Catálogo de publicaciones - revistas

<jats:title>Cold Refreshment</jats:title> <jats:p> Carbon nanotubes can function as chemical sensors by virtue of the shifts in resistance or capacitance induced when small molecules bind to their surfaces. Unfortunately, many molecules bind rather tightly, impairing reuse of such sensors. <jats:bold> Salehi-Khojin <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="1327" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1194210">1327</jats:related-article> ) showed that one solution to this problem was to run a strong current through the nanotubes after the detection event, which induced desorption of organic molecules. By comparison, thermal (as opposed to current-driven) desorption required heating to temperatures that irreparably degraded the sensor structure. </jats:p>

<jats:title>What We're In For</jats:title> <jats:p> What would our climate future look like if we stopped building any new infrastructure that used fossil fuels? <jats:bold> Davis <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="1330" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1188566">1330</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="5997" page="1292" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1195449">Hoffert</jats:related-article> </jats:bold> ) made the assumption that all existing infrastructure will be used until the end of its lifetime, after which it will be replaced by infrastructure that does not produce CO <jats:sub>2</jats:sub> . They then calculated the amount of additional CO <jats:sub>2</jats:sub> that will be added to the atmosphere. The outcome is that the concentration of atmospheric CO <jats:sub>2</jats:sub> would remain below 430 parts per million (ppm) (present levels are 390 ppm) and global mean temperatures would increase to 1.3°C above preindustrial values (about 0.5°C above present), well below current targets of 450 ppm and 2°C, respectively. </jats:p>

<jats:title>Martian Carbon Dioxide</jats:title> <jats:p> As a primary component of the martian atmosphere and as the primary greenhouse gas for Mars, carbon dioxide has played a role in climate and geological processes during martian history. <jats:bold> Niles <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="1334" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192863">1334</jats:related-article> ) present high-precision measurements of the isotopic composition of the martian atmospheric CO <jats:sub>2</jats:sub> , made in situ by the Mars Phoenix Lander. Atmospheric CO <jats:sub>2</jats:sub> on Mars was not enriched in <jats:sup>13</jats:sup> C, which implies that volcanic degassing and carbonate formation have been important in the recent past, but it was enriched in <jats:sup>18</jats:sup> O, which suggests that low-temperature water-rock interactions have been dominant on Mars. Combined with previous work on martian meteorites, the results suggest that carbonate formation has been active on Mars for the past 200 million years. </jats:p>

<jats:title>Form and Function</jats:title> <jats:p> The Planar Cell Polarity (PCP) signaling pathway governs cell movements that drive axis elongation and neural tube closure in vertebrate embryos, and certain vertebrate PCP proteins have also been implicated in ciliogenesis. Likewise, the septin cytoskeleton controls diverse cell behaviors, such as cytokinesis and cell migration, but little is known about how septin functions are regulated in vivo. <jats:bold> Kim <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="1337" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191184">1337</jats:related-article> , published online 29 July; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5997" page="1289" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1195445">Barral</jats:related-article> </jats:bold> ) found that control of septins by the PCP effector protein, Fritz, was a crucial control point for morphogenesis and ciliogenesis. During neural tube closure, Fritz-mediated septin localization maintained cell shape but not cell polarity. In ciliated epithelial cells, Fritz was required for assembly of the septin rings at the base of cilia, which are needed for normal ciliogenesis and signaling. </jats:p>

<jats:title>Pointing the Finger</jats:title> <jats:p> Filopodia are finger-like structures containing parallel bundles of actin filaments that are central to eukaryotic cell motility in a variety of contexts. <jats:bold> K. Lee <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="1341" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191710">1341</jats:related-article> ) reconstituted filopodia-like structures that grow from supported lipid bilayers to explore filopodia assembly. A structural transition from actin networks to parallel bundles was observed that mediated self-assembly of filopodia-tip complexes on the membranes. </jats:p>

