《Nature》目录要览：2010-07-15出版

封面故事：猴与人的分化
New Oligocene primate from Saudi Arabia and the divergence of apes and Old World monkeys
灵长类的化石记录很稀少，仍然存在实质性的缺口。其中一个缺口是“旧世界”的猴子与“新世界”高等灵长类内的类人猿和人类的分化。这种分化以前仅限于“非洲-阿拉伯大陆”的渐新世，但在沙特西北一个新的、处在进化树根部的狭鼻猿的发现缩小了这个缺口。沙特发现的这个材料来自距今约2800万年前的渐新世中期，它的狭鼻猿分化特征非常少，说明“旧世界”的猴子与“新世界”的类人猿之间的分化发生在那个时期之后。本期封面所示为头盖骨的前部，其犬齿和上颚宽臼齿都在原处。头盖骨的大小表明这是一个中等大小的灵长类，体重在15公斤和20公斤之间。（Letter p. 360）封面图片提供：美国密执安大学Daniel Erickson/Bonnie Miljour。


tRNA在蛋白合成过程中的运动（The ribosome in motion）
Ribosome dynamics and tRNA movement by time-resolved electron cryomicroscopy
在蛋白合成过程中，转移核糖核酸（转移RNA，即tRNA）在其所附着的氨基酸被转移到生长中的肽链之上时，依次通过核糖体的A点、P点和E点。大尺度的构形运动伴随着它们的转位。Holger Stark及其同事对核糖体数量惊人的190万幅“单颗粒”冷电子显微图像进行了处理，以观察这些动态变化。他们得出结论说，构形变化是由热驱动的，或者说是“布朗运动”，所发生的变化引起tNRA在一个狭窄路径上穿过核糖体做定向运动。（Article p. 329; News & Views）


肠道“病毒组”的变化（Variations in the gut virome）
Viruses in the faecal microbiota of monozygotic twins and their mothers
人肠道微生物群的微生物组成成分最近一直是很多研究工作所关注的焦点。现在，这个问题以第一种病毒宏基因组（亦称元基因组或环境基因组）的形式又增添了一层复杂性。这种病毒宏基因组是从四组同卵双胞胎及其母亲的粪便样品中分离出的病毒样颗粒中确定的。以前的一项研究表明，双胞胎与他们的母亲在其粪便细菌群落中所具有的相似程度显著大于不相关个体之间的相似程度。相比之下，“病毒组”被发现对个体来说是独特的，与它们的遗传相关性程度无关。然而，在每个个体中，在这项研究为期一年的时间中，“病毒组”几乎没有发生变化。（Article p. 334）


大质量恒星周围的吸积盘（High-mass stars on disk）
A hot compact dust disk around a massive young stellar object
关于大质量恒星生命周期的关键方面仍然不清楚，尤其是在早期演化阶段。例如，关于大质量恒星是否是与低质量和中等质量的恒星以相同方式通过盘吸积形成的、以及如果是这样的话那么这些盘的结构是否将与低质量恒星的盘有所不同仍然存在争论。现在，来自ESO的“甚大望远镜干涉仪”的新的观测结果显示，在一个大质量年轻星体“原恒星IRAS 13481–6124”周围有一个热的致密盘。该图像显示了一个长形的结构，大小约为13×19个天文单位，这与在45度倾角所看到的一个盘是一致的，其性质在定性上和定量上都与在低质量恒星形成过程中所观测到的盘相似。（Letter p. 339）


钻石在地球上的分布（Diamond distribution）
Diamonds sampled by plumes from the core–mantle boundary
钻石的形成发生在地球地幔中深度超过150公里处的高压条件下。钻石是在由被称为“金伯利岩”的火山岩组成的垂直管状结构中来到地面的。迄今为止，人们已经绘出了几千个这样的“金伯利岩”管道，但研究工作一直集中在非常古老的“克拉通”上，即具有最古老陆壳的地方，因为最具有经济可行性的钻石就是在这种地方发现的。Trond Torsvik及其同事利用对过去5.40亿年的一个板块重建结果来确定这些“克拉通”相对于深处地幔在“金伯利岩”喷发时的位置。“金伯利岩”被发现与地幔最深处大尺度异质性的边缘相关，本文作者们推断这些地方是地核-地幔边界区，那里岩浆上涌产生了地幔柱，“金伯利岩”就是在这些地幔柱中形成的。这些地幔柱在过去5.40亿年几乎控制了所喷发的所有“金伯利岩”的分布。（Letter p. 352）


