《科学》（20190705出版）一周论文导读

翻译 | 冯维维

Science, 05 July 2019, Vol 365, Issue 6448

《科学》2019年7月5日，第365卷第6448期

生态学Ecology

The great Atlantic Sargassum belt

大西洋马尾藻带

▲作者：Mengqiu Wang, Chuanmin Hu, Brian B. Barnes, Gary Mitchum, Brian Lapointe, Joseph P. Montoya

▲ 链接：

https://science.sciencemag.org/content/365/6448/83

▲ 摘要：

深海马尾藻在马尾藻海中大量存在，但自2011年以来，卫星图像中发现了经常从西非延伸到墨西哥湾的一个周期性的大西洋马尾藻带（GASB）。

2018年6月，8850公里长的GASB包含了2000万吨的海藻。GASB的空间分布主要受海洋环流的驱动。

2011年的暴发可能是亚马逊河排放的结果,但其最近的增加和2011年后的年际变化似乎是由于北半球冬季在西非附近的上升流和春夏季亚马逊河排放造成的，这表明潜在的季节性变化，增加了热带大西洋和加勒比海地区再次出现水华的可能性，而且可能成为新的常态。

▲ Abstract

Pelagic Sargassum is abundant in the Sargasso Sea, but a recurrent great Atlantic Sargassum belt (GASB) has been observed in satellite imagery since 2011, often extending from West Africa to the Gulf of Mexico. In June 2018, the 8850-kilometer GASB contained >20 million metric tons of Sargassum biomass. The spatial distribution of the GASB is mostly driven by ocean circulation. The bloom of 2011 might be a result of Amazon River discharge in previous years, but recent increases and interannual variability after 2011 appear to be driven by upwelling off West Africa during boreal winter and by Amazon River discharge during spring and summer, indicating a possible regime shift and raising the possibility that recurrent blooms in the tropical Atlantic and Caribbean Sea may become the new norm.

The global tree restoration potential

全球树木恢复的潜力

▲ 作者：Jean-Francois Bastin, Yelena Finegold, Claude Garcia, Danilo Mollicone, etc.

▲ 链接：

https://science.sciencemag.org/content/365/6448/76

▲ 摘要：

树木的恢复仍然是缓解气候变化最有效的策略之一。

作者绘制了全球潜在的树覆盖范围，表明在目前的气候下可存在44亿公顷的树冠覆盖。除了现有森林、农业和城市地区的树木之外，作者发现尚有另外9亿公顷的树冠覆盖空间，它可以在自然林地和森林地区储存205亿吨碳。

这表明全球树木恢复是迄今为止最有效的气候变化解决方案。但与此相反，气候变化将改变潜在的树木覆盖范围。

作者估计，如果不偏离目前的轨道，到2050年，全球潜在的冠层覆盖面积可能会缩减约2.23亿公顷，其中绝大部分损失发生在热带地区。这一研究结果强调了通过全球树木恢复减缓气候变化的机会，也强调了采取这一行动的迫切需要。

▲ Abstract

The restoration of trees remains among the most effective strategies for climate change mitigation. We mapped the global potential tree coverage to show that 4.4 billion hectares of canopy cover could exist under the current climate. Excluding existing trees and agricultural and urban areas, we found that there is room for an extra 0.9 billion hectares of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally support wood lands and forests. This highlights global tree restoration as our most effective climate change solution to date. However, climate change will alter this potential tree coverage. We estimate that if we cannot deviate from the current trajectory, the global potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority of losses occurring in the tropics. Our results highlight the opportunity of climate change mitigation through global tree restoration but also the urgent need for action.

