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J Neurosci. 2014 Jan 1;34(1):305-12. doi: 10.1523/JNEUROSCI.1880-13.2014.

ACF7 is a hair-bundle antecedent, positioned to integrate cuticular plate actin and somatic tubulin.

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Departments of Otolaryngology-Head and Neck Surgery, Biology, Genetics and Genome Sciences, and Neurosciences, Case Western Reserve University, Cleveland, Ohio 44016, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10065.


The precise morphology of the mechanosensitive hair bundle requires seamless integration of actin and microtubule networks. Here, we identify Acf7a (actin crosslinking family protein 7a) 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 CP 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 cytoskeleton of the hair cell early during hair-bundle genesis.


actin; hair cell; hearing; mechanotransduction; microtubule; zebrafish

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