Cellular epigenetic modifications of neural stem cell differentiation.

Emerging information indicates that epigenetic modification (i.e., histone code and DNA methylation) may be integral to the maintenance and differentiation of neural stem cells (NSCs), but their actual involvement has not yet been illustrated. In this study, we demonstrated the dynamic nature of epigenetic marks during the differentiation of quiescent adult rat NSCs in neurospheres. A subpopulation of OCT4(+) NSCs in the neurosphere contained histone marks, trimethylated histone 3 on lysine 27 (3me-H3K27), 2me-H3K4, and acetylated H4 (Ac-H4). A major decrease of these marks was found prior to or during differentiation, and was further diminished or reprogrammed in diverse subpopulations of migrated NSCs expressing nestin or beta-III-tubulin. The DNA methylation mark 5-methyl-cytosine (5-MeC), and DNA methyltransferase (DNMT) 1 and 3a expression also correlated to the state of differentiation; they were highly present in undifferentiated NSCs but downregulated in migrated populations. In contrast, DNA methyl-CpG-binding protein (MBD1) was low in undifferentiated NSCs in neurospheres, but highly appeared in differentiating NSCs. Furthermore, we found an outward translocation of DNA methylation marker 5-MeC, DNMT1, DNMT3a, and MBD1 in NSCs as differentiation began and proceeded; 5-MeC from homogeneous nucleus to peripheral nucleus, and DMNT1a and 3a from nuclear to cytoplasm, indicating chromatin remodeling. Treatment with DNA methylation inhibitor, 5-aza-cytidine, altered DNA methylation and disrupted migration as indicated by a reduction of migrated neurons and differentiation. These results indicate that chromatin is dynamically remodeled when NSCs transform from the quiescent state to active growth, and that DNA methylation modification is essential for neural stem cell differentiation.