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Nature Contents 24 August 2006 (Vol. 442 pp847-956)
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[自然要览] （选自英国Nature杂志，2006年8月24日出版） 封面故事：与感知酸味有关的离子通道被发现 The cells and logic for mammalian sour taste detection 近年来，研究人员发现了哺乳动物5个基本味觉中3个的分子机制，它们分别是甜 味、鲜味（谷氨酸单钠的一种味道）和苦味。其他两种味觉（即酸味和咸味）的 分子机制却捉摸不定。现在，研究人员发现，PKD2L1离子通道是哺乳动物一个候 选的酸味传感器。 PKD2L1 (一种多囊肾病类的离子通道)在舌头上一个亚组的受 体细胞中表达，这个亚组的受体细胞与主管甜味、苦味和鲜味的受体细胞明显不 同。它还存在于脊髓中央管道周围的神经元中，这些神经元会响应于细胞外pH值 的下降而诱发行动势。这些细胞可能是科学家长期寻找的脑脊髓液体化学传感系 统的构成部分。这项工作为很不相同的生理条件下酸味的感觉指出了一个共同的 基础。在本期封面图片上，舌头组织中感知甜味、鲜味和苦味的味蕾标记为绿 色，感知酸味的味蕾标记为红色。（Letter p.934, N&V） 知道认亲的变形虫 （RELATIVES VALUED） Social evolution: Kin preference in a social microbe 血亲识别帮助合作在很多哺乳动物中发展变化，甚至在微生物中似乎也是这样。 用群居变形虫Dictyostelium purpureum所做的一项实验表明，变形虫喜欢跟与 自己有亲缘关系的个体形成群体。在这些群体中，一些个体会以死帮助其他个 体。通过无私帮助自己的血亲，变形虫也许可避免加入异族群体需要付出的代 价，就像与其相关的物种D. discoideum所经历的那样。（Brief Communications p.881） RNAi诱导的转录沉寂的多代遗传（Hard-wired RNAi） Gene expression: Long-term gene silencing by RNAi 决定RNA干涉（RNAi）治疗潜力的一个重要因素是其抑制效应的寿命。以前， RNAi诱导的转录沉寂作用的遗传只在一代小鼠身上被发现。现在，研究人员发 现，线虫Caenorhabditis elegans的一次RNAi所诱发的转录沉寂作用，能在没有 这种诱发因素和没有RNAi机器的情况下，在有性生殖所产生的后代中无限制地遗 传下去。（Brief Communications p.882） 关于受损DNA修复的新模型（A new take on DNA repair (Goodman AKE)） RecA acts in trans to allow replication of damaged DNA by DNA polymerase V 关于大肠杆菌中受损DNA的修复的一个新模型，有可能解决早先观测结果和模型 中所存在的矛盾。未修复的DNA病灶可阻断基因组复制，所以细胞已经形成了防 卫机制，来在复制机器碰到这种病灶时对付它们。在大肠杆菌中，这个过程涉及 pol V（一种专门的DNA聚合酶）和RecA（一种DNA修复蛋白）。以前的研究工作 表明，RecA结合到一个单链DNA（ssDNA）上，与病灶在同一条链上，刺激pol V 在受损的模板上合成DNA。但是现在，Schlacher发现，RecA事实上结合到一个不 同的同源ssDNA上，并激发对面链上的pol V，而不是在被复制的链上的pol V。 （Article p.883） 星系与黑洞之间的关系（Galaxies versus black holes (Yi LS)） Suppression of star formation in early-type galaxies by feedback from supermassive black holes GALEX卫星在近紫外波段所做的观测，为巨大椭圆形星系中年轻恒星的形成与被 认为在其中心的超大黑洞（它们在这个地方通过以能量和物质喷射流的形式出现 的“反馈”与其主星系发生相互作用）之间的关系提供了新数据。这些数据为关 于星系形成的一个复杂的计算机模型提供了约束条件，并且说明，超大黑洞有一 个临界质量，在这个质量时，来自该黑洞的喷射流和流出物会变得如此强大，以 至于能够阻止所有气体增长和主星系的进一步增长。（Letter p.888） 磁星可以是射频脉冲星（Magnetars are radio stars (Camilo LS)） Transient pulsed radio emission from a magnetar 异常X-射线脉冲星（AXP）是慢速转动的中子星，能发出非常明亮的、可变的X- 射线辐射。它们被认为是磁星，其能量来源于强大的磁场，但与“正常”脉冲星 不同的是，它们似乎从未发出脉冲式射频辐射。Camilo等人报告，异常X-射线脉 冲星XTE J1810-197事实上的确每转一周就发出射频脉冲。这意味着，磁星可以 是射频脉冲星，没有必要用另外的模型来解释没有射频脉冲产生情况下的增长。 （Letter p.892） “稳定岛”的边界在哪里（This island race (Herzberg KS)） Nuclear isomers in superheavy elements as stepping stones towards the island of stability 一个原子核的稳定性，是由原子核强大的吸引力与原子核中质子之间的静电排斥 力二者之间的一场拉锯战的结果决定的。如果100个质子和大约150个以上的中子 组装进一个原子核中，排斥力通常会占主导地位，引起原子核裂变。对于质子和 中子的某些“神奇数字”而言，这种排斥力是可以克服的，原子核可以稳定存 在。尤其是，科学家预测，在锕系元素之外存在一个“稳定岛”，这里长寿命 的、甚至稳定的超重元素可以存在，但其精确界线却不知道。然而，实验研究可 帮助确定这个岛在什么地方。锘同位素254No的光谱分析显示了三个激发态结 构，其中两个处于亚稳态。这一发现将帮助约束关于超重元素的核模型，并为寻 找下一批神奇数字提供更多数据。（Letter p.896; N&V） MIF-S与大气中氧含量（Oxygen or what? (Ohmoto JT)） Sulphur isotope evidence for an oxic Archaean atmosphere 地球大气中的氧含量被认为在大约24亿年前曾有急剧增加。关于这种增加的最有 说服力的证据是，在比这个时间早的岩石中存在被称为MIF-S的化学签名，而在 比这个时间晚的岩石中却没有。MIF-S签名已被明确为大气中低氧含量的一个标 志，但本期Nature上一篇报告却要让人们驻足思考。24亿年前形成的一些岩石似 乎不含MIF-S。这表明，要么大气中氧含量在24亿年前波动非常大，要么MIF-S不 像曾经被假设的那样是低氧含量的可靠标志。