Catálogo de publicaciones - revistas

<jats:title>Slowing Brain Disease with Gene Therapy</jats:title> <jats:p> X-linked adrenoleukodystrophy (ALD), the hereditary brain demyelinating disorder that was featured in the movie “ <jats:italic>Lorenzo's Oil</jats:italic> ,” is typically treated by transplantation of bone marrow from matched donors. This treatment slows progression of the disease by introducing cells that differentiate into myelin-producing cells. <jats:bold> Cartier <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="818" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1171242">818</jats:related-article> ; see Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5954" page="805" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181937">Naldini</jats:related-article> </jats:bold> ) tested an alternative gene therapy–based approach in two young patients without matched donors. A lentiviral vector was used to introduce a wild-type copy of the ALD gene into the patients' hematopoietic stem cells ex vivo. The modified cells were then infused back into the patients. Expression of the transferred gene was still detectable in the patients' blood cells 2 years later, and both patients showed neurological improvement and a delay in disease progression comparable to that seen with bone marrow transplants. </jats:p>

<jats:title>Entangling Rainbows</jats:title> <jats:p> Quantum mechanical entanglement is at the heart of quantum information processing. In the future, practical systems will contain a network of quantum components, possibly operating at different frequencies. <jats:bold> Coelho <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="823" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178683">823</jats:related-article> , published online 17 September) present a technique that can entangle light beams of three different frequencies. The ability to swap entanglement between different light fields should prove useful in advanced quantum information protocols on systems comprising different operating frequencies. </jats:p>

<jats:title>Cluster Electronics and Catalysis</jats:title> <jats:p> Many practical catalysts consist of small metal clusters on oxide supports, and the activity of these clusters usually varies with their size. In order to sort out some of the competing effects that lead to such variations, <jats:bold> Kaden <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="826" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180297">826</jats:related-article> ) size-selected palladium clusters (from single atoms to clusters up to 25 atoms) and deposited them on a crystal face of the rutile phase of titanium dioxide. X-ray photoemission studies and temperature-programmed reaction measurements showed that the activity of these model catalysts for CO oxidation was related to the electronic energy, which was reflected in the Pd 3d electron binding energy. Ion-scattering studies showed that the clusters formed flat single- or double-layer islands. </jats:p>

<jats:title>Simulating Surfaces</jats:title> <jats:p> Although modern computational chemistry can often match or even exceed experimental accuracy in modeling gas phase reactions, the surface-bound processes involved in most practical catalysis pose a substantially greater challenge to theory (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5954" page="809" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181275">Hasselbrink</jats:related-article> </jats:bold> ). <jats:bold> Díaz <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="832" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178722">832</jats:related-article> ) show that a modification to standard density functional methods can predict reaction barrier heights to within 1 kilocalorie per mole for the widely studied dissociative adsorption of dihydrogen on copper. In a complementary study, <jats:bold> Shenvi <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="829" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179240">829</jats:related-article> ) apply an efficient algorithmic framework to model transitions among multiple electronic states at a metal surface and successfully account for the complex dependence of nitric oxide scattering on the small molecule's vibrations and rotations. </jats:p>

<jats:title>Simulating Surfaces</jats:title> <jats:p> Although modern computational chemistry can often match or even exceed experimental accuracy in modeling gas phase reactions, the surface-bound processes involved in most practical catalysis pose a substantially greater challenge to theory (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5954" page="809" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181275">Hasselbrink</jats:related-article> </jats:bold> ). <jats:bold> Díaz <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="832" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178722">832</jats:related-article> ) show that a modification to standard density functional methods can predict reaction barrier heights to within 1 kilocalorie per mole for the widely studied dissociative adsorption of dihydrogen on copper. In a complementary study, <jats:bold> Shenvi <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="829" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179240">829</jats:related-article> ) apply an efficient algorithmic framework to model transitions among multiple electronic states at a metal surface and successfully account for the complex dependence of nitric oxide scattering on the small molecule's vibrations and rotations. </jats:p>

<jats:title>Nitrogen Overload</jats:title> <jats:p> The cycling of essential nutrients in terrestrial ecosystems has been altered by human activities. <jats:bold> Elser <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="835" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176199">835</jats:related-article> ) report a comparative analysis of lakes in Norway, Sweden, and in the United States that suggests that this is also true in aquatic ecosystems such as lakes. Deposition of anthropogenically derived atmospheric nitrogen controls whether N or P is growth-limiting for phytoplankton. Under elevated conditions of atmospheric N inputs, lake phytoplankton become consistently P-limited because the N:P ratio is strongly distorted. This is in contrast to conditions of low N deposition when lake phytoplankton are N-limited. These effects are even observed in remote lakes, demonstrating the indirect yet wide-ranging effects of humans on global food webs. </jats:p>

<jats:title>Desert Balancing Act</jats:title> <jats:p> Ecosystem nutrient budgets are often difficult to estimate given the variety of processes and organisms that influence their flux. In deserts, for example, the loss of nitrogen—a limiting nutrient for growth—is often thought to be mediated by the generation of trace gases from biological activity. <jats:bold>McCalley and Sparks</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="837" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178984">837</jats:related-article> ) present results from the Mojave Desert that suggest most nitrogen is instead driven off by the Sun at high temperatures that inhibit microbial activity. This requires a reevaluation of the desert nitrogen budget both now and in the future when climate change may drive increased abiotic emissions in arid ecosystems. </jats:p>

<jats:title>Long-Lost Pollinators</jats:title> <jats:p> The rise of angiosperms in the Early Cretaceous (∼140 million years ago) was accompanied by coevolution of a variety of insects, including flies, bees, and wasps required for pollination. <jats:bold> Ren <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="840" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178338">840</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="5954" page="808" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181154">Ollerton and Coulthard</jats:related-article> </jats:bold> ) show that three families of scorpionflies had already evolved specialized mouth parts for feeding on the nectar of gymnosperms, as early as the Middle Jurassic (∼170 million years ago). The diversity and specialization of these insects and related plant structures suggests that they were also involved in pollination. These families died out later in the Cretaceous as angiosperms began to dominate. </jats:p>

<jats:title>Butterfly Apartheid</jats:title> <jats:p> <jats:italic>Heliconius</jats:italic> butterflies show differences in mimetic color patterns across geographic races associated with patterns of assortative mating, suggesting that ecological speciation may be ongoing. <jats:bold> Chamberlain <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="847" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179141">847</jats:related-article> ) demonstrate assortative mating on the basis of color pattern mimicry that generates reproductive isolation between <jats:italic>Heliconius cydno</jats:italic> species and subspecies within polymorphic populations in Ecuador. Furthermore, it appears that these traits are controlled by a single gene that affects color pigment in wing pattern formation and vision. Thus, these butterflies are indeed in the early stages of reproductive isolation that is being driven by an ecological trait, allowing observation of an incipient speciation event. </jats:p>

<jats:title>Bacterial Trigger of Plant Protection</jats:title> <jats:p> Innate immunity can be rapidly activated to defend a host plant against a microbial pathogen. The rice protein XA21, which is thought to be a cell surface–located receptor with a kinase domain, activates the plant's defenses in response to infection by certain strains of <jats:italic>Xanthomonas</jats:italic> bacteria. <jats:bold> Lee <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="850" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1173438">850</jats:related-article> ) have now identified the bacterial gene that encodes the protein, AvrXA21, to which the plant receptor XA21 responds. The 194–amino acid protein needs to be secreted and sulfated to trigger the rice plant defense responses. Similarities exist between the receptor XA21 and other immune response receptors in both plants and animals. </jats:p>