Catálogo de publicaciones - revistas

<jats:title>A New Rock from Mars</jats:title> <jats:p> On 18 July 2011 a meteorite originating from Mars fell on the moroccan desert. <jats:bold> Chennaoui Aoudjehane <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="785" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224514">785</jats:related-article> , published online 11 October) show that this meteorite was ejected from the surface of Mars 700,000 years ago and contains components derived from the interior, surface, and atmosphere of the red planet. Previous to this fall, only four other martian meteorites have been collected after being witnessed falling to Earth. All the other martian meteorites that are represented in collections around the world, have been found long after their arrival on Earth, and thus have suffered from exposure to the terrestrial environment. </jats:p>

<jats:title>Maya and Climate</jats:title> <jats:p> Climate has affected the vitality of many different societies in the past, as shown by numerous records across the globe and throughout human history. One of the most obvious and spectacular examples of this is from the Classic Maya civilization, whose advanced culture left highly detailed records of all aspects of their existence between 300 and 1000 C.E. <jats:bold> Kennett <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="788" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226299">788</jats:related-article> ; see the cover) present a detailed climate record derived from a stalagmite collected from a cave in Belize, in the midst of the Classic Maya settlement. The fine resolution and precise dating of the record allows changes in precipitation to be related to the politics, war, and population fluctuations of the Mayans. </jats:p>

<jats:title>Sensitivity Training</jats:title> <jats:p> Equilibrium climate sensitivity—the increase in global mean surface air temperature caused by the doubling of the concentration of atmospheric CO <jats:sub>2</jats:sub> —is needed to predict anthropogenic climate change. For decades, models have estimated its value to be between 1.5° and 4.5°C, but with too high an uncertainty to have strong predictive value. <jats:bold>Fasullo and Trenberth</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="792" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227465">792</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="6108" page="755" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1231083">Shell</jats:related-article> </jats:bold> ) show that the seasonal variation of tropospheric relative humidity is related to climate sensitivity and could be used to constrain models and narrow the range of equilibrium climate sensitivity estimates, thereby allowing more accurate predictions of future warming. </jats:p>

<jats:title>Wound Healing and Immunity</jats:title> <jats:p> Although wound healing and infection are often overlapping processes, whether the wound healing response modulates the immune response is not well understood. <jats:bold> Doronin <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="795" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226625">795</jats:related-article> , published online 27 September; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6108" page="748" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230342"> <jats:bold>Herzog and Ostrov</jats:bold> </jats:related-article> ) now show that coagulation factor X, an important component of the blood clotting cascade, helps to trigger antiviral immunity in response to adenovirus infection in mice. Factor X binds to human type C adenovirus with very high affinity. Structural analysis identified the critical binding residues between factor X and adenovirus, which, when mutated, inhibited binding. Despite being able to infect splenic macrophages in mice, transcriptional profiling of spleens from mice infected with a mutant adenovirus unable to bind to factor X revealed impaired activation of signaling cascades associated with innate immunity. </jats:p>

<jats:title>Observing Sperm Factories</jats:title> <jats:p> The blood-testis barrier creates a permissive microenvironment for germ cell differentiation and protects meiotic germ cells from autoimmunity. To become sperm, large cysts of germline progenitors must cross the blood-testis barrier without causing damage. <jats:bold>Smith and Braun</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="798" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1219969">798</jats:related-article> , published online 20 September) show that somatic Sertoli cells, the gate-keepers of the blood-testis barrier, manage this task by building a network of compartments bounded by old and new tight junctions. Intercellular bridges, which connect germ cells within cysts, span the transient compartments by passing through vertical strands at tricellular junctions. Only after the formation of a new blood-testis barrier are old tight junctions removed and germ cells released. </jats:p>

<jats:title>Sexual Versus Natural Selection</jats:title> <jats:p> In a 1948 experiment with <jats:italic>Drosophila</jats:italic> , Angus Bateman showed that sexual selection is strongest in males (versus females) because the number of mates they obtain is correlated with the number of offspring they produce. This relationship between mate number and offspring number has since become known as the Bateman slope, but there has been much debate concerning whether such a relationship can be expected in nature. Using a 30-year data set collected from a closed population of pronghorn antelope in Montana, <jats:bold>Byers and Dunn</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="802" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224660">802</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="6108" page="749" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230395">Wade</jats:related-article> </jats:bold> ) show that the relationship between mate number and offspring number indeed provides an opportunity for strong sexual selection in this polygynous and dimorphic species—however, environmental effects can make such selection null. In years when coyote predation on newborn fawns was high, sexual selection could not operate and reproductive success was instead determined by natural selection. </jats:p>

