Proteoglycans provide neurite guidance at an astrocyte boundary.

Astrocytes in the developing brain direct neurites through their synthesis of cell surface and extracellular matrix molecules. We introduce a novel culture system to identify and examine the guidance properties of astrocyte-derived molecules. The permissive A7 and nonpermissive Neu7 cell lines were co-cultured to form an A7/Neu7 monolayer. Neurites extended on A7 cells but avoided Neu7 cells and instead stopped or turned at the A7/Neu7 Interface. Enzymatic treatment with trypsin and hyaluronic acid increased neurite extension, but neither altered the boundary. Only, removal of keratan and chondroitin sulfate residues reduced the guidance capacity of the A7/Neu7 boundary. Since no treatment individually abolished the boundary, neurite guidance appears to be due to a combination of factors. The A7/Neu7 astrocyte substrate demonstrates the functional role for KSPGs and CSPGs, but more interestingly, suggests that simply increasing the capacity of a substrate to permit neurite outgrowth does not necessarily eliminate or even reduce its guidance properties.