Catálogo de publicaciones - revistas

<jats:title>Mitigating Nitrogen Enrichment?</jats:title> <jats:p> Nitrogen enrichment reduces the species diversity of plants in herbaceous communities. By contrast, the effects of increasing CO <jats:sub>2</jats:sub> on plant species richness is poorly documented, and the interaction of both N deposition and CO <jats:sub>2</jats:sub> elevation are unknown. <jats:bold>Reich</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1399" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178820">1399</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="5958" page="1353" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1183271">Collins</jats:related-article> </jats:bold> ) performed a 10-year open-air field experiment in a North American perennial grassland assemblage. Reductions in plant species richness resulting from N deposition were half as large under elevated CO <jats:sub>2</jats:sub> concentrations as under ambient atmospheric CO <jats:sub>2</jats:sub> . Given that both N and CO <jats:sub>2</jats:sub> are projected to increase globally, these results provide a pointer to the types of ecological change that could be expected, at least in relatively simple plant communities. </jats:p>

<jats:title>Metamorphosis Receptor Identified</jats:title> <jats:p> One of the challenges facing many multicellular organisms is when to change from the juvenile stage to the reproductively mature adult. In insects, this metamorphosis is activated by the brain-derived neuropeptide, prothoracicotropic hormone (PTTH), when larvae reach a characteristic weight. Almost a century after this brain hormone was discovered, <jats:bold> Rewitz <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="1403" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176450">1403</jats:related-article> ) have identified the PTTH receptor and its signaling cascade. The PTTH receptor is Torso (a receptor tyrosine kinase that signals through Ras/Raf/Erk), which patterns the embryonic termini during early development in response to the distantly related PTTH factor, Trunk. </jats:p>

<jats:title>Hedgehog, Flatworms, and Regeneration</jats:title> <jats:p> The Hedgehog (Hh) signaling pathway plays pivotal roles during embryonic development, post-embryonic tissue maintenance, and disease. In spite of having at its core a collection of highly conserved components, the Hh pathway displays unusual differences in signal transduction mechanisms among flies, fish, and mammals. Using planarians (nonparasitic flatworms), <jats:bold> Rink <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="1406" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178712">1406</jats:related-article> , published online 22 October) report a key role for Hh signaling during adult regeneration and provide evidence that the perplexing diversity of transduction mechanisms may have arisen from animal-specific losses of an ancestral association between cilia and Hh signaling. </jats:p>

<jats:title>For the Love of Science</jats:title> <jats:p> Which is a better predictor of a student's continued participation in science, facile understanding or personal interest? <jats:bold>Hulleman and Harackiewicz</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1410" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177067">1410</jats:related-article> ) designed an experiment to find out what drives high-school students. First-year high-school students were asked either to write about what they had just learned or about how what they had just learned connected to some facet of their personal lives. Connections of personal relevance were stronger than good grades for predicting interest in further science courses and future science careers. This low-cost intervention seemed to have its largest effect on students who began the class with the least amount of confidence in their abilities. </jats:p>

<jats:title>Nascent Chains Revealed</jats:title> <jats:p> Detailed analysis of protein translation and translocation across membranes requires the identification and structural analysis of intermediates involved in these processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5958" page="1352" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1183690">Kampmann and Blobel</jats:related-article> </jats:bold> ). <jats:bold> Seidelt <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="1412" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177662">1412</jats:related-article> , published online 29 October) report the visualization by cryo-electron microscopy of a nascent polypeptide chain in the tunnel of the ribosome at 5.8 angstroms. This resolution allows analysis of the conformation and distinct contacts of the nascent chain within the ribosomal tunnel, which suggests a mechanism by which translational stalling is induced by this peptide. Protein translocation across cellular membranes involves the Sec61 protein, a component of a protein-conducting channel. Whether Sec61 acts as a monomer or as an oligomer during protein translocation has been unclear. <jats:bold> Becker <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="1369" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178535">1369</jats:related-article> , published online 29 October) describe active yeast and mammalian ribosome-Sec61 structures that show the Sec61 complex interacting with the ribosome and a nascent secretory protein signal sequence. The analysis unambiguously reveals that the active protein-conducting channel is a single Sec61 copy with its central pore serving as conduit for the nascent polypeptide. </jats:p>

<jats:title>Targeting DNA Gyrase</jats:title> <jats:p> DNA gyrase, an enzyme that unwinds double-stranded DNA, is essential in bacteria, but missing in humans, and is thus an important antibiotic target. DNA gyrase is inhibited by the well-known fluoroquinolines and aminocoumarins antibiotics, as well as by symocyclinones—bifunctional antibiotics comprising an aminocoumarin and a polyketide group. Surprisingly, symocyclinones, unlike aminocoumarin inhibitors, do not inhibit DNA gyrase GTPase activity, but instead inhibit binding to DNA. Now <jats:bold> Edwards <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="1415" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179123">1415</jats:related-article> ) use biochemical and structural studies to show that the two functional groups of the antibiotic bind in separate pockets on the gyrase. Each group is a relatively weak inhibitor that together potently inhibit DNA binding. </jats:p>

<jats:title>Coordinating Neuronal Assemblies</jats:title> <jats:p> Theoretical models predict the existence of so-called hub neurons—highly connected cells that strongly influence the synchronization of spiking activity in a large group of neurons. However, experimental evidence for the existence of these neuronal hubs is lacking. <jats:bold> Bonifazi <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="1419" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175509">1419</jats:related-article> ) used high-resolution, two-photon calcium imaging to measure spontaneous calcium fluctuations in hundreds of neurons simultaneously and determined the relative timing of these fluctuations. Examination of functional connectivity maps, based on temporal correlation measurements, revealed a subpopulation of GABAergic hub neurons displaying a remarkably widespread axonal arborization that orchestrated network synchrony in developing hippocampal networks. Spontaneous network synchronizations in developing hippocampus caused giant depolarizing potentials in individual neurons, and manipulating the spike activity in potential hub cells influenced network activity. </jats:p>

<jats:title>Medulloblastoma and Atoh1</jats:title> <jats:p> The Atoh1 transcription factor is needed for normal brain development and is also implicated in some cancers of the brain. In order to study the latter function and avoid the perinatal lethality that follows early disruption of the <jats:italic>Atoh1</jats:italic> gene, <jats:bold> Flora <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="1424" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181453">1424</jats:related-article> ) knocked out the <jats:italic>Atoh1</jats:italic> gene in mice after birth. A few days after the genetic knockout, cells at the surface of the cerebellum had begun to differentiate earlier than normal. Overexpression of <jats:italic>Atoh1</jats:italic> , on the other hand, led to excessive cell growth and even preneoplastic lesions at the surface of the cerebellum. <jats:italic>Atoh1</jats:italic> was found to regulate expression of the <jats:italic>Gli2</jats:italic> gene, and thereby Sonic Hedgehog signaling, which normally keeps cerebellar precursor cells undifferentiated. </jats:p>

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

<jats:p>The show includes a microRNA target for treating hepatitis C, the combined effects of nitrogen and CO2 on plant diversity, the future of evolution, and more.</jats:p>