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Thomas Jenuwein

Publications and source records attributed to Thomas Jenuwein.

48 records · Page 3Linked to original sources
PubMed2003

Maintenance of stable heterochromatin domains by dynamic HP1 binding.

One function of heterochromatin is the epigenetic silencing by sequestration of genes into transcriptionally repressed nuclear neighborhoods. Heterochromatin protein 1 (HP1) is a major component of heterochromatin and thus is a candidate for establishing and maintaining the transcriptionally repressive heterochromatin structure. Here we demonstrate that maintenance of stable heterochromatin domains in living cells involves the transient binding and dynamic exchange of HP1 from chromatin. HP1 exchange kinetics correlate with the condensation level of chromatin and are dependent on the histone methyltransferase Suv39h. The chromodomain and the chromoshadow domain of HP1 are both required for binding to native chromatin in vivo, but they contribute differentially to binding in euchromatin and heterochromatin. These data argue against HP1 repression of transcription by formation of static, higher order oligomeric networks but support a dynamic competition model, and they demonstrate that heterochromatin is accessible to regulatory factors.

Amanitins↗
PubMed2003

Partitioning and plasticity of repressive histone methylation states in mammalian chromatin.

Methylation of position-specific lysine residues in histone N termini is a central modification for regulating epigenetic transitions in chromatin. Each methylatable lysine residue can exist in a mono-, di-, or trimethylated state, thereby extending the indexing potential of this particular modification. Here, we examine all possible methylation states for histone H3 lysine 9 (H3-K9) and lysine 27 (H3-K27) in mammalian chromatin. Using highly specific antibodies together with quantitative mass spectrometry, we demonstrate that pericentric heterochromatin is selectively enriched for H3-K27 monomethylation and H3-K9 trimethylation. This heterochromatic methylation profile is dependent on the Suv39h histone methyltransferases (HMTases) but independent of the euchromatic G9a HMTase. In Suv39h double null cells, pericentric heterochromatin is converted to alternative methylation imprints and accumulates H3-K27 trimethylation and H3-K9 monomethylation. Our data underscore the selective presence of distinct histone lysine methylation states in partitioning chromosomal subdomains but also reveal a surprising plasticity in propagating methylation patterns in eukaryotic chromatin.

Amino Acid Sequence↗
PubMed2003

Establishment of histone h3 methylation on the inactive X chromosome requires transient recruitment of Eed-Enx1 polycomb group complexes.

Previous studies have implicated the Eed-Enx1 Polycomb group complex in the maintenance of imprinted X inactivation in the trophectoderm lineage in mouse. Here we show that recruitment of Eed-Enx1 to the inactive X chromosome (Xi) also occurs in random X inactivation in the embryo proper. Localization of Eed-Enx1 complexes to Xi occurs very early, at the onset of Xist expression, but then disappears as differentiation and development progress. This transient localization correlates with the presence of high levels of the complex in totipotent cells and during early differentiation stages. Functional analysis demonstrates that Eed-Enx1 is required to establish methylation of histone H3 at lysine 9 and/or lysine 27 on Xi and that this, in turn, is required to stabilize the Xi chromatin structure.

Amino Acid Sequence↗
PubMed2003

Consequences of the depletion of zygotic and embryonic enhancer of zeste 2 during preimplantation mouse development.

Enhancer of zeste 2 (Ezh2), a SET domain-containing protein, is crucial for development in many model organisms, including early mouse development. In mice, Ezh2 is detected as a maternally inherited protein in the oocyte but its function at the onset of development is unknown. We have used a conditional allele of Ezh2 to deplete the oocyte of this maternal inheritance. We show that the loss of maternal Ezh2 has a long-term effect causing severe growth retardation of neonates despite 'rescue' through embryonic transcription from the paternal allele. This phenotypic effect on growth could be attributed to the asymmetric localisation of the Ezh2/Eed complex and the associated histone methylation pattern to the maternal genome, which is disrupted in Ezh2 mutant zygotes. During subsequent development, we detect distinct histone methylation patterns in the trophectoderm and the pluripotent epiblast. In the latter where Oct4 expression continues from the zygote onwards, the Ezh2/Eed complex apparently establishes a unique epigenetic state and plasticity, which probably explains why loss of Ezh2 is early embryonic lethal and obligatory for the derivation of pluripotent embryonic stem cells. By contrast, in the differentiating trophectoderm cells where Oct4 expression is progressively downregulated Ezh2/Eed complex is recruited transiently to one X chromosome in female embryos at the onset of X-inactivation. This accumulation and the associated histone methylation are also lost in Ezh2 mutants, suggesting a role in X inactivation. Thus, Ezh2 has significant and diverse roles during early development, as well as during the establishment of the first differentiated cells, the trophectoderm, and of the pluripotent epiblast cells.

