The active enhancer regions were defined by the overlapping regions of H3K4me1 and H3K27ac markers.
The interaction between enhancer regions and promoters is represented by lines with one end yellow (promoter) and the other arrows.
These enhancer regions seem to contain transcription factor binding sites which are essential to maintain SOX9 expression during development.
Mechanistically, Oct4 is required for Otx2 expression, and reciprocally, Otx2 is required for efficient Oct4 recruitment to many enhancer regions.
Gene activity is controlled by specific, short DNA sequences (called cis-control elements) in the promoter and enhancer regions associated with the gene.
The trans-acting elements are related to a group of transcription factors that bind to specific sites within promoter and/or enhancer regions [53, 54].
For example, H3K4me2/3 is found at TSSs of active genes, whereas H3K4me1 tends to localize to enhancer regions (Greer and Shi, 2012; Kampranis and Tsichlis, 2009).
The cis-acting elements comprise promoters as well as enhancer regions (ex: CArG box, TATA box and CCAAT) that regulate expression of a distinct gene [52].
PREs were prominent within enhancer regions near cytokine-encoding DEGs (IL17A, IL19 and IL1B), suggesting that PREs might be incorporated into complex decoy oligonucleotides (cdODNs).
Finally, PR domain containing 16 (PRDM16) is implicated in positioning and removing specific chromatin modifications at enhancer regions of Notch target genes during olfactory neuron differentiation [41].
As a result, the Hox clusters consist of closely spaced transcription units and enhancer regions.
