Heterochromatic Histone Modifications Research Articles

The chromatin remodelling complex NoRC safeguards genome stability by heterochromatin formation at telomeres and centromeres

Constitutive heterochromatin is crucial for the integrity of chromosomes and genomic stability. Here, we show that the chromatin remodelling complex NoRC, known to silence a fraction of rRNA genes, also establishes a repressive heterochromatic structure at centromeres and telomeres, preserving the structural integrity of these repetitive loci. Knockdown of NoRC leads to relaxation of centromeric and telomeric heterochromatin, abnormalities in mitotic spindle assembly, impaired chromosome segregation and enhanced chromosomal instability. The results demonstrate that NoRC safeguards genomic stability by coordinating enzymatic activities that establish features of repressive chromatin at centromeric and telomeric regions, and this heterochromatic structure is required for sustaining genomic integrity.

Epigenetic switches of tobacco transgenes associate with transient redistribution of histone marks in callus culture

In plants, silencing is usually accompanied by DNA methylation and heterochromatic histone marks. We studied these epigenetic modifications in different epialleles of 35S promoter (P35S)-driven tobacco transgenes. In locus 1, the T-DNA was organized as an inverted repeat, and the residing neomycin phosphotransferase II reporter gene (P35S-nptII) was silenced at the posttranscriptional (PTGS) level. Transcriptionally silenced (TGS) epialleles were generated by trans-acting RNA signals in hybrids or in a callus culture. PTGS to TGS conversion in callus culture was accompanied by loss of the euchromatic H3K4me3 mark in the transcribed region of locus 1, but this change was not transmitted to the regenerated plants from these calli. In contrast, cytosine methylation that spread from the transcribed region into the promoter was maintained in regenerants. Also, the TGS epialleles generated by trans-acting siRNAs did not change their active histone modifications. Thus, both TGS and PTGS epialleles exhibit euchromatic (H3K4me3 and H3K9ac) histone modifications despite heavy DNA methylation in the promoter and transcribed region, respectively. However, in the TGS locus (271), abundant heterochromatic H3K9me2 marks and DNA methylation were present on P35S. Heterochromatic histone modifications are not automatically installed on transcriptionally silenced loci in tobacco, suggesting that repressive histone marks and cytosine methylation may be uncoupled. However, transient loss of euchromatic modifications may guide de novo DNA methylation leading to formation of stable repressed epialleles with recovered eukaryotic marks. Compilation of available data on epigenetic modification of inactivated P35S in different systems is provided.

Accumulation of DNA Damage-Induced Chromatin Alterations in Tissue-Specific Stem Cells: The Driving Force of Aging?

Accumulation of DNA damage leading to stem cell exhaustion has been proposed to be a principal mechanism of aging. Using 53BP1-foci as a marker for DNA double-strand breaks (DSBs), hair follicle stem cells (HFSCs) in mouse epidermis were analyzed for age-related DNA damage response (DDR). We observed increasing amounts of 53BP1-foci during the natural aging process independent of telomere shortening and after protracted low-dose radiation, suggesting substantial accumulation of DSBs in HFSCs. Electron microscopy combined with immunogold-labeling showed multiple small 53BP1 clusters diffusely distributed throughout the highly compacted heterochromatin of aged HFSCs, but single large 53BP1 clusters in irradiated HFSCs. These remaining 53BP1 clusters did not colocalize with core components of non-homologous end-joining, but with heterochromatic histone modifications. Based on these results we hypothesize that these lesions were not persistently unrepaired DSBs, but may reflect chromatin rearrangements caused by the repair or misrepair of DSBs. Flow cytometry showed increased activation of repair proteins and damage-induced chromatin modifications, triggering apoptosis and cellular senescence in irradiated, but not in aged HFSCs. These results suggest that accumulation of DNA damage-induced chromatin alterations, whose structural dimensions reflect the complexity of the initial genotoxic insult, may lead to different DDR events, ultimately determining the biological outcome of HFSCs. Collectively, our findings support the hypothesis that aging might be largely the remit of structural changes to chromatin potentially leading to epigenetically induced transcriptional deregulation.

