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2009年7月23日Nature中文摘要
封面故事:南北极的极光可以不对称
Asymmetric auroral intensities in the Earth's Northern and Southern
hemispheres
新的证据表明,通常认为北极光(发生在北半球)和南极光(发生在南半球)是互为镜
像的观点并非总是正确的。极光的确往往同时在北极和南极区域出现,其出现的地点由
地磁场线连接,这种联系预计也许会将两个极光的图案、位置和时间关联起来。2001年
5月12日,两个地球观测飞船“IMAGE” 和“Polar”处在对两极同时进行观测的较好位
置,当时对南极来说是黄昏,对北极来说是黎明。此次观测获得的图片现已得到分析,
它们所提供的清楚证据表明,两个极光可以是不对称的。这种不对称性可能是由因导电
性差异而产生的半球间电流引起的,但以前这一点并没有得到证明。本期封面图片上部
为北半球(来自“IMAGE”),下部为南半球(来自“Polar VIS Earth Camera”)。
(Letter p. 491)


成熟精子中核小体的作用(Paternal influence)
Distinctive chromatin in human sperm packages genes for embryo development
在精子发育过程中,正常情况下与DNA结合、将其包裹进染色质中的组蛋白大部分被交
换成鱼精蛋白,后者是形成正常精子功能所需的紧凑DNA结构的小蛋白。于是,核小体
(染色质中含组蛋白的重复单元)在精子中明显罕见。虽然罕见,但根据一项利用高分
辨率基因组技术来定位人成熟精子中所保留的核小体的研究工作,它们却有潜在重要
性。保留下来的少数核小体所含具有极为重要发育功能的基因显著增多,而且具有鲜明
的组蛋白修饰模式。这一发现提出一个可能性:它们之所以被保留下来,是为了在胚胎
中执行一种表观遗传功能。(Article p. 473)


miRNA和mRNA之间的相互作用(miRNA–mRNA interactions)
Argonaute HITS-CLIP decodes microRNA–mRNA interaction maps
由抑制性微RNA(miRNA)诱导的基因沉默在调控基因表达中的重要性现已非常明显。但
因为一个信使RNA(mRNA)的miRNA调控在它们的序列中只需要有一个短的匹配段(长度
为8个核苷酸或更少),所以事实证明,要明确确定所预测的很多mRNA结合点中哪个是
每个miRNA在活体中的目标几乎不可能。现在,对HITS-CLIP方法所做的一种改进(这种
改进的方法以miRNA和 mRNA与Argonaute蛋白的相互作用为关注点;Argonaute蛋白是普
遍存在的核酸内切酶,它们形成由RNA诱导的沉默复合物的一部分),被用来解析miRNA
与大脑mRNA转录体的结合点的一个精确分布图。该方法具有普遍适用性,应能为了解
miRNA在生物学中的作用提供了一个新手段。另外,这种分布图可让研究人员确定具有
临床意义的mRNA上用于RNA干涉(RNAi)疗法的目标作用点。(Article p. 479)


“土卫二”上存在液态水的新证据(Another gas from Enceladus)
Liquid water on Enceladus from observations of ammonia and 40Ar in the plume
自从“卡西尼”探测器图片2006年显示出从土星卫星“土卫二”喷发出的水蒸气柱和冰
粒以来,寻找这种水的来源的工作就一直在进行。这种水的可能来源包括冰壳下的液态
水和受到加热作用影响的冰。喷出物的化学组成可以为它们的来源提供线索。“卡西
尼”探测器2008年10月9 日掠过时提供了一个非常适合这一目的的数据集——迄今所获
得的具有最好信噪比的质谱,其信噪比之好足以能够让研究人员来识别以痕量存在的化
学物质。Waite等人利用这些数据显示了喷发柱中氨的存在,这是表明至少存在一些液
态水的有力证据。喷发柱的总体组成表明,它既来自一个液态水库(或来自从这样一个
水库形成的冰),又来自含冰挥发性物质所挥发出的气体。(Letter p. 487)


