Developmental and gene expression patterns during neurogenesis in basal branching Annelida

环节动物是由各种各样的类群具有巨大的生态和形态特征。尽管如此，大多数环节动物表现出真正的分割，这是由不同的器官系统的连续重复和整个身体检测。值得注意的是，由于缺乏一个良好的支持环节动物系统发育，以前关于最后一个共同环节动物祖先特征的讨论是困难的。最近，转录组学数据和几个环节动物科在环节动物辐射的基础上的位置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，本项目的目标是调查底枝环节动物Magelona johnstoni（Magelonidae）的幼虫发育，以揭示一般的发育模式。有趣的是，处理幼虫和成虫神经系统特征的初步结果表明，这些特征与衍生环节动物分类群已知的条件有很大不同，例如，扁头虫属或小头虫属。因此，成年环节动物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表皮下排列。专注于神经系统的发展，免疫细胞化学的调查沿着基因表达的研究（原位杂交）将被用来调查在这个成员的基底分支Magelonidae的神经发生。着重研究了该虫的幼虫发育过程。johnstoni和神经发生基因Pax 6、Pax 3/7、msx、nk2.1、nk 6、enrailed和神经外胚层标记物synaptotagmin和elav的表达模式，沿着免疫组织化学方法，预期的项目将提供稀少研究的基底分支环节动物的可比较的发育和基因表达模式。因此，这些研究将有助于阐明环节动物神经系统的进化和环节动物总体的身体结构。Magelona johnstoni的生成数据与现有的调查，在所谓的环节动物模式生物，如，例如，Platynereis或Capitella的比较，将大大拓宽有关环节动物体内的身体计划和器官系统的进化的稀缺知识。此外，调查的基础分支环节动物Magelona johnstoni提供了基本的和可比的见解lophotrochozoon神经系统的演变和后生动物神经元模式的演变一般。

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.