致病疫霉组蛋白H2A变异体序列与表达

在真核生物中,DNA缠绕在组蛋白上形成核小体,一个组蛋白分子包括H2A、H2B、H3和H4各2个核心组蛋白亚基。在这4种核心组蛋白中,H2A富含多样化,且在细胞的生物途径中起重要作用的变异体,因此,H2A家族一直是研究热点。致病疫霉是重要的病原菌也是研究卵菌的模式物种之一,目前关于卵菌表观遗传的研究还未见报道。本研究针对致病疫霉组蛋白H2A变异体,利用基因组信息和基因芯片数据,通过序列比对、系统发育分析以及基因表达水平检测,发现在致病疫霉基因组中存在组蛋白H2A变异体H2A.X.1、H2A.X.2和H2A.Z,它们在不同生长发育阶段和侵染过程呈现特异的表达谱。研究结果为进一步研究致病疫霉表观遗传机制奠定了基础。     

基于组蛋白甲基化信息的H2A.Z和H2A核小体识别

组蛋白H2A的变体H2A.Z在基因的表达过程中发挥着重要的作用。根据H2A.Z和H2A核小体中组蛋白甲基化修饰方式的不同,作者应用多样性增量二次判别方法(increment of diversity with quadratic discriminant,IDQD)成功地对H2A.Z和H2A核小体进行了识别,说明了以组蛋白甲基化信息作为特征参数的IDQD模型对H2A.Z和H2A核小体识别的有效性。通过计算DNA序列的柔性,发现H2A.Z核小体对应的DNA序列的平均柔性比常规H2A核小体对应的DNA序列的平均柔性弱。     

A Synthetic Approach to Reconstruct the Evolutionary and Functional Innovations of the Plant Histone Variant H2A.W

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Multivalent binding of PWWP2A to H2A.Z regulates mitosis and neural crest differentiation

Replacement of canonical histones with specialized histone variants promotes altering of chromatin structure and function. The essential histone variant H2A.Z affects various DNA‐based processes via poorly understood mechanisms. Here, we determine the comprehensive interactome of H2A.Z and identify PWWP2A as a novel H2A.Z‐nucleosome binder. PWWP2A is a functionally uncharacterized, vertebrate‐specific protein that binds very tightly to chromatin through a concerted multivalent binding mode. Two internal protein regions mediate H2A.Z‐specificity and nucleosome interaction, whereas the PWWP domain exhibits direct DNA binding. Genome‐wide mapping reveals that PWWP2A binds selectively to H2A.Z‐containing nucleosomes with strong preference for promoters of highly transcribed genes. In human cells, its depletion affects gene expression and impairs proliferation via a mitotic delay. While PWWP2A does not influence H2A.Z occupancy, the C‐terminal tail of H2A.Z is one important mediator to recruit PWWP2A to chromatin. Knockdown of PWWP2A in Xenopus results in severe cranial facial defects, arising from neural crest cell differentiation and migration problems. Thus, PWWP2A is a novel H2A.Z‐specific multivalent chromatin binder providing a surprising link between H2A.Z, chromosome segregation, and organ development.     

Structural basis of nucleosome dynamics modulation by histone variants H2A.B and H2A.Z.2.2

Nucleosomes are dynamic entities with wide‐ranging compositional variations. Human histone variants H2A.B and H2A.Z.2.2 play critical roles in multiple biological processes by forming unstable nucleosomes and open chromatin structures, but how H2A.B and H2A.Z.2.2 confer these dynamic features to nucleosomes remains unclear. Here, we report cryo‐EM structures of nucleosome core particles containing human H2A.B (H2A.B‐NCP) at atomic resolution, identifying large‐scale structural rearrangements in the histone octamer in H2A.B‐NCP. H2A.B‐NCP compacts approximately 103 bp of DNA wrapping around the core histones in approximately 1.2 left‐handed superhelical turns, in sharp contrast to canonical nucleosome encompassing approximately 1.7 turns of DNA. Micrococcal nuclease digestion assay reveals that nineteen H2A.B‐specific residues, including a ROF (“regulating‐octamer‐folding”) sequence of six consecutive residues, are responsible for loosening of H2A.B‐NCPs. Unlike H2A.B‐NCP, the H2A.Z.2.2‐containing nucleosome (Z.2.2‐NCP) adopts a less‐extended structure and compacts around 125 bp of DNA. Further investigation uncovers a crucial role for the H2A.Z.2.2‐specific ROF in both H2A.Z.2.2‐NCP opening and SWR1‐dependent histone replacement. Taken together, these first high‐resolution structure of unstable nucleosomes induced by histone H2A variants elucidate specific functions of H2A.B and H2A.Z.2.2 in enhancing chromatin dynamics.     

