Heterochromatin and epigenetic control of gene expression

Eukaryotic DNA is organized into structurally distinct domains that regulate gene expression and chromosome behavior. Epigenetically heritable domains of heterochromatin control the structure and expression of large chromosome domains and are required for proper chromosome segregation. Recent studies have identified many of the enzymes and structural proteins that work together to assemble heterochromatin. The assembly process appears to occur in a stepwise manner involving sequential rounds of histone modification by silencing complexes that spread along the chromatin fiber by self-oligomerization, as well as by association with specifically modified histone amino-terminal tails. Finally, an unexpected role for noncoding RNAs and RNA interference in the formation of epigenetic chromatin domains has been uncovered.     

Noise in gene expression: origins, consequences, and control

Genetically identical cells and organisms exhibit remarkable diversity even when they have identical histories of environmental exposure. Noise, or variation, in the process of gene expression may contribute to this phenotypic variability. Recent studies suggest that this noise has multiple sources, including the stochastic or inherently random nature of the biochemical reactions of gene expression. In this review, we summarize noise terminology and comment on recent investigations into the sources, consequences, and control of noise in gene expression.     

Wasp gene expression supports an evolutionary link between maternal behavior and eusociality

The presence of workers that forgo reproduction and care for their siblings is a defining feature of eusociality and a major challenge for evolutionary theory. It has been proposed that worker behavior evolved from maternal care behavior. We explored this idea by studying gene expression in the primitively eusocial wasp Polistes metricus. Because little genomic information existed for this species, we used 454 sequencing to generate 391,157 brain complementary DNA reads, resulting in robust hits to 3017 genes from the honey bee genome, from which we identified and assayed orthologs of 32 honey bee behaviorally related genes. Wasp brain gene expression in workers was more similar to that in foundresses, which show maternal care, than to that in queens and gynes, which do not. Insulin-related genes were among the differentially regulated genes, suggesting that the evolution of eusociality involved major nutritional and reproductive pathways.     

农田系统中兽用抗生素的污染及其行为研究进展

抗生素在畜禽生产中的大量使用及其大部分可残留于畜禽粪便中并以有机肥形式进入农田,增加了其对生态环境及农作物生产的危害,加速了抗生素抗性基因的迁移与传播,可对人类和生态系统健康产生深远的影响。兽用抗生素及其代谢产物在土壤环境中能维持很长时间的活性,认识兽用抗生素在农业系统中的残留、迁移规律及其生理毒害作用对全面了解兽用抗生素的环境行为,保障农产品安全具有重要的意义。本文从农田系统中抗生素的来源、土壤中抗生素的残留、植物对抗生素的吸收、抗生素对土壤微生物的影响、土壤对抗生素的吸附及农田系统中抗生素的消解与迁移等方面对农田系统中兽用抗生素污染及其行为的研究进展进行了综述,并探讨了今后需要加强研究的科学问题。     

H2S: a universal defense against antibiotics in bacteria

Many prokaryotic species generate hydrogen sulfide (H(2)S) in their natural environments. However, the biochemistry and physiological role of this gas in nonsulfur bacteria remain largely unknown. Here we demonstrate that inactivation of putative cystathionine β-synthase, cystathionine γ-lyase, or 3-mercaptopyruvate sulfurtransferase in Bacillus anthracis, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli suppresses H(2)S production, rendering these pathogens highly sensitive to a multitude of antibiotics. Exogenous H(2)S suppresses this effect. Moreover, in bacteria that normally produce H(2)S and nitric oxide, these two gases act synergistically to sustain growth. The mechanism of gas-mediated antibiotic resistance relies on mitigation of oxidative stress imposed by antibiotics.     

热处理和抗生素对桉树固有内生细菌去除的研究

为获得无内生细菌干扰的尾叶桉组培苗,本试验采用尾叶桉种子干热和湿热处理、组培苗热处理结合茎尖培养及组培苗抗生素处理3种方法去除内生细菌,并用透明染色法和血球计数法对其体内内生细菌的分布及数量的变化开展了研究.结果表明:经种子热处理桉树种苗根部内生细菌含量略高于对照,而茎、叶部略低于对照组;组培苗恒温37℃热处理第20、...     

Spatial control of gut-specific gene expression during Caenorhabditis elegans development

The nematode Caenorhabditis elegans was transformed with constructs containing upstream deletions of the gut-specific ges-1 carboxylesterase gene. With particular deletions, ges-1 was expressed, not as normally in the gut, but rather in muscle cells of the pharynx (which belong to a sister lineage of the gut) or in body wall muscle and hypodermal cells (which belong to a cousin lineage of the gut). These observations suggest that gut-specific gene expression in C. elegans involves not only gut-specific activators but also multiple repressors that are present in particular nongut lineages.     

磺胺类药物在环境中的生态行为研究综述

综述国内外对环境中磺胺类药物的来源、生态行为（吸附、迁移、降解）等方面的研究进展,展望今后的研究方向。     

孔雀石绿降解菌对池塘水体微生物菌群的影响

对使用孔雀石绿降解菌M3后含孔雀石绿的池塘水体和底泥微生物菌群的变化进行了研究,与对照组相比,M3菌液的使用使水体微生物菌群的结构发生了明显变化:总细菌含量明显上升,葡萄球菌含量下降,孔雀石绿对真菌的抑制作用受到削弱,放线菌、假单胞菌、芽孢杆菌的数量变化与对照组无差异.与水体相比,施用M3菌液对底泥中各菌群的影响不大,底泥中各菌群的稳定性相对较高.     

