This Week in Science

Science  10 Apr 2015:
Vol. 348, Issue 6231, pp. 196
  1. Primate Genomics

    Genomes in the mist

    1. Laura M. Zahn

    Mountain gorillas are highly inbred

    IMAGE: © JOE MCDONALD/CORBIS

    The mountain gorilla is an iconic species that is at high risk of extinction. Xue et al. have sequenced 13 gorillas from two different populations to probe their genetic diversity. The genomes show large tracts of homozygosity and the loss of highly deleterious genetic variants, indicating population bottlenecks and inbreeding. This loss of genetic diversity appears to have started over 20,000 years ago and may have been caused by changes in climate and human-associated effects.

    Science, this issue p. 242

  2. Protein Targeting

    Sorting out cell sorting

    1. Stella M. Hurtley

    The sorting of proteins into appropriate compartments is vital for proper cell function. After its discovery 20 years ago, various potential roles for nascent chain-associated complex (NAC) in the specificity of intracellular protein sorting have been proposed. Until now, no clear phenotypes have been discovered. Gamerdinger et al. explored the role of NAC in protein translocation in Caenorhabditis elegans (see the Perspective by Kramer et al.). They found that NAC prevents the importation of incorrect cargo, such as mitochondrial proteins, into the endoplasmic reticulum.

    Science, this issue p. 201; see also p. 182

  3. Proteostasis

    Giving protein folding a helping hand

    1. Stella M. Hurtley

    The reversible phosphorylation of proteins controls virtually all aspects of cell and organismal function. Targeting phosphorylation offers a broad range of therapeutic opportunities, and thus kinases have become important therapeutic targets. As targets, phosphatases should be as attractive, but in fact they are more challenging to manipulate. Das et al. have found a safe and specific inhibitor, called Sephin1, that targets a regulatory subunit of protein phosphatase 1 in vivo. Sephin1 binds and inhibits PPP1R15A, but not the related regulatory phosphatase PPP1R15B. In mice, Sephin1 prolonged a stress-induced phospho-signaling pathway to prevent the pathological defects of the unrelated protein-misfolding diseases Charcot-Marie-Tooth 1B and amyotrophic lateral sclerosis.

    Science, this issue p. 239

  4. Paleoceanography

    Early closing between oceans

    1. H. Jesse Smith

    Ancient Pacific-Caribbean link

    IMAGE: DAVID FARRIS

    The Central American Seaway, which once separated the Panama Arc from South America, may have closed 10 million years earlier than is believed. Montes et al. report that certain minerals of Panamanian provenance began to appear in South America during the Middle Miocene, 15 to 13 million years ago (see the Perspective by Hoorn and Flantua). The presence of the minerals indicates that rivers were flowing from the Panama Arc into the shallow marine basins of northern South America. One interpretation of this finding is that large-scale ocean flow between the Atlantic and Pacific had ended by then. If this is true, then many models of paleo-ocean circulation and biotic exchange between the Americas need to be reconsidered.

    Science, this issue p. 226; see also p. 186

  5. Drug Discovery

    Allergy drug inhibits viral infection

    1. Megan Frisk

    A drug used to dry up a runny nose and itchy eyes may be repurposed for treating hepatitis C virus (HCV). This viral infection often goes undetected, but it can exacerbate liver diseases, including cancer. The fact that allergy-relieving antihistamines can treat HCV was uncovered by He et al. in a screen of a library of approved drugs. Among these, the first-generation antihistamine chlorcyclizine showed highly specific anti-HCV activity in vitro and in mice with “humanized” livers, without evidence of drug resistance, a common problem with antivirals. Moreover, chlorcyclizine synergized with other anti-HCV drugs such as ribavirin, sofosbuvir, and interferon-α. Antihistamines are widely available, safe, and inexpensive: ideal candidates for use in HCV-endemic countries.

    Sci. Transl. Med. 7, 282ra49 (2015).

  6. Mars Atmosphere

    Mapping Mars' water history

    1. Margaret M. Moerchen

    We know the water cycle on Earth is complex. Neither is it simple on Mars. Infrared maps of water isotopes made by Villanueva et al. show the distribution of H2O and “semiheavy” water (HDO: deuterated water containing a mixture of hydrogen isotopes) across Mars. HDO enrichment varies with time and location; for example, irregular isotopic signals associate with different terrain features. The measurements also allow seasonal sublimation levels of the northern ice cap to be estimated and thus could be used to reveal past climate behavior.

    Science, this issue p. 218

  7. Bioanalysis

    Imaging lipid composition

    1. Phil Szuromi

    Chemical imaging of cell membranes can be performed with matrix-assisted laser desorption/ionization mass spectrometry (MALDI), but low ionization efficiency often leads to a signal dominated by the main lipid components, such as abundant phosphatidylcholine species. Soltwisch et al. used a tunable laser for post-ionization of neutral species to boost the signal for other membrane components, such as cholesterol and phospho- and glycolipids. Imaging of cells and tissues with these methods allows differentiation based on a more extensive chemical signature.

    Science, this issue p. 211

  8. Human Genetics

    Chromosome number varies in humans

    1. Laura M. Zahn

    Pregnancy loss is often associated with a loss of chromosome number, a condition known as aneuploidy. When examining aneuploid embryos during in vitro fertilization cycles, McCoy et al. found a large genomic region associated with defects in maternal chromosome number (see the Perspective by Vohr and Green). This region contains a gene, Polo-like Kinase 4 (PLK4), that is known to affect chromosome segregation and has variants that correlate with an increased rate of maternal aneuploidy. Surprisingly, such variants occur at relatively high levels in human populations and may be under positive selection.

