Catálogo de publicaciones - revistas

<jats:title>Hot Enough to See</jats:title> <jats:p> Over the last decade, detection of fluorescence from individual molecules has allowed for increasingly detailed probing of biochemical reaction mechanisms. The key advantage of fluorescence detection is the absence of background; the signal appears as a glowing point in a void. However, not all molecules fluoresce, and so alternative detection methods are needed. <jats:bold> Gaiduk <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="353" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195475">353</jats:related-article> ) now show that a photothermal detection scheme can resolve absorption events by individual molecular dyes that exhibit poor fluorescence efficiency. The technique relies on each molecule's release of heat to the surrounding solvent after light absorption, an energy dissipation mechanism that is enhanced as fluorescence efficiency declines. The solvent heating alters the local refractive index just enough to scatter a portion of a probe beam backwards, revealing the absorption. </jats:p>

<jats:title>Turning Up the Heat</jats:title> <jats:p> The physical effect of atmospheric carbon dioxide on Earth's energy budget—that is, its “greenhouse effect”—has been understood for more than 100 years, but its role in climate warming is still not universally accepted. <jats:bold> Lacis <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="356" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1190653">356</jats:related-article> ) conducted a set of idealized climate model experiments in which various greenhouse gases were added to or subtracted from the atmosphere in order to illustrate their roles in controlling the temperature of the air. The findings clearly show that carbon dioxide exerts the most control on Earth's climate, and that its abundance determines how much water vapor the atmosphere contains, even though the radiative effect of the water vapor is greater than that of carbon dioxide itself. </jats:p>

<jats:title>Packing the Core</jats:title> <jats:p> The packing and arrangement of atoms in Earth's solid inner core can dictate processes such as core growth and rotation. Seismology and modeling suggest the inner core is composed primarily of iron, but the structure is less clear due to anisotropic splitting of seismic waves. <jats:bold> Tateno <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="359" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194662">359</jats:related-article> ) performed static compression experiments on pure iron at the extremely high pressures and temperatures found in the inner core and saw that iron prefers a hexagonal close-packed structure, as opposed to cubic structures. The results help to explain the observed seismic anisotropy, and also suggest that individual iron crystals in the core may prefer orienting themselves with their long crystallographic axes parallel to Earth's rotation axis. </jats:p>

<jats:title>Inflammation Response in Living Color</jats:title> <jats:p> Besides responding to microbial infection, our immune system also plays an important role in responding to sterile injury, for example, during trauma or organ necrosis. In a mouse model of sterile liver inflammation, <jats:bold> McDonald <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="362" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195491">362</jats:related-article> ) used dynamic in vivo imaging to visualize the innate immune response, which is dominated by neutrophils. Neutrophils were rapidly recruited to the site of inflammation through intravascular channels. Adenosine triphosphate generated from necrotic cells at the injury site and the Nlrp3 inflammasome were required for neutrophils to exit the circulation into the vascular endothelium, where they used integrins to adhere. A luminal chemokine gradient guided integrin-dependent, intravascular migration toward the site of injury. Finally, formyl peptides provided a signal to override the chemokine gradient and draw neutrophils into the site of injury. </jats:p>

<jats:title>Arresting Meiosis</jats:title> <jats:p> In mammals, meiotic maturation of oocytes must be coordinated precisely with ovulation to produce a developmentally competent egg at the right time for fertilization. How is coordination achieved? Follicular granulosa cells prevent precocious resumption of meiosis in oocytes, maintaining meiotic arrest until the pre-ovulatory hormone surge. Granulosa cells produce cyclic guanosine monophosphate, which is delivered to oocytes and arrests meiotic progression by inhibiting oocyte cyclic adenosine monophosphate degradation. How cGMP production is regulated is unclear. Now, <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" page="366" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193573">366</jats:related-article> ) report that NPPC (natriuretic peptide precursor type C), produced by mural granulosa cells, and its receptor NPR2, a guanylyl cyclase expressed by cumulus cells, together promote cGMP production by cumulus cells and are thus essential for maintaining meiotic arrest in mouse oocytes. </jats:p>

