Catálogo de publicaciones - revistas

<jats:title>Lessons from SIV</jats:title> <jats:p> HIV infection in humans is a chronic infection and, if left untreated, the majority of infected individuals will succumb to AIDS. Many species of African nonhuman primates are chronically infected with simian immunodeficiency virus (SIV); however, in the majority of these species, the animals remain healthy despite the presence of high viral loads. <jats:bold> Chahroudi <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="1188" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217550">1188</jats:related-article> ) review the underlying immune mechanisms that help protect natural hosts from progressing to AIDS and how these responses differ from what is observed in HIV-infected humans and SIV-infected nonhuman primate species that develop AIDS. </jats:p>

<jats:p>Cellular metabolites are detected within living cells by fluorescent RNA-based ligand-binding sensors.</jats:p>

<jats:title>Making Immune Cells Young Again</jats:title> <jats:p> Hematopoiesis, the development of the immune system, occurs in distinct waves. The immune system is first populated by cells that arise from fetal hematopoietic stem cells (HSCs) and then later by cells derived from adult HSCs. Furthermore, fetal HSCs give rise to lymphocytes with innate immunelike properties, whereas adult HSCs give rise to classical T and B cells. <jats:bold> Yuan <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="1195" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1216557">1195</jats:related-article> , published online 16 February) now uncover the molecular mechanism behind these distinct waves of hematopoiesis. Expression of the RNA binding proteins Lin28 and Lin28b is enriched in fetal hematopoietic stem/progenitor cells (HSPCs) in mice and humans. Ectopic expression of Lin28 in mouse adult HSPCs was sufficient to induce the differentiation of both classical and innate-like lymphocyte lineages. </jats:p>

<jats:title>Smooth Operator</jats:title> <jats:p> When thin sheets are compressed they can buckle and wrinkle, such as when the edges of a sheet of paper, or two areas of skin, are pushed together. Variations in local thickness and stiffness will alter the buckling patterns, but controlling this in a simple and predictable way is difficult. <jats:bold> Kim <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="1201" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215309">1201</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="6073" page="1179" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219020">Sharon</jats:related-article> </jats:bold> ) used halftone lithography with two photomasks to create highly cross-linked dots embedded in a lightly cross-linked matrix of a swellable polymer. This material could generate “smooth” swelling profiles on thin sheets with arbitrary two-dimensional geometries so that complex three-dimensional structures could be produced. </jats:p>

<jats:title>A Useful Cover-Up</jats:title> <jats:p> Many industrial catalysts that consist of metal nanoparticles adsorbed on metal oxide supports undergo deactivation after prolonged use. Organic reactants can decompose and cover the metal with carbon (“coking”), and other processes can push the size distribution to fewer but larger particles that have less overall surface area available for reaction (“sintering”). <jats:bold> Lu <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="1205" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1212906">1205</jats:related-article> ) used atomic-layer deposition to apply a uniform overlayer of alumina onto supported palladium nanoparticles. This coating greatly increased the resistance of the nanoparticles to coking and sintering during the oxidative dehydration of ethane to ethylene. </jats:p>

<jats:title>Tuning Hydrogen Adsorption</jats:title> <jats:p> Heterogeneous metal catalysts for hydrogenating unsaturated organic compounds need to bind molecular hydrogen strongly enough that it dissociates and forms adsorbed hydrogen atoms, but must not bind these atoms too strongly, or the transfer to the organic molecule will be impeded. <jats:bold> Kyriakou <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="1209" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215864">1209</jats:related-article> ) examined surface alloy catalysts created when palladium (Pd) atoms are adsorbed on a copper (Cu) surface using scanning tunneling microscopy and desorption techniques under ultrahigh vacuum conditions. The Pd atoms could bind hydrogen dissociatively—which, under these conditions, the Cu surfaces could not—allowing the Cu surface to take up adsorbed hydrogen atoms. These weakly bound hydrogen atoms were able to selectively hydrogenate styrene and acetylene. </jats:p>

<jats:title>Bringing Magnetic Materials to the Moon</jats:title> <jats:p> The Apollo missions to the Moon revealed that portions of the lunar crust are strongly magnetized. Lunar rocks are poor at recording the magnetic field, thus these magnetic anomalies have been difficult to explain. Based on numerical simulations of large-scale impacts, <jats:bold> Wieczorek <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="1212" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214773">1212</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="6073" page="1176" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1217681">Collins</jats:related-article> </jats:bold> ) show that the vast majority of lunar magnetic anomalies can be explained by highly magnetic materials that originated outside the Moon and were delivered by the asteroid that hit the Moon and formed the South Pole–Aitken basin, the largest impact basin in the solar system. </jats:p>

<jats:title>Flashy Feathers</jats:title> <jats:p> Feather colors play key roles in the lives of birds, functioning in everything from camouflage, to thermoregulation, to sexual signaling. Much recent research has revealed that some dinosaurs also had feathers, and examination of feather components in fossil and preserved feathers has begun to reveal how feather color may have played a role in the lives of these dinosaurs. <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="1215" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1213780">1215</jats:related-article> ) compared the characteristics of the melanosomes of the paravian dinosaur <jats:italic>Microraptor</jats:italic> to those found in extant birds, which suggest that its feathers were black and iridescent. The existence of this subtle color reflectance, together with morphological aspects of the feathered tail, suggests an important role for signaling in the early evolution of feathers. </jats:p>

<jats:title>A Price of Civilization</jats:title> <jats:p> Large expanses of rainforests in parts of Central Africa were abruptly replaced by savannas around 3000 years ago, presumably because of climate change. However, that succession occurred at a time of expansion by Bantu tribes, from near the border of present-day Cameroon and Nigeria to the south and east, in a migration that brought with it agriculture and iron-smelting technologies. <jats:bold> Bayon <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="1219" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215400">1219</jats:related-article> , published online 9 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6073" page="1180" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219903">Dupont</jats:related-article> </jats:bold> ) analyzed the nearby marine sedimentary record and found that chemical weathering in Central Africa also increased markedly at this time. This increase in weathering could have been caused by forest clearing by the Bantu to create arable land and to fuel their smelters, rather than climate change alone. </jats:p>

<jats:title>Avoiding Infanticide</jats:title> <jats:p> In male dominated hierarchies, newly dominant males will sometimes kill resident infants. In lab studies in mice conducted in the 1950s, Hilda Bruce showed that females introduced to an unfamiliar male will terminate their pregnancies, a process subsequently referred to as a Bruce Effect. <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="1222" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1213600">1222</jats:related-article> , published online 23 February) followed multiple dominance transitions within wild gelada baboons and showed that live birthrate among females previously identified as pregnant within unstable groups was much lower than within stable groups. Furthermore, females that terminated their pregnancies following transitions had a much shorter interbirth interval than those that did not, suggesting a higher overall reproductive success and fitness. </jats:p>