Catálogo de publicaciones - revistas

<jats:p>Signaling pathways that control cellular responses to stress may also specify T cell differentiation.</jats:p>

<jats:title>Two Ways to Redox Regulation</jats:title> <jats:p> Eukaryotic cells control the redox environment within their cytoplasm to be generally reducing. However, the endoplasmic reticulum provides an oxidizing environment for secretory and membrane proteins. In addition, a subcompartment of mitochondria—the powerhouses of the cell—also generates an oxidizing environment for constituent and itinerant proteins. <jats:bold> Riemer <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="1284" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170653">1284</jats:related-article> ) review the current understanding of both eukaryotic redox machineries and highlight their implications for the biogenesis and regulation of protein function, focusing on the impact of these systems on health and disease. </jats:p>

<jats:p>The isotopic composition of nitrogen in nitrate deposited in Greenland has changed markedly over the past 150 years.</jats:p>

<jats:title>Coordinating Response to Stress</jats:title> <jats:p> Sirtuin 1 (Sirt1) (a protein deacetylase implicated in aging), senses the metabolic state of the cell and modulates the activity of substrate proteins that in turn regulate cellular transcriptional responses. In response to hypoxia, cells activate the transcription factor hypoxia-inducible factor 2 alpha (HIF-2α), which promotes adaptive responses. <jats:bold> Dioum <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="1289" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1169956">1289</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1281" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175679">Guarente</jats:related-article> </jats:bold> ) discovered a link between these two important cellular stress response systems—HIF-2α is a substrate of Sirt1. Direct interaction between Sirt1 and HIF-2α results in deacetylation of HIF-2α and enhances its transcriptional activity. In mice lacking Sirt1, the ability of HIF-2α to promote synthesis of the growth factor erythropoietin is diminished. Thus, the regulation of HIF-2α helps to coordinate responses of cells to various stresses. </jats:p>

<jats:title>War and Peace?</jats:title> <jats:p> Modern behavior, including the development of advanced tools, musical instruments, and art, seems to have arisen in humans in stages. The earliest hints are seen in Africa about 70 to 90,000 years ago, but later in Europe about 45,000 years ago. An ongoing discussion centers on the origins and significance of human prosociality. During early human development, could the benefits of altruistic behavior have outweighed its costs (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1280" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175383">Mace</jats:related-article> </jats:bold> )? <jats:bold>Bowles</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1293" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1168112">1293</jats:related-article> ) constructed a model of conflict between groups of humans and extracted estimates of the critical parameters from archaeological and ethnographic data sets. Provocatively, it appears that warfare might have enhanced the emergence and persistence of altruistic behavior. <jats:bold> Powell <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="1298" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170165">1298</jats:related-article> ) present a population model that shows that the development of modern behaviors may rely on the attainment of critical population densities and migratory patterns required for stable cultural transmission. The model is consistent with genetic inferences of population dynamics in Africa and Europe and suggests that these cultural changes may not solely reflect increased cognitive evolution. </jats:p>

<jats:title>War and Peace?</jats:title> <jats:p> Modern behavior, including the development of advanced tools, musical instruments, and art, seems to have arisen in humans in stages. The earliest hints are seen in Africa about 70 to 90,000 years ago, but later in Europe about 45,000 years ago. An ongoing discussion centers on the origins and significance of human prosociality. During early human development, could the benefits of altruistic behavior have outweighed its costs (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1280" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175383">Mace</jats:related-article> </jats:bold> )? <jats:bold>Bowles</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1293" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1168112">1293</jats:related-article> ) constructed a model of conflict between groups of humans and extracted estimates of the critical parameters from archaeological and ethnographic data sets. Provocatively, it appears that warfare might have enhanced the emergence and persistence of altruistic behavior. <jats:bold> Powell <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="1298" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170165">1298</jats:related-article> ) present a population model that shows that the development of modern behaviors may rely on the attainment of critical population densities and migratory patterns required for stable cultural transmission. The model is consistent with genetic inferences of population dynamics in Africa and Europe and suggests that these cultural changes may not solely reflect increased cognitive evolution. </jats:p>

<jats:title>Extending Platinum Catalysts</jats:title> <jats:p> Platinum performs extremely well as a catalyst for the oxygen-reduction reaction that runs under highly acidic conditions in proton-exchange membrane fuel cells, but is expensive. One strategy for reducing costs is to increase the surface area of the platinum. <jats:bold> Lim <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="1302" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170377">1302</jats:related-article> , published online 14 May) describe a simple chemical route, in which Pt ions in solution are reduced onto Pd seed crystals, which creates faceted Pt nanocrystals with a high area owing to their dendritic architecture. On a Pt mass basis, these catalysts are several times more active than conventional Pt catalysts. </jats:p>

<jats:title>Forbidden Crystals</jats:title> <jats:p> In crystalline materials, a unit cell is replicated in space through a series of rotations, inversions, and reflections. In order to fully fill space, only certain rotational symmetries are allowed. Quasicrystals contain aperiodic tilings of two or more basic shapes that allow these forbidden rotation symmetries. A number of quasicrystalline materials have been synthesized in the lab, including a number of aluminum alloys. <jats:bold> Bindi <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="1306" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170827">1306</jats:related-article> ) examined samples of the mineral khatyrkite, with a nominal composition of (Cu,Zn)Al <jats:sub>2</jats:sub> . A number of quasicrystalline grains with composition similar to synthetically formed materials were observed. Thus, quasicrystals can form in nature under geological conditions. </jats:p>

<jats:title>Mergers and Acquisitions</jats:title> <jats:p> The crystallization of small molecules or polymers is often described in terms of a nucleation stage, where initial clusters form, followed by a distinct growth stage. Growth can come from the addition of unbound molecules, or through “Ostwald ripening” where larger crystals grow at the expense of smaller ones due to thermodynamic effects. <jats:bold> Zheng <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="1309" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172104">1309</jats:related-article> ) studied the growth of platinum nanocrystals inside a transmission electron microscope using a special liquid cell, allowing observation of crystal growth in situ. Both monomer addition to growing particles and the coalescence of two particles were observed. The specific growth mechanism appeared to be governed by the size of each of the particles. The combination of growth processes makes it possible for an initially broad distribution of particles to narrow into an almost uniform one. </jats:p>

<jats:title>Growing Graphene</jats:title> <jats:p> The highest quality graphene samples, single-atom-thick layers of carbon, are suspended flakes exfoliated from graphite, but these samples are very small in size (square micrometers). For many electronics applications, larger areas are needed. <jats:bold> Li <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="1312" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171245">1312</jats:related-article> , published online 7 May) show that graphene grows in a self-limiting way on copper films as large-area sheets (one square centimeter) from methane through a chemical vapor deposition process. The films, which are mainly one layer in thickness, can be transferred to other substrates and have electron mobilities as high as 4300 square centimeters per volt second. </jats:p>