Evolution of photoreceptors as illuminated by fossils and development

我的计划的长期目标是对光感受器进化和视觉生态做出基础性的见解。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(EVO-DEVO)来实现这一点。我们经常以斑马鱼为平台，对探索其他更有趣的动物(无颌鱼、迁徙鱼类、甲壳类动物)所产生的新假设进行实验测试。在接下来的几年里，我们将研究最近工作中出现的具有挑衅性的新想法：*大多数哺乳动物的棒状光感受器是由锥形感光器发育和进化而来的，尤其是短波(SWS-或UV-)视锥；*为了完善细胞类型的同源性概念，并测试是否由SWS视锥进化而来，我们将比较4种视锥类型的光感受器是否容易转分化为视锥；*通过评估关键发育基因的表达以及斑马鱼平台中的基因功能，可揭示棱镜鱼与圆锥体的相同和进化(从而揭示脊椎动物的早期进化)。*我的HQP将很好地为双链视网膜的生物学和进化做出基础性的见解，即同时拥有视杆和视锥背后的生物学，这使得脊椎动物辐射获得了巨大的成功。*此外，我们仍然对在大多数动物的视网膜中观察到的精心排列的光感受器模式感到困惑和着迷(尽管在哺乳动物中消失了)。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计划，以比较甲壳类动物光感受器阵列的发展。小眼的个体发育变化和其中的光感受器模式具有显著的(可能是趋同的？)与鱼类光感受器的相似之处。十足类甲壳类(螃蟹、小龙虾等)特别有趣的是，它们有正方形(“镜盒”)小眼，但它们以熟悉的六角形小眼开始幼虫的生活。令人惊讶的是，与脊椎动物不同的是，这些光感受器形态在化石记录中保存得很好。我们将把化石与现存的螃蟹和虾的小眼和光感受器互补进行比较，特别关注在个体发育过程中发生变化和/或具有区域特化的阵列，以便在每一只眼睛中同时出现多种形态。由于缺乏化石记录，理解脊椎动物光感受器的进化受到阻碍。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的同源性。第二：我们将通过询问可以根据化石光感受器校准的发育系统，来确定这种EVO-DEVO方法应用于感觉系统的陷阱和机会。

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.**