Cytosine methylation enhances Z-DNA formation in vivo.

The influence of cytosine methylation on the supercoil-stabilized B-Z equilibrium in Escherichia coli was analyzed by two independent assays. Both the M.EcoRI inhibition assay and the linking-number assay have been used previously to establish that dC-dG segments of sufficient lengths can exist as left-handed helices in vivo. A series of dC-dG plasmid inserts with Z-form potential, ranging in length from 14 to 74 base pairs, was investigated. Complete methylation of cytosine at all HhaI sites, including the inserts, was obtained by coexpression of the HhaI methyltransferase (M.HhaI) in cells also carrying a dC-dG-containing plasmid. Both assays showed that for all lengths of dC-dG inserts, the relative amounts of B and Z helices were shifted to more Z-DNA in the presence of M.HhaI than in the absence of M.HhaI. These results indicate that cytosine methylation enhances the formation of Z-DNA helices at the superhelix density present in E. coli. The B-Z equilibrium, in combination with site-specific base methylation, may constitute a concerted mechanism for the modulation of DNA topology and DNA-protein interactions.     

Heteropycnosis of an underreplicating chromosome

Drosophila nasutoides has an extraordinary genome since 62% of its DNA resides in chromosome4. This element mainly consists of constitutive heterochromatin which does not polytenize. Earlier studies of heterochromatin attributed little attention to the fact that condensed chromosomes often vary in condensation. This paper reports that chromosomes of the same complement display different degrees and kinetics of condensation. InD. nasutoides, even sex specific differences can be observed. The results of a comparative microphotometric study on neuroblast metaphases in both sexes revealed the following picture. The process of chromosome condensation is not restricted to mitotic prophase but continues into the metaphase. The mean condensation is not equal for all chromosomes. In the metaphase of the female, Feulgen density increases from theX chromosome, via3 and2, to chromosome4. In the male, the order isX, 2, 3, Y, and4. During the metaphase of the male, chromosomes condense with similar kinetics. In contrast, chromosomes of the female display asynchrony as monitored by area and length determinations. TheX chromosomes of the female probably have enhanced shortening during prophase. This would explain the metaphase of the female where theX chromosomes shorten less than the autosomes, and why each of theX chromosomes is 15% shorter than theX chromosome in the metaphase of the male. Further differences were observed in the longitudinal and lateral compaction of the chromosomes in males and females. The sex chromosomes and chromosome3 condense by shortening, while chromosomes2 and4 preferentially reduce their diameter. The large amount of DNA engaged in heteropycnosis and the isochromosome nature allow the identification of chromosome4 during interphase. At this stage, a new category of extreme DNA packaging was detected. The interphase density of chromosome4 can exceed that of metaphase by a factor of up to 8. Two events account for this high degree of condensation:(1) the homologues are particularly associated due to somatic pairing and (2) the arms are further tightened as a result of pericentric folding. The features of the isochromosome suggest that the interaction of chromatids during interphase is essentially caused by specific DNA sequences. The data confirm that heteropycnosis not only interferes with gene expression but also strongly inhibits DNA synthesis in endocycles.     

Microspectrophotometric comparison of the genome sizes of Drosophila hydei and some related species

The relative genome sizes and the proportions of X- and Y-chromosomal DNA in Drosophila hydei, D. neohydei and D. eohydei were measured by microspectrophotometry. Some implications of the results with respect to genome evolution in these species are discussed.     

Bead rings at the endoplasmic reticulum-golgi complex boundary: morphological changes accompanying inihibition of intracellular transport of secretory proteins in arthropod fat body tissue

Golgi complex beads are 10-nm particles arranged in rings on the smooth surface of rough endoplasmic reticulum (ER) makind the forming face of the Golgi complex (GC). In arthropod cells they stain specifically with bismuth. Their morphology has been studied after treatment with reagents known to interfere with GC function. Inhibitors of oxidative phosphorylation (antimycin A, cyanide, and anoxia), but not an inhibitor of glycolysis (iodoacetate), both cause the bead rings to collapse and the GC saccules to round up, and inhibit transition vesicle (TV) formation. Cycloheximide blocks protein synthesis on ribosomes but does not stop TV formation or disrupt bead rings, even after prolonged treatment (6 h) to allow emptying of the rough ER cisternae. Thus the collapse of bead rings is not attributable to inhibition of protein synthesis, and the ring structure of beads does not require continued protein synthesis and secretion for its maintenance. Valinomycin has effects on the GC similar to those of antimycin A, but {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187, monensin, and lasalocid do not affect bead ring structure or TV formation. These results are consistent with valinomycin’s secondarily uncoupling mitochondria, which collapses bead rings and prevents TV formation. Thus inhibitors of oxidative phosphorylation do not influence the beads through cation movement. Because mononsin and lasalocid block secretion at the level of the condensing vacuoles, bead rings are not influenced by blocks in secretion distal to them or by the backup of secretory material. These experiments are consistent with inhibitors of oxidative phosphorylation collapsing bead rings by decreasing intracellular ATP. The concomitant block to TV formation and the collapse of bead rings suggests that integrity of the bead rings is essential for the transport of secretory material from the rough ER to the GC.     

