Staurosporine-induced collapse of cochlear hair bundles.
Bottom Line: Staurosporine exposure results in the fusion of the hair bundle's stereocilia, a resorption of the parallel actin bundles of the stereocilia into the cytoplasm of the hair cell, a detachment of the apical, non-stereociliary membrane of the hair cell from the underlying cuticular plate, and a severing of the hair-bundle's rootlets from the actin cores of the stereocilia.It does not block membrane retrieval at the apical pole of the hair cells, nor does it elicit the externalization of phosphatidylserine.Staurosporine treatment causes a reduction in levels of the phosphorylated forms of ezrin, radixin, and moesin in cochlear cultures during the period of hair-bundle loss, indicating the integrity of the hair bundle may be actively maintained by the phosphorylation status of these proteins.
Affiliation: Sussex Neuroscience and School of Life Sciences, University of Sussex, Brighton, BN1 9QG, UK.Show MeSH
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Mentions: Transmission electron microscopy revealed that staurosporine caused the stereociliary rootlets to become thinned or even severed from their associated stereocilia (Fig. 5A–F). Furthermore, the apical plasma membrane was detached from the underlying cuticular plate and numerous vesicles and other cellular components were observed between the hair-cell surface and the severed end of the rootlets (Fig. 5A–F). To determine if the vesicles observed in this region were involved in apical membrane turnover, cultures were labeled with cationic ferritin during treatment with staurosporine. Numerous ferritin-labeled vesicles were observed in the region where the apical membrane had detached from the cuticular plate (Fig. 5E,F). Cationic ferritin-labeled vesicles were also present, as in control cultures, in the region of the pericuticular necklace in staurosporine-treated cultures (not shown). The observed increase in cationic ferritin-labeled vesicles in the region of cuticular plate detachment suggests that this structure may normally restrict membrane retrieval to the more peripheral regions of the hair cell’s apical surface.
Affiliation: Sussex Neuroscience and School of Life Sciences, University of Sussex, Brighton, BN1 9QG, UK.