The Chromatin Remodeling Factor CSB Recruits Histone Acetyltransferase PCAF to rRNA Gene Promoters in Active State for Transcription Initiation

The promoters of poised rRNA genes (rDNA) are marked by both euchromatic and heterochromatic histone modifications and are associated with two transcription factors, UBF and SL1 that nucleate transcription complex formation. Active rRNA genes contain only euchromatic histone modifications and are loaded with all components of transcriptional initiation complex including RNA polymerase I. Coupled with histone acetylation and RNA polymerase I targeting, poised promoters can be converted to active ones by ATP-dependent chromatin remodeling factor CSB for initiation of rDNA transcription. However, it is not clear how dynamic histone modifications induce the assembly of polymerase I transcription initiation complex to active promoters during such conversion. Here we show that a complex consisting of CSB, RNA polymerase I and histone acetyltransferase PCAF is present at the rDNA promoters in active state. CSB is required for the association of PCAF with rDNA, which induces acetylation of histone H4 and histone H3K9. Overexpression of CSB promotes the association of PCAF with rDNA. Knockdown of PCAF leads to decreased levels of H4ac and H3K9ac at rDNA promoters, prevents the association of RNA polymerase I and inhibits pre-rRNA synthesis. The results demonstrate that CSB recruits PCAF to rDNA, which allows histone acetylation that is required for the assembly of polymerase I transcription initiation complex during the transition from poised to active state of rRNA genes, suggesting that CSB and PCAF play cooperative roles to establish the active state of rRNA genes by histone acetylation.

Kinetics of Facultative Heterochromatin and Polycomb Group Protein Association with the Herpes Simplex Viral Genome during Establishment of Latent Infection

ABSTRACTThe herpes simplex virus (HSV) genome is associated with heterochromatic histone modifications, including trimethylation of the lysine 27 residue of histone H3 (H3K27me3), during latent infection of neurons. Here we have examined the kinetics of general chromatin and H3K27me3 association with the viral genome during establishment of latent infection. Using both wild-type virus and a mutant virus that is unable to undergo replication in neurons, we found that histone H3 associates with viral gene promoters by 7 days postinfection (dpi). Levels of H3K27me3 were low at 7 dpi but increased dramatically by 14 dpi. Hence, general chromatin association and/or other factors may play a key role(s) in the initial silencing of lytic genes, and H3K27me3 may play a role in further suppression of the genome and/or the maintenance of latency. A component of Polycomb repressive complex 2 (PRC2), which mediates the addition of K27me3 to histone H3 (Suz12), was also recruited by 14 dpi. We have shown previously that the levels of H3K27me3 during latent infection are increased in the presence of the latency-associated transcript (LAT). However, the initial targeting of PRC2 was not found to be dependent on the LAT. We found that a component of the PRC1 complex (Bmi1), which binds to H3K27me3, was not enriched at promoters found previously to be enriched for H3K27me3. Our results are consistent with (i) chromatinization of viral DNA or other mechanisms causing the initial silencing of HSV lytic genes and (ii) facultative heterochromatin maintaining that silencing during latent infection of neurons.

Expression of the rice microRNA <i>miR820</i> is associated with epigenetic modifications at its own locus

