The canonical Wnt signaling pathway. Drugs used in epistasis experiments are indicated (red). C59 is a porcupine inhibitor that suppresses Wnt secretion, XAV939 is a tankyrase inhibitor that stabilizes the destruction complex, LiCl and CT99021 are inhibitors of GSK3β, valproic acid (VPA) is an activator of β-catenin-dependent transcription, and iCRT14 inhibits β-catenin-dependent transcription. TCF/LEF, T cell factor/lymphoid enhancer factor; LRP, low-density lipoprotein receptor-related protein.