自然保护工作的选择性（Conservation: where to save）
Replacing underperforming protected areas achieves better conservation outcomes
有人提出，表现差的保护区应当失去其保护地位，所节省的资金应用到效果好的其他地方。这种观点不易被保护工作者和地方游说团体所接受。但根据对澳大利亚近7,000个保护区的表现所做的一项研究，从长期来看这种观点可能是最好的政策。大约70个被取消资格的保护区（所评估土地的单位价值产生的保护价值最低的保护区）的出售，可能获得大约210亿澳元（约177亿美元）的资金。如果这些钱然后再重新投入到生物多样性保护策略更可能获得成功的保护区，将有可能以同样支出获得更大程度的保护。随着全世界保护区的新投资额持续下降，本文作者们提出，面对破坏植被行为的泛滥猖獗，保留那些最有价值、最有生产力的区域比以往任何时候都显得更为重要。（Letter p.365; News & Views）


自闭症的遗传因素（The genetics of autism）
Functional impact of global rare copy number variation in autism spectrum disorders
“自闭症候群”(ASDs)是一类症候，其典型特征是重复性行为、严重受限的兴趣以及社交和沟通有困难。ASD具有高度遗传性，然而造成这种病症的遗传决定因素在很大程度上仍然不清楚。一项全基因组分析显示，ASD患者所携带的“罕见版本号变异体”(CNVs，即版本号在不同基因组之间有所不同的DNA片段)较多，这种情况要么是遗传的，要么是后天形成的。这些分析结果表明，几个新基因可能是ASD的候选基因，同时也指出了细胞增殖、投射（projection）和运动以及特定信号作用通道在这种病症中的重要性。（Letter p. 368）


“盲视”的视觉通道（The blindsight pathway）
Blindsight depends on the lateral geniculate nucleus
“初级视皮层”(V1)对视力非常关键，但近40年前人们注意到，很有意思的是，V1受伤的患者仍能指出或避开视觉刺激，尽管他们并没有意识到这些刺激的存在。人们早就认为，这种“盲视”依赖于能够绕过从“外侧膝状体核”(LGN) 到V1的通常路径的视觉通道。通过将永久性和可逆性病灶结合起来，同时采用行为测试和对猕猴的多个视觉区域进行fMRI测绘，Schmid等人发现，LGN本身是“替代通道”中的一个关键环节。在V1受损动物中，LGN失活会废止高等视觉区域的视觉检测和fMRI激发，说明直接LGN投射不仅存在于“盲视”中，而且在视力正常期间也是快速检测的一个可行的二级通道。（Letter p. 373）


身体轴线的形成次序及其机制（Body line decisions）
Planar cell polarity breaks bilateral symmetry by controlling ciliary positioning
动物的三个身体轴是在发育过程中依次形成的——先是前-后轴和背-腹轴，然后是左-右非对称性，但后者是怎样源自前者的却不清楚。现在，Yingzi Yang及其同事发现，属于“planar cell polarity”家族的两个小鼠基因(Vangl1 和 Vangl2) 是纤毛在身体后部沉积所必需的，后者又决定穿过后部脊索的左向“节流动”。这项工作表明，平面细胞极性是一个在演化过程中保留下来的机制，它传输预先确定的前-后位置信息，并将其转换成胚胎中第一个打破侧向对称的事件。（Letter p. 378）


