Meeting Abstract

99.4  Monday, Jan. 6 14:15  Selective nuclearization of beta-catenin is sufficient to induce formation of a normal pluteus embryo from ectodermal precursors BYRUM, CA*; WIKRAMANAYAKE, AH; College of Charleston, Charleston, SC; University of Miami, Miami, FL byrumc@cofc.edu

In metazoans, canonical Wnt signaling is critical for formation of the primary body axis. Translocation of beta-catenin to the nucleus during Wnt signaling activates the production of posterior structures whereas repression of this pathway allows formation of anterior structures. In the 16-cell stage sea urchin embryo, nuclear accumulation of beta-catenin in the micromeres is known to trigger a signaling cascade that defines the primary body axis and causes subsequent specification of the endomesoderm. At this stage, transplanting micromeres to the animal pole induces formation of ectopic endomesoderm in the mesomeres, cells which normally give rise to ectodermal derivatives, via a cell non-autonomous process. To test whether activation of the canonical Wnt pathway is sufficient to impart organizer-like abilities to blastomeres that do not have overt signaling capacity, we overexpressed a constitutively active form of beta-catenin in a pair of mesomeres and recombined them with an isolated animal half at the 16-cell stage. We found that nuclear beta-catenin was sufficient to convert the injected mesomeres into an organizer-like signaling center. Chimeras exhibited normal patterning of the body plan, and nuclear accumulation of beta-catenin had both cell autonomous and cell non-autonomous effects on the specification of cell fates. Furthermore, these results support the hypothesis that a shift in the location of canonical Wnt signaling during early embryogenesis could have contributed to modifications in polarity of the main body axes during metazoan evolution.