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Abstract

Serum-free mouse embryo (SFME) cells were established by D. Barnes et al., and are known to be a neural stem cell line, which differentiate into astrocytes upon treatment with TGF-beta. Therefore, SFME cells is thought to be a model well suited to analyze the differentiation mechanism of neural stem cells. Until now, we have investigated the regulation mechanisms of telomerase activity and telomere length in human cancer and normal cells. Telomerase is the enzyme responsible for the synthesis and maintenance of telomere repeats located at chromosomal ends and is normally expressed in embryonic and germline cells, but not in most normal cells. Here, using SFME cells, we attempted to analyze the regulation mechanism of telomerase activity in neural stem cells and to detect a change upon differentiation into astrocytes. When SFME cells were cultured in the presence of TGF-beta, cells showed anelongated morphology and decreased its growth to 50% of control culture. Cells also expressed the glial fibrillary acidic protein (GFAP), a marker for astrocytes,indicating that TGF-beta induced differentiation in SFME cells from neural stem cells into astrocytes. At the same time,TGF-beta also inhibited telomerase activity and repressed the expression of the mouse telomerase reverse transcriptase(mTERT), demonstrating that SFME cells was vested with a finite replicative life span upon treatment with TGF-beta. To understand the mechanisms regulating mTERT levels during differentiation into astrocytes, we have estimated the expression level of c-myc, which is known to be a key molecule in activating the TERT promoter. As a result, TGF-beta-treated SFME cells were shown to repress the expression of c-myc. Furthermore, promoter analysis, using the 5'-region of the mTERT gene, which possess two E-box elements bound to c-Myc/Max, demonstrated that mTERT promoter activity greatly decreased in TGF-beta-treated SFME cells as compared to non-treated SFME cells. These suggest that c-myc might play a critical role in the expression of mTERT, and that down-regulation of c-myc dependent upon the astrocytic differentiation in SFME cells might cause the repression of mTERT in TGF-beta-treated SFME cells.

The Emerging Roles for Telomerase in the Central Nervous System

“…This expression pattern indicates that telomerase is present in the brain during embryonic development, which is supported by its elevated expression in embryonic neuronal stem or progenitor cells (Mattson and Klapper, 2001 ). Additionally, NSCs lose telomerase activity upon differentiating into astrocytes or neurons (Kruk et al, 1996 ; Miura et al, 2001 ; Caporaso et al, 2003 ; Cheng et al, 2007 ). It remains unclear how exactly telomerase activity decreases in differentiating cells.…”

“…NSCs possess the capability to self-renew and differentiate into mature nerve cells including neurons, astrocytes and oligodendrocytes (Miura et al, 2001 ; Ming and Song, 2011 ; Würth et al, 2014 ). The activity of telomerase rapidly decreases when NSCs stop dividing and differentiate into nerve cells (Kruk et al, 1996 ; Klapper et al, 2001 ).…”

Is There Such a Thing as a Genuine Cancer Stem Cell Marker? Perspectives from the Gut, the Brain and the Dental Pulp

“…Telomere length has also been demonstrated to be important for neuronal differentiation and neuritogenesis [216] (see also review [217]). Its deficiency leads to a compromised olfactory bulb neurogenesis [215] although NSCs lose telomerase activity upon differentiation into astrocytes [218]. DPSCs also lose progressively their telomerase activity upon their spontaneous in vitro differentiation to osteoblastic/odontoblastic cells in conditions of high culture passages [212].…”

Telomerase reverse transcriptase (TERT)-expressing cells mark a novel stem cell population in the adult mouse brain

“…For example, prior work revealed that telomerase activity was localized to cellular fractions containing Type A, B, and C neural progenitor cells (NPCs) from the adult mouse V-SVZ, 15 and differentiation of embryonic stem cells into astrocytes or neurons induced loss of telomerase activity. 17,18 As mice age, they exhibit decreased TERT expression in the V-SVZ, which is accompanied by reduced rates of proliferation and neurogenesis, consistent with an aginginduced decline in the stem cell pool. 19 Further evidence for the importance of telomerase activity in neurogenic niches is supported by decreased levels of V-SVZ neurogenesis in mice with telomerase RNA component (TERC) deletion.…”