Catálogo de publicaciones - revistas

<jats:title>Cold Glacier Growth</jats:title> <jats:p> Pine Island Glacier in Antarctica has thinned significantly during the last two decades and has provided a measurable contribution to sea-level rise as a result. Both glacier dynamics and climate are thought to be responsible for thinning, but exactly how they influence the glacier are incompletely known. <jats:bold> Dutrieux <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="6167" page="174" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1244341">174</jats:related-article> , published online 2 January) provide another layer of detail to our understanding of the process through observations of ocean temperatures in the surrounding waters. The thermocline adjacent in the sea adjacent to the glacier calving front (where ice is discharged) lowered by 250 meters in the austral summer of 2012. This change exposed the bottom of the ice shelf to colder surface waters rather than to the warmer, deeper layer, thereby reducing heat transfer from the ocean to the overlying ice and decreasing basal melting of the ice by more than 50% compared to 2010. Those 2012 ocean conditions were partly caused by a strong La Niña event, thus illustrating how important atmospheric variability is for regulating how the Antarctic Ice Sheet responds to climate change. </jats:p>

<jats:title>Make Way for the Emerging Rootlet</jats:title> <jats:p> Plant cells are immobilized by their rigid cells walls, and the root endodermal cell layer maintains a impervious perimeter seal made of an indigestible irregular polymer. Despite these mechanical obstacles, lateral root primordia, which initiate in the deep layers of the root, manage to break through to the surface. <jats:bold> Vermeer <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="6167" page="178" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245871">178</jats:related-article> ; see the cover) used live-tissue imaging and genetics to show that signals are exchanged between the root primordium and the handful of cells overlying it, which then cave in on themselves to open up a channel for the growing root primordium. </jats:p>

<jats:title>Carbon Budding in the Ocean</jats:title> <jats:p> Bacterial vesicles are gaining increasing attention for their roles in pathogenesis, but the abundance of these structures and their ecological roles in nonpathogenic contexts have received little notice. <jats:bold> Biller <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="6167" page="183" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1243457">183</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="6167" page="143" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1248566">Scanlan</jats:related-article> </jats:bold> ) provide evidence that membrane vesicles ∼100 nm in diameter are released by marine cyanobacteria and are a major feature of marine ecosystems. Studies of cultures of <jats:italic>Prochlorococcus</jats:italic> —the most abundant photoautotroph in the oligotrophic oceans—show that vesicles are continually released by this cyanobacterium and are abundant in the marine environment. These vesicles have properties that change the way we think about genetic and biogeochemical exchange among plankton and the dissolved organic carbon pool in marine ecosystems. </jats:p>

<jats:title>Out with the Old, In with the New</jats:title> <jats:p> In adult animals, resident stem or progenitor cells residing in niches replenish old tissues with new cells, but how they form new tissue is not well understood. <jats:bold>Chen and Krasnow</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6167" page="186" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1241442">186</jats:related-article> ) examined how progenitor cells in the fruit fly form new tracheae as the old tracheae are destroyed during metamorphosis. Proliferating progenitors move out of their niche by crawling along the surface of decaying tracheal branches. The decaying branches express the chemoattractant FGF (fibroblast growth factor) and create a track that directs progenitors. </jats:p>

<jats:title>Back with a Vengeance</jats:title> <jats:p> After surgery, gliomas (a type of brain tumor) recur in nearly all patients and often in a more aggressive form. <jats:bold> Johnson <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="6167" page="189" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1239947">189</jats:related-article> , published online 12 December 2013) used exome sequencing to explore whether recurrent tumors harbor different mutations than the primary tumors and whether the mutational profile in the recurrences is influenced by postsurgical treatment of patients with temozolomide (TMZ), a chemotherapeutic drug known to damage DNA. In more than 40% of cases, at least half of the mutations in the initial glioma were undetected at recurrence. The recurrent tumors in many of the TMZ-treated patients bore the signature of TMZ-induced mutagenesis and appeared to follow an evolutionary path to high-grade glioma distinct from that in untreated patients. </jats:p>

<jats:title>Expressing One Allele at a Time</jats:title> <jats:p> Although genetic traits are often dominant or recessive, the impact of the same heterozygous genotype can vary quite a bit between individuals. <jats:bold> Deng <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="6167" page="193" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245316">193</jats:related-article> ), analyzed global gene expression in hundreds of individual mouse cells and found that a substantial fraction of the genes only expressed one of the alleles, chosen randomly, at any given point in time. Such stochasticity in transcription increases the heterogeneity among cells and likely contributes to the phenotypic variance among individuals of identical genotype. </jats:p>

<jats:title>Spinal Circuit Complexity in Fish</jats:title> <jats:p> Rapid coordination of opposing muscle groups helps zebrafish zip through water. <jats:bold>Bagnall and McLean</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6167" page="197" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1245629">197</jats:related-article> ) now describe the neuronal circuits that stabilize swimming fish in their three-dimensional environment. By studying the self-righting behavior of larval zebrafish immobilized in agar, the authors identified parallel excitatory and inhibitory circuits driving dorsal and ventral hemisegments that could be activated independently. </jats:p>

<jats:title>Developing Neurons Make the Cut</jats:title> <jats:p> Neurons in the developing central nervous system of vertebrates derive from cells adjacent to the ventricles that then proliferate and differentiate to populate the brain. As one of these cells begins to differentiate, the cell nucleus migrates toward its new residence, away from the ventricle surface, and the cell stretches out. At some point, like any maturing adolescent, the cell has to leave home. <jats:bold>Das and Storey</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6167" page="200" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1247521">200</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6167" page="146" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249497"> <jats:bold>Tozer and Morin</jats:bold> </jats:related-article> ) show that instead of letting go and drawing the trailing process up into the migrating cell, the cell cuts off and discards its first roots. The abscission process leaves behind the primary cilium and any signaling systems localized to the cilium. </jats:p>

<jats:title>Persistent Survival</jats:title> <jats:p> The role of persister cells—dormant cells that survive multidrug treatment—in the context of bacterial pathogenesis has not been explored in depth. Using a single-cell fluorescent dilution technique, <jats:bold> Helaine <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="6167" page="204" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1244705">204</jats:related-article> ) examined <jats:italic>Salmonella</jats:italic> Typhimurium persister-cell formation in vitro and in infections in mice. Within 30 min after phagocytosis by macrophages, <jats:italic>Salmonella</jats:italic> cells follow one of two fates, either to replication and generation of virulence effectors or to remaining viable but become nonreplicating persisters. <jats:italic>Salmonella</jats:italic> living within a macrophage vacuole are exposed to potentially stressful conditions that induce the expression of 14 Type II toxin-antidote loci in a ppGpp/lon protease-dependent manner, and this system appears to play a role in both virulence factor induction and persister-cell formation. The nonreplicating bacteria represent at least four distinct subpopulations, as defined by their ability to resume growth and their metabolic activity, but different phenotypes are observed in different pathogens and <jats:italic>Escherichia coli</jats:italic> persisters are distinct from <jats:italic>Salmonella</jats:italic> persisters. </jats:p>

<jats:p>This week's show features the abundance and diversity of bacterial vesicles in the world's oceans and a roundup of stories from our daily news site.</jats:p>