Animals↗
PubMed2002

Essential function of histone deacetylase 1 in proliferation control and CDK inhibitor repression.

Histone deacetylases (HDACs) modulate chromatin structure and transcription, but little is known about their function in mammalian development. HDAC1 was implicated previously in the repression of genes required for cell proliferation and differentiation. Here we show that targeted disruption of both HDAC1 alleles results in embryonic lethality before E10.5 due to severe proliferation defects and retardation in development. HDAC1-deficient embryonic stem cells show reduced proliferation rates, which correlate with decreased cyclin-associated kinase activities and elevated levels of the cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(KIP1). Similarly, expression of p21 and p27 is up-regulated in HDAC1-null embryos. In addition, loss of HDAC1 leads to significantly reduced overall deacetylase activity, hyperacetylation of a subset of histones H3 and H4 and concomitant changes in other histone modifications. The expression of HDAC2 and HDAC3 is induced in HDAC1-deficient cells, but cannot compensate for loss of the enzyme, suggesting a unique function for HDAC1. Our study provides the first evidence that a histone deacetylase is essential for unrestricted cell proliferation by repressing the expression of selective cell cycle inhibitors.

Alleles↗
PubMed2002

Central role of Drosophila SU(VAR)3-9 in histone H3-K9 methylation and heterochromatic gene silencing.

Su(var)3-9 is a dominant modifier of heterochromatin-induced gene silencing. Like its mammalian and Schizosaccharomyces pombe homologues, Su(var) 3-9 encodes a histone methyltransferase (HMTase), which selectively methylates histone H3 at lysine 9 (H3-K9). In Su(var)3-9 null mutants, H3-K9 methylation at chromocentre heterochromatin is strongly reduced, indicating that SU(VAR)3-9 is the major heterochromatin-specific HMTase in Drosophila. SU (VAR)3-9 interacts with the heterochromatin-associated HP1 protein and with another silencing factor, SU(VAR)3-7. Notably, SU(VAR)3-9-HP1 interaction is interdependent and governs distinct localization patterns of both proteins. In Su(var)3-9 null mutants, concentration of HP1 at the chromocentre is nearly lost without affecting HP1 accumulation at the fourth chromosome. By contrast, in HP1 null mutants SU(VAR)3-9 is no longer restricted at heterochromatin but broadly dispersed across the chromosomes. Despite this interdependence, Su(var)3-9 dominates the PEV modifier effects of HP1 and Su(var)3-7 and is also epistatic to the Y chromosome effect on PEV. Finally, the human SUV39H1 gene is able to partially rescue Su(var)3-9 silencing defects. Together, these data indicate a central role for the SU(VAR)3-9 HMTase in heterochromatin-induced gene silencing in Drosophila.

Animals↗
PubMed2002

Higher-order structure in pericentric heterochromatin involves a distinct pattern of histone modification and an RNA component.

Post-translational modification of histone tails is thought to modulate higher-order chromatin structure. Combinations of modifications including acetylation, phosphorylation and methylation have been proposed to provide marks recognized by specific proteins. This is exemplified, in both mammalian cells and fission yeast, by transcriptionally silent constitutive pericentric heterochromatin. Such heterochromatin contains histones that are generally hypoacetylated and methylated by Suv39h methyltransferases at lysine 9 of histone H3 (H3-K9). Each of these modification states has been implicated in the maintenance of HP1 protein-binding at pericentric heterochromatin, in transcriptional silencing and in centromere function. In particular, H3-K9 methylation is thought to provide a marking system for the establishment and maintenance of stably repressed regions and heterochromatin subdomains. To address the question of how these two types of modifications, as well as other unidentified parameters, function to maintain pericentric heterochromatin, we used a combination of histone deacetylase inhibitors, RNAse treatments and an antibody raised against methylated branched H3-K9 peptides. Our results show that both H3-K9 acetylation and methylation can occur on independent sets of H3 molecules in pericentric heterochromatin. In addition, we identify an RNA- and histone modification-dependent structure that brings methylated H3-K9 tails together in a specific configuration required for the accumulation of HP1 proteins in these domains.

Fluorescent Antibody Technique↗
PubMed2002

Histone H3 lysine 9 methylation occurs rapidly at the onset of random X chromosome inactivation.