Structural insight into H4K20 methylation on H2A.Z-nucleosome by SUV420H1

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Proteomic analysis of MOLT-4 cells treated by valproic acid

The effect of valproic acid (VA) on protein expression in human T-lymphocytic leukemia cells MOLT-4 was studied. VA is an inhibitor of histonedeacetylases and has a potential use as antitumor agent in leukemia treatment. The authors in this work prove that 4 h long incubation with 2 mmol/l VA causes phosphorylation of histone H2A.X and its colocalization with 53BP1 in nuclear foci. Their co-localization is typical for DSB signaling machinery. These foci were detected in cells after 4 h exposure without increase of Annexin V positive apoptotic cells. Slight increase in apoptosis (Annexin V positivity) after 24 h is accompanied by more intensive increase in phosphorylation of H2A.X and also by formation of nuclear foci containing γH2A.X and 53BP1. Treatment of cells with 2 mmol/l VA resulted in induction of apoptosis affecting about 30% of cells after incubation for 72 h. The changes in protein expression were examined after cell incubation with 2 mmol/l VA for 4 h. Proteins were separated by two-dimensional electrophoresis and quantified using image evaluation system. Those exhibiting significant VA-induced abundance alterations were identified by mass spectrometry. Changes in expression of 22 proteins were detected, of which 15 proteins were down-regulated. Proteomic analysis resulted in successful identification of three proteins involving alfa-tubulin 3, tubulin-specific chaperone and heterogeneous nuclear ribonucloprotein F. Expression of seven proteins was up-regulated, including heterogeneous nuclear ribonucloprotein A/B. Identified proteins are related to microtubular system and hnRNP family. Suppression of microtubular proteins and changes of balance among hnRNPs can contribute to proliferation arrest and apoptosis induction.     

Recycling of modified H2A-H2B provides short-term memory of chromatin states

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Analysis of a histone H2A variant from fission yeast: evidence for a role in chromosome stability

We have isolated and characterised the pht1 gene from the fission yeast Schizosaccharomyces pombe. The sequence of the predicted translation product has revealed a striking similarity to the family of H2A.F/Z histone variant proteins, which have been found in a variety of different organisms. Cells deleted for the pht1 gene locus grow slowly, exhibit an altered colony morphology, increased resistance to heat shock and show a significant decrease in the fidelity of segregation of an S. pombe minichromosome. We propose that the histone H2A variant encoded by the pht1 gene is important for chromosomal structure and function, possibly including a role in controlling the fidelity of chromosomal segregation during mitosis.     

Quantitative regulation of histone variant H2A.Z during cell cycle by ubiquitin proteasome system and SUMO-targeted ubiquitin ligases

Quantitative control of histones and histone variants during cell cycle is relevant to their epigenetic functions. We found that the level of yeast histone variant H2A.Z in the G2/M-phase is actively kept low by the ubiquitin proteasome system and SUMO-targeted ubiquitin ligases. Overexpression of H2A.Z induced defects in mitotic progression, suggesting functional importance of this quantitative control.     

Expression of the Arabidopsis thaliana Histone Gene AtHTA1 Enhances Rice Transformation Efficiency

We expressed the Arabidopsis thaliana histone AtHTA1 in rice under the control of the maize ubiquitin promoter. Transformation efficiencies of rice plants that constitutively expressed AtHTA 1 were 28-44% higher than calli containing an empty vector control. Furthermore, co-infection of rice calli with a vector containing AtHTA 1 and another vector with the target gene increased transformation by 27-50%. Thus, expression of AtHTA 1 either transiently or in stably transformed cells improved rice transformation efficiency.     

Clinical relevance of the cagA,vacA and iceA genotypes of Helicobacter pylori in Brazilian clinical isolates

Infection with Helicobacter pylori strains harboring determinants of pathogenicity may lead to a strong inflammatory response in gastric mucosa. In this work, we examined the frequency of the cagA, vacA and iceA genotypes in H. pylori strains isolated from Brazilian patients and correlated these with the clinical manifestations. H. pylori was isolated from 165 patients [30 with non-ulcer dyspepsia cases (NUD); 93 peptic ulcer disease (PUD): 31 gastric ulcers (GU) and 62 duodenal ulcer disease (DU); 18 with erosive gastritis (EG); and 24 gastroesophageal reflux disease (GERD)]. Allelic variants of cagA, vacA and iceA were identified using the polymerase chain reaction. More than one H. pylori strain was detected in 28 cases (17%), and these were excluded from the statistical analysis. We were unable to confirm an association between iceA status and clinical outcome. There was a strong association between the genotype cagA-positive vacA s1 and PUD. However, logistic regression analysis showed that vacA s1 was the only predictive factor for PUD (OR=4.19; 95% CI 1.95-8.98). The presence of the less virulent strain vacA s2 was related to GERD (OR=8.59; 95% CI 2.85-25.91). Our results support the hypothesis that virulent strains may protect against the development of GERD.