GUILLERMO NUNEZ ABOGADOS ASESORES FISCALES
 

    The cover shows the Amundsen Sea, offshore of the West Antarctic Ice Sheet. As Tyler Jones and his colleagues reveal in this issue, this region experienced a large change in year-to-year climate variability some 16,000 years ago. The Last Glacial Maximum saw ice cover vast areas of the Northern Hemisphere and this significantly influenced the climate of the Southern Hemisphere. The brightness and high altitude of the ice sheets altered the atmospheric pathways linking the tropics to West Antarctica by moving the location of tropical convection. Using water isotope data from a West Antarctic ice core, Jones and his colleagues traced the effects of this influence. They find that the interannual and decadal climate variability at high southern latitudes was almost twice as high during the Last Glacial Maximum as during the past 11,700 years of the warmer Holocene epoch. Through this they reveal the intimate climate linkages between the high latitudes, and the key role of the tropics as a climate mediator between the hemispheres. Cover image: Bradley R. Markle

      The cover shows a model of a solar eruption in progress. In this week's issue, Tahar Amari and his colleagues suggest that one phenomenon could control the nature and behaviour of all such eruptions. There are two types of eruption: eruptive, which result in coronal mass ejections, and confined, which do not. The exact origin of confined eruptions has been hotly debated between two alternatives: topological complexity in the magnetic structure above the Sun's surface, or an unstable twisted magnetic flux rope. Amari and his team show that the latter process is more likely. To study this, the researchers focused on an eruption that took place in October 2014, predicting its evolution using a two-stage model. Their work reveals a strong multilayer magnetic cage (orange) in which a twisted flux rope (blue) develops. The magnetic energy of the rope increases over the course of several hours before the eruption, but is still not enough to break all of the layers of the cage. However, the twist in the rope is enough to trigger an instability that results in partial destruction of the cage. The resistance of the cage to the assault from the rope determines the type and amount of energy released in the eruption. If the rope is stronger than the cage and can break free, the result is eruptive; if the cage is stronger than the rope, the eruption is confined. Understanding the conditions that lead to solar eruptions may help to predict the events that might affect satellites, communications and ground-based power generation. Cover image: Tahar Amari/Centre de Physique Théorique, CNRS-Ecole Polytechnique

     In this issue, Elly Tanaka, Eugene Myers and their colleagues report the 32-billion-base genome of the axolotl (Ambystoma mexicanum), a model organism for developmental, regeneration and evolutionary studies. The team overcame the challenges of sequencing and assembling this large and complex genome, which features many lengthy repetitive regions, by using long-read sequencing, optical mapping and a new computer algorithm known as MARVEL. The researchers estimate that the genome contains around 23,000 protein-coding genes and note that the gene Pax3, which is essential in many animals for development, is absent. Gene editing of the related gene, Pax7, showed that it steps into the breach for some functions. The assembled genome should offer fresh opportunities for the study of evolution, development and regeneration. Cover image: Avalon/Photoshot/Alamy

     The cover shows an artist’s impression of a cancerous cell in which DNA has formed micronuclei as a result of chromosomal instability. As Samuel Bakhoum and his colleagues reveal in this issue, when these micronuclei rupture, they spill exposed DNA into the cytosol (green), which prompts an inflammatory response that helps to drive metastasis. These findings draw a direct link between chromosomal instability and metastasis and may offer novel avenues for prevention. Cover image: Wenjing Wu

       The cover is a surface–ribbon hybrid image showing the topology of the RNA Pol III/TFIIIB/DNA complex. RNA polymerase III (Pol III) catalyses the transcription of short RNAs that are essential for protein synthesis during cell growth. Pol III is predominantly regulated at the level of transcription initiation, and dysregulated Pol III activity is linked to diseases including cancer. In this issue, two independent studies from the labs of Alessandro Vannini and Christoph Müller describe cryo-electron microscopy structures of the yeast Pol III pre-initiation complex (PIC) comprising the full 17-subunit Pol III and the three TFIIIB subunits TBP (pink), Brf1 (yellow) and Bdp1 (orange) bound to promoter DNA in various functional states (the loops stabilizing the unwound DNA strands at both sides of the cleft are depicted as bright cyan ribbons). The structures elucidate the detailed mechanisms of how Pol III is recruited to its target promoters and how promoter DNA is opened to form a stable transcription bubble. They also allow a comparison with the structures of Pol I and Pol II PICs. Cover image: Alessandro Vannini/Jeroen Claus (Phospho Biomedical Animation)

      The cover shows the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico. Jason Hessels and his colleagues used the telescope in their attempt to clarify the physical nature of the only known source of repeating fast radio bursts. Lasting about a millisecond each, these bursts come from a star-forming region in a dwarf galaxy. Hessels and his co-authors observed that the bursts were nearly 100% linearly polarized and had a very high Faraday rotation measure. Such results require the presence of an environment of extreme magnetized plasma, which has previously been seen only around massive black holes. As a result, the authors suggest that the radio bursts possibly come from a neutron star in such an environment (although the team notes that, in principle, the bursts could originate from a neutron star surrounded by either a highly magnetized wind nebula or a supernova remnant). Image: Image design: Danielle Futselaar; Photo usage: Brian P. Irwin/Dennis van de Water/Shutterstock.com

     The ability to monitor microbial populations within the gut and other body organs poses significant challenges. In this issue, Mikhail Shapiro and his colleagues tackle this problem and reveal a technique that allows bacteria to be imaged deep inside the body using ultrasound. To achieve this, the team created genetically modified bacteria that express acoustic reporter genes. These genes encode components of gas vesicles — gas-filled nanostructures normally used by water-dwelling photosynthetic organisms to control their buoyancy. These gas vesicles scatter sound waves and so can be detected by ultrasound. The researchers show that populations of modified Escherichia coli and Salmonella typhimurium can be imaged non-invasively within the gastrointestinal tract and in tumours, offering a potential route for studying the microbiome and monitoring cancer progression and therapy. Image: Barth van Rossum for Caltech

       As 2017 draws to a close, we once again select 'Nature's 10' — ten people who this year played an important part in shaping the trends, events and challenges for science. The cover design speaks to the increasingly important role of artificial intelligence in science and technology. The image was created in the style of a machine-learning algorithm designed to solve the travelling salesman problem, which asks for the optimum path between a given set of points. Thus, the '10' was created using a single line. Image by Martin KrzywinskiAs 2017 draws to a close, we once again select 'Nature's 10' — ten people who this year played an important part in shaping the trends, events and challenges for science. The cover design speaks to the increasingly important role of artificial intelligence in science and technology. The image was created in the style of a machine-learning algorithm designed to solve the travelling salesman problem, which asks for the optimum path between a given set of points. Thus, the '10' was created using a single line. Image by Martin Krzywinski

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