Small RNAs, such as small interfering RNAs (siRNAs) or microRNAs (miRNAs), regulate gene expression at transcriptional and posttranscriptional levels in eukaryotes. miRNAs are processed from duplexes formed on single-stranded RNA. They regulate expression of their target gene either by cleaving mRNA or supressing translation. In general, the primary miRNA transcripts are synthesized by RNA polymerase II and processed similarly to mRNAs. MIRNA genes are usually located in transcriptionally active euchromatic regions. In contrast, siRNAs are processed from duplexes made of two RNA molecules. One of them is often derived from a transposable element (TE) or from repetitive sequences that reside in heterochromatic regions. The other strand is synthesized by the RNA-dependent RNA polymerase on the first strand as a template. siRNAs establish epigenetic marks in parasitic DNA such as TEs, thus they usually act in cis. The rice miRNA miR820, encoded by CACTA TEs (five copies, located on different chromosomes), reduces the expression of the de novo DNA methyltransferase gene OsDRM2. Because miR820 is derived from silent TEs, in which the heterochromatic histone modifications are enriched, the mechanism of MIR820 transcription could be expected to differ from typical miRNAs. Here we show that the primary transcript of MIR820 is mainly derived from the CACTA TE copy on chromosome 7 (MIR820b). Histone modification and DNA methylation status around MIR820b differed from that of the other four loci. These unique epigenetic modifications in MIR820b were only found around the miR820 coding region. We conclude that MIR820b transcription may depend on the unique epigenetic modifications, which in turn may be established by the action of miR820 in cis. This suggests a dual function of miR820 in cis and in trans.

Regulatory Impact of RNA Secondary Structure across the Arabidopsis Transcriptome

The secondary structure of an RNA molecule plays an integral role in its maturation, regulation, and function. However, the global influence of this feature on plant gene expression is still largely unclear. Here, we use a high-throughput, sequencing-based, structure-mapping approach in conjunction with transcriptome-wide sequencing of rRNA-depleted (RNA sequencing), small RNA, and ribosome-bound RNA populations to investigate the impact of RNA secondary structure on gene expression regulation in Arabidopsis thaliana. From this analysis, we find that highly unpaired and paired RNAs are strongly correlated with euchromatic and heterochromatic epigenetic histone modifications, respectively, providing evidence that secondary structure is necessary for these RNA-mediated posttranscriptional regulatory pathways. Additionally, we uncover key structural patterns across protein-coding transcripts that indicate RNA folding demarcates regions of protein translation and likely affects microRNA-mediated regulation of mRNAs in this model plant. We further reveal that RNA folding is significantly anticorrelated with overall transcript abundance, which is often due to the increased propensity of highly structured mRNAs to be degraded and/or processed into small RNAs. Finally, we find that secondary structure affects mRNA translation, suggesting that this feature regulates plant gene expression at multiple levels. These findings provide a global assessment of RNA folding and its significant regulatory effects in a plant transcriptome.

Nuclear c-Abl-mediated tyrosine phosphorylation induces chromatin structural changes through histone modifications that include H4K16 hypoacetylation

c-Abl tyrosine kinase, which is ubiquitously expressed, has three nuclear localization signals and one nuclear export signal and can shuttle between the nucleus and the cytoplasm. c-Abl plays important roles in cell proliferation, adhesion, migration, and apoptosis. Recently, we developed a pixel imaging method for quantitating the level of chromatin structural changes and showed that nuclear Src-family tyrosine kinases are involved in chromatin structural changes upon growth factor stimulation. Using this method, we show here that nuclear c-Abl induces chromatin structural changes in a manner dependent on the tyrosine kinase activity. Expression of nuclear-targeted c-Abl drastically increases the levels of chromatin structural changes, compared with that of c-Abl. Intriguingly, nuclear-targeted c-Abl induces heterochromatic profiles of histone methylation and acetylation, including hypoacetylation of histone H4 acetylated on lysine 16 (H4K16Ac). The level of heterochromatic histone modifications correlates with that of chromatin structural changes. Adriamycin-induced DNA damage stimulates translocation of c-Abl into the nucleus and induces chromatin structural changes together with H4K16 hypoacetylation. Treatment with trichostatin A, a histone deacetylase inhibitor, blocks chromatin structural changes but not nuclear tyrosine phosphorylation by c-Abl. These results suggest that nuclear c-Abl plays an important role in chromatin dynamics through nuclear tyrosine phosphorylation-induced heterochromatic histone modifications.