（Letter p.908; N&V） 对内的无私与对外的自私并存（Local favourites (Fehr RH)） Parochial altruism in humans 利他主义是人类社会中合作与社会秩序的维护的一个至关重要的源泉。近年来， 关于人类利他主义的演化模型曾预测，狭隘思想（偏爱自己民族、种族或语言群 体成员的表现）是人类利他主义的一个重要特征，但关于这个问题几乎没有经验 证据或实验证据。现在，对巴布亚新几内亚的土著群体所做的惩罚实验表明，利 他性的规范的遵守和规范的实行，受到民族、种族或语言群体内部徇私行为的强 烈影响。在很多现代社会中，存在强大的政治力量，他们会利用社会群体对内的 利他情感和对外的侵略情感。该研究表明，这种行为可能存在一个深层基础，因 而向现有演化理论提出了挑战。（Letter p.912） 能引起痴呆的突变（Dementia-causing mutation (Hutton/van Broekhoven JP)） Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17 / Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21 两组神经科学家发现，为一种生长因子编码的progranulin基因所发生的一个突 变，能引起“额颞叶痴呆症”(FTD)。该疾病是65岁以下人群中第二种最常见的 痴呆形式，能够损坏记忆和个性，而且还可能影响运动。这一发现也许可帮助解 决关于该疾病病因的困惑：以前的研究工作表明，一个相邻的被称为“与微管相 关的tau蛋白”的基因中所发生的突变与某些FTD病例有关，但并不是与全部FTD 病例有关。（Letters pp.916, 920） 神经元的增添怎样影响大脑功能（Well connected (Gage TC)） NMDA-receptor-mediated, cell-specific integration of new neurons in adult dentate gyrus 成年大脑会不断增添新的神经元，但这一现象怎样影响大脑功能却不清楚。 Tashiro等人通过研究一项新的单细胞基因剔除技术，发现选择让哪些新神经元 存活取决于它们的突触输入。该发现为在学习和记忆过程中新的、但却一致的神 经回路的建立提供了一个可能的机制。在上图中，成年齿状脑回中的新神经元通 过绿色荧光蛋白由逆转录酶病毒调控的表达而显示出来，通过对神经核蛋白 （NeuN）进行免疫染色（红色），齿状颗粒和CA3锥形细胞层被显示了出来。 （Letter p. 929） 中心体复制与染色体分离（Centrosomes: two’s a crowd (Stearns BM)） Mechanism limiting centrosome duplication to once per cell cycle 中心体每个细胞周期只复制一次，所以在细胞周期开始有一个中心体，而在有丝 分裂中有两个。这一过程中的缺陷能引起基因组不稳定，甚至癌症。一项体外研 究表明，在细胞控制中心体复制的方式与染色体分离之间存在一个惊人的相似 性。中心体中的中心粒对在有丝分裂的最后分开，这是一个需要分离酶的过程。 分离酶是姐妹染色单体在有丝分裂中分离时所涉及的一种蛋白酶。分开的中心粒 是下一个细胞周期中复制过程的一个基质。新复制的中心粒是成对的，所以它们 在通过有丝分裂之前是不能再次复制的，而在通过有丝分裂之后，它们就可以通 过由分离酶调控的分离过程进行复制。这项工作揭示了导致每个周期只有一次复 制的两个细胞过程背后的一个共同机制。（Letter p.947; N&V） |
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ningkeqing
木虫 (正式写手)
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---------------------- NEWS AND VIEWS ---------------------- Earth Sciences: Signature required Most geologists agree that Earth's atmosphere was oxygen-free until 2. 4 billion years ago. But the latest sulphur-isotope measurements from sedimentary rocks suggest otherwise. L. Paul Knauth 10.1038/442873a http://www.nature.com/nature/journal/v442/n7105/full/442873a.html Cell biology: A licence for duplication Genome stability in animal cells requires strict control over the numbers of the organelles called centrosomes. An attractive 'licensing' model now explains how centrosome duplication is restricted to just once per cell cycle. Erich A. Nigg 10.1038/442874a http://www.nature.com/nature/journal/v442/n7105/full/442874a.html 50 & 100 years ago 10.1038/442875a http://www.nature.com/nature/journal/v442/n7105/full/442875a.html Nuclear physics: Island ahoy! Measurements of the energy levels of unstable superheavy nuclei are beginning to afford distant vistas of a promised land -- 'the island of stability' beyond the bounds of the conventional periodic table. Mark A. Stoyer 10.1038/442876a http://www.nature.com/nature/journal/v442/n7105/full/442876a.html Biochemistry: Mussel muscle Andrew Mitchinson 10.1038/442877b http://www.nature.com/nature/journal/v442/n7105/full/442877b.html Physiology: Nitrate at the ion exchange The distinction between CLC ion channels and ion exchangers has become