Catálogo de publicaciones - revistas

<jats:title>Earthquake in a Maze</jats:title> <jats:p> The 11 April 2012 magnitude 8.6 earthquake offshore of Sumatra was the largest measured earthquake along a strike-slip boundary that modern seismological instruments have ever recorded. Despite its size and proximity to a large population, there was no subsequent tsunami and there were no reported fatalities. <jats:bold> Meng <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="724" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224030">724</jats:related-article> , published online 19 July) used teleseismic data from seismological networks in Japan and Europe to image the source of high-frequency radiation generated by the earthquake to understand the mechanics of this unique event. The resultant back projections showed that the earthquake slowly ruptured along a complex series of faults. The deeper-than-usual rupture path and large stress drop are both features that may not be unique to this earthquake, suggesting that regions in a similar tectonic environment may have the potential for more complex—or larger—intraplate earthquakes than might have been expected. </jats:p>

<jats:title>Phosphoinositide Contributions</jats:title> <jats:p> To study the roles of phosphoinositides in the plasma membrane of mammalian cells, <jats:bold> Hammond <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="727" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222483">727</jats:related-article> , published online 21 June; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6095" page="653" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227096">Fairn and Grinstein</jats:related-article> </jats:bold> ) engineered phosphatase molecules that could be targeted to the membrane on demand, where they would alter the concentrations of the phospholipids phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P <jats:sub>2</jats:sub> ] and phosphatidylinositol 4-phosphate (PI4P). PI4P was thought to provide a major source for the synthesis of PI(4,5)P <jats:sub>2</jats:sub> , but depletion of PI4P did not have much affect on synthesis of PI(4,5)P <jats:sub>2</jats:sub> . Instead, PI4P appears to help to establish the negative charge at the membrane and thus promote electrostatic interactions with positively charged amino acids in membrane-associated proteins and influencing function of ion channels. </jats:p>

<jats:title>Cancer Stem Cells in Color</jats:title> <jats:p> One of the liveliest debates in contemporary cancer research centers on whether cancer stem cells (CSCs) exist and, if so, how these cells are defined phenotypically. CSCs are hypothesized to be a small population of cells within a tumor that are endowed with the unique capacity to drive tumor growth—a scenario that in principle would offer important therapeutic opportunities. By studying mice expressing multicolor reporter genes, <jats:bold> Schepers <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="730" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224676">730</jats:related-article> , published online 1 August) were able to visualize and monitor the fate of a candidate stem cell for intestinal adenomas, an early stage of cancer. This “lineage tracing” analysis suggests that tumor cells expressing the intestinal crypt stem cell marker Lgr5 (leucine-rich repeat containing G protein–coupled receptor 5) are the cells that fuel the growth of intestinal adenomas. </jats:p>

<jats:title>Current on Demand</jats:title> <jats:p> Deep brain electrical stimulation can be a successful therapy in Parkinson's disease, in depression, and in several other psychiatric diseases, especially in drug-resistant cases. Unfortunately, chronic, continuous stimulation is associated with multiple side effects. This could be alleviated by delivering the electrical perturbation only when it is necessary, using closed-loop stimulation. Such an approach is essential for epilepsy, where seizures occur very rarely but with serious consequences. In a rat model for epilepsy, <jats:bold> Berényi <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="735" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223154">735</jats:related-article> ) prevented seizures by transcranial electrical stimulation using a closed-loop system. Transcranial electrical stimulation was highly effective and reduced seizure duration, on average, by 60 %. </jats:p>

<jats:title>Bio-Inspired Drug Delivery</jats:title> <jats:p> Noting that platelets naturally migrate to narrowed blood vessels characterized by high fluid shear stress, <jats:bold> Korin <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="738" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1217815">738</jats:related-article> , published online 5 July; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6095" page="658" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227097">Lavik and Ustin</jats:related-article> </jats:bold> ) developed a nanoparticle-based therapeutic that uses a similar targeting mechanism to deliver a drug to vessels obstructed by blood clots. Aggregates of nanoparticles coated with the clot-dissolving drug tPA (tissue plasminogen activator) were designed to fall apart and release the drug only when encountering high fluid shear stress. In preclinical models, the bio-inspired therapeutic dissolved clots and restored normal blood flow at lower doses than free tPA, suggesting that this localized delivery system may help reduce the risk of side effects such as excessive bleeding. </jats:p>

<jats:title>Promoting the Male X Chromosome</jats:title> <jats:p> In mammals and fruit flies, females have a double dose of the X chromosome compared to males, and to compensate for this imbalance, in fruit flies, transcription from across most of the male X chromosome is boosted by twofold. <jats:bold> Conrad <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="742" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221428">742</jats:related-article> , published online 19 July) measured the binding of RNA polymerase II, responsible for the majority of the transcription on the X chromosome, and found a consistent increase at the promoters of genes on the male X chromosome. Thus, the increase in transcription on the male X chromosome is not driven by increased rates of transcriptional elongation, as has been suggested previously, but must involve up-regulation of transcription initiation. </jats:p>

<jats:title>Generating the Cortex</jats:title> <jats:p> During development of the cerebral cortex, radial glial neural progenitor cells generate layer-specific subtypes of excitatory neurons in a defined temporal sequence, in which deep layers are formed before upper layers. The prevailing model for cortical neurogenesis over the last 20 years has been the common progenitor model, which proposes that the neurogenic potential of the radial glial cell is progressively restricted over time. In contrast to this model, <jats:bold> Franco <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="746" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223616">746</jats:related-article> ) now show that, in mice, two radial glial cell subtypes appear to be specified at the onset of cortical development: one for neurons of the evolutionarily older lower cortical layers and a second for the upper cortical layers that are present in placental mammals and are enlarged in primates, especially humans. </jats:p>

<jats:title>Crucial Cerebellar Glial Cells</jats:title> <jats:p> The role of glial cells and their interaction with neurons in normal behavior is unclear. To address this question, <jats:bold> Saab <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="749" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221140">749</jats:related-article> , published online 5 July) studied a special type of glial cell in the cerebellum. Conditional mutant mice were produced in which the two glutamate receptor subunits normally present in Bergmann glial cells were efficiently ablated in a temporally controlled manner. Glutamate signaling of the glial cells contributed to the structural and functional integrity of the cerebellar network. Bergmann glial cells also played a role in the “fine-tuning” of neuronal processing, which is crucial for the fast and precise control of complex motor behavior. </jats:p>

<jats:title>The Conductor in the Thalamus</jats:title> <jats:p> The pulvinar is the largest thalamic nucleus in the brain but its functions remain unclear. The pulvinar is ideally positioned to synchronize activity across the visual cortex. <jats:bold> Saalmann <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="753" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1223082">753</jats:related-article> ) combined diffusion tensor imaging with multi-electrode recordings from three different brain areas in monkeys to probe thalamo-cortical interactions during visual attention. The pulvinar was found to play a vital role in attention by routing behaviorally relevant information across the visual cortex. </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>