The architecture of interphase chromosomes and gene positioning are altered by changes in DNA methylation and histone acetylation

Wheat nuclei have a remarkably well defined interphase organisation, and we have made use of this to determine the relationship between interphase chromosome organisation, the positioning of specific transgenes and induced changes in DNA methylation and histone acetylation, using in situ hybridisation and confocal 3D imaging. After germinating seeds either in the presence of 5-Azacytidine (5-AC), which leads to DNA hypomethylation, or trichostatin A (TSA), which results in histone hyperacetylation, the architecture of the interphase chromosome arms changes significantly even though the overall Rabl configuration is maintained. This suggests that specific chromosome segments are remodelled by these treatments but that there is a strong link of both centromeres and telomeres to the nuclear envelope. In lines carrying multiple transgene integrations at widely separated sites, we show that the multiple transgenes, which are usually colocalised during interphase, are dispersed after 5-AC or TSA treatment and that there is an increase in transgene activity. This suggests that the colocalisation/dispersion of the transgenes may be a function of specific interphase chromosome organisation and that these lines containing multiple transgene copies may all be partially transcriptionally repressed.