Meeting Abstract
The discovery of conserved homologs of the Wnt/beta-catenin pathway in sponges (one of the earliest branching metazoan lineages) raised questions about whether a functional Wnt/beta-catenin pathway is present in sponges and what its role may be in organisms of such relative simplicity. To gain more insight in the role of beta-catenin in sponges, we identified tissue-specific and subcellular localization patterns of beta-catenin by performing immunostaining using a peptide antibody against beta- catenin of the freshwater sponge Ephydatia muelleri. The sponge body plan is composed of two primary tissues, the pinacoderm (outer epithelium) and the choanoderm (composed of choanoflagellate-like cells) that pumps water through a water canal system used for feeding and respiration. The area between these two tissues is called the mesohyl and is composed of ECM, spicules and migratory mesenchymal cells called archaeocytes. Our immunostaining data show that beta-catenin is detected in the nuclei of mesenchymal cells and pinacoderm cells, suggesting a conserved role as a transcription factor, possibly part of the Wnt pathway. We also observed staining at cell boundaries of the pinacoderm, which is consistent with a role in cell-cell adhesion. Staining was not detected in cell boundaries of the choanoderm, which could indicate this “ancient” tissue does not use cadherin/catenin adhesion mechanisms. To further test the role of beta- catenin in sponges, we will use Co-IP to identify binding partners of beta-catenin; Chip-sequencing to identify target genes that are regulated by the beta-catenin/TCF transcriptional complex; and develop techniques for studying gene function in vivo in sponges, so we can silence or overexpress beta-catenin in vivo.
