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，发现了一种特殊的组合，两个睫状光感受器（一个有透镜，另一个有阴影色素）形成的腕足动物Terebratalia transversa幼虫的眼睛。另外的原位杂交实验检测到Pax 6和Ttr-c-Opsin在这些睫状光感受器中的表达，质疑lophotrochozoans的光敏器官（“眼睛”）专门部署横纹肌光感受器的“规则”。由于几个腕足类物种被描述为有幼虫的“眼睛斑点”的未知结构，并显示光反应行为的成年人，在腕足类（幼虫和成年人）的所有可能的光敏感结构的形态普查计划在这个项目中使用组织学，超微结构，免疫细胞化学和分子/基因表达方法。除了幼虫的“眼斑”外，还将检查成虫的外套膜组织。利用表征腕足动物幼虫眼睛和成年光感受器的形态学和分子数据，我们旨在描述腕足动物中所有可能的眼睛/光感受器形式，以假设腕足动物光感受器的地面模式，并提供与其他lophotrochozoan类群比较的全面数据集。我们希望我们的研究结果将为我们理解lophophorates，lophotrochozoans和Bilateria（包括最后一个共同的bilaterian祖先）中光敏结构的进化提供新的思路。

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.