Germ layer specific regulation of cell polarity and adhesion gives insight into the evolution of mesoderm

Abstract

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. 37All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx

An alternative mode of epithelial polarity in the Drosophila midgut

“…Thus, it is possible that endodermal epithelia are intrinsically different in the way that they polarise. In support of this view, it has recently been found that PAR-3, PAR-6, and aPKC are degraded in the invaginating endomesoderm of the Cnidarian Nematostella vectensis and are not required for this tissue to form an epithelium [ 67 ]. Thus, the difference between endodermal and ectodermal polarity systems may have evolved before the origin of Bilateria.…”

Par protein localization during the early development of Mnemiopsis leidyi suggests different modes of epithelial organization in the metazoa

“…In bilaterians and cnidarians, the apical localization of MlPar-6 induces the phosphorylation of MlPar-1, displacing this protein to basolateral cortical regions 4,5,21,22 . Using our specific MlPar-1 antibody, we characterized the subcellular localization of the MlPar-1 protein during the early M. These results were also supported in vivo when we overexpressed the mRNA encoding for MlPar-1 fused to mCherry (MlPar-1-mCherry) into M. leidyi embryos by microinjection ( Figure 3 To discount the possibility that the observations recorded in vivo for both MlPar-6-mVenus and MlPar-1-mCherry proteins are caused by a low-quality mRNA or lack of structural conservation, we overexpressed each ctenophore mRNA into embryos of the cnidarian Nematostella vectensis and followed their localization by in vivo imaging (Figure 4).…”

“…While the asymmetric cortical distribution of the Wnt Planar Cell Polarity (PCP) pathway components polarizes the cells along the tissue plane, the asymmetric cortical distribution of Par system components polarizes the cells along the apical-basal axis 2,3,[13][14][15][16][17][18][19][5][6][7][8][9][10][11][12] . The mechanisms that organize cell-polarity are highly conserved in all animals that have been studied and most likely been present in the most recent common ancestor (MRCA) of Cnidaria and Bilateria 3,5,9,11,[20][21][22][23] ( Figure 1A).…”

“…Par-3/aPKC/Par-6), and the Scribble complex (e.g. Scribble/Lgl/Dlg) in the cortex of bilaterian and cnidarian cells maintains epithelial integrity by stabilizing cell-cell junctions 4,5,20,22,23 via the Cadherin-Catenin complex (CCC) of mature Adherens Junctions (AJs) 1,23,[31][32][33][34][35][36] . The maturation of AJs is essential for the maintenance of the Par/aPKC complex localization at the apical cortex that displaces members of the Scribble complex and Par-1 to basolateral localizations associated with Septate Junctions (SJs) 23,37-45 . This mechanism is deployed in bilaterian cells to establish embryonic and epithelial cell polarity during early development and is critical for axial organization 5,8,51-60,10,61,62,21,22,46-50 . Components of the Par system are unique to, and highly conserved, across Metazoa, including placozoans, poriferans, and ctenophores 20,23 .…”

Feeding-dependent tentacle development in the sea anemone Nematostella vectensis

“…In recent years, N. vectensis has become an established cnidarian model in developmental biology due to its relative ease of laboratory spawning 14,15 , tractable developmental biology [16][17][18][19][20] , extensive regenerative capacity [21][22][23][24] , and robust molecular genetic approaches [25][26][27][28][29] . Nematostella polyps can harbor a variable number of tentacles ranging from 4 to 18, but the common number in adulthood is 16 (refs.…”