Fig. 6. Absence of localized expression of mammary placode markers in induced K5-rtTA, tetO-Dkk1 embryos and presence of mammary rudiments in Wnt5a-null embryos. (A-P) K5-rtTA, tetO-Dkk1 double transgenic (DT) (B,D,F,H,J,L,N,P) and single transgenic (ST) control littermate (A,C,E,G,I,K,M,O) embryos that were doxycyline-treated throughout gestation, harvested at E12.5 (A-J), E11.75 (K,L), E11.5 (M,N) and E10.5 (O,P), and subjected to whole-mount in-situ hybridization with the probes indicated. Control E12.5 and E11.75 embryos show discrete upregulation of ß-catenin (A), Wnt10b (C), Krm2 (I) and Tbx3 (K) in mammary buds (A,C,I) and placodes (K). Limbs were removed from the embryo in A to show all five buds on the left side. Localized expression of all of these genes is absent from the mammary region of induced K5-rtTA, tetO-Dkk1 double transgenic littermates (B,D,J,L). Wnt11 is weakly expressed in ring shapes around the buds of control (G) (blue arrows) but not Dkk1-expressing (H) embryos. Weak expression of Wnt11 in a broad stripe of mesenchyme is present in both control and Dkk1-expressing embryos (G,H, yellow arrows). Expression of Wnt5a in mammary region mesenchyme is unaffected by ectopic Dkk1 (E,F) (arrows). Upregulated Wnt10b expression is first apparent in the mammary line of controls at E11.5 (M, arrow), and is absent in the induced K5-rtTA, tetO-Dkk1 double transgenic littermate (N). Fgf10 is expressed in somites of doxycyline-treated control and K5-rtTA, tetO-Dkk1 double transgenic littermates at E10.5 (O,P, arrows). (Q,R) Transverse hematoxylin and eosin-stained paraffin sections of E15.5 Wnt5a^+/– control (Q) and Wnt5a^–/– (R) female embryos showing thoracic mammary rudiments (arrows). (S,T) Wnt10b expression in mammary buds of Wnt5a^+/– (S) and Wnt5a^–/– (T) E12.5 embryos (arrows).