2010). immature stages of differentiation in a cell-intrinsic manner. Moreover, transcriptome analysis identified genes differentially expressed between these OPC populations, including those encoding transcription factors (TFs), cell surface molecules, and signaling molecules. Particularly, FB and SC OPCs retained the expression of FB- or SC-specific TFs, such as Foxg1 and Hoxc8, respectively, even after serial passaging revealed that these OLCs are cell-intrinsically different in terms of proliferation, susceptibility to excitotoxicity, and myelin sheet formation. Transcriptome analysis exhibited that OLCs retain region-specific transcription factors of their origin, such as Foxg1 and Hoxc8, suggesting their role in the phenotypic differences of OLCs. Introduction During the development of the mammalian central nervous system (CNS), the differentiation of oligodendroglial progenitor cells (OPCs) into myelinating oligodendrocytes occurs mainly after neurogenesis, astrocytogenesis, and axonal wiring in the CNS. The proliferation and migration of OPCs and their differentiation to RETF-4NA oligodendrocytes have been considered to be regulated mainly by external stimuli produced by other PIK3C2G cell types in the CNS rather than by OPC-intrinsic mechanisms. A variety of growth factors and neurotrophic factors such as PDGFA homodimer (PDGFAA), FGF2, neuregulins, and NT-3, have been identified as factors essential for generation and development of oligodendroglial lineage cells (OLCs) and CNS myelination (Barres & Raff 1994, Miller 2002). In pathological conditions, such as perinatal brain injury, myelination by OPCs is usually negatively affected by extracellular glutamate and inflammatory cytokines, such as IL-1 and TNF (Cai et al. 2004, Carty et al. 2011, Johnston 2005). We previously exhibited that interferon- (IFN), a type-I T helper cell-derived cytokine, also induces apoptosis of OPCs suggesting its negative effects on developmental myelination (Horiuchi et al. 2006, Horiuchi et al. 2011). Studies suggest that these factors also affect remyelination in the adult CNS after demyelination occurring in multiple sclerosis and traumatic brain or spinal cord injury (Bannerman et al. 2007, Levine 2016, Lin et al. 2006). Highly purified primary OLC cultures from rodents have provided a useful model to examine the direct effects of these factors on OLCs (Horiuchi et al. 2010). In most studies, OPCs isolated from optic nerves or brains were employed as models representing the OPCs in the entire CNS regions (Barres & Raff 1994, Groves et al. 1993). However, little is known about whether or not OPCs from different CNS regions are the same in terms of the response to these extracellular factors. OLC heterogeneity in morphology, including variability in number and length of internodes of myelinating oligodendrocytes, has been reported (Weruaga-Prieto et al. 1996). A recent study using single cell RNA sequencing revealed molecular heterogeneity of OLCs in different CNS regions as well (Marques et al. 2016). Several studies have also resolved the heterogeneity in the origins of OPCs. In the forebrain (FB), multiple subpopulations of OPCs are generated from different domains along the dorsoventral (DV) axis of the neural tube at distinct embryonic ages, and these subpopulations compete for space in the developing FB (Kessaris et al. 2006). In the spinal cord (SC), there are two waves of OPC generation; the first wave occurs around embryonic day 12.5 (E12.5) from the ventral midline at, and then the second wave of OPCs is generated from the lateral and dorsal plates. These two populations show distinct preferences in axonal tracts they myelinate (Tripathi et al. 2011). Phenotypic differences RETF-4NA between white and gray matter OPCs have also been RETF-4NA reported. Hill and his colleagues, using organotypic slice cultures, exhibited that OPCs in neonatal mouse white and gray matter differ in their proliferative response to PDGFAA due to OPC-intrinsic mechanisms (Hill et al. 2013). A study using a transplantation strategy exhibited that adult OPCs from cortical white matter differentiate into myelinating oligodendrocytes more efficiently than those isolated from gray matter in either white or gray.

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