The precise morphology of the mechanosensitive hair bundle requires seamless integration of actin and microtubule networks. Here, we identify Acf7a as a protein positioned to bridge these distinct cytoskeletal networks in hair cells. By imaging Acf7a-Citrine fusion protein in zebrafish and immunolabeling of vestibular and cochlear mouse hair cells, we show that Acf7a and ACF7 circumscribe, underlie, and are interwoven into the cuticular plate (CP), and they also encircle the basal body of the kinocilium. In cochlear hair cells, ACF7 localization is graded, with the highest concentration near each fonticulus-an area free of F-actin in the region of the cuticular plate that contains the basal body. During hair-cell development and regeneration, Acf7a precedes formation of the hair bundle and CP. Finally, electron tomography demonstrates that the ends of microtubules insert into the CP and are decorated with filamentous linkers connecting microtubules to the CP. These observations are consistent with ACF7 being a linker protein, which may shape the hair cell's cytoskeleton early during hair-bundle genesis. This grant proposal further studies the role of this protien in hair bundle formation.
The hair cell is a mechanoreceptor of the inner ear and lateral line system, which is responsible for hearing, balance, and the detection of water movement by some aquatic vertebrates. We have identified a protein that may govern the formation of this intriguing structure called ACF7. In this grant we aim to understand the role of this protein in hearing.
