Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin

We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells.     

ANTIPYRETIC ACTION OF DEXAMETHASONE ON EGTAZIC ACIDINDUCED FEVER IN RABBITS

本文用脑室灌注和Ｆｕｒａ２测定细胞内游离钙技术观察了地塞米松（ｄｅｘａｍｅｔｈａｓｏｎｅ,ＤＥＸ）对家兔乙二醇双（２氨基乙醚）四乙酸性发热效应和下丘脑细胞内游离钙浓度（［Ｃａ２＋］ｉ）的影响,借此深入探讨地塞米松解热作用的中枢机制。结果发现：脑室灌注乙二醇双（２氨基乙醚）四乙酸（０６ｎｍｏｌ）引起家兔结肠温度明显升高,静脉注射地塞米松（５ｍｇ／ｋｇ）显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,地塞米松（６０～１２０μｍｏｌ／Ｌ）并不影响下丘脑细胞内［Ｃａ２＋］ｉ,而事先脑室灌注抑制基因转录的放线菌素Ｄ（３ｎｍｏｌ）则完全取消了地塞米松对乙二醇双（２氨基乙醚）四乙酸性发热的解热作用。这些结果提示：地塞米松显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,其机制与地塞米松激活脑内某些基因的表达有关,而与下丘脑神经细胞跨膜钙离子流无关。     

人眼微光下夜近视机制的研究

本文利用激光散斑屈光测试系统详细探讨了夜近视(night myopia)的产生机制。夜近视在环境亮度降低到产生暗视觉时出现,并随亮度继续降低而增大,平均值为1.35D。实验证明眼睛球差和色差不是造成夜近视的主要因素。夜近视数值在暗适应过程中呈增大的趋势。在暗视觉时,由于视野中缺少适宜的刺激,眼睛处于暗焦(dark focus)休止状态,这是造成夜近视的主要原因。     

瓜类枯萎病研究进展(综述)

瓜类枯萎病是由尖孢镰刀菌Fusarium oxysporum侵染引起,在全球大部分瓜类产区均有发生。该病已成为影响我国瓜类品质和产量的重要病害。本文从瓜类作物枯萎病的防治方法、致病机理和分子生物学研究等方面综述其研究现状,并对今后的研究方向进行展望。     

beta1,6 N-acetylglucosaminyltransferase (core 2 GlcNAc-T) expression in normal rat tissues and different cell lines: evidence for complex mechanisms of regulation

The distribution of the Golgi enzyme beta1, 6-N- acetylglucosaminyltransferase (core 2 GlcNAc-T for short) has been investigated in several tissue and cell systems by combining the potentials of a polyclonal antibody and a novel, sensitive fluorescent enzyme assay. In normal rat tissues, levels of the protein were found to vary and as a general trend did not correlate with enzyme activities. Additionally, we observed tissue-specific core 2 GlcNAc-T forms of various size: 75 kDa (liver), 70 kDa (spleen), 60 kDA (heart), and 50 kDa (heart and lung). These forms might arise from differential protein modifications; alternatively, the smaller form may be a product of proteolytic cleavage, given the presence of a catalytically inactive 50 kDa species in rat serum. Chinese hamster ovary (CHO), MDAY-D2, PSA- 5E, and PYS-2 cell lines consistently displayed a 70 kDa enzyme. When induced to retrodifferentiate in the presence of butyrate + cholera toxin, CHO cells exhibited a 21-fold increase in enzyme activity, while protein levels remained constant. A similar trend was observed in the embryonal endoderm cell lines PSA-5E and PYS-2, where an approximately 100-fold difference in core 2 GlcNAc-T activity was found notwithstanding unchanged amounts of the protein and identical mRNA levels, as evidenced by RT-PCR. In contrast, levels of core 2 GlcNAc-T activity in MDAY-D2 cells correlated well with protein expression. Taken together, these observations demonstrate that core 2 GlcNAc-T expression may be subjected to multiple mechanisms of regulation and suggest that in at least some instances (i.e., PSA-5E and PYS-2 cells) expression may be regulated exclusively via posttranslational mechanism(s) of control.      

Non-coding nuclear DNA markers in phylogenetic reconstruction

Molecular DNA based data sets are the most important resource for phylogenetic reconstruction. Among the various marker systems, which were introduced and optimized within the last decade, coding sequences played an important role, especially when molecular clock approaches and multi-gene datasets were assembled. However, non-coding DNA sequences do not only play a quantitatively dominant role, as demonstrated by the two examples nuclear ITS (Internal transcribed spacer regions of nuclear ribosomal DNA) and plastidic trnL-F region, but there is also a wide range of different marker systems that can be applied in different ways. Herein, we review the application of several non-coding nuclear DNA marker systems for phylogenetic reconstructions and summarize valuable information for future research.     

