Catálogo de publicaciones - revistas

<jats:title>Strength Under Pressure</jats:title> <jats:p> Above a lower cutoff value, shrinking the grain size of a metal tends to strengthen it because the overall increase in grain boundaries limits the activity of the dislocations as the material undergoes plastic deformation. <jats:bold> Chen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1448" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228211">1448</jats:related-article> ) explore the question of whether this restriction in dislocation activity occurs when a metal is subjected to high pressures. Foils of nickel made from particles of different sizes were subjected to high pressures inside a diamond anvil cell. An increase in pressure extended dislocation activity to smaller grain sizes, indicating that pressure compensates for the inhibition of dislocation activity in small volumes. </jats:p>

<jats:title>Gold Cluster Catalysis</jats:title> <jats:p> A variety of gold salts and complexes have been used to catalyze different organic reactions. Often, the catalytic rates for these reactions are similar. <jats:bold> Oliver-Meseguer <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1452" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227813">1452</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6113" page="1434" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1231901">Hashmi</jats:related-article> </jats:bold> ) observed an induction period for the onset of catalysis of organic reactions, such as the ester-assisted hydration of alkynes, for different gold salts and complexes. Mass spectrometry and absorption spectroscopy revealed that small gold clusters (three to ten atoms) formed during these induction periods and are likely to represent the active catalysts. The catalytic reaction rates could be extremely high—up to 10 <jats:sup>5</jats:sup> turnovers of the catalyst per hour. </jats:p>

<jats:title>From C=C to C=O</jats:title> <jats:p> The palladium-catalyzed Heck reaction is widely used to form carbon-carbon bonds between aryl rings and olefins, after which elimination of a hydrogen atom restores the olefin's double bond. <jats:bold> Werner <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1455" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1229208">1455</jats:related-article> ; see the Perspective by <jats:bold>Gilbertson</jats:bold> ) present a variant of this reaction in which a hydrogen atom is instead lost from an alcohol center elsewhere in the molecule, yielding a ketone and a chiral center where the arene is bound. The process is highly enantioselective and also versatile: The alcohol can be sited one, two, or even three carbons away from the olefin. </jats:p>

<jats:title>Speeding Up Nanoscale DNA Assembly</jats:title> <jats:p> An impressive array of three-dimensional (3D) nanoscale objects has been assembled by folding a long, single-stranded DNA scaffold by binding of short DNA staples. However, these processes tend to be slow and inefficient. <jats:bold> Sobczak <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1458" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1229919">1458</jats:related-article> ) examined the folding process with an intercalating fluorescence dye to measure the formation of double-stranded DNA in folding processes or single-stranded DNA in unfolding. Reaction conditions were identified that sped up folding by orders of magnitude and increased yields of the 3D nanoscale objects to nearly 100%. </jats:p>

<jats:title>Spots to Remember</jats:title> <jats:p> Scent marking is an essential component of communication for most mammals. Individuals remember the location of scent marks and regularly revisit marked sites, presumably to assess the condition and status of the animal doing the marking. It is known that individuals can follow odor or pheromone gradients to locate another individual, but relocating scent marks is a much more difficult task given the small amount of volatile compounds deposited, and their static nature. <jats:bold> Roberts <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1462" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225638">1462</jats:related-article> ) show that a nonvolatile component of male urine, the protein pheromone darcin, stimulates spatial preference and learning in mice. Female mice preferred locations where male urine (or synthesized darcin) had been found, and remembered these spatial locations for 2 weeks post-exposure. </jats:p>

<jats:title>Alternative Role for EZH2</jats:title> <jats:p> Epigenetic regulators are implicated in cancer progression and proposed as therapeutic targets. <jats:bold> Xu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1465" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227604">1465</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6113" page="1430" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1232332">Cavalli</jats:related-article> </jats:bold> ) report that EZH2 (Enhancer of zeste homolog 2), a factor previously thought to exert its oncogenic function primarily as part of the polycomb repressive complex, acts through a distinct mechanism in cells of castration-resistant prostate cancer. Rather than exclusively silencing gene expression through histone methylation, EZH2 acts as a transcriptional coactivator. The activation function of EZH2 plays a critical role in the growth of castration-resistant prostate cancer cells, which could be relevant in future drug development. </jats:p>

<jats:title>Long Noncoding RNAs</jats:title> <jats:p> The past 5 years have uncovered thousands of long (&gt;100 nucleotides) noncoding RNAs (lncRNAs) outpacing our understanding of their functions and mechanisms in regulating the genome. <jats:bold>Lee</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1435" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1231776">1435</jats:related-article> ) reviews the known and suspected means by which these intriguing molecules control gene expression locally and at great distances, considers potential universal roles for lncRNAs, and warns that classifying these intriguing molecules may be quite challenging given their diversity. The very long noncoding RNA, <jats:italic>Airn</jats:italic> , silences the <jats:italic>Igf2r</jats:italic> (insulin-like growth factor 2 receptor) imprinted gene cluster in mammals. <jats:bold> Latos <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1469" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228110">1469</jats:related-article> ) show in mouse cells that, rather than recruiting enzymes that modify histones to repress the locus, it is the act of transcription of <jats:italic>Airn</jats:italic> (and not the <jats:italic>Airn</jats:italic> gene product) that results in the silencing. </jats:p>

<jats:title>Gonads and Life Span</jats:title> <jats:p> Animals develop through successive life stages and have life spans that are determined by their genes and the environment. Yet how the molecular circuitry underlying life-stage structure relates to longevity is poorly understood. <jats:bold> Shen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1472" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1228967">1472</jats:related-article> ) now show that components of a steroid receptor-microRNA switch used for <jats:italic>Caenorhabditis elegans</jats:italic> developmental timing is co-opted to regulate adult longevity in response to signals from the reproductive system. Thus, the gonad can be coupled to metazoan life span via a developmental clock. </jats:p>

<jats:title>Digit Determination</jats:title> <jats:p> Pentadactyly has been an early and rapid innovation of tetrapods. <jats:bold> Sheth <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1476" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226804">1476</jats:related-article> ) report that a dramatic reduction in distally expressed <jats:italic>Hox</jats:italic> genes, in the absence of a functional morphogen signaling pathway, results in extreme polydactyly in mice. Mutant digits exhibited patterns reminiscent of the endoskeleton of fins, suggesting that an ancestral patterning mechanism has been deeply conserved in evolution. </jats:p>

<jats:title>Assessing Creepy Crawlies</jats:title> <jats:p> Arthropods are the most diverse group of terrestrial animal species, yet estimates of the total number of arthropod species have varied widely, especially for tropical forests. <jats:bold> Basset <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1481" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226727">1481</jats:related-article> , see the cover) now provide more reliable estimates of total arthropod species richness in a tropical rainforest in Panama. Intensive sampling of a half hectare of forest yielded just over 6000 arthropod species. Scaling up this result to the whole forest suggests that the total species diversity lies between 17,000 and 40,000 species. </jats:p>