Genomic Prevalence of Heterochromatic H3K9me2 and Transcription Do Not Discriminate Pluripotent from Terminally Differentiated Cells

Cellular differentiation entails reprogramming of the transcriptome from a pluripotent to a unipotent fate. This process was suggested to coincide with a global increase of repressive heterochromatin, which results in a reduction of transcriptional plasticity and potential. Here we report the dynamics of the transcriptome and an abundant heterochromatic histone modification, dimethylation of histone H3 at lysine 9 (H3K9me2), during neuronal differentiation of embryonic stem cells. In contrast to the prevailing model, we find H3K9me2 to occupy over 50% of chromosomal regions already in stem cells. Marked are most genomic regions that are devoid of transcription and a subgroup of histone modifications. Importantly, no global increase occurs during differentiation, but discrete local changes of H3K9me2 particularly at genic regions can be detected. Mirroring the cell fate change, many genes show altered expression upon differentiation. Quantitative sequencing of transcripts demonstrates however that the total number of active genes is equal between stem cells and several tested differentiated cell types. Together, these findings reveal high prevalence of a heterochromatic mark in stem cells and challenge the model of low abundance of epigenetic repression and resulting global basal level transcription in stem cells. This suggests that cellular differentiation entails local rather than global changes in epigenetic repression and transcriptional activity.

HP1 Recruits Activity-Dependent Neuroprotective Protein to H3K9me3 Marked Pericentromeric Heterochromatin for Silencing of Major Satellite Repeats

H3 lysine 9 trimethylation (H3K9me3) is a histone posttranslational modification (PTM) that has emerged as hallmark of pericentromeric heterochromatin. This constitutive chromatin domain is composed of repetitive DNA elements, whose transcription is differentially regulated. Mammalian cells contain three HP1 proteins, HP1α, HP1β and HP1γ These have been shown to bind to H3K9me3 and are thought to mediate the effects of this histone PTM. However, the mechanisms of HP1 chromatin regulation and the exact functional role at pericentromeric heterochromatin are still unclear. Here, we identify activity-dependent neuroprotective protein (ADNP) as an H3K9me3 associated factor. We show that ADNP does not bind H3K9me3 directly, but that interaction is mediated by all three HP1 isoforms in vitro. However, in cells ADNP localization to areas of pericentromeric heterochromatin is only dependent on HP1α and HP1β. Besides a PGVLL sequence patch we uncovered an ARKS motif within the ADNP homeodomain involved in HP1 dependent H3K9me3 association and localization to pericentromeric heterochromatin. While knockdown of ADNP had no effect on HP1 distribution and heterochromatic histone and DNA modifications, we found ADNP silencing major satellite repeats. Our results identify a novel factor in the translation of H3K9me3 at pericentromeric heterochromatin that regulates transcription.

Retrotransposon-specific DNA hypomethylation and two-step loss-of-imprinting during WW45 haploinsufficiency-induced hepatocarcinogenesis

Liver cancer development follows a multistep process that includes epigenetic changes beginning at the initiation stage, changes that have been studied for their potential diagnostic value. Here, we examined long-term, cancer-associated epigenetic changes during carcinogenesis using a mouse model of liver cancer. WW45-haploinsufficient ( WW45 +/−) mice developed liver cancer after 12 months due to dysregulation of the Hippo pathway and consequent Yap overexpression. There was no pathological sign of neoplastic regions in the livers of 10-month-old WW45 +/− mice but whole-gene expression patterns statistically proved the resemblance between 10-month-old livers and hepatomas from WW45 +/− mice. We found epigenetic features in the livers of 10-month-old WW45 +/− mice which were already distinctive from the wild-type counterparts prior to tumorigenesises. H19 ICR showed loss-of-imprinting in two steps and allelic histone marker signature during tumorigenesis showed similarity with ES cells. Progressive cancer pathognomonic global hypomethylation was a characteristic post-10-month feature and was well reflected in retrotransposons. Heterochromatic histone modifications also decreased in retrotransposons after 10 months in the liver of WW45 +/− mice. This study showed potential epigenetic features for cancer prognostic use and supported the epigenetic progenitor model of cancer.

