Developmental and gene expression patterns during neurogenesis in basal branching Annelida

环节动物有许多不同的类群，具有各种各样的生态和形态特征。然而，大多数环节动物表现出真正的分割，这是由不同器官系统的连续重复所代表的，并且在整个身体上都可以检测到。值得注意的是，以前关于最后一个共同环节动物祖先的特征的讨论是困难的，因为缺乏一个很好的支持环节动物的系统发育。最近，转录组学数据和几个环节动物家族在环节动物辐射基础上的定位为进一步研究不同环节动物器官系统的进化和发育模式提供了坚实的框架。因此，本项目的目标将是研究麦哲龙（Magelona johnstoni）基础分支环节动物的幼虫发育，以揭示其普遍的发育模式。有趣的是，处理幼虫和成虫神经系统特征的初步结果表明，这些特征与已知的衍生环节动物类群（如Platynereis或Capitella）的条件有很大不同。因此，成年麦哲伦虫表现出非分节的表皮内神经系统，而不是大多数其他环节动物所描述的阶梯状的表皮下神经系统。以神经系统发育为重点，免疫细胞化学研究和基因表达研究（原位杂交）将用于研究这一基础分支麦哲伦科成员的神经发生。本项目将重点研究M. johnstoni的幼虫发育和神经发生基因Pax6、Pax3/7、msx、nk2.1、nk6、engrailed以及神经外胚层标记synaptotagmin和elav的表达模式，并结合免疫组织化学方法，为研究较少的基支环节动物提供可比较的发育和基因表达模式。因此，调查将阐明环节动物神经系统的进化和环节动物的身体计划。将Magelona johnstoni的生成数据与对所谓的环节动物模式生物（如Platynereis或Capitella）的现有研究进行比较，将大大拓宽有关环节动物身体结构和器官系统进化的匮乏知识。此外，对基础分支环节动物Magelona johnstoni的研究为光复动物神经系统的进化和后生动物神经元模式的进化提供了基本的和可比的见解。

The Annelida are represented by various taxa possessing a huge variety of ecological and morphological features. Nevertheless, most annelids exhibit true segmentation, which is represented by the serial repetition of different organ systems and detectable over the whole body. Notably, former discussions about characteristics of the last common annelid ancestor were difficult due to the lack of a well-supported annelid phylogeny. Recently, transcriptomic data and the placement of several annelid families at the base of the annelid radiation provide a solid framework for further investigations concerning the evolution of different annelid organ systems and developmental patterns.Therefore, goal of the project will be the investigation of the larval development in the basal branching annelid Magelona johnstoni (Magelonidae) to uncover general developmental patterns. Interestingly, preliminary results dealing with larval and adult nervous system characters indicate characters that strongly differ from the conditions known for derived annelid taxa like, e.g., Platynereis or Capitella. Thus, adult magelonids exhibit a non-segmented, intra-epidermal nervous system instead of the ladder-like, sub-epidermal arrangement described for most other annelids. Focusing on nervous system development, immunocytochemical investigations along with gene expression studies (in situ hybridization) will be used to investigate the neurogenesis in this member of the basal branching Magelonidae. With emphasis on the larval development of M. johnstoni and the expression pattern of the neurogenesis genes Pax6, Pax3/7, msx, nk2.1, nk6, engrailed, and the neuroectoderm markers synaptotagmin and elav, along with immunohistochemical methods, the intended project will provide comparable developmental and gene expression patterns of the sparsely investigated basal branching annelids. The investigations therefore will shed light on the evolution of the annelid nervous system and the annelid body plan in general. Comparisons of the generated data of Magelona johnstoni with existing investigations in so-called annelid model organisms like, e.g, Platynereis or Capitella, will substantially broaden the scarce knowledge concerning the evolution of body plans and organ systems within the Annelida. Furthermore, investigations of the basal branching annelid Magelona johnstoni provide fundamental and comparable insights into the evolution of lophotrochozoan nervous systems and into the evolution of metazoan neuronal patterns in general.