物理学Physics

Matrix Fourier optics enables a compact full-Stokes polarization camera

傅里叶光学矩阵让紧凑的全斯托克斯偏振相机成为可能

▲ 作者：Noah A. Rubin, Gabriele Aversa, Paul Chevalier, Zhujun Shi, Wei Ting Chen, Federico Capasso

▲ 链接：

https://science.sciencemag.org/content/365/6448/eaax1839

▲ 摘要：

从一个物体散射的光的偏振成像，为从一个场景中获取信息提供了额外的自由度。传统的偏振计体积庞大，通常由机械活动部件组成（通过偏振仪和分析仪装置的旋转显示偏振程度）。

Rubin等人设计了一种基于元表面的全斯托克斯紧凑偏振相机，该相机不需要传统偏振光学，也不需要活动部件。研究结果为偏振成像提供了一种简便的方法。

▲ Abstract

Imaging the polarization of light scattered from an object provides an additional degree of freedom for gaining information from a scene. Conventional polarimeters can be bulky and usually consist of mechanically moving parts (with a polarizer and analyzer setup rotating to reveal the degree of polarization). Rubin et al. designed a metasurface-based full-Stokes compact polarization camera without conventional polarization optics and without moving parts. The results provide a simplified route for polarization imaging.

Direct mapping of curve-crossing dynamics in IBr by attosecond transient absorption spectroscopy

利用阿秒瞬态吸收光谱法直接绘制IBr曲线交叉动力学

▲ 作者：Yuki Kobayashi, Kristina F. Chang, Tao Zeng, Daniel M. Neumark, Stephen R. Leone

▲ 链接：

https://science.sciencemag.org/content/365/6448/79

▲ 摘要：

当光脉冲在时间上变短时，它们的频率相应地变宽。Kobayashi等人利用阿秒脉冲的这两种特性，通过同时检测超快溴和碘光谱位移，阐明了单溴化碘（IBr）的光解作用。初步的光线削弱了I-Br键。

然后，当原子飞离时，它们达到一种结构，其中键振动可将基态和激发态耦合起来。宽带探针脉冲显示了每个原子的电子结构在这个节点上的快速变化。

▲ Abstract

As light pulses get shorter in time, they correspondingly get broader in frequency. Kobayashi et al. take advantage of both properties of attosecond pulses to elucidate iodine monobromide (IBr) photo dissociation by detecting ultra fast bromine and iodine spectral shifts simultaneously. A preliminary burst of light weakens the I–Br bond. Then, as the atoms fly apart, they reach a configuration where the bond vibration can couple ground and excited electronic states. The broad band probe pulse reveals rapid changes ineach atom's electronic structure at this juncture.

生命科学Life science

A glycine-specific N-degron pathway mediates the quality control of protein N-myristoylation

甘氨酸特异性N端降解因子通路介导蛋白N-肉豆蔻酰基化的质量控制

▲ 作者：Richard T. Timms, Zhiqian Zhang, David Y. Rhee, J. Wade Harper, Itay Kore, etc.

▲ 链接：

https://science.sciencemag.org/content/365/6448/eaaw4912

▲ 摘要：

30多年来，人们已经知道N端序列会影响蛋白质的稳定性，但这些N端规则，或N端降解因子通路的其他特征仍未被发现。

Timms等人利用全球蛋白质稳定性（GPS）技术对人类细胞中的这些通路进行了更广泛的研究。

出乎意料的是，暴露N端的甘氨酸可以作为一个强大的降解因子；通过底物适配器ZYG11B和ZER1，用两个Cullin-RING E3泛素连接酶对含N端甘氨酸的蛋白进行蛋白酶体降解。

例如，这一途径可能对降解不能正确定位于细胞膜的蛋白质和破坏细胞死亡过程中产生的蛋白质片段很重要。

▲ Abstract

For more than 30 years, N-terminal sequences have been known to influence protein stability, but additional features of these N-end rule, or N-degron, pathways continue to be uncovered. Timms et al. used a global protein stability (GPS) technology to take a broader look at these pathways in human cells. Unexpectedly, glycine exposed at the N terminus could act as a potent degron; proteins bearing N-terminal glycine were targeted for proteasomal degradation by two Cullin-RING E3 ubiquitin ligases through the substrate adaptors ZYG11B and ZER1. This pathway may be important, for example, to degrade proteins that fail to localize properly to cellular membranes and to destroy protein fragments generated during cell death.

