《科學》（20190412出版）一周論文導讀

翻譯 | 唐一塵

Science, 12 April 2019, Volume 364 Issue 6436

《科學》2019年4月12日，第6436期364卷

生命科學Bioscience

The NASA Twins Study:A multidimensional analysis of a year-long human spaceflight

NASA孿生兄弟研究結果發表

作者：Francine E. Garrett-Bakelman、Manjula Darshi、Stefan J. Green、Ruben C. Gur、Ling Lin，et al

鏈接：

https://science.sciencemag.org/content/364/6436/eaau8650

摘要：

與太空飛行相關的風險包括與輻射和微重力的接觸；然而，當長期逗留於太空時，這些風險影響健康的方式則一直不為人知。NASA歷時最長的人類在太空中飛行會對健康產生何種影響？

本研究將在太空軌道中待了近1年之久的宇航員Scott Kelly與他待在地球上的孿生兄弟Mark Kelly進行了比較。結果表明，Scott的健康沒有發生明顯的變化。研究人員用一種多組學整合、分子、生理和行為學方法評估了Kelly兄弟的情況。

分析發現了Scott和他孿生兄弟相比所發生的幾個變化，其中有些變化在他離開太空軌道後持續存在。這些變化包括DNA甲基化呈現小幅（不到5%）差異。同樣地，Scott的某些基因表達（尤其是那些與免疫系統相關的基因表達）有了改變，儘管這些基因表達在太空飛行之後6個月時逾9成恢復到正常水平。Scott眼球形狀被報告發生變化，其中包括視網膜神經增厚；一系列測試還檢測到Scott的某些認知能力下降。

Abstract

To understand the health impact of long-duration spaceflight, one identical twin astronaut was monitored before, during, and after a 1-year mission onboard the International Space Station; his twin served as a genetically matched ground control. Longitudinal assessments identified spaceflight-specific changes, including decreased body mass, telomere elongation, genome instability, carotid artery distension and increased intima-media thickness, altered ocular structure, transcriptional and metabolic changes, DNA methylation changes in immune and oxidative stress–related pathways, gastrointestinal microbiota alterations, and some cognitive decline postflight. Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within 6 months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted. These multiomic, molecular, physiological, and behavioral datasets provide a valuable roadmap of the putative health risks for future human spaceflight.

Sustained rescue of prefrontal circuit dysfunction by antidepressant-induced spine formation

抗抑鬱劑誘導脊柱形成持續緩解額前神經功能障礙

作者：R. N. Moda-Sava、M. H. Murdock、P. K. Parekh，et al

鏈接：

https://science.sciencemag.org/content/364/6436/eaat8078

摘要：

美國有近兩成人口受到重性抑鬱症的影響，他們中有許多在經過臨床治療後會出現癥狀複發。但人們對驅動抑鬱症起伏性發作的神經迴路還不十分了解，因而令治療選項有限。最近的研究展示了氯胺酮具有看好的抗抑鬱症性質，而且美國食品藥品監督管理局批准使用一種用於治療阻抗性抑鬱症的源自氯胺酮的噴鼻劑。但該葯的基礎作用機制仍然未知，其抗抑鬱症效果也常常是短暫的。

本研究通過深深潛入「抑鬱」小鼠的神經迴路中，研究人員揭示了氯胺酮是如何在細胞中實現其快速抗抑鬱作用的。研究人員發現，小鼠中的與抑鬱症相關的行為與前額皮層中神經元上的樹突棘的消除有關。然而，當給予抗抑鬱劑量的氯胺酮時，該效應被逆轉。氯胺酮恢復了某些被消除的樹突棘，因此維持了前額皮層神經微環路突觸間的交流。此外，結果顯示，前額皮層樹突棘生成是維持該效應所需的。

Abstract

The neurobiological mechanisms underlying the induction and remission of depressive episodes over time are not well understood. Through repeated longitudinal imaging of medial prefrontal microcircuits in the living brain, we found that prefrontal spinogenesis plays a critical role in sustaining specific antidepressant behavioral effects and maintaining long-term behavioral remission. Depression-related behavior was associated with targeted, branch-specific elimination of postsynaptic dendritic spines on prefrontal projection neurons. Antidepressant-dose ketamine reversed these effects by selectively rescuing eliminated spines and restoring coordinated activity in multicellular ensembles that predict motivated escape behavior. Prefrontal spinogenesis was required for the long-term maintenance of antidepressant effects on motivated escape behavior but not for their initial induction.

