The Evolution of Embryonic Polarity: A Molecular and Phylogenetic Approach

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AbstractThis grant is focused on understanding the developmental and evolutionary origin of embryonic axial properties that are responsible for organizing the segregation of germ layers in a small solitary sea anemone Nematostella vectensis (Anthozoa, Cnidaria). Anthozoans are basal members of the diploblastic, "radially" symmetric Cnidaria: the sister phylum to all bilaterally symmetrical triploblastic metazoans. Unlike bilaterally symmetrical metazoans, N. vectensis eggs have no apparent molecular polarity, and asymmetries generated at, or soon after, fertilization result in the activation of nuclear beta-catenin signaling at the future site of gastrulation. Because cnidarians like N. vectensis possess many of the same genes involved in axial organization in bilaterians, they have the potential to provide insight into the mechanisms that led to the evolution of egg anisotropies in all multicellular animals.Three specific aims will be pursued: 1) To use experimental embryological methods to characterize the onset of axis formation and origins of developmental polarity in the N. vectensis egg/zygote, 2) To identify the roles of the PAR proteins in establishing early asymmetries in the N. vectensis zygote and determine the possible role of these proteins in regulating asymmetric beta-catenin signaling. These experiments will establish the function of the par genes in a cnidarian and will reveal if cnidarians use these genes to polarize the early egg/embryo as in bilaterians. Additionally, these experiments will reveal if the PAR proteins play a functional role in polarizing canonical Wnt signaling, 3) To produce the critical regents and further develop methodologies necessary for further exploitation of N. vectensis as a model system for developmental and evolutionary studies.This work is the first comprehensive experimental and molecular analysis of anthozoan cnidarian development. It provides a unique opportunity to understand how these embryos "work", and thus provide insight into the development of more commonly studied bilaterian systems. These studies will link sperm-derived asymmetries to the localization of the PAR proteins and the activation of the Wnt/beta-catenin signal transduction pathway, and thus, provide insight into the evolution of the A/V axis and the evolution of germ layers. The proposed work involves postdocs, graduate students and undergraduate students from groups under-represented in science. The findings from this research will also incorporated into the undergraduate and graduate curricula. Additionally, the proposed collaborative work will also improve the research and training infrastructure at the University of Hawaii.