CYTOSKELETAL AND CALCIUM-BINDING PROTEINS IN THE MAMMALIAN ORGAN OF CORTI - CELL-TYPE-SPECIFIC PROTEINS DISPLAYING LONGITUDINAL AND RADIAL GRADIENTS

Whole mounts and tissue sections of the organ of Corti from two repres entative mammalian species, the Mongolian gerbil (Meriones unguiculatu s) and the guinea pig (Caven porcellus) were probed with antibodies to cytoskeletal and calcium-binding proteins (actin, tubulin, including post-translational modifications, spectrin, fimbrin, calmodulin, parva lbumin, calbindin, S-100 and calretinin). kll of the proteins tested w ere expressed in both species. New findings include the following. Act in is present in large accumulations in cell bodies of the Deiters cel ls under the outer hair cells (OHC), as well as in the filament networ ks previously described. These accumulations are more prominent in the apical turns. Tubulin is present in sensory cells in the tyrosinated (more dynamic) form, while tubulin in the supporting cells is post-tra nslationally modified, indicating greater stability. Fimbrin, present in the stereocilia of both IHCs and OHCs, is similar to the isoform of fimbrin found in the epithelial cells of the intestine (fimbrin-I), w hich implies that actin bundling by fimbrin is reduced in the presence of increased calcium. Parvalbumin appears to be an IHC-specific calci um-binding protein in the gerbil as well as in the guinea pig; labelin g displays a longitudinal gradient, with hair cells at the apex staini ng intensely and hair cells at the base staining weakly. Calbindin dis plays a similar longitudinal gradient, with staining intense in the IH Cs and OHCs at the apex and weak to absent in the base. In the middle turns of the guinea pig cochlea, OHCs in the first row near the pillar cells lose immunoreactivity to calbindin before those in the second a nd third rows. Calmodulin is found throughout the whole cochlea in the IHCs and OHCs in the stereocilia, cuticular plate, and cell body. Cal retinin is present in IHCs and Deiters cells in both species, as well as the tectal cell (modified Hensen cell) in the gerbil. S-100 is a su pporting cell-specific calcium-binding protein which has not been loca lized in the sensory cells of these two species. The supporting cells containing S-100 include the inner border, inner phalangeal, pillar, D eiters, tectal (in gerbil) and Hensen cells, where labeling displays a longitudinal gradient decreasing in intensity towards the apex (oppos ite to what has been seen with labeling for other proteins in the coch lea).