Cytoskeletal Network of Intermediate Filament Proteins in the Adult Human Vestibular Labyrinth

The cytoskeleton of adult human vestibular hair cells lacks intermediate filament (IF) proteins, whereas in fetal material immunoreactivity for cytokeratin (cks; a subclass of IFs) occurs in both types of hair cells. The shift in the cytoskeletal composition can be hypothesized to their onset of physiological function. Since the IFs are extremely rigid intracellular structures, they provide considerable mechanical stability. The entire cytoplasm of all supporting cells in the epithelial lining of all five vestibular organs is filled with cks. In this way most vestibular hair cells become compartmentalized, each with a rigid shell surrounding it. The distinct delineation of IF proteins in adult tissues, in contrast to fetal inner ear organs in which often a rather general cytoplasmic expression occurs, probably reflects their anatomical basis for their function.