blurred. The physiological role of CLC exchangers has been a mystery, but one function is evidently to concentrate nitrate in plant vacuoles. Julian I. Schroeder 10.1038/nature04999 http://www.nature.com/nature/jou ... ll/nature04999.html Solid-state-chemistry: Framework for a molecular prison A remarkable family of solids exists in which host compounds hold guest molecules captive in their rooms. The latest example has an unprecedented topology and opens up fresh avenues for investigation. Michel Pouchard 10.1038/442878a http://www.nature.com/nature/journal/v442/n7105/full/442878a.html ---------------------- BRIEF COMMUNICATIONS ---------------------- Social evolution: Kin preference in a social microbe Given the right circumstances, even an amoeba chooses to be altruistic towards its relatives. Natasha J. Mehdiabadi et al. 10.1038/442881a Abstract: http://www.nature.com/nature/journal/v442/n7105/abs/442881a. html Article: http://www.nature.com/nature/journal/v442/n7105/full/442881a. html Gene expression: Long-term gene silencing by RNAi Nadine L. Vastenhouw et al. 10.1038/442882a Abstract: http://www.nature.com/nature/journal/v442/n7105/abs/442882a. html Article: http://www.nature.com/nature/journal/v442/n7105/full/442882a. html BRIEF COMMUNICATIONS ARISING Protein evolution: Causes of trends in amino-acid gain and loss Laurence D. Hurst, Edward J. Feil and Eduardo P. C. Rocha 10.1038/nature05137 Abstract: http://www.nature.com/nature/jou ... bs/nature05137.html Article: http://www.nature.com/nature/jou ... ll/nature05137.html Protein evolution: Causes of trends in amino-acid gain and loss (Reply) I. K. Jordan et al. 10.1038/nature05138 Abstract: http://www.nature.com/nature/jou ... bs/nature05138.html Article: http://www.nature.com/nature/jou ... ll/nature05138.html ---------------------- ARTICLE ---------------------- RecA acts in trans to allow replication of damaged DNA by DNA polymerase V Katharina Schlacher, Michael M. Cox, Roger Woodgate and Myron F. Goodman 10.1038/nature05042 Abstract: http://www.nature.com/nature/jou ... bs/nature05042.html Article: http://www.nature.com/nature/jou ... ll/nature05042.html ---------------------- LETTERS ---------------------- Suppression of star formation in early-type galaxies by feedback from supermassive black holes Kevin Schawinski et al. 10.1038/nature04934 Abstract: http://www.nature.com/nature/jou ... bs/nature04934.html Article: http://www.nature.com/nature/jou ... ll/nature04934.html Transient pulsed radio emission from a magnetar The X-ray pulsar XTE J1810-197 emits bright, narrow, highly linearly polarized radio pulses, observed at every rotation, thereby establishing that magnetars can be radio pulsars. Fernando Camilo et al. 10.1038/nature04986 Abstract: http://www.nature.com/nature/jou ... bs/nature04986.html Article: http://www.nature.com/nature/jou ... ll/nature04986.html Nuclear isomers in superheavy elements as stepping stones towards the island of stability Spectroscopic studies of the nobelium isotope 254No -- the heaviest nucleus studied in this manner to date -- details three excited structures, two of which are metastable, which should help to constrain nuclear models of the superheavy elements. R.