海外部分，将在加拿大皇后大学的C W Hawryshyn教授的实验室进行。这种综合方法将回答细胞分子特性的微小变化如何导致惊人的视觉能力的重要问题。

Can you imagine what it would be like to see ultra-violet light, the polarization patterns in the sky or even your surroundings when it's almost completely dark? These are some of the amazing visual abilities that are common in many animals and we can only imagine how the world appears to them. In all vertebrates, such remarkable specializations stem from how the retina at the back of the eye absorbs light. In the retina there are two types of cells which are light sensitive, rod and cone photoreceptors. Both kinds of cell perform different tasks; for example rods are responsible for low light level vision whilst cones provide colour and polarized light sensitivity. One of the most intriguing aspects of the way the retina works is how the different microscopic properties of rods and cones determine the diverse tasks these cells perform. The central aim of this proposed research is to provide a detailed insight into how the different structure and different physical properties of rod and cone photoreceptors contributes to their distinct roles in the retina.I propose to use several complementary methods such as x-ray scattering, optical absorption and laser tweezing to study different properties such as membrane structure, membrane fluidity and polarized light absorbance in both rods and cones. My research programme will achieve the following.1. I will investigate the layered structures of the membrane stacks in the parts of rods and cones that absorb light. Using a new alignment technique to orientate the cells for x-ray scattering, I will make the first comparative studies between these two cell types, analyzing the results to provide new information on why rod and cones show differences in sensitivity and speed of reaction. 2. I will measure and compare how the light absorbing pigment rotates within the cellular membranes of both rods and cones. Again I will use these results to relate the microscopic physical properties of these photoreceptors to their different roles in the retina. 3. I will determine how polarized light is absorbed at different wavelengths in each of the cone types from a polarization sensitive species (Coho salmon). I will use the new alignment technique to change the cells into their end on orientation, as they actually exist in the eye. These will be the first detailed absorbance measurements in this orientation. The results will answer specific questions of how the individual photoreceptors can supply information on the polarization of light to the brain. This section will form the overseas part of the project and will be undertaken at Queens University, Canada in the laboratory of Professor C W Hawryshyn.In summary, all three parts of this research programme will provide complementary information. This integrated approach will answer important questions of how small changes to the molecular properties of a cell results in amazing visual abilities.