Catálogo de publicaciones - revistas

<jats:title>Swine Flu Benchmark</jats:title> <jats:p> The World Health Organization (WHO) announced on 29 April 2009, a level-5 pandemic alert for a strain of H1N1 influenza originating in pigs in Mexico and transmitting from human to human in several countries. <jats:bold> Fraser <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="1557" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176062">1557</jats:related-article> , published online 11 May; see the cover) amassed a team of experts in Mexico and WHO to make an initial assessment of the outbreak with a view to guiding future policy. The outbreak appears to have originated in mid-February in the village of La Gloria, Veracruz, where over half the population suffered acute respiratory illness, affecting more than 61% of children under 15 years old in the community. The basic reproduction number (the number of people infected per patient) is in the range of 1.5—similar or less than that of the pandemics of 1918, 1957, and 1968. There remain significant uncertainties about the severity of this outbreak, which makes it difficult to compare the economic and societal costs of intervention with lives saved and the risks of generating antiviral resistance. </jats:p>

<jats:title>Rapid Tree Building</jats:title> <jats:p> Phylogenetic reconstruction is used to determine the relationships between organisms and requires an accurate alignment and analysis of multiple sequences. Iterative rounds of alignment and tree building are often necessary to prevent errors in the phylogeny estimate. One such way to address this problem is to assess alignment and trees in a single step. However, efficient algorithms to analyze data sets of reasonable size have been lacking. <jats:bold> Liu <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="1561" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171243">1561</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1528" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175949">Löytynoja and Goldman</jats:related-article> </jats:bold> ) describe an iterative approach that simultaneously incorporates both alignment and phylogeny and applies a fast maximum likelihood algorithm to the tree-building part. By assembling the components of the methods in this way, accurate results were obtained for up to 1000 sequences. Thus, it is possible to produce coestimation of sequence alignment and phylogeny that is both rapid and accurate. </jats:p>

<jats:title>Antiporter Antics</jats:title> <jats:p> Bacteria that survive in the acidic environment of the stomach have mechanisms to maintain a high intracellular pH. In <jats:italic>Escherichia coli</jats:italic> , glutamate (Glu) and arginine (Arg) are decarboxylated intracellularly and the reaction products are exchanged with extracellular Glu and Arg. <jats:bold> Gao <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="1565" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1173654">1565</jats:related-article> , published online 28 May) now report a crystal structure of AdiC, an arginine:agmatine antiporter from <jats:italic>E. coli</jats:italic> . AdiC exhibits the same fold as that of the Na <jats:sup>+</jats:sup> -coupled symporters, including LeuT. It contains 12 transmembrane segments, forms a homodimer, and exists in an outward-facing, open conformation in the crystals. The structure, together with biochemical data, suggests how the antiporter senses the pH and responds to transport the reaction product agmatine out of the cell and Arg into the cell. </jats:p>

<jats:title>Controlling Chronic Viral Infections</jats:title> <jats:p> Chronic viral infections such as HIV and hepatitis B and C viruses are major public health concerns. T cell—mediated immune responses are critical for controlling viral infections. In contrast to acute infections, chronic viral infections are characterized by “exhausted” cytotoxic CD8 <jats:sup>+</jats:sup> T cells, cells which exhibit reduced proliferative capacity, cytokine secretion, and cytotoxicity. Treatments that reverse exhaustion result in increased viral control. Despite their exhaustion, these CD8 <jats:sup>+</jats:sup> T cells eventually help to control chronic infections by killing virally infected cells, and require CD4 <jats:sup>+</jats:sup> T cell help to do so. How do CD4 <jats:sup>+</jats:sup> T cells provide help to CD8 <jats:sup>+</jats:sup> T cells during chronic infection (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1525" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176487">Johnson and Jameson</jats:related-article> </jats:bold> )? <jats:bold> Elsaesser <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="1569" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174182">1569</jats:related-article> , published online 7 May), <jats:bold> Yi <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="1572" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175194">1572</jats:related-article> , published online 14 May), and <jats:bold> Fröhlich <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="1576" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172815">1576</jats:related-article> , published online 28 May) now show that the cytokine, interleukin-21 (IL-21), known to be critical for the differentiation of certain CD4 <jats:sup>+</jats:sup> T cell effector subsets, is an essential factor produced by CD4 <jats:sup>+</jats:sup> T cells that helps CD8 <jats:sup>+</jats:sup> T cells to control chronic lymphocytic choriomeningitis virus infection in mice. Acute and chronic infections resulted in differing amounts of IL-21 production by virus-specific CD4 <jats:sup>+</jats:sup> T cells. CD8 <jats:sup>+</jats:sup> T cells required IL-21 directly, and when CD8 <jats:sup>+</jats:sup> T cells were unable to signal through IL-21 or IL-21 was not available, they were reduced in number, exhibited a more exhausted phenotype, and were not able to control the virus. In contrast, the absence of IL-21–dependent signaling did not affect primary CD8 <jats:sup>+</jats:sup> T cell responses to acute infection or responses to a viral rechallenge, suggesting that differentiation of memory CD8 <jats:sup>+</jats:sup> T cells is independent of IL-21. </jats:p>