Nucleolar Follistatin Promotes Cancer Cell Survival under Glucose-deprived Conditions through Inhibiting Cellular rRNA Synthesis

Solid tumor development is frequently accompanied by energy-deficient conditions such as glucose deprivation and hypoxia. Follistatin (FST), a secretory protein originally identified from ovarian follicular fluid, has been suggested to be involved in tumor development. However, whether it plays a role in cancer cell survival under energy-deprived conditions remains elusive. In this study, we demonstrated that glucose deprivation markedly enhanced the expression and nucleolar localization of FST in HeLa cells. The nucleolar localization of FST relied on its nuclear localization signal (NLS) comprising the residues 64-87. Localization of FST to the nucleolus attenuated rRNA synthesis, a key process for cellular energy homeostasis and cell survival. Overexpression of FST delayed glucose deprivation-induced apoptosis, whereas down-regulation of FST exerted the opposite effect. These functions depended on the presence of an intact NLS because the NLS-deleted mutant of FST lost the rRNA inhibition effect and the cell protective effect. Altogether, we identified a novel nucleolar function of FST, which is of importance in the modulation of cancer cell survival in response to glucose deprivation.

Histone Modifications within the Human X Centromere Region

Human centromeres are multi-megabase regions of highly ordered arrays of alpha satellite DNA that are separated from chromosome arms by unordered alpha satellite monomers and other repetitive elements. Complexities in assembling such large repetitive regions have limited detailed studies of centromeric chromatin organization. However, a genomic map of the human X centromere has provided new opportunities to explore genomic architecture of a complex locus. We used ChIP to examine the distribution of modified histones within centromere regions of multiple X chromosomes. Methylation of H3 at lysine 4 coincided with DXZ1 higher order alpha satellite, the site of CENP-A localization. Heterochromatic histone modifications were distributed across the 400–500 kb pericentromeric regions. The large arrays of alpha satellite and gamma satellite DNA were enriched for both euchromatic and heterochromatic modifications, implying that some pericentromeric repeats have multiple chromatin characteristics. Partial truncation of the X centromere resulted in reduction in the size of the CENP-A/Cenp-A domain and increased heterochromatic modifications in the flanking pericentromere. Although the deletion removed ∼1/3 of centromeric DNA, the ratio of CENP-A to alpha satellite array size was maintained in the same proportion, suggesting that a limited, but defined linear region of the centromeric DNA is necessary for kinetochore assembly. Our results indicate that the human X centromere contains multiple types of chromatin, is organized similarly to smaller eukaryotic centromeres, and responds to structural changes by expanding or contracting domains.

TAF12 Recruits Gadd45a and the Nucleotide Excision Repair Complex to the Promoter of rRNA Genes Leading to Active DNA Demethylation

Many studies have detailed the repressive effects of DNA methylation on gene expression. However, the mechanisms that promote active demethylation are just beginning to emerge. Here, we show that methylation of the rDNA promoter is a dynamic and reversible process. Demethylation of rDNA is initiated by recruitment of Gadd45a (growth arrest and DNA damage inducible protein 45 alpha) to the rDNA promoter by TAF12, a TBP-associated factor that is contained in Pol I- and Pol II-specific TBP-TAF complexes. Once targeted to rDNA, Gadd45a triggers demethylation of promoter-proximal DNA by recruiting the nucleotide excision repair (NER) machinery to remove methylated cytosines. Knockdown of Gadd45a, XPA, XPG, XPF, or TAF12 or treatment with drugs that inhibit NER causes hypermethylation of rDNA, establishes heterochromatic histone marks, and impairs transcription. The results reveal a mechanism that recruits the DNA repair machinery to the promoter of active genes, keeping them in a hypomethylated state.

