Project description:H1 linker histones are the most abundant chromatin binding proteins. Their association with chromatin determines the spacing between nucleosomes and enables arrays of nucleosomes to fold into more compact chromatin structures. Mammals express multiple H1 proteins and are able to compensate for the loss of one or even two members by increasing synthesis of other members to maintain a constant H1 to nucleosome stoichiometry. To study the role of H1 in mammalian development, we generated a conditional triple H1 knockout (H1cTKO) mouse strain that enables depletion of H1 in specific cell types. Here, we report on the effects of depleting H1 in adult hematopoietic cells. Deletion of the genes encoding three widely expressed H1 subtypes (H1c, H1d, and H1e) has particularly profound effects on B- and T- lymphocyte development. H1 depletion leads to de-repression of T-cell activation genes, and a shift in T-cells towards effector functions, a process that mimics normal T-cell activation. Comparison of chromatin structure in normal and H1-depleted CD8+ T-cells revealed that H1 binding produces localized chromatin compaction within spatially defined chromatin domains containing above average levels of H1. Reduction of H1 stoichiometry in these regions leads to decreases in H3K27 methylation and increases in H3K36 methylation. In vitro, H1 promotes PRC2-mediated H3K27 methylation and inhibits NSD2-mediated H3K36 methylation. Mechanistically, H1 mediates these opposite effects by promoting physical compaction of the chromatin substrate. These findings identify H1 as a critical regulator of the epigenetic landscape in mammalian cells.
Project description:The nucleosome plays a central role in genome regulation. Traditional methods for mapping nucleosomes depend on the resistance of the nucleosome core to micrococcal nuclease (MNase). However, the lengths of the protected DNA fragments are heterogeneous, limiting the accuracy of nucleosome position information. To resolve this problem, we removed residual linker DNA by simultaneous digestion of yeast chromatin with MNase and exonuclease III (ExoIII). Paired-end sequencing of mono-nucleosomes revealed not only core particles (145-147 bp), but also intermediate particles in which ~8 bp project from one side (154 bp) or both sides (161 bp) of the nucleosome core. We term these particles "pseudo-chromatosomes" because they are present in yeast lacking linker histone. They are also observed after MNase-ExoIII digestion of chromatin reconstituted using recombinant core histones. We propose that the pseudo-chromatosome provides a DNA framework to facilitate H1 binding. Comparison of budding yeast nucleosome sequences obtained using micrococcal nuclease (MNase-seq) and MNase + exonuclease III (ExoIII) (MNase-ExoIII-seq): wild type cells and hho1-null cells. Nucleosome sequences from native chromatin and H1-depleted chromatin from mouse liver. Nucleosome sequences from a plasmid reconstituted into nucleosomes using recombinant yeast histones or native chicken erythrocyte histones.
Project description:Eukaryotic chromosomal DNA is assembled into regularly spaced nucleosomes, which play a central role in gene regulation by determining accessibility of control regions. The nucleosome contains ~147 bp of DNA wrapped ~1.7 times around a central core histone octamer. The linker histone, H1, binds both to the nucleosome, sealing the DNA coils, and to the linker DNA between nucleosomes, directing chromatin folding. Micrococcal nuclease (MNase) digests the linker to yield the chromatosome, containing H1 and ~160 bp, and then converts it to a core particle, containing ~147 bp and no H1. Sequencing of nucleosomal DNA obtained after MNase digestion (MNase-seq) generates genome-wide nucleosome maps that are important for understanding gene regulation. We present an improved MNase-seq method involving simultaneous digestion with exonuclease III, which removes linker DNA. Remarkably, we discovered two novel intermediate particles containing 154 or 161 bp, corresponding to 7 bp protruding from one or both sides of the nucleosome core. These particles are detected in yeast lacking H1 and in H1-depleted mouse chromatin. They can be reconstituted in vitro using purified core histones and DNA. We propose that these "proto-chromatosomes" are fundamental chromatin subunits, which include the H1 binding site and influence nucleosome spacing independently of H1.
Project description:H1 linker histones are the most abundant chromatin binding proteins. Their association with chromatin determines the spacing between nucleosomes and enables arrays of nucleosomes to fold into more compact chromatin structures. Mammals express multiple H1 proteins and are able to compensate for the loss of one or even two members by increasing synthesis of other members to maintain a constant H1 to nucleosome stoichiometry. To study the role of H1 in mammalian development, we generated a conditional triple H1 knockout (H1cTKO) mouse strain that enables depletion of H1 in specific cell types. Here, we report on the effects of depleting H1 in adult hematopoietic cells. Deletion of the genes encoding three widely expressed H1 subtypes (H1c, H1d, and H1e) has particularly profound effects on B- and T- lymphocyte development. H1 depletion leads to de-repression of T-cell activation genes, and a shift in T-cells towards effector functions, a process that mimics normal T-cell activation. Comparison of chromatin structure in normal and H1-depleted CD8+ T-cells revealed that H1 binding produces localized chromatin compaction within spatially defined chromatin domains containing above average levels of H1. Reduction of H1 stoichiometry in these regions leads to decreases in H3K27 methylation and increases in H3K36 methylation. In vitro, H1 promotes PRC2-mediated H3K27 methylation and inhibits NSD2-mediated H3K36 methylation. Mechanistically, H1 mediates these opposite effects by promoting physical compaction of the chromatin substrate. These findings identify H1 as a critical regulator of the epigenetic landscape in mammalian cells.
Project description:H1 linker histones are the most abundant chromatin binding proteins. Their association with chromatin determines the spacing between nucleosomes and enables arrays of nucleosomes to fold into more compact chromatin structures. Mammals express multiple H1 proteins and are able to compensate for the loss of one or even two members by increasing synthesis of other members to maintain a constant H1 to nucleosome stoichiometry. To study the role of H1 in mammalian development, we generated a conditional triple H1 knockout (H1cTKO) mouse strain that enables depletion of H1 in specific cell types. Here, we report on the effects of depleting H1 in adult hematopoietic cells. Deletion of the genes encoding three widely expressed H1 subtypes (H1c, H1d, and H1e) has particularly profound effects on B- and T- lymphocyte development. H1 depletion leads to de-repression of T-cell activation genes, and a shift in T-cells towards effector functions, a process that mimics normal T-cell activation. Comparison of chromatin structure in normal and H1-depleted CD8+ T-cells revealed that H1 binding produces localized chromatin compaction within spatially defined chromatin domains containing above average levels of H1. Reduction of H1 stoichiometry in these regions leads to decreases in H3K27 methylation and increases in H3K36 methylation. In vitro, H1 promotes PRC2-mediated H3K27 methylation and inhibits NSD2-mediated H3K36 methylation. Mechanistically, H1 mediates these opposite effects by promoting physical compaction of the chromatin substrate. These findings identify H1 as a critical regulator of the epigenetic landscape in mammalian cells.
Project description:Control ChIP-seq on human H1-hESC For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODE_Data_Use_Policy_for_External_Users_03-07-14.pdf
Project description:Control ChIP-seq on human H1-hESC For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODE_Data_Use_Policy_for_External_Users_03-07-14.pdf