Catálogo de publicaciones - revistas

<jats:title>Wearable Monitors</jats:title> <jats:p> Advances in microelectronics have yielded high-quality devices that allow for intensive signal collection or transmission. <jats:bold> S. Xu <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="6179" page="70" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250169">70</jats:related-article> ) show how to make a soft wearable system that is constructed like a stretchable circuit board, where the electronic components are bridged electrically by thin, meandering conducting traces that float in a highly visco-elastic polymer. A complete soft circuit capable of multisignal physiological sensing on skin was created, with potential for use in health monitoring or neonatal care. </jats:p>

<jats:title>Cyanide Hitches a Ride</jats:title> <jats:p> Cyanide is a by-product of the biosynthesis of ethylene in plants and it has been somewhat puzzling how the ion is safely removed before it can shut down enzymatic pathways by coordination to catalytic iron centers. A proposed mechanism has implicated the cyanoformate ion—essentially, a weak adduct of cyanide and carbon dioxide—as the initial product, although its lifetime was uncertain. <jats:bold> Murphy <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="6179" page="75" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250808">75</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6179" page="45" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252466"> <jats:bold>Alabugin and Mohamed</jats:bold> </jats:related-article> ) crystallized this previously elusive adduct and found that its solution-phase stability varies inversely with the dielectric properties of the medium. The results bolster a picture in which the adduct shuttles the cyanide away from the hydrophobic confines of the enzyme before releasing the cyanide into the more polar aqueous surroundings. </jats:p>

<jats:title>Inside Enceladus</jats:title> <jats:p> Saturn's moon Enceladus has often been the focus of flybys of the Cassini spacecraft. Although small—Enceladus is roughly 10 times smaller than Saturn's largest moon, Titan—Enceladus has shown hints of having a complex internal structure rich in liquid water. <jats:bold> Iess <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="6179" page="78" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250551">78</jats:related-article> ) used long-range data collected by the Cassini spacecraft to construct a gravity model of Enceladus. The resulting gravity field indicates the presence of a large mass anomaly at its south pole. Calculations of the moment of inertia and hydrostatic equilibrium from the gravity data suggest the presence of a large, regional subsurface ocean 30 to 40 km deep. </jats:p>

<jats:title>Deep, Driving Temperatures</jats:title> <jats:p> Convection in Earth's mantle is largely controlled by the physical properties of the mantle such as density and viscosity. Because these factors are influenced by both temperature and composition, it has been difficult to ascribe one as the primary control over mantle convection or explain the long-wavelength features associated with mid-ocean ridges. Examining correlations between a global seismic velocity model with constraints on the depth and geochemical signature of mid-ocean ridges, <jats:bold> Dalton <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="6179" page="80" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249466">80</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="6179" page="51" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252089">Kelley</jats:related-article> </jats:bold> ) suggest that large temperature variations extending into the upper mantle explain most of the geophysical and geochemical observations. Moreover, the analysis provides support for deeply rooted mantle plumes as the source of hot spot volcanism. </jats:p>

<jats:title>Old Gradients</jats:title> <jats:p> The surface ocean temperature gradient between the warmer Western Equatorial Pacific and the cooler Eastern Equatorial Pacific is smaller during El Niño episodes than during neutral periods or during La Niñas. Some reconstructions of Pacific Ocean sea surface temperatures (SST) covering periods before ∼3 million years ago have suggested a permanent El Niño–like state. <jats:bold> Zhang <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="6179" page="84" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1246172">84</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="6179" page="52" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252246">Lea</jats:related-article> </jats:bold> ) present data from a biomarker-derived proxy for SST that indicate a sizable east-west gradient has existed for the past 12 million years, contradicting the concept of a permanent El Niño–like state existed. </jats:p>

<jats:title>Designer Embryo</jats:title> <jats:p> Numerous signaling pathways have been implicated in controlling early vertebrate embryogenesis. <jats:bold> P.-F. Xu <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="6179" page="87" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248252">87</jats:related-article> ) identify the minimal set of factors necessary to get uncommitted cells to organize a complete embryo. Two opposing gradients of the growth factors Nodal and Bone Morphogenetic Protein were sufficient to instruct zebrafish embryonic pluripotent cells to organize a complete embryo, not only in vivo but also in vitro. These findings may provide guidance for regenerative medicine studies aimed at constructing tissues and organs in vitro from cultured pluripotent cells. </jats:p>

<jats:title>Constructed for Deconstruction</jats:title> <jats:p> Lignin provides strength to wood but also impedes efficient degradation when wood is used as biofuel. <jats:bold> Wilkerson <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="6179" page="90" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250161">90</jats:related-article> ) engineered poplar to produce lignin that is more amenable to degradation. From a handful of plants that contain more digestible lignin monomers, <jats:italic>Angelica sinensis</jats:italic> was selected and its monolignol transferase activities analyzed. The enzyme involved, coniferyl ferulate feruloyl-CoA monolignol transferase, was then expressed in poplar. The resulting poplar trees showed no difference in growth habit under greenhouse conditions, but their lignin showed improved digestibility. </jats:p>

<jats:title>Optogenetics Applied to Motorneuron Control</jats:title> <jats:p> Nerves damaged by disease or injury do not always regenerate. In such cases, therapies involving transplanted stem cells show some promise. However, the new neurons derived from transplanted cells cannot communicate with the central control systems that would normally regulate movement. To avoid the need for such communication, in a proof-of-principle study, <jats:bold> Bryson <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="6179" page="94" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248523">94</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6179" page="44" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253088"> <jats:bold>Iyer and Delp</jats:bold> </jats:related-article> ) added optogenetic control to differentiation and transplantation of motor neurons. In the mouse, these engineered neurons were able to reestablish connections within a damaged sciatic nerve and, when activated by localized light stimulation, could drive muscle contractions. </jats:p>

<jats:title>Backward or Forward</jats:title> <jats:p> Although land animals generally walk forward, they readily switch to walking backward if they sense an obstruction or danger in the path ahead. Such a switch is likely to involve a neural signal sent from the brain down to local motor circuits, instructing these motor circuits to alter the phase at which specific leg muscles are activated. <jats:bold> Bidaye <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="6179" page="97" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249964">97</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="6179" page="48" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252431">Mann</jats:related-article> </jats:bold> ) identified such a neuron in <jats:italic>Drosophila</jats:italic> , which they call MDN (moonwalker descending neuron). Blocking synaptic transmission from MDN inhibited backward walking, and conversely artificially activating MDN caused flies to walk backward. </jats:p>

<jats:title>Dissecting SRP</jats:title> <jats:p> In the secretory pathway, inserting transmembrane and secretory proteins into and through hydrophobic cell membranes is facilitated by a highly conserved RNA and protein-containing molecular machine, the signal recognition particle (SRP). <jats:bold> Grotwinkel <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="6179" page="101" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249094">101</jats:related-article> ) determined the x-ray crystal structures of human SRP RNA (7SL RNA) bound to the RNA-binding domain (RBD) of the protein SRP subunit SRP68, both in the presence and absence of the SRP19 subunit. The 7SL RNA is remodeled by the SRP68-RBD, which bends one domain of the RNA and remodels a loop, exposing two nucleotides, which allow direct interaction with the ribosome. The findings explain how the SRP RNA drives translation elongation arrest, which is required for membrane insertion. </jats:p>