Many genes are turned off by chemical modifications (epigenetic marks) that prevent activation of the gene. One hypothesis is that mammals cannot activate a hair cell regeneration program after the first few postnatal days because the responsible genes have been epigenetically silenced. This second-year project looks at these epigenetic marks in the ear for every gene, during both early and late development. The investigators will use this analysis to find candidate promoter regions, which control gene activity. Preliminary data support the idea that supporting cells turn off expression of key hair cell genes (e.g., Atoh1), and so a plausible approach to triggering regeneration in the mammalian ear is to reverse such changes.