The large presence of OCT4+ that associates with progenitor cells in the neurospheres confirms that NSCs from adult DRG are maintained as progenitors in nature and are capable of long-term, if not indefinite, renewal. Not all NSCs were in the same stage of stem-cell-ness, thus presenting an opportunity to observe a relationship between the differentiation state and the cellular level of epigenetic marks. For example, the major euchromatin histone marks 2me-H3K4 and Ac-H4 were found to associate with OCT4+ cells and obviously prevailed in the NSC neurospheres over the period of long-term maintenance; these observations indicate that these gene activation histone marks might associate with genes in the active recycling of general stem cells in the neurospheres. On the other hand, the heterochromatic 3me-H3K27 also prevailed in the non-differentiated NSCs. This is similarly demonstrated in embryonic stem (ES) cells; it is suggested that lineage-specific genes are primed for expression in ES cells but are held in check by opposing histone marks or chromatin state (5). The pluripotency of ES cells is characterized by a specific epigenetic profile where lineage-specific genes
