Expression of the major basement membrane-associated proteins during postnatal development in the murine cochleae

The major basement membrane-associated proteins, including laminin-1, fibronectin, heparan sulfate proteoglycan (HSP), and entactin, were examined by immunofluorescence microscopy during postnatal development of the mouse cochlea. Samples were collected every 2 days through 8 days, and again at 14 days after birth. In the neonate, staining for HSP entactin and laminin-1 was barely visible; however, antibodies against fibronectin displayed intense immunoreactivity in nearly every cochlear tissue. Fibronectin is progressively inactivated in all tissues except the basilar membrane where it persists at high levels to adulthood. Laminin-1, entactin, and HSP illustrate remarkable temporal and spatial coordinate regulation. Elevated expression of these proteins is observed at 2 postnatal days (PND), and persists in the membranes surrounding the spiral ganglion cell bodies. Transient expression of laminin-1 and entactin, and to a lesser extent HSP, is observed from PND4 to PND8 in a track of membrane running from the interdental cells of the spiral limbus down the inner sulcus, across the basilar membrane, up the external sulcus to the spiral prominence, and branching into the spiral ligament ensheathing the root cell processes. By PND 14 the abundance of these proteins is greatly reduced along this track. The abundance and dynamic regulation of these major basement membrane-associated proteins suggests that they play an important role in postnatal cochlear development.