In female mammals, a single X chromosome is stably and heritably silenced early in embryogenesis. The inactive X is characterized by asynchronous DNA replication and epigenetic chromatin modifications, including DNA methylation, histone H3/H4 hypoacetylation, and incorporation of a variant histone macroH2A. X inactivation is initiated by a cis-acting RNA molecule, the X-inactive specific transcript (Xist), which coats the chromosome. However, the mechanism by which Xist induces chromosome silencing is poorly understood. An important approach towards answering this question has been to determine the temporal order of epigenetic chromatin modifications in an in vitro model system, differentiating XX embryonic stem (ES) cells, and thereby to identify candidate targets for Xist RNA. To date, these studies have demonstrated that, following accumulation of Xist RNA, the transition to late replication of the X chromosome is the earliest detectable event. H4 hypoacetylation, macroH2A1.2 incorporation, and DNA methylation all occur subsequently. Recently, it has been shown that chromatin of the inactive X is also characterized by methylation of histone H3 at lysine 9 (H3-K9). Here we show that H3-K9 methylation is a very early event in the process of X inactivation, which closely parallels the onset of Xist RNA accumulation.

Cell Differentiation↗
PubMed2002

The many faces of histone lysine methylation.

Diverse post-translational modifications of histone amino termini represent an important epigenetic mechanism for the organisation of chromatin structure and the regulation of gene activity. Within the past two years, great progress has been made in understanding the functional implications of histone methylation; in particular through the characterisation of histone methyltransferases that direct the site-specific methylation of, for example, lysine 9 and lysine 4 positions in the histone H3 amino terminus. All known histone methyltransferases of this type contain the evolutionarily conserved SET domain and appear to be able to stimulate either gene repression or gene activation. Methylation of H3 Lys9 and Lys4 has been visualised in native chromatin, indicating opposite roles in structuring repressive or accessible chromatin domains. For example, at the mating-type loci in Schizosaccharomyces pombe, at pericentric heterochromatin and at the inactive X chromosome in mammals, striking differences between these distinct marks have been observed. H3 Lys9 methylation is also important to direct additional epigenetic signals such as DNA methylation--for example, in Neurospora crassa and in Arabidopsis thaliana. Together, the available data strongly establish histone lysine methylation as a central modification for the epigenetic organisation of eukaryotic genomes.

Animals↗
PubMed2002

Selective interactions between vertebrate polycomb homologs and the SUV39H1 histone lysine methyltransferase suggest that histone H3-K9 methylation contributes to chromosomal targeting of Polycomb group proteins.

Polycomb group (PcG) proteins form multimeric chromatin-associated protein complexes that are involved in heritable repression of gene activity. Two distinct human PcG complexes have been characterized. The EED/EZH2 PcG complex utilizes histone deacetylation to repress gene activity. The HPC/HPH PcG complex contains the HPH, RING1, BMI1, and HPC proteins. Here we show that vertebrate Polycomb homologs HPC2 and XPc2, but not M33/MPc1, interact with the histone lysine methyltransferase (HMTase) SUV39H1 both in vitro and in vivo. We further find that overexpression of SUV39H1 induces selective nuclear relocalization of HPC/HPH PcG proteins but not of the EED/EZH2 PcG proteins. This SUV39H1-dependent relocalization concentrates the HPC/HPH PcG proteins to the large pericentromeric heterochromatin domains (1q12) on human chromosome 1. Within these PcG domains we observe increased H3-K9 methylation. Finally, we show that H3-K9 HMTase activity is associated with endogenous HPC2. Our findings suggest a role for the SUV39H1 HMTase and histone H3-K9 methylation in the targeting of human HPC/HPH PcG proteins to modified chromatin structures.

Active Transport, Cell Nucleus↗
PubMed2001

Histone H3 lysine 9 methylation is an epigenetic imprint of facultative heterochromatin.

Post-translational modifications of histone amino termini are an important regulatory mechanism that induce transitions in chromatin structure, thereby contributing to epigenetic gene control and the assembly of specialized chromosomal subdomains. Methylation of histone H3 at lysine 9 (H3-Lys9) by site-specific histone methyltransferases (Suv39h HMTases) marks constitutive heterochromatin. Here, we show that H3-Lys9 methylation also occurs in facultative heterochromatin of the inactive X chromosome (Xi) in female mammals. H3-Lys9 methylation is retained through mitosis, indicating that it might provide an epigenetic imprint for the maintenance of the inactive state. Disruption of the two mouse Suv39h HMTases abolishes H3-Lys9 methylation of constitutive heterochromatin but not that of the Xi. In addition, HP1 proteins, which normally associate with heterochromatin, do not accumulate with the Xi. These observations suggest the existence of an Suv39h-HP1-independent pathway regulating H3-Lys9 methylation of facultative heterochromatin.

Amniocentesis↗