生態/進化Ecology/Evolution

Cascading impacts of large-carnivore extirpation in an African ecosystem

大型食肉動物滅絕對非洲生態系統的影響

作者：Justine L. Atkins、Ryan A. Long、Johan Pansu、Joshua H. Daskin，et al

鏈接：

https://science.sciencemag.org/content/364/6436/173

摘要：

世界上最大型的食肉動物的數量正在減少，現在棲息地只佔其歷史範圍的小部分。理論預測，當頂端捕食者消失時，大型食草動物變得無所畏懼，將佔據新的棲息地，並通過吃新的食物植物來改變這些棲息地。然而，在大型哺乳動物系統中，這種預測很難得到實驗支持。

在莫三比克戈龍戈薩國家公園裡的豹子和非洲野狗滅絕後，居住在其中的羚羊擴展到沒有樹木的洪泛區，在那裡它們吃著新奇的食物，抑制了一種常見食用植物的生長。通過對捕食風險的實驗模擬，本研究證明了這種行為是可逆的。因此，儘管人為的食肉動物滅絕破壞了營養級聯，但食肉動物的恢復可能同樣快速地重建這個級聯。

Abstract

Populations of the world』s largest carnivores are declining and now occupy mere fractions of their historical ranges. Theory predicts that when apex predators disappear, large herbivores become less fearful, occupy new habitats, and modify those habitats by eating new food plants. Yet experimental support for this prediction has been difficult to obtain in large-mammal systems. After the extirpation of leopards and African wild dogs from Mozambique』s Gorongosa National Park, forest-dwelling antelopes [bushbuck (Tragelaphus sylvaticus)] expanded into treeless floodplains, where they consumed novel diets and suppressed a common food plant [waterwort (Bergia mossambicensis)]. By experimentally simulating predation risk, we demonstrate that this behavior was reversible. Thus, whereas anthropogenic predator extinction disrupted a trophic cascade by enabling rapid differentiation of prey behavior, carnivore restoration may just as rapidly reestablish that cascade.

Rapid plant evolution driven by the interaction of pollination and herbivory

由授粉和食草動物相互作用驅動的植物快速進化

作者：Sergio E. Ramos、Florian P. Schiest

鏈接：

https://science.sciencemag.org/content/364/6436/193

摘要：

授粉動物會受到優美的花朵的吸引，例如那些色彩鮮艷、氣息芳香及花蜜充沛的花朵會因為授粉動物增加了其繁殖潛力而受益。然而，這些特質同時也會吸引毛毛蟲等食草蟲類。植物的防禦特點可幫助抵擋食草蟲類，但它們也會無法吸引授粉動物。儘管由授粉動物與食草動物所帶來的演化得失已得到公認，但實驗研究一直聚焦於兩者作為單獨選擇性因子所產生的影響。因此，互動性生物對植物演化的組合影響仍然是未知的。

本研究通過在一個有著快速生長周期的蕪菁類植物群中探索花朵特性的演化、交合系統及植物的防禦來論述這一問題。研究人員將這些植物分成4組，並對授粉的大黃蜂和食草的毛毛蟲的存在與否進行操控，使它們在這些選擇條件下進行6個世代的演化。

結果顯示，蕪菁類植物在選擇只有大黃蜂時會演化出較大且芳香的花朵，但這些特質會在有毛毛蟲時變得很不明顯。此外，受到大黃蜂和毛毛蟲雙重選擇下的蕪菁類植物會演化出更強的通過自主性自花授粉繁衍後代的能力。而且，這些特質的演化頗為迅速，在僅僅6個世代之後發生。

Abstract

Pollination and herbivory are both key drivers of plant diversity but are traditionally studied in isolation from each other. We investigated real-time evolutionary changes in plant traits over six generations by using fast-cycling Brassica rapa plants and manipulating the presence and absence of bumble bee pollinators and leaf herbivores. We found that plants under selection by bee pollinators evolved increased floral attractiveness, but this process was compromised by the presence of herbivores. Plants under selection from both bee pollinators and herbivores evolved higher degrees of self-compatibility and autonomous selfing, as well as reduced spatial separation of sexual organs (herkogamy). Overall, the evolution of most traits was affected by the interaction of bee pollination and herbivory, emphasizing the importance of the cross-talk between both types of interactions for plant evolution.

