Editors' Choice

Science  22 Nov 2013:
Vol. 342, Issue 6161, pp. 910
  1. Biomedicine

    NO Mechanism

    1. L. Bryan Ray

    Although nitrogen-containing compounds have been used to treat heart failure for well over 1000 years, in many cases their mechanisms of action are unclear. Huang et al. now show that agents that increase the production of nitric oxide (NO) can influence heart function through S-nitrosylation of the enzyme GRK2; this protein kinase phosphorylates G protein—coupled receptors, most notably the β-adrenergic receptor, that have critical roles in regulating heart function. They found that GRK2 associates with endothelial NO synthase, the enzyme that produces NO, and nitrosylation of GRK2 inhibits its activity. In a mouse model of heart failure, treatment with agents that increased NO concentrations protected myocytes from cell death, but this effect was lost in animals expressing a mutant form of GRK2 that could not be S-nitrosylated.

    Sci. Signal. 6, ra95 (2013).

  2. Geology

    Uptake Uptick

    1. Nicholas S. Wigginton

    Foraminifera are tiny aquatic organisms that have mineralized shells composed of calcium carbonate. In marine environments, these structures precipitate from seawater; thus foraminifera shells preserved in the sedimentary record reflect the chemistry and temperature of ancient oceans. However, models of the uptake of Ca and other trace elements do not entirely explain the concentration and ratio of ions preserved in carbonate shells. Using a combination of isotopic and fluorescent imaging of incubated cultures, Nehrke et al. show that passive ion transport is important for trace elements such as Mg and Sr in an extant foraminifera species, but not Ca. Transmembrane transport as the predominant uptake mechanism of Ca helps explain not only the observed Mg/Ca and Sr/Ca ratios in recently grown shells but also their relation to changes in seawater chemistry, and thus past ocean temperatures.

    Biogeosciences 10.5194/bg-10-6759-2013 (2013).

  3. Virology

    Stochastic Reservoir

    1. Barbara R. Jasny

    A major challenge in attempting to eradicate HIV is the virus that remains latent (transcriptionally inactive) in infected cells; current pharmacological therapies focus on inhibiting various steps in the HIV life cycle. It has been thought that the reason latent viruses are inactive is either that they infected T cells that were transitioning to a resting state or that the viruses themselves were defective. The latent reservoir has been measured in the past by one of two methods: forcing all T cells to become active and then measuring viruses that have been induced to replicate (which could lead to underestimates, because not all proviruses have been induced) or identifying all integrated proviral DNA (which may include defective genomes that would never replicate). Ho et al. have gone further, by analyzing the viruses that remained inactive after T cell activation. Intact viral genomes were found in nearly 12% of the clones analyzed. When they synthesized a sample of the genomes and reconstructed these viruses, replication occurred with normal growth kinetics, and promoter function appeared normal. The reason for latency was not that the viruses had integrated into heterochromatin, whence transcription would be suppressed, nor had these noninduced viruses been silenced by CpG methylation. This makes the prospects for a sterilizing cure look somewhat farther away—the authors conclude that the latent reservoir may be as much as 60 times larger than previous estimates.

    Cell 155, 540 (2013).

  4. Ecology

    Maternal Choice

    1. Sacha Vignieri

    Temperature-dependent sex determination (TDSD), a phenomenon in which offspring sex is affected by the temperature experienced during embryonic development, occurs in many ectothermic species, such as reptiles and fishes. However, a purely environmental control of sex could lead to evolutionarily unstable sex ratios, suggesting that selection for a maternal behavior, such as the choice of nest sites, could be strong. Mitchell et al. used a set of controlled experiments in painted turtles to test whether nest sites selected by females affected sex ratios. That is, they cross-fostered eggs and hatchlings in nest sites that had been chosen by mother turtles, relative to sites selected at random, across both the incubation and hatchling hibernation stages. They found no difference in survival or success between maternally or randomly selected nest sites, but random sites yielded a significant male bias in offspring, with maternal sites—characterized by a more open canopy, more solar radiation, and warmer temperatures in the nest—being more balanced. These results show that maternal influence on sex ratio is probably an important component of reproduction in species with TDSD. Further, the habitats selected by female turtles in this study, specifically warmer sites with less vegetation, indicate the potential for conflict with viability selection in this and other ectothermic species as the climate warms.

