Mesenchymal/epithelial induction mediates olfactory pathway formation

In the olfactory pathway, as in the limbs, branchial arches, and heart, mes enchymal/epithelial induction, mediated by retinoic acid (RA), FGF8, sonic hedgehog (shh), and the BMPs, defines patterning, morphogenesis, and differ entiation. Neuronal differentiation in the olfactory epithelium and directe d growth of axons in the nascent olfactory nerve depend critically upon thi s inductive interaction. When RA, FGF8, shh, or BMP signaling is disrupted, distinct aspects of olfactory pathway patterning and differentiation are c ompromised. Thus, a cellular and molecular mechanism that facilitates muscu loskeletal and vascular development elsewhere in the embryo has been adapte d to guide the differentiation of the olfactory pathway in the developing f orebrain.