Heparin is a unique marker of progenitors in the glial cell lineage

The oligodendrocyte-type-2 astrocyte progenitor cells (precursors of oligod endrocytes and type-2 astrocytes) are an excellent system in which to study differentiation as they can be manipulated in vitro. Maintenance of oligod endrocyte-type-2 astrocyte progenitor cells requires basic fibroblast growt h factor, a growth factor whose action normally depends on a heparan sulfat e coreceptor. Biochemical analysis revealed a most surprising result: that the oligodendrocyte type-2 astrocyte progenitors did not synthesize heparan sulfate, the near ubiquitous N-sulfated cell surface polysaccharide, but t he chemically related heparin in a form that was almost completely N- and O -sulfated. The heparin was detected in the pericellular fraction of the cel ls and the culture medium. In contrast the differentiated glial subpopulati ons (oligodendrocytes and type-2 astrocytes) synthesized typical heparan su lfate but with distinctive fine structural features for each cell type. Thu s heparin is a unique differentiation marker in the glial lineage. Previous ly heparin has been found only in a subset of mature mast cells called the connective tissue mast cells. Its presence within the developing nervous sy stem on a precise population of progenitors may confer specific and essenti al recognition properties on those cells in relation to binding soluble gro wth and/or differentiation factors and the extracellular matrix.