Expression and localization of the fibronectin receptor in the mouse nervous system

Cell surface receptors for extracellular matrix components have recently been characterized as integral membrane complexes with common features in their structural and functional properties. We have investigated the expression of the mammalian fibronectin receptor in the mouse nervous system using immunocytological and immunochemical methods. The fibronectin receptor was detectable on immature oligodendrocytes and immature and mature astrocytes in culture, while central nervous system neurons did not reveal detectable levels of fibronectin receptor at the developmental stages studied. In the peripheral nervous system both glia and neurons were found to express the fibronectin receptor. The receptor complex in both peripheral and central nervous system has an apparent molecular weight of approximately 140 kD under reducing conditions and resolves into two or three distinct protein bands under nonreducing conditions. The fibronectin receptor expresses the L2/HNK-1 epitope that is characteristic of several adhesion molecules, including L1, N-CAM, the myelin-associated glycoprotein, and J1 and thus is another member of the L2/HNK-1 family of adhesion molecules. The L2/HNK-1 carbohydrate epitope is expressed differently and independently of the fibronectin receptor protein backbone in that it is detectable in neonatal brain but not in adult brain. Our observations attribute a functional role to the fibronectin receptor and its L2/HNK-1 carbohydrate epitope during development and maintenance of cell interactions in the central and peripheral nervous systems.