- Development of the inner ear: This starts out with the induction of the otic placode and consists of 3 major stages
1. Pre-placodal domain: After gastrulation, a pre-placodal domain is present adjacent to the anterior neural plate. The various placodes will arise from this domain.
2. Pre-otic field: Local signals establish the identity of each placode, including the otic placode. FGF signals from both rhombomeres and the cranial paraxial mesoderm are important otic inducers.
3. Otic placode/epidermis fate decision: signalling occurs to determine precisely which cells become the otic placode and which cells aquire the epidermal fate. FGF and Wnt signalling is necessary in this step, which could possibly be dependent or independent of each other.
- Neural component: During the early stages of embryonic development, a neural competent domain is established as part of the otic placode. FGF, Sox and Notch signalling play a role in creating and maintaining this domain. Once invagination occurs and an otocyst has formed, signalling pathways allow for patterning of the otocyst and formation of prosensory patches. Hair cells develop from the sensory patches and neurons develop from the remaining neural competent domain.
- Establishing polarity and formation of inner ear structures: The ventral inner ear consists of the cochlea and saccule, and the dorsal inner ear is made up of semicircular canals, endolymphatic duct, cristae and utricle. For this reason, it is important for normal development of the inner ear to establish polarity, such as the dorso-ventral axis. Various signals are involved, including Shh and Wnt signalling. Hedgehog signalling needs to be suppressed.