<jats:title>Stop, No-Go</jats:title> <jats:p> The decoding of messenger RNA (mRNA) into protein by eukaryotic ribosomes is constantly monitored to prevent errors. As well as mechanisms that detect and degrade messages with premature stop codons, no-go decay (NGD) results in the degradation of mRNA with inhibitory secondary structure or chemical damage. <jats:bold> Shoemaker <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="369" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192430">369</jats:related-article> ) show that in <jats:italic>Saccharomyces cerevisiae</jats:italic> the protein complex formed between Dom34 and Hbs1 is involved in NGD. The complex acts as a translational “reset button,” recognizing failed translation events and initiating an abortive program that results in the destruction of the stalled mRNA. </jats:p>

<jats:title>Selection and Variation</jats:title> <jats:p> In order to understand adaptation and evolution, it is necessary to understand the relationship between natural phenotypic variation and population genetics. <jats:bold> Rockman <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="372" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194208">372</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="6002" page="326" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1197700">Charlesworth</jats:related-article> </jats:bold> ) examined the level of genetic variance affecting gene expression through the comparison of two strains of the nematode <jats:italic>Caenorhabditis elegans</jats:italic> . Surprisingly, the variation observed in each trait was better explained by the genomic pattern of background selection than by selection on the traits themselves. Thus, the removal of deleterious mutations from the population by selection reduces phenotypic variability caused by genetic variation at closely linked neutral or nearly neutral sites, and quantitative variability in gene expression shows a similar pattern to sequence diversity and is affected by local rates of genetic recombination and the effective population size. </jats:p>

<jats:title>Nonrandom Walks</jats:title> <jats:p> Fitness landscapes of RNA sequences can help us to see the connection between all possible phenotypes and all possible genotypes. In molecular evolution, the fitness landscape is formalized as the distribution of fitness in sequence space, a hyperdimensional object of staggering complexity. To better understand these complex processes, <jats:bold>Pitt and Ferré-D'Amaré</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="376" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192001">376</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="6002" page="330" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1197667">Kluwe and Ellington</jats:related-article> </jats:bold> ) used deep sequencing to analyze the composition of a population of variants of an RNA ligase ribozyme, both before and after one round of in vitro selection. Relating the sequences of individuals in the population to a measure of their corresponding fitness provides a detailed picture of an evolutionary fitness landscape from empirical data. </jats:p>

<jats:title>Time and Temperature</jats:title> <jats:p> Daily cycles in environmental temperature are an important cue for many organisms to synchronize their endogenous circadian clock. However, mammals do not respond to this cue. Studying mouse tissue, <jats:bold> Buhr <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="379" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195262">379</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="6002" page="329" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1197747">Edery</jats:related-article> </jats:bold> ) find that this resistance to temperature is a feature specific to the suprachiasmatic nucleus (SCN), a region of the mammalian brain that functions as the body's master clock. In contrast, the clocks in peripheral tissues (for example, lung, liver) are fully capable of resetting in response to temperature changes and do so by a mechanism involving the heat shock pathway. The SCN drives daily rhythms in body temperature, and SCN-driven changes in temperature may synchronize the body's peripheral clocks. Without its intrinsic resistance to temperature, the SCN could be subject to disruptive feedback effects. </jats:p>

<jats:title>BDNF, Dopamine, and Cocaine Reward</jats:title> <jats:p> The nucleus accumbens plays a crucial role in mediating the rewarding effects of drugs of abuse. Different subpopulations of nucleus accumbens projection neurons exhibit balanced but antagonistic influences on their downstream outputs and behaviors. However, their roles in regulating reward behaviors remains unclear. <jats:bold> Lobo <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="385" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1188472">385</jats:related-article> ) evaluated the roles of the two subtypes of nucleus accumbens projection neurons, those expressing dopamine D1 versus D2 receptors, in cocaine reward. Deleting TrkB, the receptor for brain-derived neurotrophic factor, selectively in each cell type, and selectively controlling the firing of each cell type using optogenetic techniques allowed for confirmation that D1- and D2-containing neurons produced opposite effects on cocaine reward. </jats:p>