@article {Schippers164012, author = {Klaske J. Schippers and Scott A. Nichols}, title = {β-catenin has both conserved and novel functions in the sponge Ephydatia muelleri}, elocation-id = {164012}, year = {2017}, doi = {10.1101/164012}, publisher = {Cold Spring Harbor Laboratory}, abstract = {β-catenin acts as a transcriptional co-activator in the Wnt/β-catenin signaling pathway and a cytoplasmic effector in cadherin-based cell adhesion. These functions are ancient within animals, but the earliest steps in β-catenin evolution remain unresolved due to limited data from key lineages -- sponges, ctenophores and placozoans. Previous studies in sponges have characterized β-catenin expression dynamics and have ectopically activated the Wnt pathway through pharmacological inhibition of GSK3β, a negative regulator of β-catenin. However, both approaches rely upon untested assumptions about the conservation of β-catenin function and regulation in sponges. Here, we test these assumptions using a custom antibody raised against β-catenin from the sponge Ephydatia muelleri. We find that cadherin-complex genes coprecipitate with Emβcatenin from endogenous cell lysates, but that Wnt pathway components do not. However, through immunostaining we detect both cell boundary and nuclear populations, and we find evidence that Emβcatenin is a conserved substrate of GSK3β. Collectively, these data support the conservation of Emβcatenin in adhesion and signaling. In addition to its conserved functions shared with bilaterians, we also find evidence for an entirely novel Emβcatenin function. Emβcatenin localizes to the distal ends of F-actin stress fibers in focal adhesion-like structures (typically integrin-based adhesions) in the substrate-attachment epithelium. This finding suggests a fundamental difference in β-catenin function and in the cell adhesion mechanisms operating in sponge versus bilaterian tissues.}, URL = {https://www.biorxiv.org/content/early/2017/07/15/164012}, eprint = {https://www.biorxiv.org/content/early/2017/07/15/164012.full.pdf}, journal = {bioRxiv} }