量子理论的经典解释(Quantum theory put in context)
State-independent experimental test of quantum contextuality
量子力学理论自其近90年前首次建立以来已取得了显著成就,它的预测已在无数实验中
得到证实。然而,并不满足该理论之公理的很多物理学家一直在寻求用一种经典理论来
对量子物理预测做出一个解释。经典模型的一个直观特征是“非情境性”
(non-contextuality):即任何一个测量结果都有独立于同时完成的其他可比测量结
果的一个值这样一种性质。理论表明,“非情境性”与量子力学是冲突的,而且用光子
和中子所做实验似乎也支持这一点。然而,这些测试要求产生特殊的量子态,存在各种
不同的漏洞。Kirchmair等人用束缚的离子做了一个实验,该实验克服了这些问题,并
且不能用“非情境性”来解释。因此,“情境性”是一种自然性质,不要求特殊量子态
或量子纠缠的产生。(Letter p. 494; News & Views)


超越衍射极限的纳米透镜(Nanolenses beat the barrier)
Near-field focusing and magnification through self-assembled nanoscale
spherical lenses
光学显微镜的性能内在受限于阿贝衍射极限。不管一个成像系统在光学性能上有多接近
完美,它都无法分辨超过这一自然极限的两个物体,该极限取决于所观察到的光的波长
及其角分布。几种方法曾被用来超越衍射极限,但这些方法一般都需要深奥的激发方
案,所以都还不实用。Lee等人正在研究超越这一极限的一种新方法,他们所采用的是
纳米尺度的球面透镜,这些透镜由被称为“杯芳烃”的杯状有机分子由下向上自组装而
成。以这种方式产生的透镜有非常短的焦距,可以产生超过衍射极限的近场放大效果,
使特征分辨率达到200纳米的数量级。这些透镜可被随意放在一个表面上,而且还可用
来减小深紫外光刻特征的大小。(Letter p. 498)


对山脊和山谷景观特征的一个定量解释(Landscapes explained)
Formation of evenly spaced ridges and valleys
从上向下看,显然在很多山地景观中山脊和山谷似乎是相间均匀的。目前关于景观演化
的物理模型能够产生看起来符合实际情况的地形,但不能预测自然景观中相间均匀的山
脊和山谷的典型“波长”。Taylor Perron及其同事利用质量守恒和沉积物输送方程式
推导出一个特征长度尺度,该尺度与地形演化模型中的山脊-山谷波长直接成比例,也
与美国五个野外研究地点(包括加州的Nappa Valley和犹他州的Point of the
Mountain)的山脊-山谷波长直接成比例。他们的发现为最常见的景观特征之一提供了
一个定量解释,而且也表明,山谷间隔距离可以记录物质性质和气候对侵蚀过程的影
响。(Letter p. 502; News & Views)


光照制约湖泊生产力(Light limits lake productivity)
Light limitation of nutrient-poor lake ecosystems
人们通常的假设是,湖泊生态系统的生产力一般受到养分供应的制约。现在,这个假设
受到来自对瑞典北部12个天然湖泊所做一项研究的新发现的挑战。研究表明,在这些湖
泊中,限制生物质积累的是光照而不是养分。很多天然湖泊像这些湖泊一样相对较小,
缺乏养分,所以有可能大多数湖泊受光照制约,而养分则主要在养分输入量异常高的湖
泊中制约生产力。(Letter p. 506; News & Views)


黑猩猩所患的艾滋病(‘AIDS’ in chimpanzees)
Increased mortality and AIDS-like immunopathology in wild chimpanzees
infected with SIVcpz
超过40种不同类型的“猿免疫缺陷病毒”(SIV)影响非洲灵长类动物,其中两种跨越
了物种障碍而在人体中产生了艾滋病病毒HIV-1 和 HIV-2。现在,对在“贡贝国家公
园”中自由漫游的黑猩猩所做的一项全面的自然史研究,推翻了关于SIVcpz(HIV-1的
前体)的一个常见假设。人们曾经普遍假设,所有SIV病毒在它们的自然宿主身上都是
非致病性的。但这项新的研究(该研究对94只黑猩猩进行了超过9年跟踪)表明,
SIVcpz感染与黑猩猩身上与艾滋病相似的症候相关,其中包括死亡风险增加10倍、生育
能力降低、以及渐进性CD4+ T细胞耗竭等。通过对人类和黑猩猩身上这些相关的逆转录
病毒的致病机制进行比较,也许有可能识别出用于预防和治疗HIV感染的药物和疫苗的
开发人员所感兴趣的病毒及宿主因子。(Letter p. 515; News & Views)


