Drummond, Meghan C.Barzik, MelanieBird, Jonathan E.Zhang, Duan-SunLechene, ClaudeCorey, DavidCunningham, Lisa L.Friedman, Thomas B.2015-06-022015Drummond, Meghan C., Melanie Barzik, Jonathan E. Bird, Duan-Sun Zhang, Claude P. Lechene, David P. Corey, Lisa L. Cunningham, and Thomas B. Friedman. 2015. “Live-cell imaging of actin dynamics reveals mechanisms of stereocilia length regulation in the inner ear.” Nature Communications 6 (1): 6873. doi:10.1038/ncomms7873. http://dx.doi.org/10.1038/ncomms7873.2041-1723http://nrs.harvard.edu/urn-3:HUL.InstRepos:16121063The maintenance of sensory hair cell stereocilia is critical for lifelong hearing; however, mechanisms of structural homeostasis remain poorly understood. Conflicting models propose that stereocilia F-actin cores are either continually renewed every 24–48 h via a treadmill or are stable, exceptionally long-lived structures. Here to distinguish between these models, we perform an unbiased survey of stereocilia actin dynamics in more than 500 utricle hair cells. Live-imaging EGFP-β-actin or dendra2-β-actin reveal stable F-actin cores with turnover and elongation restricted to stereocilia tips. Fixed-cell microscopy of wild-type and mutant β-actin demonstrates that incorporation of actin monomers into filaments is required for localization to stereocilia tips. Multi-isotope imaging mass spectrometry and live imaging of single differentiating hair cells capture stereociliogenesis and explain uniform incorporation of 15N-labelled protein and EGFP-β-actin into nascent stereocilia. Collectively, our analyses support a model in which stereocilia actin cores are stable structures that incorporate new F-actin only at the distal tips.en-USJournal Article2015-06-0210.1038/ncomms7873