The cnidarian and the canon: the role of Wnt/beta-catenin signaling in the evolution of metazoan embryos.
In a recent publication, Wikramanayake and colleagues have implicated the canonical Wnt/beta-catenin signaling pathway as a mediator of axial polarity and germ-layer specification in embryos of the cnidarian Nematostella. In this anthozoan, beta-catenin is localized in nuclei of blastomeres in one region of the 16- to 32-cell embryo whose descendants subsequently form the entoderm of the embryo. They claim that the pattern of nuclear localization is significant for two reasons: (1) when nuclear localization of beta-catenin was inhibited, gastrulation does not occur, and (2) when localization of beta-catenin took place in all cells of the pregastrula embryo, the number of entodermal cells increases. Since the Wnt/beta-catenin signaling pathway also plays a role in establishing axial polarity and specifying endoderm and mesoderm in a number of bilaterians, Wikramanayake et al. imply that this developmental mechanism is an evolutionary inheritance from a radially symmetrical ancestor. Some of the gaps in the current evidence, which must be filled to evaluate their interpretation, are discussed.
Primus
Alex
A
Section of Integrative Biology, University of Texas, Austin, TX 78712, USA. primus_alexander@mail.utexas.edu
Freeman
Gary
G
D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D003063:Cnidaria / Q000033:anatomy & histology / Q000196:embryology* / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D009024:Morphogenesis; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D051153:Wnt Proteins; D051176:beta Catenin
D003598:Cytoskeletal Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D051153:Wnt Proteins; D051176:beta Catenin