Induction of cytochrome P450 1A and DNA damage in isolated rainbow trout (Oncorhynchus mykiss) hepatocytes by 2,3,7,8 tetrachlorodibenzo-p-dioxin

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatocytes isolated from immature rainbow trout (Oncorhynchus mykiss) by collagenase perfusion were investigated with respect to induction of cytochrome P450 1A (CYP1A) enzyme activities and protein contents as well as DNA damage. Exposure of primary rainbow trout hepatocytes to TCDD resulted in increased CYP1A contents, as determined by immunoblotting, enhanced activities of 7-ethoxyresorufin-O-deethylase (EROD) and increased DNA damage as determined by the comet assay. By means of electron microscopy, no symptoms of cytotoxicity could be observed except for slight increases of lysosomal components and the smooth endoplasmic reticulum. Whereas CYP1A contents constantly increased over the duration of the entire experiment, EROD activities remained constant from day 3 of exposure to 1 nM TCDD; maximum induction of CYP1A activities was reached with 0.1 nM TCDD after 5 days. DNA damage increased in a time- and dose-dependent fashion until day 3. After 5 days, DNA damage was less pronounced, and the number of damaged nuclei declined in all TCDD concentrations. Since TCDD has been shown to not directly react with DNA, metabolism of TCDD or TCDD-induced changes in other metabolic pathways are suspected to result in the production of DNA-reactive (endogenous) substances.     

The spatial pattern of soil-dwelling termites in primary and logged forest in Sabah, Malaysia

Abstract.  1. Primary and logged lowland dipterocarp forest sites were sampled for subterranean termites using soil pits located on a grid system in order to detect any patchiness in their distribution.
2. A spatial pattern in termite distributions was observed in the primary and logged sites, but the response differed between soil-feeding and non-soil-feeding termites.
3. Spatial analysis showed that soil-feeding termites were homogeneously distributed in the primary forest but significantly aggregated in the logged forest. This pattern was reversed for non-soil-feeding termites and may result from differences in resource provisioning between the two sites.
4. Gaps in termite distribution comprised a greater area than patches for both feeding groups and sites, but gaps dominated the logged site.
5. A significant association between soil-feeding and non-soil-feeding termite distributions occurred at both sites. This arose from an association between patches in the primary forest and between gaps in the logged forest.
6. Termite spatial pattern was optimally observed at a minimum extent of 64 m and lag of 2 m.
7. The spatially explicit SADIE (Spatial Analysis by Distances IndicEs) analyses were more successful than (non-spatially explicit) multivariate analysis (Canonical Correspondence Analysis) at detecting associations between termite spatial distributions and that of other biotic and abiotic variables.     

Dampening DNA damage checkpoint signalling via coordinated BRCT domain interactions

In response to DNA damage, checkpoint signalling protects genome integrity at the cost of repressing cell cycle progression and DNA replication. Mechanisms for checkpoint down‐regulation are therefore necessary for proper cellular proliferation. We recently uncovered a phosphatase‐independent mechanism for dampening checkpoint signalling, where the checkpoint adaptor Rad9 is counteracted by the repair scaffolds Slx4‐Rtt107. Here, we establish the molecular requirements for this new mode of checkpoint regulation. We engineered a minimal multi‐BRCT‐domain (MBD) module that recapitulates the action of Slx4‐Rtt107 in checkpoint down‐regulation. MBD mimics the damage‐induced Dpb11‐Slx4‐Rtt107 complex by synergistically interacting with lesion‐specific phospho‐sites in Ddc1 and H2A. We propose that efficient recruitment of Dpb11‐Slx4‐Rtt107 or MBD via a cooperative ‘two‐site‐docking’ mechanism displaces Rad9. MBD also interacts with the Mus81 nuclease following checkpoint dampening, suggesting a spatio‐temporal coordination of checkpoint signalling and DNA repair via a combinatorial mode of BRCT‐domains interactions.     

Assembly of Slx4 signaling complexes behind DNA replication forks

Obstructions to replication fork progression, referred to collectively as DNA replication stress, challenge genome stability. In Saccharomyces cerevisiae, cells lacking RTT107 or SLX4 show genome instability and sensitivity to DNA replication stress and are defective in the completion of DNA replication during recovery from replication stress. We demonstrate that Slx4 is recruited to chromatin behind stressed replication forks, in a region that is spatially distinct from that occupied by the replication machinery. Slx4 complex formation is nucleated by Mec1 phosphorylation of histone H2A, which is recognized by the constitutive Slx4 binding partner Rtt107. Slx4 is essential for recruiting the Mec1 activator Dpb11 behind stressed replication forks, and Slx4 complexes are important for full activity of Mec1. We propose that Slx4 complexes promote robust checkpoint signaling by Mec1 by stably recruiting Dpb11 within a discrete domain behind the replication fork, during DNA replication stress.     

