Differentiation of Neural Stem Cells into Oligodendrocytes: Involvement of the Polycomb Group Protein Ezh2

Abstract

The mechanisms underlying the regulation of neural stem cell (NSC) renewal and maintenance of their multipotency are still not completely understood. Self-renewal of stem cells in general implies repression of genes that encode for cell lineage differentiation. Enhancer of zeste homolog 2 (Ezh2) is a Polycomb group protein involved in stem cell renewal and maintenance by inducing gene silencing via histone methylation and deacetylation. To establish the role of Ezh2 in the maintenance and differentiation of NSCs, we have examined the expression of Ezh2 in NSCs isolated from embryonic (embryonic day 14) mice during proliferation and differentiation in vitro. Our results show that Ezh2 is highly expressed in proliferating NSCs. In accordance with its suggested role as a transcription repressor, the expression of Ezh2 decreased when the NSCs differentiated into neurons and was completely suppressed during differentiation into astrocytes. Surprisingly, Ezh2 remained highly expressed in NSCs that differentiated into an oligodendrocytic cell lineage, starting from oligodendrocyte precursor cells (OPCs) up to the immature (premyelinating) oligodendrocyte stage. To further establish the role of Ezh2 in NSC differentiation, we silenced and induced overexpression of the Ezh2 gene in NSCs. High levels of Ezh2 in differentiating NSCs appeared to be associated with an increase in oligodendrocytes and a reduction in astrocytes, whereas low levels of Ezh2 led to completely opposite effects. The increase in the number of oligodendrocytes induced by enhanced expression of Ezh2 could be ascribed to stimulation of OPC proliferation although stimulation of oligodendrocyte differentiation cannot be excluded. Disclosure of potential conflicts of interest is found at the end of this article.