p53和miRNA之间的联系(Link between p53 and miRNA)
Modulation of microRNA processing by p53
p53肿瘤抑制因子是一种具有很多生长抑制目标的众所周知的转录激活因子。p53功能的
破坏在多数癌症的发展过程中是一个根本性事件。微RNA(miRNA)已成为肿瘤抑制中的
重要因子,在这项研究工作中,p53 和miRNA之间一个出乎意料的联系被发现。在一个
独立于它在调控转录中所扮演角色的相互作用中,作为对DNA损伤的反应,p53增强几种
生长抑制性miRNA的转录后成熟过程,其中包括miR-16-1、miR-143和miR-145。这表
明,p53调控miRNA生物生成的能力可能会有助于提高其致癌潜力。(Letter p. 529;
News & Views)


禁食过程中的体内反应及CRTC2的功能(Fast reactions)
The CREB coactivator CRTC2 links hepatic ER stress and fasting
gluconeogenesis
在禁食的哺乳动物中,循环的胰高血糖素会刺激肝脏中葡萄糖的产生,该功能部分是通
过CREB共活化剂CRTC2/TORC2实现的。现在研究表明,CRTC2的功能是充当禁食信号和肝
脏中内质网((ER)压力的一个双重传感器。禁食和ER压力通道之间在这个转录共活化
剂层面上的交汇,有助于消瘦条件下葡萄糖体内平衡及肥胖症中多糖症的形成。
(Letter p. 534)


----------------------
NEWS AND VIEWS
----------------------
Ecology: Production in pristine lakes pp463-464
An investigation of lakes in Sweden has delivered results that run counter
to the idea that primary production is generally limited by the availability

of nutrients. There are lessons for limnologists in this.
Jonathan J. Cole
doi:10.1038/460463a
http://www.nature.com/nature/journal/v460/n7254/full/460463a.html

Quantum mechanics: Hidden context pp464-465
The idea that physical phenomena might be described by a more downto-earth
theory than quantum physics has met with resistance from many physicists.
Indeed, it seems that nature is not as simple as we would like.
Boris Blinov
doi:10.1038/460464a
http://www.nature.com/nature/journal/v460/n7254/full/460464a.html

Materials science: Soft particles feel the squeeze pp465-466
It's hard to fit in when you're different [mdash] especially if you're a
large particle trying to squeeze into an array of smaller ones. But some
soft, polymeric particles simply shrink to fit the space available.
Daan Frenkel
doi:10.1038/460465a
http://www.nature.com/nature/journal/v460/n7254/full/460465a.html

Cancer: Three birds with one stone pp466-467
The core domain of the p53 protein has been found to affect microRNA
processing [mdash] its third known antitumour activity. Most cancerous
p53 mutations affect this domain and may abolish all tumour-suppressor
functions.
Franck Toledo and Boris Bardot
doi:10.1038/460466a
http://www.nature.com/nature/journal/v460/n7254/full/460466a.html

50 & 100 years ago p467
doi:10.1038/460467a
http://www.nature.com/nature/journal/v460/n7254/full/460467a.html

Geomorphology: Landscape texture set to scale pp468-469
Why, in many landscapes, does ridge-valley spacing show such regularity?
The combination of high-resolution data and an elegant model offers a
solution to this long-standing puzzle, for some cases at least.
Kelin X. Whipple
doi:10.1038/460468a
http://www.nature.com/nature/journal/v460/n7254/full/460468a.html

Bioengineering: Cellular control in two clicks pp469-470
If complex tissues are to be engineered, synthetic materials will be needed
that provide cells with precisely located molecular cues. A method that
attaches such cues to specific areas of a gel could be the answer.
Jason A. Burdick
doi:10.1038/460469a
http://www.nature.com/nature/journal/v460/n7254/full/460469a.html

