WNT ligands stimulate transient signaling in human pluripotent cells and synergize with TGF-β ligands to stimulate sustained signaling during differentiation
WNT/{beta}-catenin signaling is crucial to all stages of life. It controls early morphogenetic events in embryos, maintains stem-cell niches in adults, and is disregulated in many types of cancer. Despite its ubiquity, little is known about the dynamics of signal transduction or whether it varies across contexts. Here we probe the dynamics of signaling by monitoring nuclear accumulation of {beta}-catenin, the primary transducer of canonical WNT signals, using quantitative live-cell imaging. We show that {beta}-catenin signaling responds adaptively to constant WNT signaling in pluripotent stem cells, and that these dynamics become sustained upon differentiation. Varying dynamics were also observed in the response to WNT in commonly used mammalian cell-lines. Signal attenuation in pluripotent cells is controlled by both intra- and extra-cellular negative regulation of WNT signaling. TGF{beta}-superfamily ligands Activin and BMP, which coordinate with WNT signaling to pattern the gastrula, increase the {beta}-catenin response in a manner independent of their ability to induce new WNT-ligand production. Our results reveal how variables external to the pathway, including differentiation status and crosstalk with other pathways, dramatically alter WNT/{beta}-catenin dynamics.