GTP-dependent regulation of heterochromatin fluctuations at subtelomeric regions in Saccharomyces cerevisiae.

In eukaryotes, single cells in a population display different transcriptional profiles. One of the factors regulating this heterogeneity is the chromatin state in each cell. However, the mechanisms of epigenetic chromatin regulation of specific chromosomal regions remain unclear. Therefore, we used single-cell tracking system to analyze IMD2. IMD2 is located at the subtelomeric region of budding yeast, and its expression is epigenetically regulated by heterochromatin fluctuations. Treatment with mycophenolic acid, an inhibitor of de novo GTP biosynthesis, triggered a decrease in GTP, which caused heterochromatin fluctuations at the IMD2 locus. Interestingly, within individually tracked cells, IMD2 expression state underwent repeated switches even though IMD2 is positioned within the heterochromatin region. We also found that 30% of the cells in a population always expressed IMD2. Furthermore, the addition of nicotinamide, a histone deacetylase inhibitor, or guanine, the GTP biosynthesis factor in salvage pathway of GTP biosynthesis, regulated heterogeneity, resulting in IMD2 expression being uniformly induced or suppressed in the population. These results suggest that gene expression heterogeneity in the IMD2 region is regulated by changes in chromatin structure triggered by slight decreases in GTP.