A temporospatial map of adhesive molecules in the organ of Corti of the mouse cochlea

In the nervous system, several classes of cell-surface and extracellular ma trix molecules have been implicated in processes such as neural growth, fas ciculation, pathfinding, target recognition and synaptogenesis, which requi re cell-to-cell or cell-to-substrate binding. In the developing mouse cochl ea, little is known about the types of cell-surface and extracellular matri x molecules existing along the neural growth paths or their possible roles in development. Whole mount and sectioned cochlear tissue were immunolabele d for six different adhesive molecules - neural cell adhesion molecule (NCA M), polysialic acid (PSA), neural cell adhesion molecule L1, E-cadherin, sy ndecan-1 and tenascin-C. A temporospatial map of adhesive molecule distribu tion in the basal turns of the mouse cochlea was generated. Distributions o f adhesive molecules were compared to each other and to the known progress of neural development in the region. This comparison demonstrated differenc es in the complements of adhesive molecules between the inner and outer hai r cell regions, and variations in the expressions of adhesion molecules amo ng different types of nerve fibers. In addition, developmental changes in t he adhesive environment around and beneath the outer hair cells coincided w ith the known timing of the appearance of morphologically defined efferent synapses. These observations raise the possibility that molecular differenc es at the cell surface of inner and outer hair cells are one way that ingro wing neurites distinguish different environments to determine their growth routes and synaptic partners in the cochlea. In addition these observations demonstrate the potential for differential signaling of afferent and effer ent innervation by altering the microenvironments in which synapses are for med.