Figure 1.

Expression of Bmp4 during cardiogenesis. (a-e) Embryonic hearts of Bmp4^lacZ/+ embryos on ICR background were collected at stages labeled in each panel, and were stained with X-gal. In the Bmp4^lacZ allele, the lacZ reporter gene was knocked into the Bmp4 locus, and lacZ expression faithfully recapitulates endogenous Bmp4 transcription in Bmp4^lacZ/+ embryos. (f-o) Transverse sections of whole embryos (f-g) or frontal sections of hearts (h-o) after whole-mount X-gal staining. All sections were counterstained with eosin. In addition to expression in the muscle layer of the OT (g,j,l,n,o) in cardiomyocytes overlying the IEC (f,h) and in muscular portions of ASP (i,k) described in the text, positive signals were also detected in the mesenchyme of the truncus cushion at E10.5 (green arrowhead in j), in the dorsal wall of the atrium (f,h,i), in venous valves (i,k), and in the annulus of mitral and tricuspid valves (m). The Bmp4 expression pattern was confirmed with in situ hybridization analysis (data not shown). (at) Aorta trunk; (ca) common atrium; (la) left atrium; (lv) left ventricle; (nb) newborn; (ot) outflow tract; (pt) pulmonary trunk; (ra) right atrium; (rv) right ventricle; (vv) venous valve; (^*) AV endocardial cushions; (black arrow) atrial septum primum. Bars, 0.2 mm.