Catálogo de publicaciones - revistas

<jats:title>Pondering Pulsars</jats:title> <jats:p> Pulsars are rapidly rotating, magnetized neutron stars that are powered by the loss of rotational energy. Because their emission is beamed, their light appears to pulse on and off at regular intervals. Changes in radio emission behavior have been observed for a number of pulsars, manifesting themselves as switches between ordered and disordered variations in intensity and pulse shapes, but these changes have not been seen at other wavelengths. Based on simultaneous radio and x-ray observations of pulsar PSR B0943+10, <jats:bold> Hermsen <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="6118" page="436" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1230960">436</jats:related-article> ) show that changes in emission state identified in radio measurements show counterpart fluctuations in the strength and temporal behavior of x-rays. Some of these changes were unexpected in their character and physical properties, challenging pulsar emission theories. </jats:p>

<jats:title>Hunger and Memory</jats:title> <jats:p> During starvation, are all brain functions slowed down, or are specific functions disabled to save energy? <jats:bold>Plaçais and Preat</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6118" page="440" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1226018">440</jats:related-article> ) investigated how the brain of <jats:italic>Drosophila</jats:italic> deals with severe resource limitation. The brain cut selected expenses to reduce the threat to survival and switched off the formation of aversive long-term memory that depends on costly protein synthesis. However, <jats:bold> Hirano <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="6118" page="443" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1227170">443</jats:related-article> ) focused on mild food-deprivation, which actually enhanced long-term memory formation. Presumably, improved memory should enhance survival when competing for limited food. After longer food deprivation, enhancement of aversive long-term memory decreased, while that of appetitive long-term memory remained high: Presumably, as starvation nears, it becomes more important to pursue food at all costs, and so appetitive memory takes precedence over aversive memories. </jats:p>

<jats:title>Hunger and Memory</jats:title> <jats:p> During starvation, are all brain functions slowed down, or are specific functions disabled to save energy? <jats:bold>Plaçais and Preat</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6118" page="440" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1226018">440</jats:related-article> ) investigated how the brain of <jats:italic>Drosophila</jats:italic> deals with severe resource limitation. The brain cut selected expenses to reduce the threat to survival and switched off the formation of aversive long-term memory that depends on costly protein synthesis. However, <jats:bold> Hirano <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="6118" page="443" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1227170">443</jats:related-article> ) focused on mild food-deprivation, which actually enhanced long-term memory formation. Presumably, improved memory should enhance survival when competing for limited food. After longer food deprivation, enhancement of aversive long-term memory decreased, while that of appetitive long-term memory remained high: Presumably, as starvation nears, it becomes more important to pursue food at all costs, and so appetitive memory takes precedence over aversive memories. </jats:p>

<jats:title>Mobilizing Transposable Elements</jats:title> <jats:p> Transposable elements are parasitic DNA elements that can jump around the genome. They make up large portions of eukaryotic genomes (up to 50% of the human genome). In the short term, transposable elements can generate mutations and cause large-scale damage; but, in the long term, they can drive evolution. <jats:bold> Majumdar <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="6118" page="446" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231789">446</jats:related-article> ) show that the human THAP9 gene (hTh9), which contains a THAP DNA binding domain also found in the <jats:italic>Drosophila P</jats:italic> -element transposase, is capable of mobilizing <jats:italic>P</jats:italic> -elements in <jats:italic>Drosophila</jats:italic> cells. The hTH9 gene also caused the excision of plasmid-borne <jats:italic>Drosophila P</jats:italic> -elements in human cells. Furthermore, hTh9 is able to nick <jats:italic>P</jats:italic> -element DNA and direct its transposition into the human genome. </jats:p>

<jats:title>Epigenetic Controls</jats:title> <jats:p> Germ cells in mammals give rise to sperm and eggs. During their development, germ cells undergo extensive epigenetic reprogramming, including global DNA demethylation, which is vital for the totipotency of the developing embryo. <jats:bold> Hackett <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="6118" page="448" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1229277">448</jats:related-article> ) show that the enzymes Tet1 and Tet2 are involved in the demethylation of individual genes and in imprinted gametic differentially methylated regions. The enzymes were also responsible for the global conversion of CpG methylation to 5-hydroxymethylcytosine, which then progressively declines. The findings suggest that demethylation can occur by replication-coupled dilution, although active mechanisms cannot be excluded. A small number of loci escape demethylation, providing a possible mechanistic basis for transgenerational inheritance. </jats:p>

<jats:title>Axonal Actin</jats:title> <jats:p> How actin is organized in the axons and dendrites of neurons is largely unknown. <jats:bold> 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="6118" page="452" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1232251">452</jats:related-article> , published online 13 December) imaged actin in axons and dendrites using stochastic optical reconstruction microscopy. Surprisingly, while actin in dendrites formed long filaments, the actin in axons was organized into evenly spaced ringlike structures at the axon circumference. Spectrin, which is known to interact with actin to form a membrane cytoskeleton in erythrocytes, formed periodic structures that alternated with those of actin. This actin-spectrin cytoskeletal structure might give mechanical support to axons and could also organize other membrane proteins. </jats:p>

<jats:title>Bat Genomes</jats:title> <jats:p> Bats are of great interest because of their ability to fly and as hosts for infectious disease. <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="6118" page="456" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1230835">456</jats:related-article> , published online 20 December) sequenced the genomes of two distantly related bat species, David's Myotis and Black flying fox. Analysis of the two genomes revealed likely changes that accompanied the evolution of bats, including selection for increased expression of genes involved in the oxidative phosphorylation pathway needed to generate the energy required for flight. Furthermore, while some immune genes have been lost, others are under positive selection, which may potentially explain bats' status as viral reservoirs. </jats:p>

<jats:title>Transcription Factor as Computer</jats:title> <jats:p> Cellular signaling pathways can serve to process information so that cells respond appropriately to various environmental stimuli. <jats:bold> Hao <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="6118" page="460" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1227299">460</jats:related-article> ) show that a single yeast transcription factor that is activated in response to stress—Msn2—can act as a signal processor. In an experimental setup in which the amplitude and duration of signaling in the cells could be tightly controlled, sites of phosphorylation on Msn2 that determine its transport into or out of the nucleus allowed it to have different dynamic responses depending upon the amplitude of the signal detected. The transcription factor could either track with the incoming signal, filter (ignore) it, or integrate it. Understanding such properties may be useful in designing behavior of biological control systems. </jats:p>

<jats:title>Masterminding Mitochondrial Fission</jats:title> <jats:p> Mitochondria are highly dynamic and undergo fusion and fission and they move in cells. Defects in mitochondrial dynamics are implicated in many neurodegenerative diseases. Recent findings have suggested that mitochondrial fission occurs preferentially at endoplasmic reticulum (ER) contact sites, with ER circumscribing mitochondria and possibly promoting the constriction of mitochondria during fission. <jats:bold> Korobova <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="6118" page="464" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1228360">464</jats:related-article> ) now suggest that an ER-localized formin, INF2, is required for mitochondrial fission and that INF2-mediated actin polymerization facilitates mitochondrial constriction. </jats:p>

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