Catálogo de publicaciones - revistas

<jats:title>Tracking Triplet-State Transfers</jats:title> <jats:p> In devices such as organic transistors and photovoltaic cells, energy flow from donor to acceptor sites can occur via electrons that have been excited into higher electronic levels, which create a triplet state with two unpaired spins. At short distances between donor and acceptor, the transfer occurs through direct tunneling, but at longer distances, the electron “hops” in a multistep process. <jats:bold> Vura-Weis <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="1547" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189354">1547</jats:related-article> ) used femtosecond transient absorption spectroscopy to observe this crossover in transfer mechanism directly in a series of molecules with varying bridge lengths between the donor and acceptor. </jats:p>

<jats:title>Birth of the Cool</jats:title> <jats:p> Over the past 4 million years or so, tropical sea surface temperatures have experienced a cooling trend (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5985" page="1488" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189748">Philander</jats:related-article> </jats:bold> ). <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="1530" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1185435">1530</jats:related-article> ) analyzed sea surface temperature records of the past 3.5 million years from low-latitude sites spanning the world's major ocean basins in order to determine the timing and magnitude of the cooling that has accompanied the intensification of Northern Hemisphere ice ages since the Pliocene. <jats:bold> Martínez-Garcia <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="1550" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1184480">1550</jats:related-article> ) found that the enigmatic eastern equatorial Pacific cold tongue, a feature one might not expect to find in such a warm region receiving so much sunlight, first appeared between 1.8 and 1.2 million years ago. Its appearance was probably in response to a general shrinking of the tropical warm water pool caused by general climate cooling driven by changes in Earth's orbit. </jats:p>

<jats:title>Date with the Pharaohs</jats:title> <jats:p> Ancient Egypt dominated the Mediterranean world for several thousand years. However, the absolute chronology of this civilization has been uncertain, even though the sequence of rulers is well documented. <jats:bold> Bronk Ramsey <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="1554" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189395">1554</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="5985" page="1489" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191410">Bruins</jats:related-article> </jats:bold> ) now provide a detailed radiocarbon-based record using more than 200 samples that spans much of this time and reduces uncertainties in some cases to less than 20 years. To avoid artifacts, the authors dated only short-lived plant remains from known contexts (i.e., that were associated with specific reigns). They then used the known reign lengths as a further constraint to obtain a final chronology. The final dates agree most closely with the previous older chronology but force some revisions to the timing of events in the Old Kingdom, the period in the third millennium B.C.E. when Egypt attained its first continuous peak of civilization. </jats:p>

<jats:title>Don't Forget the Edges</jats:title> <jats:p> Reef-building corals are highly diverse, and many are threatened with extinction. In order to make predictions about coral survival, <jats:bold>Budd and Pandolfi</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1558" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188947">1558</jats:related-article> ) examined morphological changes occurring over the evolutionary history of Caribbean corals. Long-term evolutionary patterns, including hybridization between species and diversification into new species (so-called lineage fusion and splitting) differed depending on the geographical location within the colony, with higher change occurring at a species' geographic margin relative to those in central locations. Thus, edge zones, which often experience limited gene flow, are responsible for the predominance of evolutionary innovation. If conservation strategies are biased toward biodiversity hotspots, which represent centers of high species richness, they may miss important sources of evolutionary novelty during global change. </jats:p>

<jats:title>Keeping Egg Production Going</jats:title> <jats:p> Whether oogenesis ceases around birth in vertebrate ovaries has been a topic of long-standing interest and considerable debate. <jats:bold> Nakamura <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="328" xlink:href="10.1126/science.1185473">1561</jats:related-article> , published online 20 May) now identify germline stem cells in the ovary of the teleost fish medaka. The stem cells are found as clusters of germ cells (termed germinal cradles) in a cord-like structure that expresses <jats:italic>sox9</jats:italic> , a gene critical for testis formation in mammals. The cords are buried within the ovary within the germinal epithelium. This work in fish shows that there can indeed be continuing egg production from vertebrate germline stem cells. </jats:p>

<jats:title>Herpes Virus MiRNA Modulation</jats:title> <jats:p> Viruses use a number of strategies to manipulate the cells of their host to ensure a successful infection. <jats:italic>Herpesvirus saimiri</jats:italic> (HVS) generates highly conserved small noncoding RNAs <jats:italic>HSUR 1</jats:italic> and <jats:italic>HSUR 2</jats:italic> , which modulate expression of a number of proteins in infected primate T cells. <jats:bold> Cazalla <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="1563" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1187197">1563</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="5985" page="1494" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191531">Pasquinelli</jats:related-article> </jats:bold> ) observed complementarity between HSUR sequences and the seed regions of three different miRNAs—miR-142-3p, miR-27, and miR-16—and found that these HSURs could bind to the miRNAs. Furthermore, the level of mature miR-27 was modulated by binding to <jats:italic>HSUR 1</jats:italic> , which targeted the miRNA for degradation. </jats:p>

