Meeting Abstract
The emergence of organized epithelia was undoubtedly one of the most significant events in metazoan evolution. The integrity of this tissue depends on the polarization and adhesion of its cells. One of the most studied systems in epithelial cell polarity is the Par system: a core set of five proteins (Par-1, Par-3, Par-6, aPKC, and Lgl) that, in bilateral animals, localize asymmetrically at the cell cortex beginning at the earliest stages of development. But, in embryos of Nematostella vectensis (phylum Cnidaria), Par components do not display asymmetric localization until later stages epithelial layers form. Are the protein-protein interactions within this system described in the Bilateria present in N. vectensis embryos? Immunoprecipitation experiments showed that NvaPKC, NvPar-6, and NvLgl all interact with one another throughout embryonic development, even though they are not asymmetrically localized at pre-blastula stages. In addition, experimental dominant-negative modifications of NvPar-3 and NvPar-6 resulted in modifications of their localization causing defects in cell adhesion, cell shape, and the integrity of cells in the endoderm (where Par proteins are not normally expressed). This suggests that the interactions of the Par/aPKC complex in the ectoderm maintain epithelial integrity of the entire embryo. From our data we conclude that some other factors that are expressed during later stages are not present during early cleavage stages. These factors were likely temporally co-opted in bilterian taxa to be expressed at earlier embryonic stages to regulate embryonic polarity and that, therefore, different molecular mechanisms operate to set up polarity in early cnidarian embryogenesis.
