Catálogo de publicaciones - revistas

<jats:title>Planted Evidence</jats:title> <jats:p> To understand the spatial patterns and consequences of past climate change requires the identification of reliable proxies that reflect specific aspects of those changes, such as temperature or rainfall in a given location. Also of interest are proxies for broader categories of change, such as methane production or the sources of carbon dioxide. <jats:bold> Severinghaus <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="1431" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1169473">1431</jats:related-article> ) present a 100,000-year-long record of the oxygen isotopic composition of atmospheric O <jats:sub>2</jats:sub> (δ <jats:sup>18</jats:sup> O <jats:sub>atm</jats:sub> ) extracted from air from polar ice cores. δ <jats:sup>18</jats:sup> O <jats:sub>atm</jats:sub> is a general measure of the strength of low-latitude terrestrial photosynthesis and thus of local rainfall because plant metabolism is controlled in large part by water availability. δ <jats:sup>18</jats:sup> O <jats:sub>atm</jats:sub> changes were related to Heinrich and Dansgaard-Oeschger events, two modes of abrupt climate change common over that interval, and δ <jats:sup>18</jats:sup> O <jats:sub>atm</jats:sub> was controlled mostly by the strength of the Asian and North African monsoons. The rapid changes observed should also help to synchronize ice core records. </jats:p>

<jats:title>Boom and Bust</jats:title> <jats:p> The Brazilian Amazon is renowned for its biodiversity and for its influence on climate regulation and geochemical cycles. It is also one of the country's poorest regions. For decades, much economic development has been pursued through conversion of forest for agriculture and cattle-ranching. <jats:bold> Rodrigues <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="1435" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174002">1435</jats:related-article> ) investigated whether this pattern of land use brings lasting prosperity by analyzing data on the economic development of nearly 300 municipalities across the deforestation frontier. Relative development, in terms of life expectancy, literacy, and standard of living, increases as deforestation begins but then declines again as the frontier passes through. As a result, pre- and postfrontier levels of development are similarly low, indicating a pattern of boom and bust. </jats:p>

<jats:title>Helicopter Seed Lift</jats:title> <jats:p> The “helicopter” seeds of maple trees and other similar autorotating seeds detach from their parent tree under windy conditions and gyrate as they are dispersed by the wind. The reproductive success of the tree depends on the flight performance of its seeds. Autorotating seeds are known to generate high lift as they slowly descend through the air, but the means by which they do so is unclear. <jats:bold> Lentink <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="1438" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174196">1438</jats:related-article> , see the cover) have elucidated the aerodynamic mechanism for high lift in autorotating seeds using a robot model seed and a three-dimensional flow measurement technique. Maple seeds and a hornbeam seed create a prominent leading-edge vortex that is similar to the flow structures that are responsible for the high lift generated by the wings of hovering insects and bats. Thus, both animals and plants have converged on an identical aerodynamic solution for generating lift. </jats:p>

<jats:title>Neurotransmission in Living Color</jats:title> <jats:p> Neurotransmission involves the release of small molecular neurotransmitters from one neuron to another across a synapse. <jats:bold> Gubernator <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="1441" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172278" xlink:type="simple">1441</jats:related-article> , published online 7 May) introduce a means to observe neurotransmitter release optically, by the design of fluorescent false neurotransmitters, which act as substrates for the synaptic vesicle monoamine transporter. These endogenous monoamine optical tracers enabled visualization of neurotransmitter uptake and release from individual synaptic terminals and were used to evaluate dopamine neurotransmission in the striatum. The fraction of synaptic vesicles that release neurotransmitter per stimulus was frequency dependent, and a frequency-dependent selection of presynaptic terminals was observed. </jats:p>

<jats:title>Rotavirus Rumbled</jats:title> <jats:p> Rotavirus infection is the primary cause of severe diarrhea in infants. For the virus to enter cells, a Ca <jats:sup>2+</jats:sup> -stabilized trimer of the outer layer protein VP7 must be dissociated. <jats:bold> Aoki <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="1444" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1170481">1444</jats:related-article> ) report the structure of the VP7 trimer in complex with the Fab fragment of a neutralizing monoclonal antibody. Based on the structure and an analysis of positions of neutralization escape mutations, the authors propose that many neutralizing antibodies inhibit cell entry by stabilizing the VP7 trimer even at low calcium concentrations. A disulfide-linked trimer was then produced that is a potential subunit immunogen. </jats:p>

