Project description:Here we analyse steady mRNA levels in wild type and COMPASS mutants across an ageing timecourse, along with H3K4me3 distribution in ageing wild type
Project description:The stimulation of trimethylation of histone H3 lysine 4 (H3K4) by H2B monoubiquitination (H2Bub) has been widely studied with multiple mechanisms proposed for this form of histone crosstalk. Cps35/Swd2 within COMPASS is considered to bridge these processes. However, a truncated form of Set1 (762-Set1) is reported to function in H3K4 trimethylation without interacting with Cps35/Swd2, and such crosstalk is attributed to the n-SET domain of Set1 and its interaction with the Cps40/Spp1 subunit of COMPASS. Here, we use biochemical, structural, in vivo, and ChIP-seq approaches to demonstrate that Cps40/Spp1 and the n-SET domain of Set1 are required for the stability of Set1 and not the crosstalk. Furthermore, the apparent wild-type levels of H3K4 trimethylation (H3K4me3) in the 762-Set1 strain is due to rogue methylase activity of this mutant resulting in the mislocalization of H3K4me3 from the promoter-proximal regions to gene bodies and intergenic regions. We have also performed detailed screens and identified yeast strains lacking H2Bub, but containing intact H2Bub enzymes, that have normal levels of H3K4me3, suggesting that ubiquitination may not directly stimulate COMPASS, but rather works in a context of the PAF and Rad6/Bre1 complexes. Our study demonstrates that the ubiquitination machinery and Cps35/Swd2 function to focus COMPASS’ H3K4me3 activity at promoter-proximal regions in a context dependent manner. ChIP-Seq for H3K4ME3 in S. cerevisie wild-type strains and strains expressing a truncated form of Set1: aa762-1080 Set1. H3K4ME3 ChIP-Seq was also compared for wild-type, leo1 knockout, and chd1 knockout strains
Project description:Histone H3 lysine 4 (H3K4) can be mono-, di-, and trimethylated by members of the COMPASS (COMplex of Proteins ASsociated with Set1) family from yeast to human and these modifications can be found at distinct regions of the genome. Monomethylation of histone H3K4 (H3K4me1) is relatively more enriched at metazoan enhancer regions compared to trimethylated histone H3K4 (H3K4me3), which are found at transcription start sites in all eukaryotes. Our recent studies in Drosophila demonstrated that the Trithorax-related (Trr) branch of the COMPASS family regulates enhancer activity and is responsible for the implementation of H3K4me1 at these regions. There are six COMPASS family members in mammals, two of which, MLL3 and MLL4, are most closely related to Drosophila Trr. Here, we use ChIP-seq of this class of COMPASS family members in both human HCT116 cells and mouse embryonic stem cells and find that MLL4 is preferentially found at enhancer regions. MLL3 and MLL4 are frequently mutated in cancer, and indeed, the widely used HCT116 cancer cell line contains inactivating mutations in the MLL3 gene. Using HCT116 cells in which MLL4 has also been knocked out, we demonstrate that MLL4 is a major regulator of H3K4me1 in these cells, with the greatest loss of monomethylation at enhancer regions. Moreover, we found a redundant role between Mll3 and Mll4 in enhancer H3K4 monomethylation in mouse embryonic fibroblast (MEF) cells. These findings suggest that mammalian MLL3/MLL4 function in the regulation of enhancer activity and enhancer-promoter communication during gene expression and that mutations of MLL3 and MLL4 found in cancer could exert their properties through enhancer malfunction. ChIP-Seq in mouse embryonic stem (mES) cells for MLL4. ChIP-seq of MLL4 and p300 in human parental HCT116 cells. ChIP-seq of H3K4me1, H3K4me2 and H3K4me3 in parental HCT116 cells and HCT116 cells with Mll4∆set.
Project description:Here we show that an unrestricted galactose diet in early life minimises pathology during replicative ageing in budding yeast, irrespective of diet later in life. Lifespan and average mother cell division rate are comparable between glucose and galactose diets, but markers of senescence and the progressive dysregulation of gene expression observed on glucose are minimal on galactose, showing these to be facets of ageing pathology rather than intrinsic parts of the replicative ageing process. Respiration on galactose is critical for minimising ageing pathology, and forced respiration during ageing on glucose by over-expression of Hap4 also has the same effect though only in a fraction of cells. This fraction maintains Hap4 activity to advanced age with low senescence and a youthful gene expression profile, whereas other cells in the same population that lose Hap4 activity undergo dramatic dysregulation of gene expression and accumulate aneuploid fragments of chromosome XII aneuploidy (ChrXIIr), which are tightly associated with ageing pathology.
Project description:The stimulation of trimethylation of histone H3 lysine 4 (H3K4) by H2B monoubiquitination (H2Bub) has been widely studied with multiple mechanisms proposed for this form of histone crosstalk. Cps35/Swd2 within COMPASS is considered to bridge these processes. However, a truncated form of Set1 (762-Set1) is reported to function in H3K4 trimethylation without interacting with Cps35/Swd2, and such crosstalk is attributed to the n-SET domain of Set1 and its interaction with the Cps40/Spp1 subunit of COMPASS. Here, we use biochemical, structural, in vivo, and ChIP-seq approaches to demonstrate that Cps40/Spp1 and the n-SET domain of Set1 are required for the stability of Set1 and not the crosstalk. Furthermore, the apparent wild-type levels of H3K4 trimethylation (H3K4me3) in the 762-Set1 strain is due to rogue methylase activity of this mutant resulting in the mislocalization of H3K4me3 from the promoter-proximal regions to gene bodies and intergenic regions. We have also performed detailed screens and identified yeast strains lacking H2Bub, but containing intact H2Bub enzymes, that have normal levels of H3K4me3, suggesting that ubiquitination may not directly stimulate COMPASS, but rather works in a context of the PAF and Rad6/Bre1 complexes. Our study demonstrates that the ubiquitination machinery and Cps35/Swd2 function to focus COMPASS’ H3K4me3 activity at promoter-proximal regions in a context dependent manner.
Project description:Here we analyzed the widespread disruption of gene expression that accompanies yeast ageing, and surprisingly observed that this is completely independent of ERCs. Furthermore, we could not find subsets of genes that are differentially regulated in the presence of ERCs. High throughput imaging showed that the accumulation of Tom70-GFP which accompanies the onset of cell division defects at the Senescence Entry Point (SEP) also correlated poorly to ERC abundance, but allowed determination of a gene expression signature for the SEP. This signature included overexpression of mRNA from the chromosome XII region between the rDNA and the telomere (ChrXIIr), which has been previously noted to amplify during ageing.