Catálogo de publicaciones - revistas

<jats:title>Protoplanet 2 Pallas</jats:title> <jats:p> With a diameter of 265 kilometers, 2 Pallas is one of the largest bodies in the main asteroid belt. Now <jats:bold> Schmidt <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="275" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177734">275</jats:related-article> ) have characterized its surface and shape using images from the Hubble Space Telescope. Color variations and topography were revealed that are possibly linked to the asteroid's thermal evolution and to the formation of its orbital family—the population of asteroids that share the same properties as 2 Pallas and are thought to be the fragments of a collision. In particular, a large-impact crater was observed that could represent the source of the Pallas family. 2 Pallas represents the third intact protoplanet in the main asteroid belt, joining asteroids 1 Ceres and 4 Vesta. </jats:p>

<jats:title>Ear, Ear</jats:title> <jats:p> One defining feature of mammals, distinguishing them from other animals, is the separation of the middle ear from the jaw, which improves hearing sensitivity. <jats:bold> Ji <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="278" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178501">278</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="5950" page="243" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181131"> <jats:bold>Martin and Ruf</jats:bold> </jats:related-article> </jats:bold> ) describe an adult Mesozoic fossil mammal, in a lineage that led to both marsupials and placentals, in which the middle ear is still ossified to the jaw. Recent developmental studies have shown that the release of the ear is tied to multiple genes and signaling pathways during development. Together, these data suggest how gene patterning may have led to the early evolution of the mammalian ear. </jats:p>

<jats:title>Quiet Clock</jats:title> <jats:p> Many physiological processes have circadian rhythms driven by a biological clock in the suprachiasmatic nuclei (SCN) of the brain. Within the SCN, some neurons express the molecular components of the clock and others do not. Exactly how the clock mechanism is coupled to neuronal activity is not precisely understood. Investigation of the electrophysiological properties of SCN neurons by <jats:bold> Belle <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="281" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1169657">281</jats:related-article> ) found that, contrary to the conventionally expected rapid firing rate of the cells during the day, clock-containing cells tended not to fire, despite being in an electrically excited state. Modeling and experimental characterization of changes in channel activity revealed unexpected electrophysiological properties of the SCN cells requiring a reassessment of how the circadian clock regulates activity of SCN neurons. </jats:p>

<jats:title>Anti-HIV Antibodies</jats:title> <jats:p> One of the top priorities for an HIV vaccine is the ability to elicit a broadly neutralizing antibody response, which should provide the best protection against infection. In the 25 years since the discovery of HIV, very few broadly neutralizing antibodies have been identified, and those that do exist were discovered nearly two decades ago. Using a high-throughput culture system, <jats:bold> Walker <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="285" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178746">285</jats:related-article> ; published online 3 September) now identify two additional broadly neutralizing antibodies isolated from a clade A HIV-infected African donor. These antibodies exhibit great potency and, in contrast to other known broadly neutralizing antibodies, are able to neutralize a wide range of viruses from many different clades. The antibodies recognize a motif in the trimerized viral envelope protein that is found in conserved regions of the variable loops of the gp120 subunit. Identification of this motif provides an intriguing new target for vaccine development. </jats:p>

<jats:title>Chromosomal Mapping</jats:title> <jats:p> The conformation of the genome in the nucleus and contacts between both proximal and distal loci influence gene expression. In order to map genomic contacts, <jats:bold> Lieberman-Aiden <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="289" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181369" xlink:type="simple">289</jats:related-article> , see the cover) developed a technique to allow the detection of all interactions between genomic loci in the eukaryotic nucleus followed by deep sequencing. This technology was used to map the organization of the human genome and to examine the spatial proximity of chromosomal loci at one megabase resolution. The map suggests that the genome is partitioned into two spatial compartments that are related to local chromatin state and whose remodeling correlates with changes in the chromatin state. </jats:p>

<jats:title>Making Split Decisions</jats:title> <jats:p> Development of the vertebrate vasculature has been thought to involve just two mechanisms of blood vessel formation. <jats:bold> Herbert <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="294" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178577">294</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="5950" page="242" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181033"> <jats:bold>Benedito and Adams</jats:bold> </jats:related-article> </jats:bold> ) identified a third mechanism in zebrafish in which two distinct, unconnected vessels can be derived from a single precursor vessel. Several vascular endothelial growth factors and signaling pathways, including ephrin and notch signaling, coordinated the sorting and segregation of a mixture of arterial and venous-fated precursor cells into distinct arterial and venous vessels. These findings provide a mechanistic framework for how mixed populations of cells can coordinate their behavior to segregate and form distinct blood vessels. </jats:p>

<jats:title>Containing Neuronal Exuberance</jats:title> <jats:p> In rats and mice, around the time of birth, neurons of the central nervous system switch from a growth mode and lose their ability to regenerate. Studying retinal ganglion cells of the rat, <jats:bold> Moore <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="298" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175737">298</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="5950" page="238" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1181038">Subang and Richardson</jats:related-article> </jats:bold> ) identified a gene, <jats:italic>Krüppel-like factor-4</jats:italic> ( <jats:italic>KLF4</jats:italic> ), that seems to contribute to the switch. The <jats:italic>KLF4</jats:italic> gene belongs to a family of related transcription factors that possess repressive or enhancing effects on axon growth. The combinatorial effect of this family of transcription factors before and after birth may fine-tune the ability of the neurons to extend axons. </jats:p>

<jats:p>Epigenetics is hot. In recent years, researchers in fields as diverse as cell biology, development, and even microbial pathogenesis have become very interested in heritable traits that don't rely on DNA. The idea itself is not new--cancer biologists have known for decades that mechanisms such as DNA methylation and chromatin modification can transmit changes to subsequent generations of cells without changing DNA sequences--but studying these phenomena has recently been increasing in popularity, aided by new technological innovations.</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 personalized cancer treatments, persistent currents in nonsuperconductors, the organization of chromosomes, and more.</jats:p>