-D. Herzberg et al. 10.1038/nature05069 Abstract: http://www.nature.com/nature/jou ... bs/nature05069.html Article: http://www.nature.com/nature/jou ... ll/nature05069.html Magnetic impurity formation in quantum point contacts A mysterious step at 0.7G0 -- a so-called '0.7 anomaly' -- in a quantum point contact experiment has been suggested to signify the presence of an intrinsic magnetic impurity (an electronic state with a spin-1/2 magnetic moment) at low electron densities. This idea receives strong support from new detailed calculations. Tomaz Rejec and Yigal Meir 10.1038/nature05054 Abstract: http://www.nature.com/nature/jou ... bs/nature05054.html Article: http://www.nature.com/nature/jou ... ll/nature05054.html Dependence of single-molecule junction conductance on molecular conformation Latha Venkataraman et al. 10.1038/nature05037 Abstract: http://www.nature.com/nature/jou ... bs/nature05037.html Article: http://www.nature.com/nature/jou ... ll/nature05037.html Sulphur isotope evidence for an oxic Archaean atmosphere Rocks formed before 2.4 Gyr have not been found to contain a mass-independently fractionated sulphur isotopes (MIF-S) chemical signature. This suggests that either atmospheric oxygen levels fluctuated dramatically before 2.4 Gyr, or that MIF-S is not a reliable indictor of when atmospheric oxygen levels were low. Hiroshi Ohmoto et al. 10.1038/nature05044 Abstract: http://www.nature.com/nature/jou ... bs/nature05044.html Article: http://www.nature.com/nature/jou ... ll/nature05044.html Parochial altruism in humans Punishment experiments with indigenous groups in Papua New Guinea demonstrate that altruistic norm compliance and norm enforcement are strongly influenced by favouritism within ethnic, racial, or language groups. The parochial patterns of human altruism constitute a challenge for existing evolutionary theories. Helen Bernhard, Urs Fischbacher and Ernst Fehr 10.1038/nature04981 Abstract: http://www.nature.com/nature/jou ... bs/nature04981.html Article: http://www.nature.com/nature/jou ... ll/nature04981.html Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17 One of two papers detailing that mutations in the gene progranulin, which is found near MAPT on chromosome 17, can cause frontotemporal dementia, a severe neurodegenerative disorder that can affect memory, personality and motor function. The progranulin gene encodes a secreted growth factor. Matt Baker et al. 10.1038/nature05016 Abstract: http://www.nature.com/nature/jou ... bs/nature05016.html Article: http://www.nature.com/nature/jou ... ll/nature05016.html Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21 One of two papers detailing that mutations in the gene progranulin, which is found near MAPT on chromosome 17, can cause Frontotemporal dementia, a severe neurodegenerative disorder that can affect memory, personality and motor function. The progranulin gene encodes a secreted growth factor. Marc Cruts et al. 10.1038/nature05017 