POSTTRANSLATIONAL MODIFICATIONS OF TUBULIN SUGGEST THAT DYNAMIC MICROTUBULES ARE PRESENT IN SENSORY CELLS AND STABLE MICROTUBULES ARE PRESENT IN SUPPORTING CELLS OF THE MAMMALIAN COCHLEA

Post-translational modifications to tubulin in the sensory and support ing cells of the cochlea were studied using antibodies specific to the tyrosinated, detyrosinated, acetylated and polyglutamylated isoforms. In the sensory cells, microtubules which label intensely with antibod ies to tyrosinated tubulin are found in networks within the cytoplasm. Microtubules which label with antibodies to detyrosinated tubulin and polyglutamylated tubulin, but not acetylated tubulin, form a small co mponent of the microtubules found in the cytoplasm only in the region below the cuticular plate. Microtubules in the supporting cells (inner and outer pillar cells and Deiters cells) are arranged in bundles and contain little tyrosinated tubulin. They are composed instead of pred ominantly post-translationally modified isoforms which include detyros inated, acetylated and polyglutamylated tubulin. The findings suggest that microtubules in the sensory cells form dynamic structures, since microtubules that undergo cyclic polymerization and depolymerization p redominantly contain tubulin that has not yet had its carboxy-terminal tyrosine residue removed. The presence of microtubules in the support ing cells in which the tubulin has been polymerized into microtubules long enough to be post-translationally modified, provides evidence tha t these microtubules are stable, long-lived and could contribute to th e structural support of the sensory organ of Corti.