Biliary ducts or sorted Lgr5-LacZ+ cells were isolated, mixed with Matrigel (BD Bioscience) and cultured as described in ref. 2 (link). Medium composition was AdDMEM/F12 (Invitrogen) supplemented with B27 and N2 (Invitrogen), N-Acetylcysteine (1.25 μM, Sigma), gastrin (10 nM, Sigma), EGF (50 ng/ml, Peprotech), 10% RSPO1 Conditioned Medium (kindly provided by Calvin Kuo), FGF10 (100 ng/ml, Peprotech), nicotinamide (10 mM, Sigma) and HGF (50 ng/ml, Peprotech). Detailed protocols are provided in Supplementary Methods.