Catálogo de publicaciones - revistas

<jats:title>The clockwork of insulin release</jats:title> <jats:p> In healthy people, blood glucose levels are maintained within a narrow range by several physiological mechanisms. Key among them is the release of the hormone insulin by pancreatic β cells, which occurs when glucose levels rise after a meal. In response to insulin, blood glucose is taken up by tissues that need fuel, such as muscle. β cells can anticipate the body's varying demand for insulin throughout the 24-hour day because they have their own circadian clock. How this clock controls insulin release has been unclear. Perelis <jats:italic>et al.</jats:italic> now show that the activity of transcriptional enhancers specific to β cells regulates the rhythmic expression of genes involved in the assembly and trafficking of insulin secretory vesicles (see the Perspective by Dibner and Schibler). </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aac4250">10.1126/science.aac4250</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6261" page="628" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aad5412">628</jats:related-article> </jats:p>

<jats:p>Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. We report the discovery of low-altitude, diffuse auroras spanning much of Mars’ northern hemisphere, coincident with a solar energetic particle outburst. The Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, detected auroral emission in virtually all nightside observations for ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo­–electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth.</jats:p>

<jats:p>Dust is common close to the martian surface, but no known process can lift appreciable concentrations of particles to altitudes above ~150 kilometers. We present observations of dust at altitudes ranging from 150 to above 1000 kilometers by the Langmuir Probe and Wave instrument on the Mars Atmosphere and Volatile Evolution spacecraft. Based on its distribution, we interpret this dust to be interplanetary in origin. A comparison with laboratory measurements indicates that the dust grain size ranges from 1 to 12 micrometers, assuming a typical grain velocity of ~18 kilometers per second. These direct observations of dust entering the martian atmosphere improve our understanding of the sources, sinks, and transport of interplanetary dust throughout the inner solar system and the associated impacts on Mars’s atmosphere.</jats:p>

<jats:p>Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.</jats:p>

<jats:p>The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability.</jats:p>

<jats:title>Function in the tree of life</jats:title> <jats:p> How does the composition of microbial communities integrate functionally with the wider environment? Martiny <jats:italic>et al.</jats:italic> review how patterns of microbial species abundances in different environments and disease states can have strong evolutionary signals. Some environmental changes select the survival of organisms with conserved metabolisms requiring complex configurations of proteins and cofactors that have long evolutionary histories, such as methane producers. In contrast, surviving antibiotic exposure may only require a single gene that can be traded promiscuously among many unrelated organisms. So, depending on the key ingredient (whether it is temperature, light, nutrient, or a dose of antibiotic) and the evolutionary history of its complementary metabolism, shifting environmental conditions will have predictable effects at different levels within the microbial tree of life. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aac9323">10.1126/science.aac9323</jats:related-article> </jats:p>