Figure 10. Epigenetic marks associated with heterochromatin coincide with the compacted chromatin at the nuclear periphery.

Cells were fixed at various times post-transfection with NET23/STING and stained for various epigenetic marks, particularly the active marks histone H3 acetylation at lysine 18 (H3K18Ac) and di-methylation at lysine 4 (H3K4me2), the silent mark histone H3 trimethylation at lysine 9 (H3K9Me3) and the strongly repressed mark combined H3K9me3 and S10ph. (A) At 21 h post-transfection no change in the H3K18Ac was observed; however an increase in H3K9Me3 was already visually observable by immunofluorescence microscopy. (B) The chromatin compaction effects begin at the nuclear periphery. Higher magnification field from panel A. At 21 h post-transfection only a small amount of internal H3K9Me3 signal was observable while most was enriched at the NE (arrowheads). (C) At 85 h post-transfection both a loss of acetylation at K18 and methylation at K4 were observed indicating a general loss of active marks. At the same time a strong increase in methylation at K9 was visually observable by immunofluorescence microscopy, consistent with increased silencing. The H3K9me3 was seen throughout the whole nucleoplasm though some concentration at the NE could often be observed. However, the stronger repression mark H3K9me3 combined with S10ph was actually reduced in the NET23/STING transfected cells. All scale bars  = 10 µm.