This Week in Science

Science  13 Feb 2015:
Vol. 347, Issue 6223, pp. 732
  1. Dental Materials

    Key trace minerals greatly strengthen teeth

    1. Marc S. Lavine

    Rodent skull shows pigmented and regular tooth enamel


    The outer layers of teeth are made up of nanowires of enamel that are prone to decay. Gordon et al. analyzed the composition of tooth enamel from a variety of rodents at the nanometer scale (see the Perspective by Politi). In regular and pigmented enamel, which contain different trace elements at varying boundary regions, two intergranular phases—magnesium amorphous calcium phosphate or a mixed-phase iron oxide—control the rates of enamel demineralization. This suggests that there may be alternative options to fluoridation for strengthening teeth against decay.

    Science, this issue p. 746; see also p. 712

  2. Superconductivity

    Light switch for superconductivity

    1. Jelena Stajic

    The conducting properties of materials sensitively depend on the available carrier concentration. Physicists can vary this concentration by inducing carriers in the material; for example, by placing it next to an ionic liquid in an electric field. Suda et al. instead used a layer of the molecule spiropyran, which changes from a non-ionic to an ionic form when it is irradiated by ultraviolet (UV) light. The authors placed the layer on top of a thin crystal of an organic material. When they shone UV light on the spiropyran, the adjacent material became superconducting, thanks to the carriers induced at the interface.

    Science, this issue p. 743

  3. Mammalian Evolution

    Taking advantage of new neighborhoods

    1. Sacha Vignieri

    Mammals are one of the most morphologically diverse organisms, with adaptation to unique ecological conditions creating a wide array of forms, from mice to whales. Two new basal mammals from the mid-Jurassic period suggest that this diversification was well under way millions of years earlier than previously thought. Luo et al. describe a burrowing species with limb and digit modifications similar to those of current burrowers and identify the likely genes and developmental pathways involved. Meng et al. describe an arboreal species with modifications for climbing and that possessed teeth clearly adapted for a herbivorous diet, including the consumption of sap.

    Science, this issue p. 760, p. 764

  4. Marine Pollution

    Dumping lots of plastics into our oceans

    1. H. Jesse Smith

    Considerable progress has been made in determining the amount and location of plastic debris in our seas, but how much plastic actually enters them in the first place is more uncertain. Jambeck et al. combine available data on solid waste with a model that uses population density and economic status to estimate the amount of land-based plastic waste entering the ocean. Unless waste management practices are improved, the flux of plastics to the oceans could increase by an order of magnitude within the next decade.

    Science, this issue p. 768

  5. Cancer

    A PET approach to imaging brain tumors

    1. Yevgeniya Nusinovich

    Cancers are readily visible with positron emission tomography, or PET, an imaging method in which a radioactively labeled tracer accumulates in the tumor. Labeled glucose is often used as a tracer because tumor cells tend to require large amounts of glucose. PET cannot be used to image brain tumors, however, because normal brain cells are also highly dependent on glucose. Now Venneti et al. show that radiolabeled glutamine, which is also taken up by tumor cells, yields clear images of brain tumors in mice and humans. With the glutamine label, cancer cells can be distinguished from normal brain cells and even from tumors that are no longer growing.

    Sci. Transl. Med. 7, 274ra17 (2015).

  6. Humoral Immunity

    For a single B cell, many roads to take

    1. Kristen L. Mueller

    To successfully fight a pathogen, immunological B cells must wage a multipronged attack: They can differentiate into antibody-secreting plasma cells or become T cell–helping germinal center cells, or even long-lived memory cells. But can a single B cell acquire all of these different fates? To find out, Taylor et al. tracked the responses of single B cells in mice. Although some B cells acquired only one fate, others differentiated into all three. The authors linked the ability of B cells to differentiate into multiple subsets to their ability to proliferate and resist cell death, and the affinity of their antigen receptor.

    Science, this issue p. 784

  7. Neural Circuits

    Taking a snapshot of active brain circuitry

    1. Peter Stern

    Active neuronal circuits revealed in zebrafish


    Neuroscientists now have a method to mark active populations of neurons in vivo to study circuit activity in the behaving animal. Fosque et al. designed and thoroughly validated a fluorescent protein–based reagent that allows permanent marking of active cells over short time scales. This indicator, termed CaMPARI, switches from its native green to a red fluorescent state by simultaneous illumination with violet light and exposure to increased levels of intracellular calcium. CaMPARI successfully marked active nerve cells in Drosophila, zebrafish, and mouse brains.