Infectious diseases: An ill wind for wild chimps? pp470-471
Simian immunodeficiency virus is associated with increased mortality in a
subspecies of chimpanzee living under natural conditions in East Africa.
This is worrying news for the chimpanzee populations involved.
Robin A. Weiss and Jonathan L. Heeney
doi:10.1038/460470a
http://www.nature.com/nature/journal/v460/n7254/full/460470a.html

----------------------
ARTICLES
----------------------
Distinctive chromatin in human sperm packages genes for embryo development
pp473-478
During spermiogenesis, canonical histones are largely exchanged for
protamines, and whether the rarely retained nucleosomes have any function
has been unclear. Here, high-resolution genomic approaches are used to
localize the nucleosomes retained in mature human sperm; they are found
to be significantly enriched at developmentally important genes and to
have distinctive patterns of histone modifications.
Saher Sue Hammoud et al.
doi:10.1038/nature08162
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08162.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08162.html

Argonaute HITS-CLIP decodes microRNA-mRNA interaction maps pp479-486
MicroRNAs (miRNAs) are short RNAs that are ubiquitous, potent regulators of
gene expression; however, as miRNA activity requires base pairing with only
6-8 nucleotides of messenger RNA, predicting target mRNAs is a major
challenge. By using a method known as HITS-CLIP, combined with bioinformatic

analysis, it has now been possible to demonstrate how the in vivo
interactions
between miRNAs and the mRNA targets can be validated.
Sung Wook Chi, Julie B. Zang, Aldo Mele and Robert B. Darnell
doi:10.1038/nature08170
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08170.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08170.html

----------------------
LETTERS
----------------------
Liquid water on Enceladus from observations of ammonia and 40Ar in the plume
pp487-490
Jets of water ice from surface fractures near the south pole of Saturn's icy

moon Enceladus produce a plume of gas and particles. The source of the jets
may be a liquid water region under the ice shell. Here, ammonia is reported
to
be present in the plume, providing strong evidence for the existence of at
least some liquid water.
J. H. Waite Jr et al.
doi:10.1038/nature08153
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08153.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08153.html

Asymmetric auroral intensities in the Earth/'s Northern and Southern
hemispheres
pp491-493
It is commonly assumed that the aurora borealis (Northern Hemisphere) and
the
aurora australis (Southern Hemisphere) are mirror images of each other.
Here,
observations are reported that clearly contradict this common assumption:
intense spots are seen at dawn in the Northern summer Hemisphere, and at
dusk in the Southern winter Hemisphere.
K. M. Laundal and N. Ostgaard
doi:10.1038/nature08154
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08154.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08154.html

State-independent experimental test of quantum contextuality pp494-497
The question of whether quantum phenomena can be explained by classical
models with hidden variables is the subject of a long-lasting debate. One
feature of classical models that is thought to be in conflict with quantum
mechanics is non-contextuality, with experiments undertaken with photons
and neutrons seeming to support this. However, these tests required the
generation of special quantum states and left various loopholes open. Here
an experiment is performed with trapped ions that overcomes these problems
and cannot be explained in non-contextual terms.
G. Kirchmair et al.
doi:10.1038/nature08172
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08172.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08172.html

Near-field focusing and magnification through self-assembled nanoscale
spherical lenses pp498-501
Cup-shaped molecules of calix[4]hydroquinone self-assemble on a surface into

a lens shape; these lenses are shown to generate near-field magnification
beyond the diffraction limit, enabling the resolution of features of the
order of 200 nanometres. Such spherical nanolenses provide new pathways for
lens-based near-field focusing and high-resolution optical imaging at very
low intensities, which are useful for, among other things, bio-imaging and
near-field lithography.
Ju Young Lee et al.
doi:10.1038/nature08173
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08173.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08173.html

Formation of evenly spaced ridges and valleys pp502-505
Ridges and valleys in many landscapes are uniformly spaced, but no theory
has predicted this fundamental topographic wavelength. A characteristic
length scale is now derived from equations of mass conservation and sediment

transport; it is found to be directly proportional to the valley spacing in
models of landform evolution, and to the measured valley spacing at five
study sites in the USA.
J. Taylor Perron, James W. Kirchner and William E. Dietrich
doi:10.1038/nature08174
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08174.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08174.html

