Polysialic acid in the cochlea of the developing mouse

Polysialic acid (PSA), an unusual molecule covalently attached to the neural cell adhesion molecule, NCAM, has been shown to regulate cell-to-cell and cell-to-matrix interactions by interfering with the binding of cell-surface adhesion molecules. We used immunocytochemistry to map the temporospatial distribution of PSA in the mouse cochlea between embryonic day 16 and postnatal day 32 and compared it to the known timetable of neural growth and development. Polysialic acid immunoreactivity develops along a temporospatial gradient beginning in the basal turn and progressing to the apical turn. The expression is transitory on spiral ganglion neurons, intraganglionic bundles, radial bundles, and outer hair cells. Immunoreactivity diminishes progressively from the basal turn to the apical turn. Immunolabeling is maintained to adulthood on fibers in the inner spiral and inner pillar bundles, bundles which have been suggested to sprout continually and grow even in older animals. Inner hair cells are never immunolabeled. The temporo-spatial expression of PSA suggests its involvement in neural growth, whereas its extinction correlates with the time of onset of nerve-receptor interactions.