TCF-reporter TOP-flash assay performed on the indicated cell lines treated with 10 μM CHIR, for 24 hrs. The control FOP-flash reporter is not activated upon CHIR administration. The data represent the mean ± s.e.m. of averages of nine independent experiments (N = 9). dBcat, β-catenin knockout cells; d4TCF, TCF/LEF quadruple knockout cells Transfection of individual TCF-expressing plasmids could restore the ability of d4TCF cells to respond to Wnt3 as measured in a TOP-flash assa 