Multiple Origins of Mesoderm in a Model Polychaete

University Of Hawaii, Honolulu

Investigators

Abstract

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.