SPARC, AN EXTRACELLULAR-MATRIX GLYCOPROTEIN CONTAINING THE FOLLISTATIN MODULE, IS EXPRESSED BY ASTROCYTES IN SYNAPTIC ENRICHED REGIONS OF THE ADULT BRAIN

Although extracellular matrix (ECM) glycoproteins play important roles in neural development, their levels are generally believed to decreas e in the adult brain. Immunohistochemical analysis indicates that the anti-adhesive ECM glycoprotein SPARC/osteonectin, which contains a fol listatin 'module,' is expressed in the adult rabbit nervous system. In the cerebellum, SPARC is present in Bergmann glia, with a strong sign al along their radial fibres. SPARC, while enriched in membrane fracti ons, is not a transmembrane protein. In the hippocampus, colocalizatio n of SPARC is observed in cells which express the astrocytic marker GF AP. The expression of SPARC by a subset of astrocytes, particularly in synaptic enriched areas, suggests a continuing role for the ECM in th e adult brain.