甲基化可以延长寿命（Methylation adds to lifespan）
Members of the H3K4 trimethylation complex regulate lifespan in a germline-dependent manner in C. elegans
Sir2家族的基因已知通过对组蛋白脱乙酰作用的一个效应来影响酵母、线虫和其他生物的寿命。这便提出一个问题：其他组蛋白修饰是否也影响寿命？Greer等人发现，组蛋白甲基化调控线虫的寿命。被称为“ASH-2复合物”的一个保守的染色质蛋白复合物（该复合物在赖氨酸-4(H3K4)处使组蛋白H3发生“三甲基化”）的构成成分的缺失都会延长线虫寿命。相反，H3K4脱甲基酶rbr-2是维持正常寿命所必需的，这与认为过多的H3K4“三甲基化”缩短寿命的观点是一致的。这种寿命延长要求一个完好的成年生殖细胞系的存在以及成熟卵的持续产生，这说明体细胞的寿命是由生殖细胞中一个H3K4甲基转移酶/脱甲基酶复合物调控的。（Letter p. 383）


植物核小体定位的全基因组分析（Plant nucleosome positioning）
Relationship between nucleosome positioning and DNA methylation
在植物拟南芥中对核小体（组织和控制对基因组DNA之接触的核蛋白分子）的定位所做的一项全基因组分析，再加上单碱基分辨率的DNA甲基化分布图，显示了与核小体结合的DNA的“DNA甲基化状态”中的10-碱基周期性。这些结果表明，核小体位置影响基因组中的DNA甲基化模式，DNA甲基转移酶优先以与核小体结合的DNA为目标。相似趋势过去也在人的核小体DNA中观察到，说明核小体与DNA甲基转移酶之间的关系是保守的。（Letter p. 388）



----------------------
NEWS AND VIEWS
----------------------
Cosmology forum: Is dark energy really a mystery? pp321-322
The Universe is expanding. And the expansion seems to be speeding up. To
account for that acceleration, a mysterious factor, 'dark energy', is often
invoked. A contrary opinion [mdash] that this factor isn't at all mysterious
[mdash] is here given voice, along with counter-arguments against that view.
Eugenio Bianchi, Carlo Rovelli and Rocky Kolb
doi:10.1038/466321a
http://www.nature.com/nature/journal/v466/n7304/full/466321a.html

Conservation science: Trade-in to trade-up pp322-323
Nature reserves and protected areas enjoy sacred status in conservation
[mdash] which translates into a 'do not touch' attitude. But selling off
some of the less worthy of them would pay conservation dividends.
Peter Kareiva
doi:10.1038/466322a
http://www.nature.com/nature/journal/v466/n7304/full/466322a.html

Solid-state physics: U-turns strictly prohibited pp323-324
According to theory, electrons on the surface of a topological insulator are
not allowed to make U-turns. This notion, and some of its main consequences,
has now been tested experimentally.
Marcel Franz
doi:10.1038/466323a
http://www.nature.com/nature/journal/v466/n7304/full/466323a.html

50 & 100 years ago p324
doi:10.1038/466324a
http://www.nature.com/nature/journal/v466/n7304/full/466324a.html

Protein synthesis: Translocation in slow motion pp325-326
Time-resolved electron microscopy can capture structural changes in active
macromolecular complexes, but detailed imaging is essential. The dynamics of
one step in protein synthesis has been deduced from two million images.
Mans Ehrenberg
doi:10.1038/466325a
http://www.nature.com/nature/journal/v466/n7304/full/466325a.html

Earth science: Proposal with a ring of diamonds pp326-327
Plate reconstructions show that ancient eruptions of diamond-bearing rocks
occurred consistently above a ring-like region of plume-generation zones
deep in Earth's mantle. Do such zones remain stationary?
David A. D. Evans
doi:10.1038/466326a
http://www.nature.com/nature/journal/v466/n7304/full/466326a.html

----------------------
ARTICLES
----------------------
Ribosome dynamics and tRNA movement by time-resolved electron
cryomicroscopy pp329-333
During protein synthesis within the ribosome, transfer RNAs (tRNAs) move
sequentially through different sites as their attached amino acids are
transferred onto the growing protein chain. Large conformational movements
accompany this process. Here, a staggering 1.9 million electron
cryomicroscopy images of the ribosome have been processed to visualize these
changes. The results reveal that the ribosome functions as a Brownian
machine that couples spontaneous changes driven by thermal energy to
directed movement.
Niels Fischer et al.
doi:10.1038/nature09206
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09206.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09206.html

