npg Fused dimerization transduces Hedgehog signal 1440 Figure 2 The binding regions of Smo with Cos2 and Fu in the absence or presence of Hh. (A) S2 cells were transfected with Smo-CFPC and Cos2-YFPC with control RNAi and Fu, or the endogenous Fu knocked down by dsRNA in the absence or presence of Hh. (B) S2 cells were transfected with Smo-CFPC and Fu-YFPN with control RNAi and Cos2, or the endogenous Cos2 was knocked down by dsRNAi in the absence or presence of Hh. Then, the co-localization of Smo with Cos2 (A) or Fu (B) was examined. (A′) Quantification of Smo co-localized with Cos2 by using dsRNA of Fu to knockdown endogenous Fu. (B′) Quantification of Smo co-localized with Fu by using dsRNA of Cos2 to knockdown endogenous Cos2. (C, D) S2 cells were transfected with indicated Smo mutant constructs and Fu construct with endogenous Cos2 knocked down (C), or Cos2 con- struct with endogenous Fu knocked down (D), treated with or without Hh, respectively. (E) FRET efficiency from the indicated constructs in S2 cells treated with or without Hh (mean ± sd, n ≥ 15). Cell Research | Vol 21 No 10 | October 2011