    Proc. R. Soc. London Ser. B. 280, 20132460 (2013).

  5. Chemistry

    Water-Splitting Standards

    1. Jake Yeston

    Widespread use of functional electrocatalytic water-splitting systems in conjunction with solar power infrastructure will probably require a composition of Earth-abundant materials that remain stable under the reaction conditions and operate efficiently at minimal overpotential (a measure of how much of the input energy gets stored in the products' chemical bonds for later use when the Sun has set, rather than lost as heat). Numerous reports highlight favorable features of particular experimental catalysts in this context, but cross-comparisons have proven challenging in the absence of established standards for the testing conditions. McCrory et al. offer a preliminary framework for making apples-to-apples comparisons of catalysts for the oxygen-evolving half of the couple. They report benchmark tests of nine representative non–precious metal catalysts deposited on glassy carbon electrodes, under standardized acidic (1 M sulfuric acid) and basic (1 M sodium hydroxide) conditions. After first assessing the active surface area for normalization, the authors measured the overpotential necessary to attain a current density of 10 mA/cm2 and then tracked performance over 2 hours. None of the tested non–precious metal catalysts were stable in acid, highlighting a priority for further research. In base, the overpotentials across the test set varied relatively little, spanning a range between 350 and 430 mV.

    J. Am. Chem. Soc. 135, 16977 (2013).

  6. Materials Science

    A Battery for Twos

    1. Marc S. Lavine

    In theory, Mg batteries can obtain higher energy density and specific energy than Li-based ones, because of the divalent nature of the Mg ion. They may also prove safer than those that rely on Li metal. However, it has been a challenge to find materials that can allow for the fast and reversible insertion of Mg2+. Wang et al. explore materials from the Prussian Blue family, which have an open framework and a crystal structure similar to those of ABX3 perovskites. For their materials, the B sites were occupied with either Ni2+ at the N-coordinated sites or Fe3+ at the C-coordinated sites, linked together with cyano (CN) groups, which increase the separation distance between the Ni and Fe ions to allow for cation insertion. Nickel hexacyanoferrate was synthesized as nanoparticles and combined with a C cloth as the working electrode. Over 2000 cycles, they were able to reversibly insert and remove Mg2+, Ca2+, Sr2+, and Ba2+, when using the appropriate electrolyte. The specific capacity tended to decrease with cycling, but that was probably due to the dissolution of Ni2+ into the electrolyte; the capacity loss was eliminated by dissolving Ni2+ into the electrolyte before cycling. Changes in the hysteresis seen with increasing charge/discharge rates suggest that there might be a rate-limiting dehydration step during the insertion process.

    Nano Lett. 10.1021/nl403669a (2013).

  7. Genetics

    Venom Genetics

    1. Laura M. Zahn

    Two papers describ e the use of genomics in identifying genes encoding venom components in arthropods. Cao et al. sequenced the scorpion (Mesobuthus martensii) genome and identified 116 neurotoxin genes specific to the scorpion lineage; von Reumont et al. profiled the transcriptome of the remipede (Speleonectes tulumensis), which is a blind crustacean that inhabits underwater caves. Both species were found to contain toxins that probably target sodium channels. Additionally, the scorpion toxins affect chloride and potassium channels, whereas the remipede delivers peptidases and chitinases into its victims. A phylogenetic analysis of agatoxins, which are found in this remipede and in venomous spiders, suggests that the remipede neurotoxins evolved independently after gene duplication from a non–venom gland paralog. Similarly, tandem arrays of toxin genes were found in the scorpion, hinting at how gene duplication contributed to the genesis of toxin diversity.

    Nat. Comm. 4, 10.1038/ncomms3602 (2013); Mol. Biol. Evol. 30, 10.1093/molbev/mst199 (2013).