F-actin in the cuticular plate and junctions of auditory hair cells is regulated by ADF and cofilin to allow for normal stereocilia bundle patterning and maintenance

Auditory hair cells, which convert sound-induced vibrations in the inner ear into neural signals, depend on multiple actin populations for normal function. Stereocilia are mechanosensory protrusions formed around a core of linear, crosslinked F-actin. They are anchored in the cuticular plate, which predominantly consists of randomly oriented actin filaments. A third actin population is found near hair cell junctions, consisting of both parallel and branched filaments. Actin depolymerizing factor (ADF) and cofilin-1 (CFL1) proteins disassemble actin filaments and are required to regulate F-actin in stereocilia, but their effect on cuticular plate and junctional actin populations is unclear. Here, we show that loss of ADF and CFL1 disrupts the patterning of stereocilia into orderly bundles and that this phenotype correlates with defective development of the cuticular plate and junctional actin populations. ADF/CFL1 continue to regulate these actin populations in mature cells, which is necessary for long-term maintenance of hair cell morphology.