<jats:title>Stem Cell Expansion</jats:title> <jats:p> The ability to expand hematopoietic stem cells (HSCs) during ex-vivo culture has been an important goal for over 20 years. Using a high-throughput chemical screen, <jats:bold> Boitano <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="1345" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1191536">1345</jats:related-article> , published online 5 August; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5997" page="1291" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1195173">Sauvageau and Humphries</jats:related-article> </jats:bold> ) found that a purine derivative, StemRegenin1 (SR1), promoted the expansion of human HSCs. Treatment of HSCs with SR1 (which blocked the activity of the aryl hydrocarbon receptor) led to the expansion of CD34 <jats:sup>+</jats:sup> cells and a 12 to 17-fold increase in the number of HSCs that engraft immune deficient mice. </jats:p>

<jats:title>UnSIRT6ain Repair</jats:title> <jats:p> Efficient and accurate repair of double-strand DNA breaks is critical for genome stability and involves a process known as homologous recombination. During repair of the sheared ends, the DNA must be resected by trimming one of the two strands on either side of the break. For the repair to be accurate, the remaining single-stranded DNA (ssDNA) has to be bound by the ssDNA-binding protein, RPA, after which the ssDNA can then bind homologous sequences. <jats:bold> Kaidi <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="1348" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192049">1348</jats:related-article> ) found that the mammalian deacetylase, SIRT6 (which has been implicated in maintaining genome stability), was critical for resection. At sites of DNA damage, SIRT6 deacetylated and activated CtIP (a protein important for resection), ensuring that resection occurred at the appropriate place and time. </jats:p>

<jats:title>Mosquito Malarial Memory</jats:title> <jats:p> During their life cycle malaria parasites produce vast numbers of successive proliferative stages in their vertebrate hosts, and yet in the field most mosquitoes are free of parasites. <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="1353" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1190689">1353</jats:related-article> ) report that the immune system of mosquitoes is primed early-on when the malaria parasite ( <jats:italic>Plasmodium</jats:italic> spp.) first crosses the mosquito gut epithelial barrier. A substantial (2- to 3.2-fold) increase in a single type of hemocyte (macrophage-like insect immune cells) is implicated in long-lived antiplasmodial immunity. This work may prove important for malaria control and for understanding immune memory in invertebrates. </jats:p>

<jats:title>CRISPR Processing</jats:title> <jats:p> Many bacteria and archaea recognize invading viruses and plasmids. Foreign DNA is integrated into so-called clustered regularly interspaced short palindromic repeat (CRISPR) loci, and transcripts from these loci are processed into RNAs that can target the invading DNA or RNA for destruction. To investigate the molecular basis for this processing, <jats:bold> Haurwitz <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="1355" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1192272">1355</jats:related-article> ) screened CRISPR-associated (Cas) proteins in the opportunistic pathogen <jats:italic>Pseudomonas aeruginosa</jats:italic> and found they were capable of cleaving the CRISPR transcripts. The crystal structure of Cas4 with the CRISPR RNA transcript revealed how the protein specifically recognized RNA repeats, as well as the mechanism of endonucleolytic cleavage. </jats:p>

<jats:title>Connectivity Map of the Brain</jats:title> <jats:p> The growing appreciation that clinically abnormal behaviors in children and adolescents may be influenced or perhaps even initiated by developmental miscues has stoked an interest in mapping normal human brain maturation. Several groups have documented changes in gray and white matter using structural and functional magnetic resonance imaging (fMRI) in cross-sectional and longitudinal studies. <jats:bold> Dosenbach <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="1358" related-article-type="in-this-issue" vol="329" xlink:href="10.1126/science.1194144">1358</jats:related-article> ) developed an index of resting-state functional connectivity (that is, how tightly neuronal activities in distinct brain regions are correlated while the subject is at rest or even asleep) from analyses of three independent data sets (each based on fMRI scans of 150 to 200 individuals from ages 6 to 35 years old). Long-range connections increased with age and short-range connections decreased, indicating that networks become sparser and sharper with brain maturation. </jats:p>