Bone morphogenetic protein-2 and -4 expression during murine orofacial development

In the developing orofacial region, epithelial-mesenchymal interactions induce a differentiation cascade leading to bone and cartilage formation. Although the nature of this interaction is unknown, bone morphogenetic proteins (BMP)-2 and -4 have been suggested as putative signalling molecules. Using 35S-labelled cDNA probes, the expression patterns of BMP-2 and -4 mRNA were examined in murine perioral tissues preceding, during and following the time of the epithelial-mesenchymal interaction leading to mandibular formation. At embryonic age (E) 9.5 days, a restricted pattern of BMP-4 mRNA was expressed in the epithelium of the developing facial processes. This decreased rapidly, with little or no signal on E10.5 or E11.5. By E13.5, BMP-4 signal was restricted to the dental lamina, follicle and papilla. BMP-2 expression was not prominent in the developing face until E13.5. At this stage, signal was widespread throughout mesenchyme of neural-crest, but not somatic origin. Different domains of expression were present in the developing epithelium: for example, there was strong signal in the floor of the mouth and the ventral tongue, in contrast to that of the dorsum of the tongue and primary palate, which were negative. These results support the role of BMP-2 and -4 as regulators of orofacial development and demonstrates different fields of BMP-2 expression in developing oral mucosal epithelium.