<jats:title>miR-33 in Cholesterol Control</jats:title> <jats:p> With the well-established link between serum cholesterol levels and cardiovascular disease and the availability of effective cholesterol-lowering drugs, cholesterol screening has rapidly become a routine part of health care. Yet, much remains to be learned about how cholesterol levels are regulated at the cellular level (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5985" page="1495" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1192409"> <jats:bold> Brown <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> </jats:bold> ). Now, <jats:bold> Najafi-Shoushtari <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="1566" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189123">1566</jats:related-article> , published online 13 May) and <jats:bold> Rayner <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="1570" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189862">1570</jats:related-article> , published online 13 May) have discovered a new molecular player in cholesterol control—a small noncoding RNA that, intriguingly, is embedded within the genes coding for sterol regulatory element-binding proteins (SREBPs), transcription factors already known to regulate cholesterol levels. This microRNA, called miR-33, represses expression of the adenosine triphosphate–binding cassette transporter A1, a protein that regulates synthesis of high-density lipoprotein (HDL, or “good” cholesterol) and that helps to remove “bad” cholesterol from the blood. Reducing the levels of miR-33 in mice boosted serum HDL levels, suggesting that manipulation of this regulatory circuit might be therapeutically useful. </jats:p>

<jats:title>miR-33 in Cholesterol Control</jats:title> <jats:p> With the well-established link between serum cholesterol levels and cardiovascular disease and the availability of effective cholesterol-lowering drugs, cholesterol screening has rapidly become a routine part of health care. Yet, much remains to be learned about how cholesterol levels are regulated at the cellular level (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5985" page="1495" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1192409"> <jats:bold> Brown <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> </jats:bold> ). Now, <jats:bold> Najafi-Shoushtari <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="1566" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189123">1566</jats:related-article> , published online 13 May) and <jats:bold> Rayner <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="1570" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1189862">1570</jats:related-article> , published online 13 May) have discovered a new molecular player in cholesterol control—a small noncoding RNA that, intriguingly, is embedded within the genes coding for sterol regulatory element-binding proteins (SREBPs), transcription factors already known to regulate cholesterol levels. This microRNA, called miR-33, represses expression of the adenosine triphosphate–binding cassette transporter A1, a protein that regulates synthesis of high-density lipoprotein (HDL, or “good” cholesterol) and that helps to remove “bad” cholesterol from the blood. Reducing the levels of miR-33 in mice boosted serum HDL levels, suggesting that manipulation of this regulatory circuit might be therapeutically useful. </jats:p>

<jats:title>The Space in Your Head</jats:title> <jats:p> Space, and events associated with places and spaces, are represented in the brain by a circuitry made of place cells, head direction cells, grid cells, and border cells. These cell types form a collective dynamic representation of our position as we move through the environment. How this representation is formed has remained a mystery. Is it acquired, or are we born with the ability to represent external space (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5985" page="1487" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191527"> <jats:bold>Palmer and Lynch</jats:bold> </jats:related-article> </jats:bold> )? <jats:bold> Langston <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="328" xlink:href="10.1126/science.1188210">1576</jats:related-article> ) and <jats:bold> Wills <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="1573" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188224">1573</jats:related-article> ) investigated the early development of spatial activity in the hippocampal formation and the entorhinal cortex of rat pups when they first began to explore their environment. Rudiments of place cells, head direction cells, and grid cells already existed when the pups made their first movements out of the nest. A neural representation of external space at this early time points to strong innate components for perception of space. These findings provide experimental support for Kant's 200-year-old concept of space as an a priori faculty of the mind. </jats:p>

<jats:title>The Space in Your Head</jats:title> <jats:p> Space, and events associated with places and spaces, are represented in the brain by a circuitry made of place cells, head direction cells, grid cells, and border cells. These cell types form a collective dynamic representation of our position as we move through the environment. How this representation is formed has remained a mystery. Is it acquired, or are we born with the ability to represent external space (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5985" page="1487" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1191527"> <jats:bold>Palmer and Lynch</jats:bold> </jats:related-article> </jats:bold> )? <jats:bold> Langston <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="328" xlink:href="10.1126/science.1188210">1576</jats:related-article> ) and <jats:bold> Wills <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="1573" related-article-type="in-this-issue" vol="328" xlink:href="10.1126/science.1188224">1573</jats:related-article> ) investigated the early development of spatial activity in the hippocampal formation and the entorhinal cortex of rat pups when they first began to explore their environment. Rudiments of place cells, head direction cells, and grid cells already existed when the pups made their first movements out of the nest. A neural representation of external space at this early time points to strong innate components for perception of space. These findings provide experimental support for Kant's 200-year-old concept of space as an a priori faculty of the mind. </jats:p>