Figure 6: Tip turnover model summarizing actin incorporation and regulation.

(a) Green represents the regions where β-actin-GFP localized when expression was induced in mature auditory hair cells. The tallest row of stereocilia incorporated a uniform level of β-actin-GFP in each member of the row, while in shorter rows, some individual stereocilia incorporated markedly more β-actin-GFP. (b) Some individual stereocilia in the shorter rows of the bundle were shorter than their neighbours when hair cells lacked ADF or expressed mutant AIP1. We suggest a model in which individual stereocilia stochastically shorten and then require ADF and AIP1 to sever actin filaments, which exposes free barbed ends where new actin polymerization can drive regrowth.