Figure 5.

Summaries of the regenerative competence of the inner ear organs in response to Notch activation for lateral induction (A) and Notch inhibition for lateral inhibition (B). A) The ability to form ectopic sensory regions in response to Notch activation (NICD overexpression) is gradually lost embryonically and occurs in a similar development timeframe as the normal prosensory formation. With age, the competence of the otic cells is restricted to specific regions near the sensory organs until it is completely lost by E16.5. Overexpression of Sox2 at this same age, however, can induce ectopic sensory regions, though still only in specific areas. B) While supernumerary hair cells can be generated much later using Notch inhibition, each of the inner ear organs exhibits a declining competence for hair cell regeneration during postnatal maturation. In the cochlea and utricle, it appears that Notch signaling has no effect in adolescent mice without significant damage to the organs. However, with damage, each of the organs does appear to have a modest capacity for hair cell generation in the adult.