FIG. 2.

Characterization of the βMHC-Cre transgenic line. βMHC-Cre mice were mated with CAG-CAT-Z reporter lines as indicated in the upper panel. LacZ expression was activated upon Cre-mediated excision of the floxed CAT gene in double transgenic embryos. Embryos at different developmental stages were stained in X-Gal solution. (A, B, and C) Whole-mount blue-stained embryos; (E, F, and G) high magnification of the cardiac region; (D and H) histological sections of E13.5 embryos. A dotted blue staining is observed in E9.25 embryos (A); the staining is increased considerably at E9.75 (E). At E10.5, blue staining remains restricted to the cardiac tissue mainly in the ventricles (B and E), whereas at E13.5 the staining extends to the atrial compartment (H), as well as to the dorsal, limb, and caudal muscles (C). At this stage, the trabeculations were most intensely stained (D and H).