Catálogo de publicaciones - revistas

<jats:title>Shape-Shifting Signals</jats:title> <jats:p> Although orthogonal signaling systems seem to direct various developmental processes, few tissues remain in the same shape as they are at initiation to that of the final form. <jats:italic>Arabidopsis</jats:italic> leaves are free of the cell migrations that complicate animal development, and thus allowed <jats:bold> Kuchen <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="1092" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214678">1092</jats:related-article> ) to track and model the trajectory of leaf growth under a variety of perturbations. Varying the values of parameters in their model produced outputs of different leaf shapes ranging from obcordate, ovate, and oval to elliptic, and offered predictions for genes that regulate the developmental process. The meristem at the growing tip of plants is home to stem cells and is the source of newly differentiating shoots and leaves. New leaves make their first appearance as bulges at the side of the dome-shaped meristem. Although these developmental events are under hormonal control, they also seem to be constrained by the physical properties of the meristem. <jats:bold> Kierzkowski <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="1096" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1213100">1096</jats:related-article> ) tested physical effects acting on the shoot apical meristem of growing tomato shoots that alter turgor pressure. Again, mathematical modeling combined with observations of plant tissue helped to define the different zones in the meristem that respond to diverse mechanical stimuli. </jats:p>

<jats:title>Outside In</jats:title> <jats:p> Acquisition and analysis of large data sets promises to move us toward a greater understanding of the mechanisms by which biological systems are dynamically regulated to respond to external cues. Now, two papers explore the responses of a bacterium to changing nutritional conditions (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1050" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219303"> <jats:bold> Chalancon <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> ). <jats:bold> Nicolas <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="1103" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1206848">1103</jats:related-article> ) measured transcriptional regulation for more than 100 different conditions. Greater amounts of antisense RNA were generated than expected and appeared to be produced by alternative RNA polymerase targeting subunits called sigma factors. One transition, from malate to glucose as the primary nutrient, was studied in more detail by <jats:bold> Buescher <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="1099" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1206871">1099</jats:related-article> ) who monitored RNA abundance, promoter activity in live cells, protein abundance, and absolute concentrations of intracellular and extracellular metabolites. In this case, the bacteria responded rapidly and largely without transcriptional changes to life on malate, but only slowly adapted to use glucose, a shift that required changes in nearly half the transcription network. These data offer an initial understanding of why certain regulatory strategies may be favored during evolution of dynamic control systems. </jats:p>

<jats:title>Outside In</jats:title> <jats:p> Acquisition and analysis of large data sets promises to move us toward a greater understanding of the mechanisms by which biological systems are dynamically regulated to respond to external cues. Now, two papers explore the responses of a bacterium to changing nutritional conditions (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1050" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219303"> <jats:bold> Chalancon <jats:italic>et al.</jats:italic> </jats:bold> </jats:related-article> ). <jats:bold> Nicolas <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="1103" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1206848">1103</jats:related-article> ) measured transcriptional regulation for more than 100 different conditions. Greater amounts of antisense RNA were generated than expected and appeared to be produced by alternative RNA polymerase targeting subunits called sigma factors. One transition, from malate to glucose as the primary nutrient, was studied in more detail by <jats:bold> Buescher <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="1099" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1206871">1099</jats:related-article> ) who monitored RNA abundance, promoter activity in live cells, protein abundance, and absolute concentrations of intracellular and extracellular metabolites. In this case, the bacteria responded rapidly and largely without transcriptional changes to life on malate, but only slowly adapted to use glucose, a shift that required changes in nearly half the transcription network. These data offer an initial understanding of why certain regulatory strategies may be favored during evolution of dynamic control systems. </jats:p>

<jats:title>Choosing a Path</jats:title> <jats:p> The β <jats:sub>2</jats:sub> -adrenergic receptor (β <jats:sub>2</jats:sub> AR) is a G protein–coupled receptor that recognizes diverse ligands to trigger signaling in the cell. Besides binding G proteins, activated β <jats:sub>2</jats:sub> AR can be phosphorylated and bind arrestin, which redirects signaling to other pathways. Some β <jats:sub>2</jats:sub> AR ligands are “biased” in that they differentially activate G protein or arrestin signaling. <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="1106" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215802">1106</jats:related-article> , published online 19 January; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6072" page="1055" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219302"> <jats:bold>Sprang and Chief Elk</jats:bold> </jats:related-article> ) used <jats:sup>19</jats:sup> F-NMR spectroscopy to examine conformational changes associated with a range of ligands and discovered that biased ligands caused differential shifts in equilibrium between two conformational states—the G protein binding state and the arrestin binding state—and thus provide a basis for rational design of pharmacological ligands. </jats:p>

<jats:title>Sulfa's Crystal View</jats:title> <jats:p> The sulfonamide antibiotics (sulfa drugs) have been used to treat infections for over 70 years; however, emerging resistance has eroded their clinical utility. Sulfa drugs target dihydropteroate synthase, a key enzyme in the bacterial folate pathway. By performing the reaction in the crystalline form of the enzyme, <jats:bold> Yun <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="1110" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214641">1110</jats:related-article> ) have characterized the key structural intermediates. In combining structural data with theoretical and mutagenesis studies, they propose a detailed mechanism for dihydropteroate synthase catalysis. By resolving this structure with a sulfa drug bound to the enzyme, they showed how inhibition occurred and indicated how resistance could emerge. </jats:p>

<jats:title>Acquire and Share</jats:title> <jats:p> Few would argue with the stance that human social cognition supports an unequaled capacity to acquire knowledge and to share it with others. <jats:bold> Dean <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="1114" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1213969">1114</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6072" page="1056" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219232"> <jats:bold>Kurzban and Barrett</jats:bold> </jats:related-article> ) compared the extent to which these social and cognitive psychological processes can be elicited in children, capuchins, and chimpanzees through the use of a three-level puzzlebox task. Incentivized by improving rewards, 3- to 4-year-old children progressed from the first to the third level by imitating observed actions, taught other members of their social group how to solve the problem, and shared the rewards obtained. By contrast, neither the capuchins nor chimpanzees, very few of which ever reached the third level, exhibited these charactertistics. </jats:p>

<jats:title>New Teacher Syndrome</jats:title> <jats:p> The employment retention of high-school science and math teachers in the United States has diminished over recent decades, such that now many students are being taught by novice teachers. <jats:bold> Henry <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="1118" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215343">1118</jats:related-article> ) have analyzed the effectiveness of teachers by examining data collected from North Carolina public schools. Less-effective teachers seem to have a greater tendency to leave teaching and the greatest gains in teacher effectiveness are when the teacher is new—within the first 3 years on the job. Some subject areas are more likely to be affected by the preponderance of novice teachers than other subjects, including math and science. </jats:p>

<jats:p>The next time you use shampoo, air freshener, or moisturizing cream, consider this: How do you know it's safe? In all likelihood, whatever toxicologic screening its component ingredients were subjected to involved laboratory animals, the method of choice for decades and the industry's reigning "gold standard." Yet as Bob Dylan once put it, the times, they are a-changing. Animal-based testing is expensive and time-consuming, morally and ethically troubling, and most significantly, often a poor predictor of human toxicity. Animals aren't going anywhere just yet. But their numbers are dropping. Driven both by legislative mandate and scientific need, a new suite of in vitro and cell culture-based animal-free methods are gaining a foothold in toxicology labs.</jats:p>

<jats:p>The show includes the roots of human cumulative culture, microbes that transform waste into energy, peak gold, and more.</jats:p>

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