Catálogo de publicaciones - revistas

<jats:title>Magnetic Weyl semimetals</jats:title> <jats:p> Weyl semimetals (WSMs)—materials that host exotic quasiparticles called Weyl fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs that break inversion symmetry have been identified, but showing unambiguously that a material is a time-reversal-breaking WSM is tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski <jats:italic>et al.</jats:italic> probed the material Co <jats:sub>2</jats:sub> MnGa using angle-resolved photoemission spectroscopy, revealing exotic drumhead surface states. Using the same technique, Liu <jats:italic>et al.</jats:italic> studied the material Co <jats:sub>3</jats:sub> Sn <jats:sub>2</jats:sub> S <jats:sub>2</jats:sub> , which was complemented by the scanning tunneling spectroscopy measurements of Morali <jats:italic>et al.</jats:italic> These magnetic WSM states provide an ideal setting for exotic transport effects. </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" issue="6459" page="1278" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aav2327">1278</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6459" page="1282" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aav2873">1282</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6459" page="1286" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aav2334">1286</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6459" page="1248" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax6190">1248</jats:related-article> </jats:p>

<jats:title>Flood-resistance from gene regulation</jats:title> <jats:p> Some plants tolerate flooding better than others. Reynoso <jats:italic>et al.</jats:italic> compared gene regulatory networks activated by flooding in rice, which is adapted to flooding, with those in species less adapted to flooding. Flood-related gene regulation was characterized according to chromatin accessibility as well as transcription. Although flood response circuitry is evident in dryland species as well, its activation is greater in wetland rice. </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" issue="6459" page="1291" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax8862">1291</jats:related-article> </jats:p>

<jats:title>The decline of resistance in old age</jats:title> <jats:p> Infection, immunity, and demography are rarely measured simultaneously, despite being intertwined. Froy <jats:italic>et al.</jats:italic> measured an immune marker of resistance to infection by worm parasites (helminths) in Soay sheep off the remote Atlantic island of St. Kilda (see the Perspective by Gaillard and Lemaître). They used a library of 2000 blood samples from 800 known individuals that have been left to run wild and unmanaged. Resistance declines as the sheep age, which reduces a sheep's chances of surviving the winter. Helminths are an important component of many natural systems, including humans, and may thus become an increasing burden on health with age. </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" issue="6459" page="1296" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aaw5822">1296</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6459" page="1244" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay9493">1244</jats:related-article> </jats:p>

<jats:p> Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[ <jats:italic>n</jats:italic> ]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized because of their high reactivity. We generated cyclo[18]carbon (C <jats:sub>18</jats:sub> ) using atom manipulation on bilayer NaCl on Cu(111) at 5 kelvin by eliminating carbon monoxide from a cyclocarbon oxide molecule, C <jats:sub>24</jats:sub> O <jats:sub>6</jats:sub> . Characterization of cyclo[18]carbon by high-resolution atomic force microscopy revealed a polyynic structure with defined positions of alternating triple and single bonds. The high reactivity of cyclocarbon and cyclocarbon oxides allows covalent coupling between molecules to be induced by atom manipulation, opening an avenue for the synthesis of other carbon allotropes and carbon-rich materials from the coalescence of cyclocarbon molecules. </jats:p>

<jats:title>Tracking nucleic acids in living cells</jats:title> <jats:p> Fluorescence in situ hybridization (FISH) is a powerful molecular technique for detecting nucleic acids in cells. However, it requires cell fixation and denaturation. Wang <jats:italic>et al.</jats:italic> found that CRISPR-Cas9 protects guide RNAs from degradation in cells only when bound to target DNA. Taking advantage of this target-dependent stability switch, they developed a labeling technique, named CRISPR LiveFISH, to detect DNA and RNA using fluorophore-conjugated guide RNAs with Cas9 and Cas13, respectively. CRISPR LiveFISH improves the signal-to-noise ratio, is compatible with living cells, and allows tracking real-time dynamics of genome editing, chromosome translocation, and transcription. </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" issue="6459" page="1301" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax7852">1301</jats:related-article> </jats:p>

<jats:title>Extinction leads to restructuring</jats:title> <jats:p> By most accounts, human activities are resulting in Earth's sixth major extinction event, and large-bodied mammals are among those at greatest risk. Loss of such vital ecosystem components can have substantial impacts on the structure and function of ecological systems, yet fully understanding these effects is challenging. Tóth <jats:italic>et al.</jats:italic> looked at the loss of large-bodied mammals in the Pleistocene epoch to identify potential community assembly effects. They found that the demise of large mammals led to a restructuring and a shift from biotic to abiotic drivers of community structure. Understanding past changes may help predict the community-level effects of the extinctions we are currently driving. </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" issue="6459" page="1305" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aaw1605">1305</jats:related-article> </jats:p>

<jats:title>A brain pathway for active forgetting</jats:title> <jats:p> Sleep affects memories via several mechanisms. Izawa <jats:italic>et al.</jats:italic> identified a possible new pathway in the brain: REM sleep–active hypothalamic melanin-concentrating hormone (MCH)–producing neurons, which, among others, project to the hippocampus. Surprisingly, genetic ablation of MCH neurons increased memory performance in mice. Conversely, pharmacogenetic activation of MCH neurons impaired memory. In vitro physiological experiments showed that activation of MCH fibers in hippocampal slices suppressed spiking activity of pyramidal cells. These findings indicate that the MCH pathway may become a target for memory modulation. </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" issue="6459" page="1308" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax9238">1308</jats:related-article> </jats:p>

<jats:title>Catch and release</jats:title> <jats:p> Chaperones are essential for proper protein folding inside cells, but their interactions with client proteins are difficult to study because they are dynamic. Jiang <jats:italic>et al.</jats:italic> used nuclear magnetic resonance spectroscopy to look at how the chaperones Hsp70 and Hsp40 work together in the client binding and release cycle. Hsp40 alters the folding properties of the client protein, perhaps unfolding a non-native state, by binding dynamically through multiple binding sites. Hsp70 binding to Hsp40 displaces the unfolded client. The released protein may either fold to its native state, or be rebound for another chaperone cycle. </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" issue="6459" page="1313" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax1280">1313</jats:related-article> </jats:p>

<jats:p> The 2019 Gordon Research Conference schedule was published on pages 1320 to 1328 of this issue of the print version of <jats:italic>Science</jats:italic> . The current schedule can also be found online at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.grc.org/">www.grc.org/</jats:ext-link> . </jats:p>

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