<jats:title>Keeping Coral Clean</jats:title> <jats:p> Seaweed overgrowth is a major problem for coral reefs and also seems to be a consequence of excessive harvesting of herbivorous fish. <jats:bold>Dixson and Hay</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="804" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225748">804</jats:related-article> ) examined this effect on Fijian reefs. Species of small herbivorous gobies and coral-associated damselfish were compared for their effect on the toxic <jats:italic>Chlorodesmis</jats:italic> seaweed in experiments that required caging colonies of the branching coral <jats:italic>Acropora nasuta</jats:italic> and the associated fish species. Only the gobies actively removed algal fronds attached to the cages and only one species (itself toxic to predators) ate them; the damselfish simply defected from the arena when toxic algae were present. The hydrophobic toxins exuded in the algal mucus lysed coral polyps releasing cell constituents that, together with the algal toxin, attract the gobies, which then eat the algal fronds. Interestingly, the toxic goby became more toxic to predators after consumption of the seaweed, which may help to drive symbiosis with a coral colony. </jats:p>

<jats:title>Dissecting Phosphine Resistance</jats:title> <jats:p> Worldwide populations of pest insects—such as the lesser grain borer, <jats:italic>Rhyzopertha dominica</jats:italic> , and the rust-red flour beetle, <jats:italic>Tribolium castaneum</jats:italic> —have become highly resistant to the fumigant phosphine, providing a potential threat to global food security. The nematode, <jats:italic>Caenorhabditis elegans</jats:italic> is vulnerable to phosphine, but phosphine-resistant strains are known. <jats:bold> Schlipalius <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="807" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224951">807</jats:related-article> ) show that mutations in the delta-1-pyrroline-5-carboxylate dehydrogenase and dihydrolipoamide dehydrogenase ( <jats:italic>dld-1</jats:italic> ) genes both give rise to phosphine resistance in <jats:italic>C. elegans</jats:italic> . Phosphine resistance mutants in <jats:italic>R. dominica</jats:italic> , and <jats:italic>T. castaneum</jats:italic> also map to the <jats:italic>dld-1</jats:italic> gene, which codes for a core metabolic enzyme. These mutants are, however, hypersensitive to arsenic, mimics of which might thus synergize with phosphine. </jats:p>

<jats:title>Optogenetic Control</jats:title> <jats:p> Fluorescent proteins are widely used as optical sensors; however, optical control of protein activity remains challenging. <jats:bold> Zhou <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="810" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226854">810</jats:related-article> ) describe an approach that allows both sensing and control. Domains of the fluorescent protein Dronpa were designed to dimerize with one another and were fused to each of the termini of an enzyme domain. In the dark, the domains dimerized and inhibited the enzyme. However, exposure to light induced Dronpa dissociation and activated the enzyme, allowing optogenetic control. </jats:p>

<jats:title>Mitochondrial Lipid Trafficking</jats:title> <jats:p> Disturbances in cellular membrane lipid composition have severe functional consequences and are often associated with disease. How mitochondria—dynamic organelles that constantly fuse and divide—maintain their phospholipid composition and adjust it to physiological needs is unknown. Some phospholipids, like cardiolipin and phosphatidylethanolamine, are synthesized in the mitochondrial inner membrane from precursor molecules that are imported from the endoplasmic reticulum. <jats:bold> Connerth <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="815" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225625">815</jats:related-article> ) examined mechanisms determining the accumulation of cardiolipin in yeast mitochondria. A combination of quantitative lipidomics, yeast genetics, ultrastructural studies, and biochemical in vitro assays suggested that the protein Ups1 shuttles the precursor lipid phosphatidic acid between outer and inner mitochondrial membranes. Ups1 mediates lipid transport in complex with another mitochondrial protein, Mdm35, which stabilizes Ups1 in a transport-competent conformation and protects it against proteolysis. High cardiolipin concentrations inhibited the transport of phosphatidic acid by Ups1, which appears to provide a feedback control system that limits the accumulation of cardiolipin in mitochondrial membranes. </jats:p>