A brachiopod's eye-sight - Understanding the evolution of light sensitive organs in the phylum Brachiopoda

在最近的一项研究中，人们发现了两个睫状光感受器(一个有晶状体，另一个有遮挡色素)组成横向腕足类幼虫眼睛的特殊组合。另外的原位杂交实验检测到Pax6和Ttr-c-Opsin在这些睫状光感受器中的表达，质疑了钩虫的光敏感器官(“眼睛”)专属部署横纹感光器的“规则”。由于一些腕足类物种被描述为具有未知结构的幼虫“眼点”，并表现出成年时的光反应行为，本项目计划利用组织学、超微结构、免疫细胞化学和分子/基因表达方法对腕足类(幼虫和成虫)所有可能的光敏感结构进行形态普查。除了幼虫的“眼斑”外，还将检查成虫的外套膜组织。利用描述腕足类幼虫眼睛和成体感光器的形态和分子数据，我们旨在描述腕足类所有可能的眼睛/光感受器形式，以推测腕足类光感受器的基本模式，并提供一个全面的数据集，用于与其他轮虫类群的比较。我们期望我们的结果将为我们理解轮虫、轮虫和双毛虫，包括最后的共同的双边祖先的光敏感结构的进化提供新的线索。

An exceptional combination of two ciliary photoreceptors (one with a lens, the other with shading pigment) forming the larval eyes of the brachiopod Terebratalia transversa was discovered during a recent study. Additional in-situ hybridization experiments detected Pax6 and Ttr-c-Opsin expression in these ciliary photoreceptors, questioning the "rule" that light sensitive organs ("eyes") of lophotrochozoans exclusively deploy rhabdomeric photorecep-tors. Since several brachiopod species are described to have larval "eye spots" of unknown structure and show photoreactive behaviour as adults, a morphological census of all possible light sensitive structures in brachiopods (larvae and adults) is planned in this project using histological, ultrastructural, immunocytochemical and molecular/gene-expression methods. Apart from larval "eye spots", mantle tissue of adults will be examined. Using both morpho-logical and molecular data characterizing brachiopod larval eyes and adult photoreceptors, we aim at describing all possible forms of eyes/photoreceptors in Brachiopoda to hypothe-size a ground pattern of brachiopod photoreceptors and to provide a comprehensive data set for comparison with other lophotrochozoan taxa. We expect that our results will shed new light on our understanding of the evolution of light sensitive structures in lophophorates, lophotrochozoans and Bilateria including the last common bilaterian ancestor.