Fig. 6. Maturation of the ureteric tree in the Foxd1 null is defective. At E18.5 in HoxB7^GFP/+;Foxd1^+/+ kidneys, branches of the ureteric bud (ub) have bifurcated numerous times (A). In HoxB7^GFP/+;Foxd1^lacZ/lacZ (B) the branches elongate but bifurcate very infrequently. Ret expression at E14.5 in wild-type whole-mount tissue (C) is limited to the tips, but has a wider distribution in the mutant (D). This result was confirmed in thin sections (E,F). Higher magnification of the bracketed regions in E and F reveals that wild-type (E') displays strong diminishment of expression in the cleft (arrowhead) of the UB, where there is no condensed mesenchyme, but the Foxd1-null (F') displays strong expression throughout this region of the UB. However, there is no detectable Ret expression in the region of the UB that is not in contact with the condensed mesenchyme (arrowheads). cm, condensed mesenchyme. Scale bar: 75 µm in A-D; 50 µm in E,F; 25 µm in E',F'.