Fig. 8. A model for a genetic pathway integrating Msx1, Bmp4, Shh and Bmp2 in the epithelial-mesenchymal interactions that regulate mammalian palatogenesis. In this model, it is proposed that in the anterior palatal shelves, mesenchymally expressed Msx1, which can be induced by Bmp4, is required for Bmp4 expression in the palatal mesenchyme. Mesenchymally expressed BMP4 maintains Shh expression in the MEE and Shh in turn induces Bmp2 expression in the mesenchyme. BMP2 functions to induce cell proliferation in the palatal mesenchyme, which leads to palatal growth.