Figure 4. Wnt/β-catenin signaling regulates Smad1 activation.

High-density undifferentiated human ES cells were treated with activin A for 24 hours followed by BMP4 or BMP4 plus Dkk1. Lane marked as “pre” indicates cells collected prior to cytokine treatment. Western blot shows probing for C-terminal phosphorylated Smad1 (p-Smad1) and total Smad1 at 30 m, 1 h, 2 h and 3 h following BMP4. Densitometry data are presented as phosphorylated Smad1 normalized to total Smad1 relative to pretreated cultures. Treatment with BMP4 increased phosphorylation of Smad1, which was reduced by inhibition of canonical Wnt signaling with Dkk1.