Meeting Abstract
20.5 Thursday, Jan. 3 Beta-catenin regulates endoderm formation in a nemertean embryo HENRY, J.Q.*; MARTINDALE, M.Q.; PERRY, K.J.; WEVER, J.M.; University of Illinois, Urbana; University of Hawaii, Kewalo; University of Illinois, Urbana; University of Illinois, Urbana j-henry4@uiuc.edu
The canonical Wnt signaling pathway regulates nuclear localization of beta-catenin and a diverse array of developmental processes including the formation of the mesendoderm. The nemertean Cerebratulus lacteus represents a member of the lophotrochozoan phyla that exhibit a highly stereotyped spiral cleavage program and conserved cell lineage fate map. We studied the embryonic distribution of beta-catenin protein by injection of GFP-tagged synthetic beta-catenin mRNA into fertilized eggs, and by using various antibodies. During early cleavage stages beta-catenin is degraded in animal hemisphere blastomeres and becomes localized to the nuclei of the four vegetal-most cells at the 64-cell stage, which give rise to the larval and adult endoderm. Functional assays demonstrate that beta-catenin plays a key role in the development of this tissue. Injections of mRNA encoding a constitutively activated form of beta-catenin converted all embryonic cells into endodermal cells that express gut-specific esterase. Likewise, expression of a dominant negative form of GSK3-beta also converted all embryonic cells into endoderm. Morpholino knockdown of endogenous beta-catenin, as assayed by Western analysis, resulted in the absence of the gut and an animalized phenotype including formation of ectopic, elongated apical tuft cilia. Similarly, over-expression of cadherin or beta-catenin coupled to the engrailed repressor, prevented gut formation. Thus, beta-catenin has a similar role in endoderm formation as it does in anthozoan cnidarians and echinoderms. Unlike the case in polychaete annelids and nematode embryos, we did not observe evidence for a role of beta-catenin in regulating asymmetric cell divisions along the anterior-posterior axis in Cerebratulus.
