《科學》（20190705出版）一周論文導讀

翻譯 | 馮維維

Science, 05 July 2019, Vol 365, Issue 6448

《科學》2019年7月5日，第365卷第6448期

生態學Ecology

The great Atlantic Sargassum belt

大西洋馬尾藻帶

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

鏈接：

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

摘要：

深海馬尾藻在馬尾藻海中大量存在，但自2011年以來，衛星圖像中發現了經常從西非延伸到墨西哥灣的一個周期性的大西洋馬尾藻帶（GASB）。

2018年6月，8850公里長的GASB包含了2000萬噸的海藻。GASB的空間分布主要受海洋環流的驅動。

2011年的暴發可能是亞馬遜河排放的結果,但其最近的增加和2011年後的年際變化似乎是由於北半球冬季在西非附近的上升流和春夏季亞馬遜河排放造成的，這表明潛在的季節性變化，增加了熱帶大西洋和加勒比海地區再次出現水華的可能性，而且可能成為新的常態。

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

全球樹木恢復的潛力

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

鏈接：

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

摘要：

樹木的恢復仍然是緩解氣候變化最有效的策略之一。

作者繪製了全球潛在的樹覆蓋範圍，表明在目前的氣候下可存在44億公頃的樹冠覆蓋。除了現有森林、農業和城市地區的樹木之外，作者發現尚有另外9億公頃的樹冠覆蓋空間，它可以在自然林地和森林地區儲存205億噸碳。

這表明全球樹木恢復是迄今為止最有效的氣候變化解決方案。但與此相反，氣候變化將改變潛在的樹木覆蓋範圍。

作者估計，如果不偏離目前的軌道，到2050年，全球潛在的冠層覆蓋面積可能會縮減約2.23億公頃，其中絕大部分損失發生在熱帶地區。這一研究結果強調了通過全球樹木恢復減緩氣候變化的機會，也強調了採取這一行動的迫切需要。

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.

物理學Physics

Matrix Fourier optics enables a compact full-Stokes polarization camera

傅里葉光學矩陣讓緊湊的全斯托克斯偏振相機成為可能

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

鏈接：

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

摘要：

從一個物體散射的光的偏振成像，為從一個場景中獲取信息提供了額外的自由度。傳統的偏振計體積龐大，通常由機械活動部件組成（通過偏振儀和分析儀裝置的旋轉顯示偏振程度）。

Rubin等人設計了一種基於元表面的全斯托克斯緊湊偏振相機，該相機不需要傳統偏振光學，也不需要活動部件。研究結果為偏振成像提供了一種簡便的方法。

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

利用阿秒瞬態吸收光譜法直接繪製IBr曲線交叉動力學

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

鏈接：

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

摘要：

當光脈衝在時間上變短時，它們的頻率相應地變寬。Kobayashi等人利用阿秒脈衝的這兩種特性，通過同時檢測超快溴和碘光譜位移，闡明了單溴化碘（IBr）的光解作用。初步的光線削弱了I-Br鍵。

然後，當原子飛離時，它們達到一種結構，其中鍵振動可將基態和激發態耦合起來。寬頻探針脈衝顯示了每個原子的電子結構在這個節點上的快速變化。

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.

生命科學Life science

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

甘氨酸特異性N端降解因子通路介導蛋白N-肉豆蔻醯基化的質量控制

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

鏈接：

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

摘要：

30多年來，人們已經知道N端序列會影響蛋白質的穩定性，但這些N端規則，或N端降解因子通路的其他特徵仍未被發現。

Timms等人利用全球蛋白質穩定性（GPS）技術對人類細胞中的這些通路進行了更廣泛的研究。

出乎意料的是，暴露N端的甘氨酸可以作為一個強大的降解因子；通過底物適配器ZYG11B和ZER1，用兩個Cullin-RING E3泛素連接酶對含N端甘氨酸的蛋白進行蛋白酶體降解。

例如，這一途徑可能對降解不能正確定位於細胞膜的蛋白質和破壞細胞死亡過程中產生的蛋白質片段很重要。

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

結構化穗序列指定了嗅覺迴路形成的基因表達模式

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

鏈接：

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

摘要：

嗅覺神經元對各種氣味的反應取決於嗅覺受體的表達。在發育過程中，表達相同嗅覺受體的嗅神經元的軸突會聚在一起形成相同的腎小球。

Nakashima等人證明，在小鼠中，神經元根據共享的活動模式建立這些連接。當嗅覺感受器被觸發時，它不僅使細胞被激發，而且以特定的方式被激發。說同樣代碼的神經元最終連接在同一個腎小球上。

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.

基因組學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傳播

作者：Mary E. Prendergast, Mark Lipson, Elizabeth A. Sawchuk, I?igo Olalde

鏈接：

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

摘要：

家畜在全球的起源和傳播也影響了人類種群的基本遺傳組成。然而，在非洲，很難確定遷移的糧食生產者和當地狩獵採集者之間相互作用的影響。

Prendergast等人想要了解畜牧業和畜牧業的時間和運動，以及它對非洲覓食群體的影響。他們對生活在大約100年到4000年前的41個古東非人的基因組進行了測序。

令人驚訝的是，在畜牧業傳播的同時發生的基因混合相對較少。

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引導的CRISPR相關轉座酶的DNA插入

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

鏈接：

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

摘要：

CRISPR-Cas核酸酶是操縱核酸的有力工具；然而，定向插入DNA仍然是一個挑戰，因為它需要宿主細胞修復機制。

作者描述了來自藍細菌Scytonema hofmanni（ShCAST）的CRISPR相關轉座酶，它由Tn7樣轉座酶亞基和V-K型CRISPR效應子（Cas12k）組成。

ShCAST通過單向插入原pacer下游的DNA 60至66個鹼基對片段，催化RNA引導的DNA轉位。ShCAST將DNA整合到大腸桿菌基因組的目標位點中，頻率高達80%，沒有陽性選擇。

這項工作擴展了人們對CRISPR-Cas系統功能多樣性的理解，並為精確的DNA插入建立了一個範例。

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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