Multiple Origins of Mesoderm in a Model Polychaete

许多动物在发育过程中由内胚层和外胚层同时产生第三胚层，即中胚层。然而，中胚层发育潜能的细胞和分子分离以及这些不同起源的系统发育意义仍未被探索。显示高度定型的细胞分裂程序称为螺旋分裂的胚胎（例如软体动物，环节动物，nemerteans, sipuncuids, echiurans, polyclad flatworms）是追踪幼虫/成虫结构来源的理想胚胎，并揭示了外内胚层和内内胚层谱系。这项工作将分子和细胞方法与胚胎学操作相结合，在多毛类模型中，Capitella sp. I，一种经历螺旋切割并在其生活史中增加新片段的分段蠕虫。在Capitella sp. I中，engrailed、coaudal和eve的表达表明，胚胎后节段的中胚层不是由内胚层终成细胞产生的，而是由外胚层前体产生的，这些前体在幼虫/幼体的整个生命过程中有效地“原胚化”，并在终末添加过程中产生成虫节段的中胚层。在拟议的研究中，中胚层电位由外胚层和内胚层来源产生的机制将被检查。将生成小头草（Capitella sp. I）胚胎卵裂球的细胞内命运图，并特别关注中胚层胚胎起源的特征。许多中胚层标记已经从小头草中鉴定出来，并将被定位到细胞谱系中，以确定哪些基因与外胚层、内胚层或两者相关。在另一组实验中，错误表达和敲低方法将被用来确定选择的外胚层和内膜基因的功能。这项拟议的研究将把科学训练与研究结合起来，将包括夏威夷大学的本科生、研究生和博士后学员。夏威夷大学是一所少数族裔机构，也是EPSCoR所在的州。PI致力于在实验室环境中培训学生，包括来自太平洋岛民等代表性不足群体的学生。该研究将为了解多毛类环节动物中胚层的形成提供重要信息，并为第三胚层的发育与外胚层、后口和其他三胚层动物系统的发育提供重要的比较。

Many animals generate their third germ layer, the mesoderm, from both endomesodermal and ectomesodermal sources during development. However, the cellular and molecular segregation of mesodermal developmental potential and the phylogenetic significance of these distinct origins remain unexplored. Embryos that display a highly stereotyped cell cleavage program called spiral cleavage (e. g. in animals that include mollusks, annelids, nemerteans, sipunculids, echiurans, polyclad flatworms) are ideal for tracing sources of larval/adult structures and have revealed both ectomesodermal and endomesodermal lineages. The proposed work combines molecular and cellular approaches with embryological manipulations in a polychaete model, Capitella sp. I, a segmented worm that undergoes spiral cleavage and adds new segments throughout its life history. Expression of engrailed, caudal, and eve in Capitella sp. I suggests that mesoderm in post-embryonic segments is not generated from endomesodermal teloblasts, but rather from ectomesodermal precursors that effectively 'gastrulate' throughout larval/juvenile life and give rise to adult segmental mesoderm during the process of terminal addition. In the proposed study, the mechanism by which mesodermal potential is generated from ectodermal and endodermal sources will be examined. An intracellular fate map for embryonic blastomeres of Capitella sp. I will be generated with special attention towards characterizing embryological origins of mesoderm. A number of mesodermal markers have been identified from Capitella sp. I, and will be mapped onto the cell lineage to determine which genes are associated with ectomesoderm, endomesoderm, or both. In an additional set of experiments, mis-expression and knockdown approaches will be utilized to determine the function of select ecto- and endomesodermal genes. The proposed study will integrate scientific training with research, and will include undergraduate, graduate, and postdoctoral trainees at the University of Hawaii, a minority institution and EPSCoR state. The PI is committed to training students in the laboratory environment, including those from underrepresented groups such as Pacific Islanders. The study will provide crucial information towards understanding how mesoderm is generated in polychaete annelids, and provide an important comparison of development of the third germ layer with ecdysosoan, deuterostome and other triploblastic animal systems.