Viruses in the faecal microbiota of monozygotic twins and their
mothers pp334-338
The microbial content of the human gut has been the focus of much research
interest recently. Now another layer of complexity has been added: the viral
content of the gut. Virus-like particles were isolated from faecal samples
from four sets of identical twins and their mothers, at three time points
over a one-year period. The viromes (metagenomes) of these particles were
then sequenced. The results show that there is high interpersonal variation
in viromes, but that intrapersonal diversity was very low over this time
period.
Alejandro Reyes et al.
doi:10.1038/nature09199
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09199.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09199.html

----------------------
LETTERS
----------------------
A hot compact dust disk around a massive young stellar object pp339-342
Circumstellar disks are an essential ingredient of the formation of low-mass
stars, but it is unclear whether they are also required for the formation of
stars more massive than about 10 solar masses. Clear observational evidence
is needed, for example the detection of dusty disks around massive young
stellar objects. Here, near-infrared interferometric observations are
reported that spatially resolve the distribution of hot material around a
high-mass young stellar object.
Stefan Kraus et al.
doi:10.1038/nature09174
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09174.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09174.html

Transmission of topological surface states through surface
barriers pp343-346
Topological surface states are a class of electronic states that might be of
interest in quantum computing or spintronic applications. They are predicted
to be robust against imperfections, but so far there has been no evidence
that these states do transmit through naturally occurring surface defects.
Here, scanning tunnelling microscopy has been used to show that topological
surface states of antimony can be transmitted through naturally occurring
barriers that block non-topological surface states of common metals.
Jungpil Seo et al.
doi:10.1038/nature09189
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09189.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09189.html

Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap
states pp347-351
In the high-transition-temperature superconductors, the pseudogap phase
becomes predominant when the density of doped holes is reduced. In this
phase it has been unclear which electronic symmetries (if any) are broken,
what the identity of any associated order parameter might be, and which
microscopic electronic degrees of freedom are active. Here, images of the
intra-unit-cell states in underdoped Bi2Sr2CaCu2O8 + [delta] are studied,
revealing electronic nematicity of the states close to the pseudogap energy.
M. J. Lawler et al.
doi:10.1038/nature09169
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09169.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09169.html

Diamonds sampled by plumes from the core-mantle boundary pp352-355
Diamonds are formed under high pressure more than 150 kilometres deep in the
Earth's mantle, and are brought to the surface mainly by volcanic rocks
called kimberlites. Here, plate reconstructions and tomographic images have
been used to show that the edges of the largest heterogeneities in the
deepest mantle, stable for at least 200 million years and possibly for 540
million years, seem to have controlled the eruption of most Phanerozoic
kimberlites. This has implications for future exploration for kimberlites.
Trond H. Torsvik et al.
doi:10.1038/nature09216
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09216.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09216.html

Striations, duration, migration and tidal response in deep
tremor pp356-359
Deep seismic tremor in subduction zones has been suggested to repeat at a
regular interval, migrate at various velocities and be modulated by tidal
stress. Here, evidence is presented that a time-invariant interface property
[mdash] possibly the ratio of brittle to ductile areas [mdash] controls
tremor behaviour in the Nankai subduction zone, Japan. Where tremor duration
is short, tremor is more strongly affected by tidal stress and migration is
inhibited. Where tremor lasts longer, diffusive migration occurs with a
constant diffusivity.
Satoshi Ide
doi:10.1038/nature09251
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09251.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09251.html

New Oligocene primate from Saudi Arabia and the divergence of apes and Old
World monkeys pp360-364
The fossil record of primates is sparse, and many gaps remain in our
knowledge. One gap relates to the divergence within the catarrhines [mdash]
the ancestors of hominoids (apes and humans) and Old World monkeys. The
discovery of a previously unknown catarrhine in Saudi Arabia, dated to 29-28
million years ago, helps to fill in some details. This specimen shows very
few catarrhine specializations, suggesting that the divergence between Old
World monkeys and hominoids must have occurred after this date.
Iyad S. Zalmout et al.
doi:10.1038/nature09094
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09094.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09094.html

Replacing underperforming protected areas achieves better conservation
outcomes pp365-367
Removing the protected status from poorly performing conservation areas,
selling the land and using the money better elsewhere is controversial, but
has a simplistic appeal. Here, it is shown that such degazetting can reap
significant conservation benefits, even for the well-designed Australian
network of protected areas, and even when there is a significant economic
cost to transferring protected status to a new area.
Richard A. Fuller et al.
doi:10.1038/nature09180
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09180.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09180.html

