Evolution of photoreceptors as illuminated by fossils and development

我的项目的长期目标是对光感受器进化和视觉生态学进行基础性的研究。我们主要通过比较不同脊椎动物和个体发育阶段之间光感受器的发育（进化-发展）来完成这一任务。我们经常用斑马鱼作为实验平台，来检验从探索其他更有趣的动物（无颌鱼类、迁徙鱼类、甲壳类动物）中产生的新假设。在未来的几年里，我们将研究从我们最近的工作中出现的具有挑挑性的新观点：***大多数哺乳动物的杆状光感受器是由锥状光感受器进化而来的，特别是从短波敏感（SWS-或UV-）锥状光感受器；***为了完善细胞类型同源性概念，并测试杆状光感受器是否从SWS视锥细胞进化而来，我们将比较4种视锥细胞类型转分化为杆状细胞的倾向；***通过评估关键发育基因的表达，并在斑马鱼平台上对盲鳗基因功能进行深入测试，可以揭示盲鳗中视杆细胞与视锥细胞的身份和进化（从而揭示早期脊椎动物的进化）。***我的HQP将很好地定位于对双视网膜的生物学和进化进行基础见解，即拥有杆状细胞和锥状细胞背后的生物学，使脊椎动物辐射取得巨大成功。******此外，我们仍然对大多数动物视网膜中观察到的精细排列的光感受器模式感到困惑和着迷（尽管在哺乳动物中没有）。我们在斑马鱼中的遗传方法继续揭示这种光感受器马赛克形成和马赛克功能的机制。为了补充这一点，我们现在将扩展我们的程序，以比较甲壳类动物中光感受器阵列的发展。小眼虫的个体发生变化和其中的光感受器模式与鱼类的光感受器有惊人的（可能是趋同的？）相似之处。十足甲壳类动物（螃蟹、小龙虾等）特别有趣的是，它们的小眼是方形的（“反射镜盒”），然而它们的幼虫生活始于我们熟悉的六边形小眼。令人惊讶的是，与脊椎动物不同的是，这些光感受器的形态在化石记录中保存得很好。我们将把化石与现存螃蟹和虾的小眼和光感受器补体进行比较，特别关注在个体发育过程中变化的阵列和/或具有区域专一性的阵列，从而使每只眼睛同时出现多种形态。******了解脊椎动物光感受器的进化受到缺乏化石记录的阻碍。我的HQP通过两种策略克服了这一挑战：第一：通过比较产生光感受器的发育程序，我们将独特地揭示古代同源性。第二：我们将通过询问一个可以根据化石光感受器校准的发育系统来确定这种进化-发展方法的缺陷和机会，并将其应用于感觉系统

The long-term Aim of my Program is to make foundational insights into photoreceptor evolution and visual ecology. We accomplish this principally by comparing the development (evo-devo) of photoreceptors between disparate vertebrates and between ontogenetic stages. We often use zebrafish as a platform to experimentally test the novel hypotheses generated from exploring other more interesting animals (jawless fishes, migrating fishes, crustaceans). In the coming years we will investigate provocative new ideas emerging from our recent work:*** The majority of Mammalian rod photoreceptors develop and evolved from cone photoreceptors, especially from the short-wavelength-sensitive (SWS- or UV-) cones;*** To refine cell type homology concepts, and to test if rod photoreceptors evolved from SWS cones, we will compare the propensity of the 4 cone types to transdifferentiate into rods;*** The identity and evolution of rods vs. cones can be revealed in hagfish (thus revealing early vertebrate evolution) by assessing expression of key developmental genes alongside incisively testing hagfish gene function in our zebrafish platform. ***My HQP will be well-positioned to make foundational insights into the biology and evolution of the duplex retina, i.e. the biology behind possessing both rods and cones that has empowered the immense success of the vertebrate radiation.******Further, we remain puzzled and fascinated by the elaborately arrayed patterns of photoreceptors observed in the retinas of most animals (though lost in mammals). Our genetic approaches in zebrafish continue to reveal mechanisms of this photoreceptor mosaic formation and mosaic functions. To complement this, we will expand our Program now to compare to the development of photoreceptor arrays in crustaceans. Ontogenetic changes in ommatidia and photoreceptor patterning therein has striking (presumably convergent?) similarities to those of fish photoreceptors. Decapod crustaceans (crabs, crayfish, etc.) of special interest have square (“reflecting mirror box”) ommatidia, however they BEGIN larval life with the familiar hexagonal ommatidia. Amazingly, and unlike in vertebrates, these photoreceptor morphologies are well-preserved in the fossil record. We will compare fossils to the ommatidia and photoreceptor complement in extant crabs and shrimps, with special focus on arrays that change during ontogeny and/or have regional specialization such that multiple morphologies occur simultaneously in each individual eye. ******Understanding the evolution of vertebrate photoreceptors is hampered by lack of fossil record. My HQP overcome this challenge via two strategies: First: by comparing the developmental program that produces photoreceptors, we will uniquely reveal ancient homologies. Second: we will identify the pitfalls and opportunities of this evo-devo approach, as applied to sensory systems, by interrogating a developmental system that can be calibrated against fossil photoreceptors.**