RPN2与肝癌患者预后及对肝癌细胞生长的作用

目的:探讨核糖蛋白2(ribophorin II,RPN2)在肝细胞肝癌(HCC)组织中的表达和对HCC患者生存的影响,同时分析RPN2对肝癌HepG2细胞生长和克隆形成的作用。方法:应用免疫组化方法和HCC公共芯片数据,从蛋白和m RNA水平检测HCC组织中RPN2的表达,同时分析RPN2与HCC患者临床参数的关系及预后相关性;进一步利用MTS法和克隆形成实验在肝癌HepG2细胞中检测RPN2对细胞生长的作用。结果:98例肝癌组织中,RPN2阳性表达率88.78%,对应癌旁肝组织中,RPN2阳性表达率74.49%;癌组织中RPN2染色评分为5.80±3.15,癌旁肝组织RPN2染色评分为2.13±1.59,肝癌组织中RPN2表达显著上调(P0.001)。3个肝癌公共芯片数据(共522例肝癌)中RPN2的m RNA表达水平同样显著升高(均P0.001)。98例肝癌患者RPN2表达水平与肿瘤直径(P=0.004)、门脉侵袭(P=0.012)和TNM分期(P=0.009)相关;RPN2高表达的患者总体生存期(OS)和无复发生存期(RFS)较RPN2低表达的患者短(OS:P=0.027;RFS:P=0.036)。肝癌HepG2细胞转染RPN2小干扰RNA后,细胞生长能力显著受抑制。结论:RPN2在肝癌中表达显著升高,RPN2的表达与肝癌的恶性进展有关,RPN2显著促进肝癌细胞生长。     

中国植被分类系统修订方案

为了推动《中国植被志》研编工作, 该文回顾了中国植被分类系统的发展过程和主要阶段性成果, 提出了作为《中国植被志》研编技术框架组成部分的中国植被分类系统修订方案, 对各植被型组及各植被型进行了简单定义和描述, 并针对中国植被分类系统若干问题, 特别就中国植被分类系统总体框架、混交林的界定以及土壤在植被分类中的重要性等问题进行了讨论。1960年侯学煜在《中国的植被》中首次提出了中国植被分类的原则和系统, 1980年出版的《中国植被》制定了分类等级和划分依据等更加完善的系统, 之后《中国植被及其地理格局——中华人民共和国1:1 000 000植被图说明书》和《中国植物区系与植被地理》以及很多省区的植被专著对该系统进行过修订。2017年宋永昌在《植被生态学》中提出了一个分类等级单位调整的方案。本次提出的中国植被分类系统修订方案基本沿用《中国植被》的植被分类原则、分类单位及系统, 采用“植物群落学-生态学”分类原则, 主要以植物群落特征及其与环境的关系作为分类依据, 包含三级主要分类单位, 即植被型(高级单位)、群系(中级单位)和群丛(低级单位); 在三个主要分类单位之上分别增加辅助单位植被型组、群系组和群丛组, 在植被型和群系之下主要根据群落的生态差异和实际需要可再增加植被亚型或亚群系。修订方案包含了森林、灌丛、草本植被(草地)、荒漠、高山冻原与稀疏植被、沼泽与水生植被(湿地)、农业植被、城市植被和无植被地段9个植被型组, 划分为48个植被型(含30个自然植被型、12个农业植被型、5个城市植被型和无植被地段)。自然植被中有23个植被型进一步划分出了81个植被亚型。     

Non-native prey species supporting fish assemblage biomass in a Neotropical reservoir

The present study aimed to investigate the role of four non-native invertebrates in supporting fish biomass as well as their influence on the carbon flow into the Volta Grande reservoir food web. The fish samples were carried out quarterly between October 2015 and July 2016 using gillnets. At the sampled sites, four non-native invertebrates (golden mussel, Asian clam, trumpet snail and Amazonian prawn), which are potential prey for fish in the Volta Grande reservoir, were collected by targeted sampling using a Petersen-type bottom dredger and semi-circular sieves. The gut contents of the fish were collected and analyzed under stereoscope, and samples of muscle tissue of these fish, as well as the four non-native invertebrate species sampled, were submitted for isotopic analysis. Results obtained by the present study, by both gut content and stable isotopic analyses, pointed to a trophic structure where non-native species represent not only a strong component of the fish community, but also their main carbon source. Based on gut contents and isotopic mixing models, we found that together, non-native prey are essential carbon sources for the fish fauna, fuelling more than 40.0% of the biomass in four dominant fish species. The consumption rate of non-native bivalves by the native omnivorous fish Leporinus friderici suggested these filter-feeding organisms potentially constitute an important trophic connection between littoral consumers and pelagic energy sources. In addition, non-native prey were also prominent carbon sources for non-native fish, fuelling more than half of the biomass in peacock bass and silver croaker, suggesting these prey have a fundamental role in maintaining non-native fish populations in this system. Our results may help to understand fundamental ecological issues bringing to light the extent to which these new combinations of species influence the energy flow and ecosystem properties of the Volta Grande reservoir.