Abstract: http://www.nature.com/nature/jou ... bs/nature05017.html Article: http://www.nature.com/nature/jou ... ll/nature05017.html Highly ordered arrangement of single neurons in orientation pinwheels In the cat visual cortex, orientation-selective neurons are arranged in characteristic patterns known as 'pinwheels'. In vivo, two-photon calcium imaging reveals the highly ordered arrangement at the level of single cells for this functional architecture -- neurons selective to different orientations are strictly segregated, even at pinwheel centres. Kenichi Ohki et al. 10.1038/nature05019 Abstract: http://www.nature.com/nature/jou ... bs/nature05019.html Article: http://www.nature.com/nature/jou ... ll/nature05019.html NMDA-receptor-mediated, cell-specific integration of new neurons in adult dentate gyrus Development of a new single-cell gene knockout technique shows how new neurons are selected for survival depending on their synaptic input. This provides a possible mechanism for the building of new neuronal circuits during learning and memory. Ayumu Tashiro et al. 10.1038/nature05028 Abstract: http://www.nature.com/nature/jou ... bs/nature05028.html Article: http://www.nature.com/nature/jou ... ll/nature05028.html The cells and logic for mammalian sour taste detection Angela L. Huang et al. 10.1038/nature05084 Abstract: http://www.nature.com/nature/jou ... bs/nature05084.html Article: http://www.nature.com/nature/jou ... ll/nature05084.html The nitrate/proton antiporter AtCLCa mediates nitrate accumulation in plant vacuoles The function of the members of the chloride channel (CLC) protein family, which encode organellar proton chloride exchangers, remains to be fully elucidated. Arabidopsis thaliana CLCa, a member of this family, mediates specific nitrate accumulation into the plant vacuole through a NO3-/H+ exchanger mechanism. A. De Angeli et al. 10.1038/nature05013 Abstract: http://www.nature.com/nature/jou ... bs/nature05013.html Article: http://www.nature.com/nature/jou ... ll/nature05013.html Signal sequence directs localized secretion of bacterial surface proteins To ensure proper identification by the secretion machinery, surface and extracellular proteins contain specific signal sequences. This paper reveals that the information contained in these short tags can also be used to target proteins to specific locations within the bacterial cell. Fredric Carlsson et al. 10.1038/nature05021 Abstract: http://www.nature.com/nature/jou ... bs/nature05021.html Article: http://www.nature.com/nature/jou ... ll/nature05021.html Mechanism limiting centrosome duplication to once per cell cycle Centrosome duplication needs to be tightly controlled to occur once and only once per cell cycle. The regulated timing of centriole disengagement in late mitosis is shown to allow one round of centrosome duplication in the next cycle. Meng-Fu Bryan Tsou and Tim Stearns 10.1038/nature04985 Abstract: http://www.nature.com/nature/jou ... bs/nature04985.html Article: http://www.nature.com/nature/jou ... ll/nature04985.html ***** |
2楼2006-08-26 12:16:00