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Polydendrocytes
Polydendrocytes (also known as NG2 cells, NG2 glia, or oligodendrocyte progenitor cells) are process-bearing glial cells (neuroglia) in the mammalian central nervous system (CNS) that are identified by the expression of the NG2 chondroitin sulfate proteoglycan (CSPG4) 〔(Ensembl genome browser 68: Homo sapiens - Result in Detail - Ensembl Lucene search )〕 and the alpha receptor for platelet-derived growth factor (PDGFRA).〔(Ensembl genome browser 68: Homo sapiens - Result in Detail - Ensembl Lucene search )〕 They are distinct from other cell populations such as neurons, astrocytes, oligodendrocytes, microglia, and neural stem cells and are recognized as the fourth major glial cell type in the mammalian CNS. Studies have implicated polydendrocytes in many cellular and physiological processes. Polydendrocytes in the postnatal mouse CNS and those grown in culture generate oligodendrocytes, and thus they are often equated with oligodendrocyte progenitor cells (OPCs). Under some culture conditions, polydendrocytes give rise to astrocytes. A subpopulation of polydendrocytes in the gray matter of the embryonic CNS also generates protoplasmic astrocytes. In addition, polydendrocytes express receptors for various neurotransmitters and undergo membrane depolarization when they receive synaptic inputs from neurons.
== History ==
It had been known since the early 1900s that astrocytes, oligodendrocytes, and microglia make up the major glial cell populations in the mammalian CNS. The presence of another glial cell population had escaped recognition because of the lack of a suitable marker to identify them in tissue sections. The notion that there exists a population of glial progenitor cells in the developing and mature CNS began to be entertained in the late 1980s by several independent groups. In one series of studies on the development and origin of oligodendrocytes in the rodent CNS, a population of immature cells that appeared to be precursors to oligodendrocytes was identified by the expression of the GD3 ganglioside.
In a separate series of studies, cells from perinatal rat optic nerves that expressed the A2B5 ganglioside were shown to differentiate into oligodendrocytes in culture. Subsequently, A2B5+ cells from other CNS regions and from adult CNS were also shown to generate oligodendrocytes. Based on the observation that these cells require PDGF for their proliferation and expansion, the expression of the alpha receptor for platelet-derived growth factor (Pdgfra) was used to search for the in vivo correlates of the A2B5+ cells, which led to the discovery of a unique population of Pdgfra+ cells in the CNS whose appearance and distribution were consistent with those of developing oligodendrocytes.
Independently, Stallcup and colleagues generated an antiserum that recognized a group of rat brain tumor cell lines, which exhibited properties that were intermediate between those of typical neurons and glial cells. Biochemical studies showed that the antiserum recognized a chondroitin sulfate proteoglycan with a core glycoprotein of 300 kDa, and the antigen was named NG2 (nerve/glial antigen 2). NG2 was found to be expressed on A2B5+ oligodendrocyte precursor cells isolated from the perinatal rat CNS tissues and on process-bearing cells in the CNS in vivo.〔 Comparison of NG2 and Pdgfra expression revealed that NG2 and Pdgfra are expressed on the same population of cells in the CNS. These cells represent 2-9% of all the cells and remain proliferative in the mature CNS.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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