Next-generation sequencing and genome evolution in allopolyploids

?Premise of the study: Hybridization and polyploidization (allopolyploidy) are ubiquitous in the evolution of plants, but tracing the origins and subsequent evolution of the constituent genomes of allopolyploids has been challenging. Genome doubling greatly complicates genetic analyses, and this has long hindered investigation in that most allopolyploid species are "nonmodel" organisms. However, recent advances in sequencing and genomics technologies now provide unprecedented opportunities to analyze numerous genetic markers in multiple individuals in any organism. ?Methods: Here we review the application of next-generation sequencing technologies to the study of three aspects of allopolyploid genome evolution: duplicated gene loss and expression in two recently formed Tragopogon allopolyploids, intergenomic interactions and chromosomal evolution in Tragopogon miscellus, and repetitive DNA evolution in Nicotiana allopolyploids. ?Key results: For the first time, we can explore on a genomic scale the evolutionary processes that are ongoing in natural allopolyploids and not be restricted to well-studied crops and genetic models. ?Conclusions: These approaches can be easily and inexpensively applied to many other plant species-making any evolutionarily provocative system a new "model" system.     

基于PBL模式的生物化学教学探索

目的:评价PBL教学模式在生物化学中应用的教学效果,对生物化学理论教学的方式进行探讨。方法:用PBL模式进行教学,采用理论考试的形式对教学效果进行评价。结果:PBL教学组的学生在学习态度和积极性等方面好于传统教学组;在考试成绩方面PBL教学组病例分析考试成绩好于传统教学组,而基础知识考试成绩没有差别。结论:PBL模式能提高学生的分析问题和解决问题的综合应用能力,而基础知识的掌握程度与传统教学相比没有区别。     

人胎儿脑的一个cDNA编码序列及其蛋白质预测

用 m RNA差异显示 PCR技术 ,从人 1 8周、2 2周胎儿脑和肝肾组织的 m RNA逆转录产物得到一些特异性显示的片段 .其中一个随机片段 GC1 0 2作为探针 ,从本实验室构建的 1 8周胎儿脑c DNA基因文库进行杂交筛选 ,得到一个阳性克隆λ gt1 0 /GC1 0 2 .该克隆内插入的 c DNA片段长2 .9kb,经过 DNA测序 ,显示具有一个开放阅读框架 ,编码 1 37个氨基酸的肽链 .用蛋白质结构的建模软件预测了该肽链的立体结构初步模型 .     

Chemistry of Cirsium and Carduus: a role in ecological risk assessment for biological control of weeds?

Prediction of host plant range and ecological impact of exotic phytophagous insects, such as insects for classical biological control of weeds, represents a major challenge. Recently, the flowerhead weevil (Rhinocyllus conicus Fröl.), introduced from Europe into North America to control exotic thistles (Carduus spp.), has become invasive. It feeds heavily on some, but not all species of native North American thistles (Cirsium spp.). We hypothesized that such non-target use among native plants could be better predicted by knowledge of characteristic chemical profiles of secondary compounds to supplement the results of host specificity testing. To evaluate this hypothesis, we reviewed the literature on the chemistry of Cirsium and Carduus thistles. We asked what compounds are known to be present, what is known about their biological activity, and whether such information on chemical profiles would have better predicted realized host range and ecological effects of R. conicus in North America. We found an extensive, but incomplete literature on the chemistry of true thistles. Two main patterns emerged. First, consistent chemical similarities and interesting differences occur among species of thistles. Second, variation occurs in biologically active groups of characteristic compounds, specifically flavonoids, sterols, alkaloids and phenolic acids, that are known to influence host plant acceptance, selection, and feeding by phytophagous insects. Surprisingly, sesquiterpene lactones, which are characterisitic in closely related Asteraceae, have not been extensively reported for Cirsium or Carduus. The minimal evidence on sesquiterpene lactones may reflect extraction methods vs. true absence. In summary, our review suggests further research on thistle chemistry in insect feeding is warranted. Also, since the exotic Canada thistle (Cirsium arvense) is an invasive thistle of current concern in North America, such research on mechanisms underlying host range expansion by exotic insects would be useful.