Fig. 1.

Timing of Cre expression and Ednra gene recombination in Wnt1-Cre and Hand2-Cre embryos. A–D. Lateral view of whole mount β-galactosidase (β-gal) staining in E8.5 (A, B) and E9.5 (C, D) R26R;Wnt1-Cre (A, C) and R26R;Hand2-Cre (B, D) embryos. A, B. In a 8.25–E8.5 R26R;Wnt1-Cre embryo, β-gal-labeled cells are observed between the midbrain/hindbrain and first pharyngeal arch (1; see also inset, A′). In an E8.5 R26R;Hand2-Cre embryo, β-gal labeled cells are observed in the heart (h) and lateral plate mesoderm but not arch 1 (see also inset, B′). C, D. At E9.5, labeled cells are observed in pharyngeal arches 1–3 of a R26R;Wnt1-Cre embryo (C) and arches 1 and 2 of a R26R;Hand2-Cre embryo (D). E, F. PCR that specifically detects recombination of the Ednra^fl allele was performed on DNA isolated from the rostral (R) and caudal (C) halves of E8.5 Ednra^fl/fl;Wnt1-Cre and Ednra^fl/fl;Hand2-Cre embryos bisected along the plane denoted by the line marked “1” (E) (see Materials and methods for details). Recombination of the Ednra^fl allele correlates with sites of β-gal staining in R26R;Wnt1-Cre and R26R;Hand2-Cre embryos. Recombination in Ednra^fl/fl;Wnt1-Cre embryos is observed in the posterior half (including the first arch) when the cut line is moved rostral to the first arch (line 2 in E). a, atrium; lb, limb bud; v, ventricle.