If you’ll recall, back in December, I provided evidence that unicellular organisms were endowed with components (beta catenins) that served as preadaptations to nudge epithelial tissue into existence when needed.
Well, feast your eyes on a paper that was published in Science just a couple of weeks ago.
A polarized epithelium organized by beta- and alpha-catenin predates cadherin and metazoan origins.
Dickinson DJ, Nelson WJ, Weis WI.
Science. 2011 Mar 11;331(6022):1336-9.
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 that contains a classical cadherin, the Wnt-signaling protein β-catenin and the actin-binding protein α-catenin. We show that the non-metazoan Dictyostelium discoideum forms a polarized epithelium that is essential for multicellular development. Although D. discoideum lacks a cadherin homolog, we identify an α-catenin ortholog that binds a β-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.