Figure 2. Dynamic expression of BMP4 in the pharyngeal arches. (A) In situ hybridization on frontal sections at E10.5 showing BMP4 expression in the oral epithelium of the first arch (mandibular and maxillary processes). Expression is also seen in the midline at the position of the developing heart. (B) Sagittal view at E11.5 showing BMP4 expression in the first-arch oral mesenchyme. Again, BMP4 expression is restricted to the first arch. Scale bar: 100 µm.