氣候變化Climate change

Sensitive intervention points in the post-carbon transition

碳過渡的敏感干預點

作者：J. D. Farmer、C. Hepburn、M. C. Ives、S. Srivastav、R. Way，et al

鏈接：

https://science.sciencemag.org/content/364/6436/132

摘要：

緩解氣候變化的傳統方法（包括全球商定的目標及旨在減緩碳排放）並不奏效。儘管2015年《巴黎協定》承諾採取行動，但實際進展遠遠不夠。

作者在此引進了「敏感干預點」概念，這指的是在社會—經濟與政治體系內的獨特處境，在這些處境中，看似簡單的干預會被放大成為劇變。與臨界點的理念相似，這是一個用於氣候科學的概念，它描述的是在複雜系統中的一個臨界閾值，一旦跨越該閾值就會觸發反饋機制而導致大規模且不可逆轉的變化。

這裡為引進旨在觸發正向的、與氣候相關的社會與政治變化的策略性干預，研究人員提供了幾個說明如何實施及操作它們以達到正向變化的例子。研究人員提出創建一個多學科研究項目以發現、建模及研發未來在系統中實施可能的「敏感干預點」方法；在這些系統中，變化可促成解決氣候改變的新方案。

Abstract

Conventional approaches to mitigating climate change are not working. Despite the actions pledged under the 2015 Paris Agreement, actual progress is falling well short (1). Given limited time and resources, traditional efforts such as the climate stabilization wedge approach (2) are unlikely to be effective on their own. Physical science has shown how complex adaptive systems can cross critical thresholds (「tipping points」) (3), such that a relatively small change can trigger a larger change that becomes irreversible (4), where nonlinear feedback effects act as amplifiers (5). We propose to examine how to exploit similar sensitive intervention points (SIPs) and amplification mechanisms in socioeconomic, technological, and political systems to advance climate change mitigation. We focus on research and policies in which an intervention kicks or shifts the system so that the initial change is amplified by feedback effects that deliver outsized impact.

物理Physics

Anti–parity-time symmetry in diffusive systems

擴散系統中反宇稱時間對稱性

作者：Ying Li、Yu-Gui Peng、Lei Han、Shanhui Fan、Cheng-Wei Qiu，et al

鏈接：

https://science.sciencemag.org/content/364/6436/170

摘要：

物理學家達成一種共識，認為對稱性和守恆規律總是相伴出現。目前，絕大多數與對稱性相關的研究都集中於經典波動體系，對擴散系統的對稱性研究並不多見。

本研究首次在熱擴散系統中提出一種新的對稱性，即反宇稱時間對稱性，並在實驗上證實了反宇稱時間對稱性的存在。研究人員發現，當熱擴散系統處於反宇稱時間對稱相時，背景載體機械運動的拖曳效應會被抑制，溫度場分布保持穩定。

據悉，研究人員構建了一對反向同速旋轉的存在熱耦合的低熱導率圓環，調節圓環的轉速為某一固定值時觀測溫度場隨時間的演化；在相對較低的轉速時，滿足反宇稱時間對稱性條件，觀測到穩定的熱溫度場分布，溫度極大值位置不隨著圓環的旋轉而演化；而在轉速較高時，反宇稱時間對稱性破缺，觀測到的溫度場分布不再穩定，溫度極大值位置會隨時間快速演化。

Abstract

Various concepts related to parity-time symmetry, including anti–parity-time symmetry, have found broad applications in wave physics. Wave systems are fundamentally described by Hermitian operators, whereas their unusual properties are introduced by incorporation of gain and loss. We propose that the related physics need not be restricted to wave dynamics, and we consider systems described by diffusive dynamics. We study the heat transfer in two countermoving media and show that this system exhibits anti–parity-time symmetry. The spontaneous symmetry breaking results in a phase transition from motionless temperature profiles, despite the mechanical motion of the background, to moving temperature profiles. Our results extend the concepts of parity-time symmetry beyond wave physics and may offer opportunities to manipulate heat and mass transport.

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