Live-cell imaging of actin dynamics reveals mechanisms of stereocilia length regulation in the inner ear

Nat Commun. 2015 Apr 21;6:6873. doi: 10.1038/ncomms7873.

Abstract

The 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 (15)N-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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actins / physiology*
  • Animals
  • Biological Transport
  • Ear, Inner / cytology*
  • Green Fluorescent Proteins
  • Humans
  • Leucine / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mutation
  • Staining and Labeling
  • Stereocilia / physiology*
  • Transfection

Substances

  • Actins
  • Green Fluorescent Proteins
  • Leucine