E Hh reporter assay of the activity of wild type and mutant forms of mSmo in Smo-/- MEFs in response to Shh or SAG stimulation. Note that mSmoA1 shows constitutive activity in the absence of either Shh or SAG whereas mSmoKRA dose not; all mutants affecting phosphorylation failed to restore the response to Shh or SAG. Data represent the mean and ± SD (n=3). Unpaired Students t-test was used for analysis. ****P<0.0001; **P<0.01; and n.s. (not significant). 