Analysis of Chromatin Structure of Genes Silenced by Heterochromatin in Trans

While heterochromatic gene silencing in cis is often accompanied by nucleosomal compaction, characteristic histone modifications, and recruitment of heterochromatin proteins, little is known concerning genes silenced by heterochromatin in trans. An insertion of heterochromatic satellite DNA in the euchromatic brown (bw) gene of Drosophila melanogaster results in bwDominant (bwD), which can inactivate loci on the homolog by relocation near the centric heterochromatin (trans-inactivation). Nucleosomal compaction was found to accompany trans-inactivation, but stereotypical heterochromatic histone modifications were mostly absent on silenced reporter genes. HP1 was enriched on trans-inactivated reporter constructs and this enrichment was more pronounced on adult chromatin than on larval chromatin. Interestingly, this HP1 enrichment in trans was unaccompanied by an increase in the 2MeH3K9 mark, which is generally thought to be the docking site for HP1 in heterochromatin. However, a substantial increase in the 2MeH3K9 mark was found on or near the bwD satellite insertion in cis, but did not spread further. These observations suggest that the interaction of HP1 with chromatin in cis is fundamentally different from that in trans. Our molecular data agree well with the differential phenotypic effect on bwD trans-inactivation of various genes known to be involved in histone modification and cis gene silencing.

Epigenetic Inheritance and Reprogramming in Plants and Fission Yeast

Plants and fission yeast exhibit a wealth of epigenetic phenomena, including transposon regulation, heterochromatic silencing, and gene imprinting. They provide excellent model organisms to address the question of how epigenetic information is propagated to daughter cells. We have addressed the questions of establishment, maintenance, and inheritance of heterochromatic silencing using the fission yeast Schizosaccharomyces pombe and the plant Arabidopsis thaliana by using a variety of genetic and genomic approaches. We present here results showing the cell cycle dependence of RNA in fission yeast RNA interference (RNAi), which is required for proper transcriptional silencing of the centromeric heterochromatin, and that this process occurs during S phase, allowing for precise copying and reestablishment of heterochromatic histone modifications following DNA replication and cell division. We also show that in plants, cells in culture and male germ-line cells undergo massive epigenomic changes correlated with the appearance of a novel class of 21-nucleotide small interfering RNA (siRNA) from transcriptionally reactivated transposable elements (TEs) following loss of heterochromatic DNA and histone methylation. We propose a model for the role of deliberate TE reactivation in germ-line companion cells as part of a developmental mechanism for first revealing and then silencing TEs via small RNA, which may contribute to reprogramming during early development in plants and animals.

14-3-3 Proteins recognize a histone code at histone H3 and are required for transcriptional activation

Interphase phosphorylation of S10 at histone H3 is linked to transcriptional activation of a specific subset of mammalian genes like HDAC1. Recently, 14-3-3 proteins have been described as detectors for this phosphorylated histone H3 form. Here, we report that 14-3-3 binding is modulated by combinatorial modifications of histone H3. S10 phosphorylation is necessary for an interaction, but additional H3K9 or H3K14 acetylation increases the affinity of 14-3-3 for histone H3. Histone H3 phosphoacetylation occurs concomitant with K9 methylation in vivo, suggesting that histone phosphorylation and acetylation can synergize to overcome repressive histone methylation. Chromatin immunoprecipitation experiments reveal recruitment of 14-3-3 proteins to the HDAC1 gene in an H3S10ph-dependent manner. Recruitment of 14-3-3 to the promoter is enhanced by additional histone H3 acetylation and correlates with dissociation of the repressive binding module HP1gamma. Finally, siRNA-mediated loss of 14-3-3 proteins abolishes the transcriptional activation of HDAC1. Together our data indicate that 14-3-3 proteins are crucial mediators of histone phosphoacetylation signals.

