NG2 cells, or polydendrocytes, are defined as glial cells that express the NG2 proteoglycan and represent a fourth major glial cell population in the mammalian central nervous system. They are morphologically, antigenically, and functionally distinct from mature astrocytes, oligodendrocytes, and microglia. Although they are most often equated with oligodendrocyte progenitor cells, they exhibit some properties that are not commonly associated with those of progenitor cells that generate myelinating cells. This review discusses recent observations and unanswered issues related to their lineage and their role in remyelination, neural signaling, and axonal growth.
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