FIG. 3.

Verification of the efficiency of Smad7^Cre-mediated genetic ablation. R26r lacZ reporter mice were crossed with Smad7^Cre mice and the double transgenics were then bred to R26^DTA mice, to enable us to visualize in triple transgenic wholemounts how penetrant the genetic cell ablation was. (a,b) E10.5 wholemount lacZ staining of Smad7^Cre;R26^DTA;R26r (a) and control Smad7^Cre;R26r only (b) littermates, revealed that most of the lacZ-expressing cells had been ablated in triple transgenic mutants when compared to the extensive lacZ expression observed in control Smad7^Cre;R26r littermates. (c,d) Higher magnification of cardiovascular and branchial arch regions in embryos shown in a and b. Note that in triple mutant transgenic embryos (c), a few lacZ-expressing cells can still be detected within the arches, ventricles, and limb buds (l), although in extremely low numbers when compared with the littermate controls (d). Arrows indicate the ectodermal pouches and asterisks indicate the AV canal.