Organogenesis and pattern formation in the mouse: RNA distribution patterns suggest a role for bone morphogenetic protein-2A (BMP-2A).

Bone morphogenetic protein-2A (BMP-2A) is a member of the transforming growth factor beta (TGF beta) gene family that has been implicated in cartilage and bone formation. Here we use in situ hybridization to show that BMP-2A RNA is expressed in a variety of embryonic epithelial and mesenchymal tissues outside of the developing skeletal system, including cell populations known to play important roles in morphogenesis. Thus, high levels of transcripts are found in developing limb buds (ventral ectoderm and apical ectodermal ridge), heart (myocardium of the atrioventricular canal), whisker follicles (ectodermal placodes, hair matrix and precortex cells), tooth buds (epithelial buds, dental papilla and odontoblasts), and craniofacial mesenchyme, as well as a number of other sites. The expression patterns of BMP-2A are different from those of TGF beta-1, -2 and -3, and this is illustrated in detail in the developing whisker follicles. These results suggest that BMP-2A plays multiple roles in morphogenesis and pattern formation in the vertebrate embryo.