Light limitation of nutrient-poor lake ecosystems pp506-509
Lake ecosystem productivity, defined by the rate of biomass synthesis, is
believed to be limited by nutrient availability. However, the comparison of
several small unproductive lakes along a water colour gradient now shows
that
coloured terrestrial organic matter controls the key process for new biomass

synthesis through its effects on light attenuation, suggesting that light is

the more important limiting factor.
Jan Karlsson et al.
doi:10.1038/nature08179
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08179.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08179.html

Partial penetrance facilitates developmental evolution in bacteria
pp510-514
Individuals with exactly the same genetic make-up can differ from one
another
in their development and resulting phenotype when the genome contains a
mutation a phenomenon called 'partial penetrance'. Exploration of the
genetic
and stochastic factors controlling the proportion of abnormal 'twin' spores
in mutant populations of the bacterium Bacillus subtilus now reveals how
mutations affecting DNA replication and cell division may act in synergy to
significantly increase the penetrance of twin sporulation.
Avigdor Eldar et al.
doi:10.1038/nature08150
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08150.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08150.html

Increased mortality and AIDS-like immunopathology in wild chimpanzees
infected with SIVcpz pp515-519
There are over 40 different simian immunodeficiency viruses (SIVs) with
which
African primates are naturally infected; two of these have crossed the
species
barrier to generate human immunodeficiency virus types 1 and 2 (HIV-1 and
HIV-2).
Although SIVs do not generally cause AIDS in primates, AIDS-like disease is
now shown to occur in chimpanzee populations in the wild who are naturally
infected with SIVcpz, a close relative of HIV-1.
Brandon F. Keele et al.
doi:10.1038/nature08200
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08200.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08200.html

Regulation of the innate immune response by threonine-phosphatase of Eyes
absent pp520-524
Innate immunity is stimulated by non-microbial danger signals, as well as
by viral or bacterial components. The threonine-phosphatase activity of the
protein Eyes absent 4 (EYA4), originally identified as a co-transcription
factor, is now shown to stimulate the innate immune response to the
undigested DNA from apoptotic cells.
Yasutaka Okabe, Teruyuki Sano and Shigekazu Nagata
doi:10.1038/nature08138
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08138.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08138.html

Helical extension of the neuronal SNARE complex into the membrane
pp525-528
In neurotransmission, synaptic vesicles fuse with the membrane of nerve
cells
to release neurotransmitter content into the synaptic cleft. This process
requires the assembly of several members of the SNARE protein family. Here,
the X-ray structure of a neuronal SNARE complex is solved, providing insight

into how these proteins assemble.
Alexander Stein, Gert Weber, Markus C. Wahl and Reinhard Jahn
doi:10.1038/nature08156
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08156.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08156.html

Modulation of microRNA processing by p53 pp529-533
Disruption of the tumour suppressor p53, a transcriptional activator with
numerous growth-suppressive targets, is a fundamental event in the
development
of most cancers. Here, p53 is found to have another function, independent of

its role in transcription, enhancing the earliest processing step of
precursors
for microRNAs that regulate genes affecting cell growth.
Hiroshi I. Suzuki et al.
doi:10.1038/nature08199
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08199.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08199.html

The CREB coactivator CRTC2 links hepatic ER stress and fasting
gluconeogenesis
pp534-537
In fasted mammals, circulating pancreatic glucagon stimulates
gluconeogenesis
in the liver in part through the CREB coactivator CRTC2. The production of
glucose by the liver is increased in obesity, reflecting chronic increases
in endoplasmic reticulum (ER) stress that promote insulin resistance.
Here, CRTC2 is shown to function as a dual sensor for fasting signals
and ER stress, thereby contributing to glucose homeostasis.
Yiguo Wang, Liliana Vera, Wolfgang H. Fischer and Marc Montminy
doi:10.1038/nature08111
Abstract:
http://www.nature.com/nature/journal/v460/n7254/abs/nature08111.html
Article:
http://www.nature.com/nature/journal/v460/n7254/full/nature08111.html

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