Catálogo de publicaciones - revistas

<jats:title>Roundabout Gypsum</jats:title> <jats:p> Calcium sulfates are a common but perhaps underappreciated group of minerals used in a number of natural and industrial processes. In many ways, these crystals precipitate from solution in the same way that most other aqueous minerals form; however, mounting evidence suggests that different, unexplored mechanisms may be at work. <jats:bold> Van Driessche <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="69" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1215648">69</jats:related-article> ; see the cover) performed high-resolution microscopy of the most common calcium sulfate mineral, gypsum, at various points along time-resolved, fast-quenching growth experiments. The images reveal that gypsum particles actually start out as crystalline nanoparticles of another mineral, bassanite, which then self-assemble into well-ordered nanorods. Finally, the nanorods transform into gypsum following a hydration reaction. The observation that the reaction pathway occurs below the solubility limit of the intermediate phase has wide-ranging implications for biomineralization processes and may provide ways to prevent fouling on the surfaces of desalination membranes. </jats:p>

<jats:title>Coming Late to the Planetesimal</jats:title> <jats:p> Highly siderophile (iron-loving) elements (Re, Os, Ir, Ru, Rh, Pt, Pd, and Au) must have been added to the mantles of Earth, the Moon, and Mars after their iron cores formed; otherwise the mantles would be devoid of these elements, which tend to be segregated to the core. <jats:bold> Dale <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="72" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1214967">72</jats:related-article> ) report data on highly siderophile elements in rocks from different planetary bodies, including asteroid 4 Vesta and other differentiated asteroids, which are representative of the planetesimals from which the solar system planets formed. Like the larger planetary bodies, differentiated asteroids, which formed over the first few million years of the solar system, bear the evidence of the late addition of highly siderophile elements to their mantles. Thus, this process was not unique to Earth, the Moon, and Mars and happened over an extended period of time in the inner solar system. </jats:p>

<jats:title>Tic TOC1 Plant Clock</jats:title> <jats:p> The molecular clocks intertwined with cellular physiology regulate daily cycles. In plants, these circadian rhythms affect processes as diverse as carbon metabolism and leaf orientation. <jats:bold> Huang <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="75" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219075">75</jats:related-article> , published online 8 March) have now analyzed the interactions driven by a key element of the circadian clock in plants, TOC1 (“TIMING OF CAB EXPRESSION 1”). TOC1 helps to coordinate responses of the morning and evening cycles, functioning to repress activity of other clock components. </jats:p>

<jats:title>Narrowing Down Artemisinin Resistance</jats:title> <jats:p> Knowing that antimalarial drug resistance is characterized by selective sweeps and reduced diversity around resistance mutations, <jats:bold> Cheeseman <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="79" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1215966">79</jats:related-article> ) looked for signatures of selection in a modified genome-wide association study in parasite populations from Cambodia, Laos, and Thailand. Thirty-three regions showed evidence of selection and enrichment of known antimalarial resistance genes. Fine-mapping of parasite samples taken during the past decade narrowed the association down to a 35-kb region of seven genes on chromosome 13 that seemed to explain at least 35% of the observed reduction in parasite clearance rate. However, the absence of strong candidate mutations suggests the involvement of noncoding regulatory mutations. </jats:p>

<jats:title>MicroDNA, Microdeletion?</jats:title> <jats:p> Extrachromosomal circular DNA (eccDNA) is widespread in eukaryotes. <jats:bold> Shibata <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="82" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1213307">82</jats:related-article> , published online 8 March) have found a new form of eccDNA—microDNA—in embryonic mouse brain, heart, and liver in adult mouse brain and in mouse and human cell lines. Unlike eccDNA, which is derived from repetitive sequences, transposable elements, or viral genomes, circular microDNA is derived from nonrepetitive genomic sequences and, very often, regions associated with genes. Length profiles—at 200 to 400 base pairs long—suggest that microDNA preferentially arises from regions of DNA occupied by nucleosomes. Furthermore, microDNA has very short regions of micro-homology at the beginning and ends of the circles. Analysis of several very common microDNAs indicates that their formation seems to result in microdeletions in somatic and germline genomes. </jats:p>

<jats:title>Macrophage Development Rewritten</jats:title> <jats:p> Macrophages provide protection against a wide variety of infections and critically shape the inflammatory environment in many tissues. These cells come in many flavors, as determined by differences in gene expression, cell surface phenotype and specific function. <jats:bold> Schulz <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="86" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219179">86</jats:related-article> , published online 22 March) investigated whether adult macrophages all share a common developmental origin. Immune cells, including most macrophages, are widely thought to arise from hematopoietic stem cells (HSCs), which require the transcription factor Myb for their development. Analysis of Myb-deficient mice revealed that a population of yolk-sac–derived, tissue-resident macrophages was able to develop and persist in adult mice in the absence of HSCs. Importantly, yolk sac–derived macrophages also contributed substantially to the tissue macrophage pool even when HSCs were present. </jats:p>

<jats:title>IL-22 Protects the Thymus</jats:title> <jats:p> One of the side effects associated with radiation treatment and some types of chemotherapy is damage to the thymus. Immunological T cells develop in the thymus, and so damage to this organ results in immunodeficiency and increased susceptibility to infectious disease. Although the organ eventually recovers, therapies that speed this recovery process are of interest. <jats:bold> Dudakov <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="91" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218004">91</jats:related-article> , published online 1 March; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6077" page="40" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221677">Bhandoola and Artis</jats:related-article> </jats:bold> ) now show in mice that interleukin-22 (IL-22) production in the thymus is increased in response to radiation damage and that this cytokine promotes thymic repair. After radiation treatment, IL-23 production by thymic dendritic cells induced IL-22 secretion by a population of radio-resistant innate lymphoid cells. IL-22 appeared to mediate its effects by promoting the survival and proliferation of thymic epithelial cells. </jats:p>

<jats:title>Looking for Greener Pastures</jats:title> <jats:p> Humans, like other animals, have evolved to forage. Brain-imaging studies by <jats:bold> Kolling <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="95" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216930">95</jats:related-article> ) suggest that activity in the dorsal anterior cingulate cortex supplies a continuous signal of environmental richness predicted by foraging theory. The signal exhibits a frame of reference that is tied to the key foraging decision of whether to engage with the current choice or to search for alternatives. The same strategy is used when humans are making other types of decisions. In contrast, the ventromedial prefrontal cortex, a brain region that lacks any signals pertinent to foraging, encodes choice values in a manner uninfluenced by environmental richness. </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 the genetics of antimalarial resistance, exploring flexoelectricity, a Nobel Prize fight, and more.</jats:p>