Interactions between epithelial and mesenchymal tissues often control the initiation of chondrogenic differentiation during embryonic development. In developing vertebrae, for example, somatic mesenchyme becomes chondrogenic in response to inductive influences from the notochord and neural tube

The otic capsule initially appears as condensations of mesenchyme around the developing otocyst, and serves as a template for the subsequent formation of the endochondral bony labyrinth of the inner ear. While it has long been known that the epithelial otocyst influences the induction and chondrogenic differentiation of the otic capsule, factors involved in epithelial control of otic capsule chondrogenesis have only recently been identified. This review discusses members of the fibroblast growth factor (FGF), transforming growth factorbeta (TGFß), and bone morphogenetic protein (BMP) families, and summarizes their roles in guiding the induction and cytodifferentiation of the otic capsule of the inner ear from periotic mesenchyme. The implications of this research to otosclerosis, a disease affecting the capsule of the inner ear, are discussed.