    Science, this issue p. 235; see also p. 180

  9. Quantum Gases

    Detecting multiple temperatures

    1. Jelena Stajic

    Most people have an intuitive understanding of temperature. In the context of statistical mechanics, the higher the temperature, the more a system is removed from its lowest energy state. Things become more complicated in a nonequilibrium system governed by quantum mechanics and constrained by several conserved quantities. Langen et al. showed that as many as 10 temperature-like parameters are necessary to describe the steady state of a one-dimensional gas of Rb atoms that was split into two in a particular way (see the Perspective by Spielman).

    Science, this issue p. 207; see also p. 185

  10. Earth History

    Ocean acidification and mass extinction

    1. Nicholas S. Wigginton

    The largest mass extinction in Earth's history occurred at the Permian-Triassic boundary 252 million years ago. Several ideas have been proposed for what devastated marine life, but scant direct evidence exists. Clarkson et al. measured boron isotopes across this period as a highly sensitive proxy for seawater pH. It appears that, although the oceans buffered the acidifiying effects of carbon release from contemporary pulses of volcanism, buffering failed when volcanism increased during the formation of the Siberian Traps. The result was a widespread drop in ocean pH and the elimination of shell-forming organisms.

    Science, this issue p. 229

  11. Quantum Computing

    Benchmarking quantum simulation

    1. Ian S. Osborne

    Finding a solution to a problem often amounts to an optimization problem and thus can be recast in terms of the lowest-energy state of a system. To find such ground states, mathematical methods based on annealing were developed. To reach the ground state more quickly than with the earlier classical methods, a quantum-mechanical approach was proposed; however, the evidence for quantum speed-up is contradictory. Heim et al. show that the results depend on how the problem is described and how the optimization routine is implemented. This development should be valuable for benchmarking quantum machines.

    Science, this issue p. 215

  12. Carbon Flux

    Down with atmospheric carbon dioxide

    1. H. Jesse Smith

    How does the ocean move carbon from surface waters to its deep interior? Current understanding is that carbon dioxide is removed from the atmosphere by phytoplankton that are eaten, and in turn their predators die and sink into deep water and seafloor sediments. In addition to this route, Omand et al. show that downwelling caused by ocean eddies 1 to 10 km across can deliver much of the carbon produced in spring to the deep sea. The eddies entrain small particles and dissolved organic carbon to augment the flux of large sinking particles.

    Science, this issue p. 222

  13. Biochemistry

    Single-molecule assay of ubiquitylation

    1. L. Bryan Ray

    Many biological processes in cells are regulated by ubiquitin peptides that are attached to proteins. Measurement of single fluorescent molecules in cell extracts can be used to trace the kinetics of such reactions. Lu et al. refined assay conditions to follow ubiquitination by an E3 ubiquitin ligase (see the Perspective by Komander). They visualized the activity of the anaphase-promoting complex (APC), a ubiquitin ligase critical for control of the cell division cycle. The processive initial reaction catalyzed by the APC was replaced by slower reactions. The results show how small, commonly occurring recognition motifs can guide specific and highly controlled enzymatic events. In a companion paper, Lu et al. explored how the number and arrangement of added ubiquitin chains affected the interaction of ubiquitylated proteins with the proteasome (a protein complex that recognizes ubiquitylated proteins and degrades them). The extent of ubiquitylation determined the strength of interaction of a substrate protein with the proteasome, and the arrangement of the ubiquitin chains determined the movement of the protein into the proteasome and thus the rate of degradation.

    Science, this issue 10.1126/science.1248737, 10.1126/science.1250834; see also p. 183

  14. Cometary Formation

    Making comets in the cold

    1. Nicholas S. Wigginton

    The speciation of nitrogen compounds in comets can tell us about their history. Comets are some of the most ancient bodies in the solar system and should contain the nitrogen compounds that were abundant when they formed. Using the ROSINA mass spectrometer aboard the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko, Rubin et al. found molecular nitrogen at levels that are depleted compared to those in the primordial solar system. Depletion of such a magnitude suggests that the comet formed either from the low-temperature agglomeration of pristine amorphous water ice grains or from clathrates.

    Science, this issue p. 232

  15. Early Warning Systems

    Crowdsourcing early warnings of natural disasters

    1. Kip Hodges

    Cellular phones and similar electronic devices contain powerful technologies that can be harnessed for location-based sensing of the environment. Minson et al. show how displacement data from consumer-grade Global Navigation Satellite System (i.e., GPS) sensors and Inertial Navigation System (e.g., accelerometer) sensors acquired from widely distributed cell phones can be combined to produce earthquake and tsunami early warnings. Such rapidly acquired crowdsourced data could be a valuable way of improving public safety and facilitating disaster responses in earthquake-prone regions.

    Sci. Adv. 10.1126/sciadv.1500036 (2015).

  16. Systems Biology

    Networking death signals to fight cancer

    1. Nancy R. Gough

    Selectively killing cancer cells without inducing resistance is the holy grail of cancer therapy. Cancer cells are particularly sensitive to cell death triggered by the secreted protein TRAIL. Unfortunately, some cancer cells evade TRAIL-induced death and develop resistance by rewiring their signaling networks. So et al. used proteomic data to map a protein interaction network of the kinases that affected TRAIL-induced cell death. The modeling of information flow through the network revealed potential targets that could be exploited to develop combination therapies with TRAIL to kill cancer cells and prevent resistance.

    Sci. Signal. 8, rs3 (2015).