Extensive DNA inversions in the B. fragilis genome control variable gene expression

The obligately anaerobic bacterium Bacteroides fragilis, an opportunistic pathogen and inhabitant of the normal human colonic microbiota, exhibits considerable within-strain phase and antigenic variation of surface components. The complete genome sequence has revealed an unusual breadth (in number and in effect) of DNA inversion events that potentially control expression of many different components, including surface and secreted components, regulatory molecules, and restriction-modification proteins. Invertible promoters of two different types (12 group 1 and 11 group 2) were identified. One group has inversion crossover (fix) sites similar to the hix sites of Salmonella typhimurium. There are also four independent intergenic shufflons that potentially alter the expression and function of varied genes. The composition of the 10 different polysaccharide biosynthesis gene clusters identified (7 with associated invertible promoters) suggests a mechanism of synthesis similar to the O-antigen capsules of Escherichia coli.     

中药渣堆肥微生物群落结构及纤维素降解酶基因表达量变化特征

本研究对不同堆制时期的中药渣堆肥样品进行Miseq高通量测序分析,并对8种纤维素降解酶基因进行荧光定量RT-PCR分析,以解析中药渣堆肥过程中微生物群落结构组成及纤维素降解酶基因表达丰度的变化特征.结果表明,在中药渣堆肥过程中,不同堆制时期的微生物群落结构组成不同,并且不同处理间的群落结构也存在差异.对样品中微生物群落...     

A glycine-dependent riboswitch that uses cooperative binding to control gene expression

We identified a previously unknown riboswitch class in bacteria that is selectively triggered by glycine. A representative of these glycine-sensing RNAs from Bacillus subtilis operates as a rare genetic on switch for the gcvT operon, which codes for proteins that form the glycine cleavage system. Most glycine riboswitches integrate two ligand-binding domains that function cooperatively to more closely approximate a two-state genetic switch. This advanced form of riboswitch may have evolved to ensure that excess glycine is efficiently used to provide carbon flux through the citric acid cycle and maintain adequate amounts of the amino acid for protein synthesis. Thus, riboswitches perform key regulatory roles and exhibit complex performance characteristics that previously had been observed only with protein factors.     

氟苯尼考联合铜环境胁迫对土壤固氮菌成膜能力及相关基因表达的研究

【目的】研究氟苯尼考和铜(Cu)残留对土壤固氮菌的生态毒性效应，为评价兽药的环境风险提供依据。【方法】对从花生根际土壤中分离出的一株优势固氮菌RpEC2071进行氟苯尼考和铜胁迫处理，试验设置空白组(0μg/mL)、氟苯尼考添加组(40μg/mL)、Cu添加组(200μg/mL)和混合组(氟苯尼考40μg/mL+Cu 200μg/mL)，并于给药后采样。采用苯酚硫酸法和96孔法研究氟苯尼考和Cu单独或联合处理对固氮菌胞外多糖产生及生物膜形成能力的影响。采用RT-qPCR测定分析固氮菌生物膜及固氮相关基因的mRNA表达水平。【结果】氟苯尼考和Cu单独胁迫会促进生物膜的形成，二者生物膜形成能力约为空白组的2倍；混合胁迫会抑制生物膜的形成，空白组生物膜形成能力是其3.1倍。胞外多糖分泌结果与生物膜形成能力测定结果基本一致。生物膜相关基因与氮代谢调控基因呈显著正相关，氟苯尼考和Cu的添加改变了fli Q、nif H和nnr R等基因的表达水平，且二者联合处理后会对其表达分别产生协同或拮抗作用。【结论】氟苯尼考与Cu的单独或联合胁迫影响固氮菌RpEC2071中生物膜相关基因表达，进而对其生物膜形...     

大蒜己糖激酶基因AsHXK2的克隆及其参与根际促生菌缓解干旱胁迫的表达分析

为明确AsHXK2基因在根际促生菌缓解干旱胁迫下的作用,采用TA克隆方法克隆得到乐都紫皮大蒜AsHXK2基因序列,并对其基本特性进行生物信息学分析。通过实时荧光定量PCR(qRT-PCR)分析了AsHXK2基因在大蒜不同组织和干旱胁迫、根际促生菌等条件下的表达情况。结果表明,AsHXK2开放阅读框全长1 500 bp,可编码499个氨基酸,分子量约为57.77 ku,理论等电点为6.37;亚细胞定位预测结果显示,AsHXK2蛋白主要定位于叶绿体,含有一个特异位点,属于己糖激酶2家族。在进化关系上,大蒜AsHXK2与天门冬科的芦笋HXK2亲缘关系最为接近。qRT-PCR分析表明,AsHXK2基因表达具有明显的组织特异性,其中鳞芽中的表达量最高。此外,不同组织中AsHXK2对根际促生菌作用下的干旱胁迫表现出不同的响应模式。干旱胁迫能够显著上调大蒜根、叶和鳞芽的AsHXK2表达水平;而在干旱胁迫施加根际促生菌的处理下,仅在叶中AsHXK2表达量显著高于干旱胁迫,表明叶片中AsHXK2对根际促生菌缓解干旱胁迫的响应较为明显。本研究为进一步探究根际促生菌缓解大蒜干旱胁迫的作用机制奠定了基础。