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

你能想象在几乎完全黑暗的时候看到紫外线、天空甚至你周围的偏振图案是什么感觉吗？这些是许多动物身上常见的一些惊人的视觉能力，我们只能想象世界是如何呈现给它们的。在所有脊椎动物中，这种非凡的专门化源于眼睛后部的视网膜吸收光线的方式。在视网膜中有两种类型的细胞，它们是光敏感细胞，视杆细胞和视锥细胞。这两种细胞执行不同的任务；例如，杆状细胞负责弱光视觉，而锥状细胞则提供颜色和偏振光敏感性。视网膜工作方式最耐人寻味的一个方面是，视杆细胞和视锥细胞的不同微观属性如何决定这些细胞执行的不同任务。这项研究的中心目的是为了详细了解视杆细胞和视锥细胞不同的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、光吸收和激光镊子来研究视杆细胞和视锥细胞的不同性质，如膜结构、膜流动性和偏振光吸收。我的研究计划将实现以下几个方面：1.我将研究吸收光线的杆和锥体部分的膜堆的层状结构。使用一种新的对准技术来定位细胞的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，以提供为什么杆状和锥状细胞在灵敏度和反应速度方面存在差异的新信息。2.我将测量和比较吸光色素在视杆细胞和视锥细胞膜中的旋转情况。我将再次利用这些结果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角色联系起来。3.我将确定偏振敏感物种(三文鱼)在每种锥体类型中如何吸收不同波长的偏振光。我将使用新的对齐技术将细胞按方向改变为其末端，因为它们实际上存在于眼睛中。这将是第一次在这个方向上进行详细的吸光度测量。这些结果将回答个体光感受器如何向大脑提供有关光偏振的信息的具体问题。这一部分将是该项目的海外部分，将在加拿大皇后大学的C·W·哈里申教授的实验室进行。总而言之，这项研究计划的所有三个部分都将提供补充信息。这种综合的方法将回答一些重要的问题，即细胞分子特性的微小变化如何导致惊人的视觉能力。

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.