Catálogo de publicaciones - revistas

<jats:title>Arsenic and Populace</jats:title> <jats:p> The solubility of arsenic in groundwater aquifers is controlled by a number of hydrologic and geochemical factors. In rural communities that rely on groundwater for drinking water, the risk from exposure may pose a public health threat, especially when groundwater pumping can increase arsenic solubility. In an effort to provide a focused assessment of risk to arsenic exposure from groundwater, <jats:bold> Rodríguez-Lado <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="866" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237484">866</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="6148" page="852" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242212">Michael</jats:related-article> </jats:bold> ) constructed a geostatistical model that incorporates a number of factors that control arsenic solubility across China. Most of the risk centers in a few provinces—Xinjiang, Inner Mongolia, Henan, Shandong, and Jiangsu—but the total population exposed to arsenic levels above 10 micrograms per liter could be upwards of 19 million people. </jats:p>

<jats:title>Gotta Get Up to Get Down</jats:title> <jats:p> By examining high-resolution satellite topography data of a ridge along the San Andreas Fault in California, <jats:bold> Hurst <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="868" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241791">868</jats:related-article> ) demonstrate how hill slope curvature may be used to infer long-term rates of tectonic uplift and erosion. Numerical modeling shows a lag phase between uplift events and changes in morphology, which, combined with the observational data, shows that topography can reveal whether landscapes are active or decaying. These fundamental relationships may help to improve seismic hazard forecasts or to interpret topographic data collected on other terrestrial planets. </jats:p>

<jats:title>European History at Depth</jats:title> <jats:p> The preferential alignment of mineral grains as a result of flow direction can polarize seismic waves traveling through Earth's interior, based on velocity and direction. <jats:bold>Zhu and Tromp</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="871" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241335">871</jats:related-article> , published online 8 August) mapped this anisotropy beneath the European continent and the North Atlantic Ocean—which are products of several tectonic events across varying temporal and spatial scales—using seismic tomography. The model generated correlates well with plate motion in the region, and, compared to geodetic measurements, much of the anisotropic features are consistent with modern strain rates. Some features below Eastern Europe, however, appear to be remnants of tectonic events that occurred over 350 million years ago. </jats:p>

<jats:title>Mn at Work</jats:title> <jats:p> Biogeochemical cycling involves oxidation-reduction reactions with common metals like iron and manganese. Depending on the oxygen concentration and pH of the surrounding water, these metals—which exist in multiple oxidation states—can either accept or donate electrons; however, detecting which chemical species is dominant in these reactions often proves difficult. Using a spectrophotometric method sensitive to Mn oxidation state, <jats:bold> Madison <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="875" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241396">875</jats:related-article> ) show that up to 90% of the total Mn in porewater collected from sediment cores in the St. Lawrence Estuary is soluble Mn(III)—a phase traditionally assumed to be unimportant in aqueous redox reactions except in a few niche environments. </jats:p>

<jats:title>Ingenol Ingenuity</jats:title> <jats:p> The diterpenoid i ngenol is the core structure of a topical drug recently commercialized to treat actinic keratosis, a precancerous skin condition. Sourcing the compound from the <jats:italic>Euphorbia</jats:italic> plants that produce it is relatively inefficient, so <jats:bold> Jørgensen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="878" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241606">878</jats:related-article> , published online 1 August) devised a chemical synthesis starting from the comparatively simple and inexpensive monoterpene chiral (+)-3-carene. The synthetic sequence involves 14 steps—less than half as long as prior chemical routes to the target—and relies on a two-stage approach, inspired by the posited biosynthetic pathway, in which preliminary assembly of the fused ring framework precedes hydroxylation of the periphery. </jats:p>

<jats:title>Mapping Molecular Linkers</jats:title> <jats:p> In metal-organic framework compounds, inorganic centers (metal atoms or clusters) are linked by bidentate organic groups. Normally, the same group is used throughout the structure, but recently, synthesis with linkers bearing different functional groups has produced well-defined materials. <jats:bold> Kong <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="882" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1238339">882</jats:related-article> , published online 25 July) combined solid-state nuclear magnetic resonance and molecular simulations to map the distributions of linkers in these materials as random, well-mixed, or clustered. </jats:p>

<jats:title>Making Crystals</jats:title> <jats:p> The initial transition from a disordered solution to the formation of nuclei that grow into crystals continues to be a puzzle. Recent experiments suggested the formation of stable ordered clusters that appear prior to the formation of the first nuclei. <jats:bold> Wallace <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="885" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1230915">885</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="855" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1243022"> <jats:bold>Myerson and Trout</jats:bold> </jats:related-article> ) used molecular dynamics to look at the potential structure and dynamics of these clusters and lattice gas simulations to explore the population dynamics of the cluster populations prior to nucleation. A liquid-liquid phase separation process was observed whereby one phase becomes more concentrated in ions and becomes the precursor for nuclei to form. </jats:p>

<jats:title>Steroid Receptor Signaling</jats:title> <jats:p> Plant brassinosteroids signal to diverse pathways in plant physiology. These steroid hormones are perceived at the cell surface, where they bind to the receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1). <jats:bold> Santiago <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="889" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1242468">889</jats:related-article> , published online 8 August) now show that somatic embryogenesis receptor kinase 1 (SERK1) complexes with BRI1. Together, these receptor kinases form the steroid binding site, with the hormone acting as a “molecular glue” that stabilizes the interaction. Hormone-induced heteromerization of BRI1 with SERK1 leads to the activation of the cytoplasmic signaling cascade, triggering plant growth and differentiation. </jats:p>

<jats:title>Regulating the MBT</jats:title> <jats:p> It has been known for more than 30 years that a defined number of cell divisions in the frog embryo precede a crucial developmental event called the midblastula transition (MBT). <jats:bold> Collart <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="893" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1241530">893</jats:related-article> , published online 1 August) now elucidate a mechanism involved in the control of the MBT. DNA replication initiation factors are titrated out during early cell divisions, which controls the elongation of the cell cycle and the onset of zygotic transcription during the MBT. </jats:p>

<jats:title>Dissecting Dystrophies</jats:title> <jats:p> Defects in α-dystroglycan lead to various congenital muscular dystrophies, and its ability to bind to extracellular matrix (ECM) is dependent on formation of a specific O-linked sugar structure. Previous efforts to understand the molecular mechanisms underlying α-dystroglycan's ability to bind to the ECM led to the identification of a phosphorylated <jats:italic>O</jats:italic> -mannosyl trisaccharide on α-dystroglycan and to the demonstration that addition of this residue is a prerequisite for formation of the ligand-binding motif. However, the biosynthetic pathway that leads to production of the phosphorylated <jats:italic>O</jats:italic> -mannosyl glycan has not been delineated. <jats:bold> Yoshida-Moriguchi <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6148" page="896" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1239951">896</jats:related-article> , published online 8 August) elucidate the functions of three genes recently found to cause dystroglycan-related disorders and explain the defects in the production of the phosphorylated <jats:italic>O</jats:italic> -mannosyl glycan that underlie the pathologies of patients with the relevant mutations. </jats:p>