An epigenetic activation role of Piwi and a Piwi-associated piRNA in Drosophila melanogaster

Heterochromatin, representing the silenced state of transcription, consists largely of transposon-enriched and highly repetitive sequences. Implicated in heterochromatin formation and transcriptional silencing in Drosophila are Piwi (P-element induced wimpy testis) and repeat-associated small interfering RNAs (rasiRNAs). Despite this, the role of Piwi in rasiRNA expression and heterochromatic silencing remains unknown. Here we report the identification and characterization of 12,903 Piwi-interacting RNAs (piRNAs) in Drosophila, showing that rasiRNAs represent a subset of piRNAs. We also show that Piwi promotes euchromatic histone modifications and piRNA transcription in subtelomeric heterochromatin (also known as telomere-associated sequence, or TAS), on the right arm of chromosome 3 (3R-TAS). Piwi binds to 3R-TAS and a piRNA uniquely mapped to 3R-TAS (3R-TAS1 piRNA). In piwi mutants, 3R-TAS loses euchromatic histone modifications yet accumulates heterochromatic histone modifications and Heterochromatin Protein 1a (HP1a). Furthermore, the expression of both the 3R-TAS1 piRNA and a white reporter gene in 3R-TAS becomes suppressed. A P element inserted 128 base pairs downstream of the 3R-TAS1 piRNA coding sequence restores the euchromatic histone modifications of 3R-TAS and the expression of 3R-TAS1 piRNA in piwi mutants, as well as partly rescuing their defects in germline stem-cell maintenance. These observations suggest that Piwi promotes the euchromatic character of 3R-TAS heterochromatin and its transcriptional activity, opposite to the known roles of Piwi and the RNA-mediated interference pathway in epigenetic silencing. This activating function is probably achieved through interaction with at least 3R-TAS1 piRNA and is essential for germline stem-cell maintenance.

Control of DNA methylation and heterochromatic silencing by histone H2B deubiquitination

Epigenetic regulation involves reversible changes in DNA methylation and/or histone modification patterns. Short interfering RNAs (siRNAs) can direct DNA methylation and heterochromatic histone modifications, causing sequence-specific transcriptional gene silencing. In animals and yeast, histone H2B is known to be monoubiquitinated, and this regulates the methylation of histone H3 (refs 10, 11). However, the relationship between histone ubiquitination and DNA methylation has not been investigated. Here we show that mutations in an Arabidopsis deubiquitination enzyme, SUP32/UBP26, decrease the dimethylation on lysine 9 of H3, suppress siRNA-directed methylation of DNA and release heterochromatic silencing of transgenes as well as transposons. We found that Arabidopsis histone H2B is monoubiquitinated at lysine 143 and that the levels of ubiquitinated H2B and trimethyl H3 at lysine 4 increase in sup32 mutant plants. SUP32/UBP26 can deubiquitinate H2B, and chromatin immunoprecipitation assays suggest an association between H2B ubiquitination and release of silencing. These data suggest that H2B deubiquitination by SUP32/UBP26 is required for heterochromatic histone H3 methylation and DNA methylation.

Comparison of Regional Brain Volume and Glucose Metabolism Between Patients with Mild Dementia with Lewy Bodies and Those with Mild Alzheimer's Disease

The aim of this study was to investigate regional differences between morphologic and functional changes in patients with mild dementia with Lewy bodies (DLB) compared with those with Alzheimer's disease (AD). Twenty patients with very mild DLB (mean age, 74.5 y; mean Mini-Mental State Examination [MMSE] score, 24.0), 20 patients with very mild AD (mean age, 74.1 y; mean MMSE score, 24.0), and 20 age- and sex-matched healthy volunteers (normal controls [NC]) underwent both (18)F-FDG PET and 3-dimensional spoiled gradient echo MRI. Fully automatic volumetry of the MRI data was used to obtain whole brain, hippocampal, occipital, and striatal volumes, which were compared with the results of a similar analysis of glucose metabolic data. In DLB patients, volumetric data indicated a significant volume decrease in the striatum, whereas (18)F-FDG PET showed significant glucose metabolic reductions in the temporal, parietal, and frontal areas--including in the occipital lobe--compared with those in the NC group. In contrast, in AD patients, both the hippocampal volume and glucose metabolism were significantly decreased, whereas the occipital volume and metabolism were preserved. Comparison of very mild DLB and AD revealed different morphologic and metabolic changes occurring in the medial temporal lobes and the occipital lobe, demonstrating characteristic pathophysiologic differences between these 2 diseases.