Fig. 4. BMP4 induces cardiac gene expression and blocks skeletal muscle differentiation in vivo. (A) Dorsal view of a stage 9 embryo, implanted with cells expressing HA-BMP4 (dashed circle). (B) Western blot analysis of HA-tagged BMP4 in the conditioned medium of the transfected cells. (C-H) In situ hybridization analyses for the indicated genes. Whole-mount and transverse sections of the embryos are shown (left panel, control; right panel, Bmp4 treated). Induction (white arrowhead) or reduction (open arrowhead) of the expression of cardiac and skeletal muscle markers following BMP4 application is indicated. Ectopically-applied Bmp4 induced expression of the cardiac markers Nkx2.5 (n=7/7), Gata5 (n=7/14) and Capsulin (n=5/6). By contrast, BMP4 cells blocked the expression of the skeletal markers Myf5 (n=4/4) and Tbx1 (n=3/4). A dual effect was observed for Isl1: although Bmp4 abolished the expression of Isl1 in the trigeminal ganglion (V), an elevated expression of this gene was found in the mesenchyme and ectoderm of the first BA (n=7/7). as, aortic sac; ba1, ba2, first, second branchial arches; lr, lateral rectus; nt, neural tube.