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  • Book
    Daniel James Dickinson.
    Digital2011
    A fundamental characteristic of metazoans is the formation of a simple, polarized epithelium. In higher animals, the structural integrity and functional polarization of simple epithelia require a cell-cell adhesion complex containing a classical cadherin, the Wnt-signaling protein [Beta]-catenin and the actin-binding protein [Alpha]-catenin. I have investigated the evolutionary origins of epithelial cell polarity and of the cadherin-catenin complex. I show that the non-metazoan Dictyostelium discoideum forms a polarized epithelium that is essential for multicellular development. Although D. discoideum lacks a cadherin homolog, I have identified and characterized an [Alpha]-catenin ortholog that binds a [Beta]-catenin-related protein. Both proteins are essential for formation of the epithelium, polarized protein secretion and proper multicellular morphogenesis. Thus the organizational principles of metazoan multicellularity may be more ancient than previously recognized, and the role of the catenins in cell polarity predates the evolution of Wnt signaling and classical cadherins.