Understanding character polarity in Deep Metazoan phylogeny - Phylogenomics of Myzostomids

主要是由于分子系统发育研究，最近出现了一种新的观点，对深后生动物系统发育的原口动物，将它们分为蜕皮（蜕皮动物）和非蜕皮原口动物（最常被称为Lophotrochozoa）。粘口动物包括棘皮动物上的一小群共生的原口动物，它们表现出具有环节动物和扁形动物典型特征的马赛克的身体平面。它们是薄壁生物，具有副足、毛、纤毛和不完全的分节。因此，并不奇怪，myzostomids的分类地位一直是一个有争议的问题，因为他们的发现。最近的分子分析的基础上的一些基因，而不是解决图片复杂，这表明密切的亲缘关系的myzostomids的扁形动物。在这里提出的项目中，我们的目标是澄清myzostomids的分类位置，通过一个新的基因组方法：为两个模型myzostomids（Myzostoma cirriferum，Pulvinomyzostomum pulvinar）表达序列标签（EST）库将产生和比较的国家的最先进的生物信息学工具，潜在的姐妹类群。由于这两个重点物种来自两个最远的myzostomids内的系统发育谱系，对它们的比较将允许相关的内部分类群（myzostomids内），分类群间（myzostomids和潜在的姐妹分类群之间）的基因分歧。对于一系列重要基因，将对更大系列的粘口虫物种进行深入分析。这些基因已在SPP深层后生动物系统发育中在申请人之间达成一致，因此将生成可比较的基因组数据集用于替代分析。我们的基因组分析将补充一个全面的myzostomid体计划的超微结构分析。虽然我们的近期目标是解决myzostomids的分类位置，我们最终的目标是提供证据的字符极性（plesiomorphic，apomorphic，或收敛）的一些基本特征的原口类身体计划，如parapodia，chaetae，cirri，和分割。

Mainly due to molecular phylogenetic studies, a new view on Deep Metazoan Phylogeny has recently emerged for the protostomia, dividing them into the molting (Ecdysozoa) and the nonmolting protostomes (most often called the Lophotrochozoa). The myzostomids comprise a small group of symbiotic protostomes on echinoderms, which exhibit a body plan with a mosaic of characters typical of annelides and platyzoans. They are parenchymous organisms with parapodia, chaetae, cirri, and an incomplete segmentation. It is therefore not surprising that the taxonomic position of myzostomids has been a matter of controversy since their discovery. Recent molecular analyses based on a few genes have rather complicated than resolved the picture, suggesting close affinities of myzostomids to platyhelminths. In the project proposed here, we aim at clarifying the taxonomic position of myzostomids by a phylogenomic approach: for two model myzostomids (Myzostoma cirriferum, Pulvinomyzostomum pulvinar) libraries of Expressed Sequence Tags (ESTs) will be generated and compared by state-of-the-art bioinformatic tools to potential sister taxa. As the two focus species derive from the two most distantly related phylogenetic lineages within myzostomids, comparison on them will allow relating intra-taxon (within myzostomids) to inter-taxon (among myzostomids and potential sister taxa) gene divergence. For a series of important genes, an in-depth analysis will be performed on a larger series of myzostomid species. These genes have been agreed on among applicants in the SPP Deep Metazoan Phylogeny , such that comparable genomic datasets will be generated for surrogate analysis. Our phylogenomic analysis will be complemented by a comprehensive ultrastructural analysis of myzostomid body plans. While our proximate goal is to resolve the taxonomic position of myzostomids, we ultimately aim at providing evidence for character polarity (plesiomorphic, apomorphic, or convergent) of some of the basic features of protostome body plans, such as parapodia, chaetae, cirri, and segmentation.