Summary
25In triploblastic animals, Par proteins regulate cell-polarity and adherens junctions of both 26 ectodermal and endodermal epithelia. But, in embryos of the diploblastic cnidarian Nematostella 27 vectensis, Par proteins are eliminated altogether in the bifunctional endomesodermal epithelia.
28Using immunohistochemistry, CRISPR/Cas9, and overexpression of specific mRNAs, we describe 29 the functional association between Par proteins, ß-catenin, and snail genes in N.
30vectensis embryos. We demonstrate that the aPKC/Par complex regulates the localization of ß-31 catenin in the ectoderm by directing its role in cell adhesion, and that endomesodermal epithelia 32 are organized by a different cell adhesion system. We also show that snail genes, which are 33 mesodermal markers in bilaterians, are sufficient to downregulate Par proteins and translocate ß-
34catenin from the junctions to the cytoplasm in N. vectensis. These data provide insight into the 35 evolution of epithelial structure and the evolution of mesoderm in metazoan embryos.
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