Structured spike series specify gene expression patterns for olfactory circuit formation

结构化穗序列指定了嗅觉回路形成的基因表达模式

▲ 作者：Ai Nakashima, Naoki Ihara, Mayo Shigeta, Hiroshi Kiyonari, Yuji Ikegaya, Haruki Takeuchi

▲ 链接：

https://science.sciencemag.org/content/365/6448/eaaw5030

▲ 摘要：

嗅觉神经元对各种气味的反应取决于嗅觉受体的表达。在发育过程中，表达相同嗅觉受体的嗅神经元的轴突会聚在一起形成相同的肾小球。

Nakashima等人证明，在小鼠中，神经元根据共享的活动模式建立这些连接。当嗅觉感受器被触发时，它不仅使细胞被激发，而且以特定的方式被激发。说同样代码的神经元最终连接在同一个肾小球上。

▲ Abstract

Olfactory neurons respond to various odorants according to which olfactory receptors, of many, they express. During development, axons from olfactory neurons that express the same olfactory receptor converge to share the same glomeruli. Nakashima et al. now show that, in mice, the neurons build these connections according to shared patterns of activity. When the olfactory receptor is triggered, it causes its cell notsimply to fire but to fire in specific patterns. Neurons that speak the same code end up connected at the same glomerulus.

基因组学Genomics

Ancient DNA reveals a multistep spread of the first herders into sub-Saharan Africa

古DNA揭示第一批牧民向撒哈拉以南非洲的多步传播

▲ 作者：Mary E. Prendergast, Mark Lipson, Elizabeth A. Sawchuk, Iñigo Olalde

▲ 链接：

https://science.sciencemag.org/content/365/6448/eaaw6275

▲ 摘要：

家畜在全球的起源和传播也影响了人类种群的基本遗传组成。然而，在非洲，很难确定迁移的粮食生产者和当地狩猎采集者之间相互作用的影响。

Prendergast等人想要了解畜牧业和畜牧业的时间和运动，以及它对非洲觅食群体的影响。他们对生活在大约100年到4000年前的41个古东非人的基因组进行了测序。

令人惊讶的是，在畜牧业传播的同时发生的基因混合相对较少。

▲ Abstract

The origin and spread of domestic animalsacross the globe also affected the underlying genetic composition of human populations. In Africa, however, it has been difficult to identify the impact of interactions among migrating food producers and local hunter-gatherers. Prendergast et al. wanted to discern the timing and movement of husbandry and pastoralism and its effects on for aging communities in Africa. They sequenced 41 ancient eastern African human genomes from individuals that lived approximately 100 to 4000 years ago. Surprisingly, relatively little genetic mixture occurred at the same time as the spread of pastoralism.

RNA-guided DNA insertion with CRISPR-associated transposases

RNA引导的CRISPR相关转座酶的DNA插入

▲ 作者：Jonathan Strecker, Alim Ladha, Zachary Gardner, Jonathan L. Schmid-Burgk, Kira S. Makarova, Feng Zhang

▲ 链接：

https://science.sciencemag.org/content/365/6448/48

▲ 摘要：

CRISPR-Cas核酸酶是操纵核酸的有力工具；然而，定向插入DNA仍然是一个挑战，因为它需要宿主细胞修复机制。

作者描述了来自蓝细菌Scytonema hofmanni（ShCAST）的CRISPR相关转座酶，它由Tn7样转座酶亚基和V-K型CRISPR效应子（Cas12k）组成。

ShCAST通过单向插入原pacer下游的DNA 60至66个碱基对片段，催化RNA引导的DNA转位。ShCAST将DNA整合到大肠杆菌基因组的目标位点中，频率高达80%，没有阳性选择。

这项工作扩展了人们对CRISPR-Cas系统功能多样性的理解，并为精确的DNA插入建立了一个范例。

▲ Abstract

CRISPR-Cas nucleases are powerful tools for manipulating nucleic acids; however, targeted insertion of DNA remains a challenge, as it requires host cell repair machinery. Here we characterize a CRISPR-associated transposase from cyanobacteria Scytonema hofmanni (ShCAST) that consists of Tn7-like transposase subunits and the type V-K CRISPR effector (Cas12k). ShCAST catalyzes RNA-guided DNA transposition by unidirectionally inserting segments of DNA 60 to 66 base pairs down stream of the protospacer. ShCAST integrates DNA into targeted sites in the Escherichia coli genome with frequencies of up to 80% without positive selection. This work expands our understanding of the functional diversity of CRISPR-Cas systems and establishes a paradigm for precision DNA insertion.

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