The NG2 chondroitin sulfate proteoglycan is a valuable marker for several types of incompletely-differentiated precursor cells, including oligodendrocyte progenitors in the central nervous system, developing mesenchymal cells in cartilage, muscle, and bone, and pericytes/smooth muscle cells in developing vasculature. In addition to extending our knowledge about the developmental roles of these cell types, current studies on NG2 are also providing information about the molecular mechanisms through which the proteoglycan itself influences progenitor development. This research suggests that interaction of NG2 with extracellular and intracellular ligands regulates signaling events that are important for both cell proliferation and cell migration.