Novel NG2‐CreERT2 knock‐in mice demonstrate heterogeneous differentiation potential of NG2 glia during development

Abstract

NG2 (nerve/glia antigen-2) is a type I transmembrane glycoprotein and also known as chondroitin sulfate proteoglycan 4. In the parenchyma of the central nervous system, NG2-expressing (NG2(+) ) cells have been identified as a novel type of glia with a strong potential to generate oligodendrocytes (OLs) in the developing white matter. However, the differentiation potential of NG2 glia remained controversial, largely attributable to shortcomings of transgenic mouse models used for fate mapping. To minimize these restrictions and to more faithfully mimic the endogenous NG2 expression in vivo, we generated a mouse line in which the open reading frame of the tamoxifen-inducible form of the Cre DNA recombinase (CreERT2) was inserted into the NG2 locus by homologous recombination. Results from this novel mouse line demonstrate that at different developmental stages of the brain, NG2(+) cells either stayed as NG2 glia or differentiated into OLs during the whole life span. Interestingly, when Cre activity was induced at embryonic stages, a significant number of reporter(+) astrocytes could be detected in the gray matter after birth. However, in other brain regions, such as olfactory bulb, brain stem, and cerebellum, all of the NG2 glia was restricted to the OL lineage. In addition, tamoxifen-sensitive and NG2 gene locus-dependent gene recombination could be detected in a small, but persistent population of cortical NeuN(+) neurons starting from the second postnatal week.

Widespread Expression of Erythropoietin Receptor in Brain and Its Induction by Injury

“…For induction of CreERT2-activity in NG2-Cre-ERT2:R26R-tdtomato-mEGFP mice (28)(29), 100 mg/kg tamoxifen (dissolved in corn oil; SigmaAldrich, Taufkirchen, Germany) was injected i.p. at postnatal d 26 and 27.…”

“…To get better insight at which stages cells of the oligodendrocyte lineage express EpoR, we labeled oligodendrocyte precursor cells by tamoxifen injections in NG2-CreERT2 mice (28). At 72 h after the second tamoxifen injection, we identified precursors double-stained for GFP and ctEPOR-AB (GFP+/EpoR+), as well as GFP+/EpoR+ cells with clear morphology (processes with parallel myelin bundles) of already differentiated oligodendrocytes ( Figures 4B-B'').…”

A new role for the P2Y-like GPR17 receptor in the modulation of multipotency of oligodendrocyte precursor cells in vitro

“…For example, following brain ischemia due to permanent middle cerebral artery occlusion (MCAo), generation of both astrocytic and neuronal precursors from NG2 + cells was observed in adult NG2creBAC:ZEG double transgenic mice, in which enhanced green fluorescent protein (EGFP) is expressed in OPCs and their progeny, thus allowing to visualize their final phenotype [10]. However, conflicting data arise from the different transgenic mouse models employed, and the controversy around the multipotency and neurogenic potential of OPCs in vivo is still an open issue [11][12][13][14][15].…”

NG2 Glia: Novel Roles beyond Re-/Myelination

“…In line with this view, a subpopulation of NG2 glia has been observed to serve as multipotent progenitors, producing protoplasmic astrocytes as well OLs in the embryonic ventral forebrain or following some kinds of CNS injury [19,[24][25][26][27]. It has also been proposed that adult NG2 glia may activate spontaneous neurogenic events within restricted brain areas [28].…”

“…CM of cultured mouse NG2 glia [26]; Gene expr. study of cultured mouse NG2 glia exposed to Il17 or Tnf [158] Neuronal and synaptic plasticity [159] Matrix Metalloprotease 9, MMP9…”