Fig. 3. Expression of WNT signalling pathway components in the mutant embryo. (A,B) Double in situ hybridization showing Dkk1 (orange) and Wnt3 (purple) expression domains. (A) At E6.5, the Dkk1 expression domain is juxtaposed to the Wnt3 domain. (B) At E7.25, the two domains become wider apart. (C-G') Wild-type (C-G) and Dkk1^-/- (C'-G') E7.0 embryos: the domain of Wnt3 (C,C') remain unchanged, but that of Wnt2b (D,D'; six out of six mutant embryos) and Wnt8a (E,E'; one out of three mutant embryos) are slightly expanded in Dkk1-null embryos. The expression domain of Sfrp1 (F,F') is reduced while that of Srfp5 (G,G') is unchanged. (H) The domain of Dkk1 expression becomes more restricted with the decrease in Wnt3 gene dose. (I) RT-PCR analysis of Dkk1 expression in NIH3T3 cells expressing lacZ, Wnt1,Wnt3a, Wnt4, Wnt5a, Wnt7a and Wnt11. -RT, no reverse transcription control; Hprt, loading control. (J) Reduced domain of Dkk1 expression in the Dkk1^+/-;Wnt3^+/- embryo, compared with Dkk1^+/+;Wnt3^+/+, Dkk1^+/+;Wnt3^+/- and Dkk1^+/-;Wnt3^+/+ embryos (top row, lateral view; bottom row, frontal view). In situ hybridization for H and J was performed under the same conditions so that the staining result can be compared among embryos of each set. Scale bar: 50 µm.