<jats:title>Dynamic Imprinting</jats:title> <jats:p> Gene imprinting—the silencing of either a maternally derived or paternally derived gene allele—is controlled in large part by DNA methylation. In plants, imprinting occurs in the endosperm, which nourishes the embryonic plant. <jats:bold> Gehring <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="1447" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171609">1447</jats:related-article> ) and <jats:bold> Hsieh <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="1451" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172417">1451</jats:related-article> ) analyzed the dynamics of DNA methylation in the endosperm and embryo of <jats:italic>Arabidopsis</jats:italic> and found extensive demethylation in the endosperm, suggesting that many imprinted genes are likely to exist. Gehring <jats:italic>et al.</jats:italic> characterized five imprinted genes in detail. Four of the 10 known imprinted genes are related homeodomain transcription factors. Furthermore, 5′ sequences demethylated in several of the genes were found to be derived from transposable elements, which supports the idea that imprinting arose as a by-product of silencing invading DNA. </jats:p>

<jats:title>Dynamic Imprinting</jats:title> <jats:p> Gene imprinting—the silencing of either a maternally derived or paternally derived gene allele—is controlled in large part by DNA methylation. In plants, imprinting occurs in the endosperm, which nourishes the embryonic plant. <jats:bold> Gehring <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="1447" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171609">1447</jats:related-article> ) and <jats:bold> Hsieh <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="1451" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172417">1451</jats:related-article> ) analyzed the dynamics of DNA methylation in the endosperm and embryo of <jats:italic>Arabidopsis</jats:italic> and found extensive demethylation in the endosperm, suggesting that many imprinted genes are likely to exist. Gehring <jats:italic>et al.</jats:italic> characterized five imprinted genes in detail. Four of the 10 known imprinted genes are related homeodomain transcription factors. Furthermore, 5′ sequences demethylated in several of the genes were found to be derived from transposable elements, which supports the idea that imprinting arose as a by-product of silencing invading DNA. </jats:p>

<jats:title>Recombining Resistance</jats:title> <jats:p> Homologous recombination is frequent in many bacteria, but few studies have addressed whether subpopulations within a species are more or less likely to undergo this process and whether it has consequences for their evolution. Taking a large data set from the pathogen <jats:italic>Streptococcus pneumoniae</jats:italic> , <jats:bold> Hanage <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="1454" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171908">1454</jats:related-article> ) discovered a group of strains characterized by an anomalous sequence of housekeeping genes. This sequence appeared to have been horizontally acquired from other pneumococci and related species and was associated with resistance to all classes of antibiotics for which data are available. Thus, hyper-recombination (in contrast to hypermutation) is important in the evolution and spread of antibiotic resistance and may play a role in determining the emergence of species clusters and the phenotypes associated with them. </jats:p>

<jats:title>It's All in the Delivery</jats:title> <jats:p> Pancreatic cancer is almost universally associated with a poor prognosis, in part because the tumors are resistant to chemotherapeutic drugs. Working with a mouse tumor model that displays many features of the human disease, <jats:bold> Olive <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="1457" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171362">1457</jats:related-article> , published online 21 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1400" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175940">Olson and Hanahan</jats:related-article> </jats:bold> ) found that the tumors were poorly vascularized, a factor likely to impede drug delivery. Treatment of the mice with the chemotherapeutic drug gemcitabine in combination with a drug that depletes tumor-associated stromal tissue led to an increase in tumor vasculature, enhanced delivery of gemcitabine, and a delay in disease progression. Thus, drugs targeting the tumor stroma may merit investigation as a way to enhance the efficacy of conventional chemotherapy for pancreatic cancer. </jats:p>

<jats:p>The show includes deforestation and development in the Amazon, stamping out Kashin-Beck disease in China, measuring the charge state of gold and silver atoms, and more.</jats:p>