Functional impact of global rare copy number variation in autism spectrum
disorders pp368-372
The autistic spectrum disorders (ASDs) are highly heritable, yet the
underlying genetic determinants remain largely unknown. Here, a genome-wide
analysis of rare copy number variants (CNVs) has been carried out, revealing
that ASD sufferers carry a higher load of rare, genic CNVs than do controls.
Many of these CNVs are de novo and inherited. The results implicate several
novel genes in ASDs, and point to the importance of cellular proliferation,
projection and motility, as well as specific signalling pathways, in these
disorders.
Dalila Pinto et al.
doi:10.1038/nature09146
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09146.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09146.html

Blindsight depends on the lateral geniculate nucleus pp373-377
The primary visual cortex (V1) is crucial for vision, yet people with V1
injuries might still point to or avoid visual stimuli, despite having no
conscious perception of them. It has been thought that this 'blindsight'
relies on visual pathways that bypass the usual route from lateral
geniculate nucleus (LGN) to V1. But it is shown here [mdash] using a
combination of permanent and reversible lesions, behavioural testing and
functional magnetic resonance imaging (fMRI) mapping [mdash] that a critical
link in the alternative pathway is in fact the LGN.
Michael C. Schmid et al.
doi:10.1038/nature09179
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09179.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09179.html

Planar cell polarity breaks bilateral symmetry by controlling ciliary
positioning pp378-382
During vertebrate development, the dorsal-ventral and anterior-posterior
(A-P) body axes are determined first, after which left-right (L-R) asymmetry
is established. But the molecular mechanism by which L-R symmetry is broken
in reference to the other two axes is poorly understood. Here it is shown
that two mouse genes, Vang1 and Vang2, which belong to the planar cell
polarity family, are required to interpret the A-P patterning information
and link it to L-R asymmetry.
Hai Song et al.
doi:10.1038/nature09129
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09129.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09129.html

Members of the H3K4 trimethylation complex regulate lifespan in a
germline-dependent manner in C. elegans pp383-387
It is shown here that the methylation of histone proteins regulates lifespan
in Caenorhabditis elegans. Deficiencies in members of the ASH-2 complex,
which trimethylates histone H3 at lysine 4 (H3K4), extend worm lifespan.
Meanwhile, the H3K4 demethylase RBR-2 is required for normal lifespan. These
findings are consistent with the idea that an excess of H3K4 trimethylation
reduces longevity. The extension of lifespan caused by ASH-2 deficiency
requires an intact adult germline and the continuous production of mature
eggs.
Eric L. Greer et al.
doi:10.1038/nature09195
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09195.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09195.html

Relationship between nucleosome positioning and DNA methylation pp388-392
Nucleosomes are composed of around 147 bases of DNA wrapped around an
octamer of histone proteins. Here, a genome-wide analysis of nucleosome
positioning in Arabidopsis thaliana has been combined with profiles of DNA
methylation at single base resolution, revealing 10-base periodicities in
the DNA methylation status of nucleosome-bound DNA. The results indicate
that nucleosome positioning influences the pattern of DNA methylation
throughout the genome.
Ramakrishna K. Chodavarapu et al.
doi:10.1038/nature09147
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09147.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09147.html

Structure of the gating ring from the human large-conductance Ca2+-gated K+
channel pp393-397
Large-conductance Ca2+-gated K+ (BK) channels are essential for many
biological processes, such as smooth muscle contraction and neurotransmitter
release. Here, the X-ray crystal structure is presented of the entire
cytoplasmic region of the human BK channel in a Ca2+-free state. Moreover, a
voltage-gated K+ channel pore of known structure is 'docked' onto the gating
ring to generate a structural model for the full BK channel.
Yunkun Wu, Yi Yang, Sheng Ye and Youxing Jiang
doi:10.1038/nature09252
Abstract:
http://www.nature.com/nature/journal/v466/n7304/abs/nature09252.html
Article:
http://www.nature.com/nature/journal/v466/n7304/full/nature09252.html

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