铜离子胁迫对两种地衣细胞结构的影响

采用光学显微镜徒手切片技术和透射电子显微镜超薄切片制备技术,以两种叶状地衣即中国树花(Ramalina sinensis)和地卷(Peltigera rufescens)为实验材料,研究了不同浓度CuSO4(0、1、2、3、4mmol/L)处理24h后地衣体细胞的存活率以及Cu2+胁迫对细胞超微结构的影响。结果显示:(1)光学显微镜下可初步确定,Cu2+浓度越大中国树花共生藻细胞存活率越小,而同样处理条件下地卷共生藻细胞的存活率则基本保持不变。(2)低浓度Cu2+(1mmol/L)对中国树花细胞结构基本无影响,细胞壁、细胞膜及细胞内的线粒体、叶绿体完整;随着Cu2+浓度增加,当处理Cu2+浓度为2mmol/L时,细胞壁无损,但细胞膜开始破坏形成小空泡,线粒体嵴变凌乱,叶绿体也出现皱缩,类囊体膨胀,基粒排列紊乱;当Cu2+处理浓度大于2mmol/L时,共生藻的细胞膜和细胞器出现不同程度的损伤;当Cu2+浓度为3mmol/L时,细胞壁变薄,细胞膜形成的空泡变大,细胞内部结构变松散,蛋白核消失,叶绿体与细胞质混在一起,基粒片层扭曲,分布混乱,线粒体变形;当Cu2+浓度达4mmol/L时,细胞结构完全受到破坏。(3)不同浓度Cu2+处理对地卷共生藻细胞结构无明显的影响,在所有处理条件下地卷共生藻细胞壁、细胞膜都完整,且大多数共生藻细胞处于分裂状态。研究认为,中国树花对Cu2+胁迫较敏感,Cu2+耐受在1~2mmol/L之间,Cu2+浓度与中国树花细胞结构的损伤程度存在着明显的剂量效应关系,Cu2+浓度越高,其属于共球藻的真核共生藻细胞受损程度越大;地卷对Cu2+胁迫具有一定的耐性,Cu2+胁迫下地卷属于蓝藻的原核共生藻细胞仍能繁殖分裂产生子代细胞。     

Ovipositor internal microsculpture in the Braconidae (Insecta, Hymenoptera)

Variation in the microsculpture of the ovipositor egg canal, the morphology of the tip of the upper valve, the structure of the valvillus and the apex of the lower valve seals, as revealed by scanning electron microscopy is described for members of 52 genera representing 30 subfamilies of Braconidae. The possible phylogenetic implications of this variation are discussed. Characters supporting monophyly of the cyclostome clade, and of the non-cyclostome subfamilies Agathidinae, Pselaphaninae and Sigalphinae are reported. Functional and phylogenetic implications are discussed and possible convergent evolution of some features associated with endoparasitism are considered in the light of recent molecular systematics findings. © 1998 The Norwegian Academy of Science and Letters     

Large scale of identification of differentially expressed genes in the regenerating rat liver after SISPH

After partial hepatectomy (PH), the remnant paren-chyma can completely recover lost liver mass and function in about one week[1,2]. Although adult hepa-tocytes are normally quiescent, they are readily primed to pass from G0 to G1 phase within 2―6 h after PH. The first peak of DNA synthesis appears 24 h after PH, while cell division peaks at 36 h. The liver cells then enter a second cell cycle, and redifferentiation and reconstruction of structure and function[3―6] take place. A great nu…     

Genetic controls on starch amylose content in wheat and rice grains

Starch accumulates in plants as granules in chloroplasts of source organs such as leaves (transitory starch) or in amyloplasts of sink organs such as seeds, tubers and roots (storage starch). Starch is composed of two types of glucose polymers: the essentially linear polymer amylose and highly branched amylopectin. The amylose content of wheat and rice seeds is an important quality trait, affecting the nutritional and sensory quality of two of the world’s most important crops. In this review, we focus on the relationship between amylose biosynthesis and the structure, physical behaviour and functionality of wheat and rice grains. We briefly describe the structure and composition of starch and then in more detail describe what is known about the mechanism of amylose synthesis and how the amount of amylose in starch might be controlled. This more specifically includes analysis of GBSS alleles, the relationship between waxy allelic forms and amylose, and related quantitative trait loci. Finally, different methods for increasing or lowering amylose content are evaluated.     

新疆焉耆盆地人类活动与气候变化的效应机制

通过对新疆焉耆盆地及其周边近40a(1973—2014)的气候变化趋势检测、LUCC和生物量估算,探讨气候变化和人类活动的生态效应机制,研究区域陆地生态系统演变及其归因。分析结果表明:(1)焉耆盆地山区和平原区降水变化都有明显的突变点,并呈现增加趋势,蒸发量在山区减少,在平原区波动性减少趋势;(2)LUCC分析表明,山区裸地面积减少5.40%,冰川面积减少3.36%,高地植被面积增加8.76%;同时平原区天然绿洲面积增加1.96%,沙漠面积减少1.62%,水域面积减少1.30%,人工绿洲面积增加15.41%,湿地面积增加1.27%;(3)山区陆地生态系统对区域气候变化非常敏感,其中降水变化是决定山区地表植被生存状态和分布的重要因素;(4)人类活动的推动作用和有益气候变化的支撑是绿洲平原区生态系统好转的原因,其中人口急剧增加和社会经济快速发展,导致绿洲平原区生态系统结构及其时空分布的主要因素。焉耆盆地及其周围区域陆地生态系统的演变对气候变化和人类活动有明显的时空尺度效应,其反应程度各不相同。