Epigenetic and molecular signature of human umbilical cord blood-derived neural stem cell (HUCB-NSC) neuronal differentiation.

In the context of cell therapy, the epigenetic status of core stemness transcription factor (STF) genes regulating the cell proliferation/differentiation program is of primary interest. Our results confirmed that in vitro differentiation of the umbilicalcord-blood-derived-neural-stem-cells (HUCB-NSC) coincides with the progressive down-regulation of Oct3/4 and Nanog gene expression. Consistently and in parallel with the repression of gene transcription, a substantial increase in the mosaic cytosine methylation CpG dinucleotide was observed in the promoter regions of these STF genes. However none of the histone-H3 post-translational-modifications (PTM) known to be associated with transcriptionally active genes (H3Ac and H3K4me3) or repressed genes (H3K9me3 and H3K27me3) seemed to vary in relation to the progression of cell differentiation and down-regulation of STF genes. This indicates an uncoupling between STF gene expression and above mentioned histone PTMs. In contrast, the overall methylation of nuclear chromatin at repressive histone H3K9me3 was significantly higher than H3K4 trimetylation in expanding HUCB-NSC cultures and then increases through the progression of cell differentiation. These observations suggest different epigenetic programs of gene repression realized in the cell nuclei of differentiating HUCB-NSC cultures with uneven involvement of the repressive histone PTMs.