<jats:title>Controlling Chronic Viral Infections</jats:title> <jats:p> Chronic viral infections such as HIV and hepatitis B and C viruses are major public health concerns. T cell—mediated immune responses are critical for controlling viral infections. In contrast to acute infections, chronic viral infections are characterized by “exhausted” cytotoxic CD8 <jats:sup>+</jats:sup> T cells, cells which exhibit reduced proliferative capacity, cytokine secretion, and cytotoxicity. Treatments that reverse exhaustion result in increased viral control. Despite their exhaustion, these CD8 <jats:sup>+</jats:sup> T cells eventually help to control chronic infections by killing virally infected cells, and require CD4 <jats:sup>+</jats:sup> T cell help to do so. How do CD4 <jats:sup>+</jats:sup> T cells provide help to CD8 <jats:sup>+</jats:sup> T cells during chronic infection (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1525" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176487">Johnson and Jameson</jats:related-article> </jats:bold> )? <jats:bold> Elsaesser <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="1569" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174182">1569</jats:related-article> , published online 7 May), <jats:bold> Yi <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="1572" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175194">1572</jats:related-article> , published online 14 May), and <jats:bold> Fröhlich <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="1576" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172815">1576</jats:related-article> , published online 28 May) now show that the cytokine, interleukin-21 (IL-21), known to be critical for the differentiation of certain CD4 <jats:sup>+</jats:sup> T cell effector subsets, is an essential factor produced by CD4 <jats:sup>+</jats:sup> T cells that helps CD8 <jats:sup>+</jats:sup> T cells to control chronic lymphocytic choriomeningitis virus infection in mice. Acute and chronic infections resulted in differing amounts of IL-21 production by virus-specific CD4 <jats:sup>+</jats:sup> T cells. CD8 <jats:sup>+</jats:sup> T cells required IL-21 directly, and when CD8 <jats:sup>+</jats:sup> T cells were unable to signal through IL-21 or IL-21 was not available, they were reduced in number, exhibited a more exhausted phenotype, and were not able to control the virus. In contrast, the absence of IL-21–dependent signaling did not affect primary CD8 <jats:sup>+</jats:sup> T cell responses to acute infection or responses to a viral rechallenge, suggesting that differentiation of memory CD8 <jats:sup>+</jats:sup> T cells is independent of IL-21. </jats:p>

<jats:title>Controlling Chronic Viral Infections</jats:title> <jats:p> Chronic viral infections such as HIV and hepatitis B and C viruses are major public health concerns. T cell—mediated immune responses are critical for controlling viral infections. In contrast to acute infections, chronic viral infections are characterized by “exhausted” cytotoxic CD8 <jats:sup>+</jats:sup> T cells, cells which exhibit reduced proliferative capacity, cytokine secretion, and cytotoxicity. Treatments that reverse exhaustion result in increased viral control. Despite their exhaustion, these CD8 <jats:sup>+</jats:sup> T cells eventually help to control chronic infections by killing virally infected cells, and require CD4 <jats:sup>+</jats:sup> T cell help to do so. How do CD4 <jats:sup>+</jats:sup> T cells provide help to CD8 <jats:sup>+</jats:sup> T cells during chronic infection (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1525" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176487">Johnson and Jameson</jats:related-article> </jats:bold> )? <jats:bold> Elsaesser <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="1569" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174182">1569</jats:related-article> , published online 7 May), <jats:bold> Yi <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="1572" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175194">1572</jats:related-article> , published online 14 May), and <jats:bold> Fröhlich <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="1576" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172815">1576</jats:related-article> , published online 28 May) now show that the cytokine, interleukin-21 (IL-21), known to be critical for the differentiation of certain CD4 <jats:sup>+</jats:sup> T cell effector subsets, is an essential factor produced by CD4 <jats:sup>+</jats:sup> T cells that helps CD8 <jats:sup>+</jats:sup> T cells to control chronic lymphocytic choriomeningitis virus infection in mice. Acute and chronic infections resulted in differing amounts of IL-21 production by virus-specific CD4 <jats:sup>+</jats:sup> T cells. CD8 <jats:sup>+</jats:sup> T cells required IL-21 directly, and when CD8 <jats:sup>+</jats:sup> T cells were unable to signal through IL-21 or IL-21 was not available, they were reduced in number, exhibited a more exhausted phenotype, and were not able to control the virus. In contrast, the absence of IL-21–dependent signaling did not affect primary CD8 <jats:sup>+</jats:sup> T cell responses to acute infection or responses to a viral rechallenge, suggesting that differentiation of memory CD8 <jats:sup>+</jats:sup> T cells is independent of IL-21. </jats:p>

<jats:title>Mysterious Merkel cells</jats:title> <jats:p> Anatomists have known about the existence of Merkel cells in our skin for over a century. However, the function of these cells has been unclear and controversial. To solve this mystery, <jats:bold> Maricich <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="1580" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172890">1580</jats:related-article> ) created a genetic deletion of Merkel cells. When Atoh1, a transcription factor expressed by Merkel cells, was conditionally deleted in the skin, Merkel cells were completely absent from Atoh1CKO mice. Using ex vivo skin and nerve preparations from the animals showed that Merkel cells are needed to properly encode light touch sensation in the skin. </jats:p>

<jats:title>Addition to the Right, Subtraction to the Left</jats:title> <jats:p> High-level cognitive achievements, such as writing and mathematics, have appeared relatively recently in the evolutionary record in comparison to low-level skills, such as the perception of bright-dark boundaries. The latter have been demonstrated to arise from the coding properties of neurons in visual cortical centers, but what do the former map onto? <jats:bold> Knops <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="1583" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1171599">1583</jats:related-article> , published online 7 May) provide evidence that addition and subtraction are encoded within the same cortical region that is responsible for eye movements to the right and left, such that the neural activity associated with addition could be distinguished from that associated with subtraction by a computational classifier trained to discriminate between rightward and leftward eye movements. </jats:p>

<jats:p>Transferring specific nucleic acids into cells can modulate gene function, thereby revealing the mechanism of action and ultimate role of specific stretches of DNA. Nonetheless, getting the nucleic acids into the right cells efficiently and without damaging them creates challenges as diverse as the cells themselves.</jats:p>

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