    Science, this issue p. 755

  8. Viral Replication

    A view of the HCV polymerase at work

    1. Paula A. Kiberstis

    More than 3% of the world's population is infected with hepatitis C virus (HCV), a predisposing factor for life-threatening liver diseases such as cirrhosis and cancer. HCV encodes a polymerase called NS5B that catalyzes replication of the viral RNA genome. Drugs inhibiting NS5B have shown impressive antiviral activity in recent clinical trials. Appleby et al. (see the Perspective by Bressanelli) reveal the inner workings of HCV RNA replication by analyzing crystal structures of stalled NS5B polymerase ternary complexes during the initiation and elongation of RNA synthesis. They also define the way in which sofosbuvir, a drug with potent clinical efficacy, interacts with the NS5B active site.

    Science, this issue p. 771; see also p. 715

  9. Sensory Perception

    How capsaicin channels pain relief

    1. Nancy R. Gough

    Ion channels are essential in sensing pain and pressure. The chemical in chilies that makes them hot is capsaicin, which activates the calcium-permeable channel TRPV1. Seemingly paradoxically, this chemical is also used as a topical analgesic. Borbiro et al. found that activation of TRPV1 by capsaicin inhibited the mechanosensitive Piezo channels by depleting specific phosphoinositides in the plasma membrane (see the Focus by Altier). These results may explain some of the analgesic effects of capsaicin.

    Sci. Signal. 8, ra15 and fs3 (2015).

  10. Environmental Science

    Changing tastes in marine microbe food webs

    1. Caroline Ash

    Protists are single-celled organisms complete with nuclei, organelles, and symbionts, and possess a multiplicity of physiological talents. They are ubiquitous, abundant, and often neglected by science. Worden et al. review the challenges of understanding the role protists play in geochemical cycling in the oceans. These organisms can photosynthesize like plants, graze on bacteria and archaea, parasitize each other and bigger creatures, have sex, and sometimes do all these things serially as conditions change. Their activities may have a significant influence on carbon cycling, and research efforts need to be amplified to understand their functional importance in marine ecosystems.

    Science, this issue 10.1126/science.1257594

  11. Sustainability

    Crossing the boundaries in global sustainability

    1. Andrew M. Sugden

    The planetary boundary (PB) concept, introduced in 2009, aimed to define the environmental limits within which humanity can safely operate. This approach has proved influential in global sustainability policy development. Steffen et al. provide an updated and extended analysis of the PB framework. Of the original nine proposed boundaries, they identify three (including climate change) that might push the Earth system into a new state if crossed and that also have a pervasive influence on the remaining boundaries. They also develop the PB framework so that it can be applied usefully in a regional context.

    Science, this issue 10.1126/science.1259855

  12. Organic Chemistry

    Optimizing a catalyst many ways at once

    1. Jake Yeston

    Optimization strategies are often likened to hikes in a hilly landscape. If your goal is to get to the top of the highest hill, and you only take steps toward higher ground, you might never find a peak on a route that requires a preliminary descent. So it is in chemistry, where optimizing each structural feature of a catalyst consecutively might gloss over subtle tradeoffs that in combination offer the best performance. Milo et al. use multidimensional analysis techniques to generate a predictive model of how selectivity depends on multiple characteristics of the catalyst and substrate in a C-N bond-forming reaction (see the Perspective by Lu). They then apply this model to improve the catalyst globally.

    Science, this issue p. 737; see also p. 719

  13. Atmospheric Chemistry

    Double trouble for Criegee intermediates

    1. Jake Yeston

    Atmospheric ozone reacts with unsaturated hydrocarbons to form unstable compounds called Criegee intermediates. Only recently did a reliable method emerge to make and study these compounds in the laboratory, and they didn't seem to react with water. Now, Chao et al. show that the simplest Criegee intermediate, CH2OO, does in fact react very rapidly with pairs of water molecules (see the Perspective by Okumura). Earlier studies may have missed this result because they were conducted at low pressure, where water dimers are scarce, or because they monitored downstream processes. The new rate measurements imply that reactivity with atmospheric water pairs is a major decay channel for Criegees.

    Science, this issue p. 751; see also p. 718

  14. Tight Junctions

    How a toxin makes epithelial sheets leaky

    1. Stella M. Hurtley

    The entire human body and its many compartments are shielded from their external environments by the barrier function of epithelial cell sheets. The paracellular barrier function of tight junctions (TJs) is critical for maintaining homeostasis in any multicellular organism, especially in the skin and internal organs and at the blood-brain barrier. One of the major components of TJs is a family of adhesive membrane proteins known as claudins. Several members of the claudin family are receptors for the bacterial toxin Clostridium perfringens enterotoxin. This toxin often causes food-borne illness both in humans and animals. Saitoh et al. crystallized a complex between the toxin and a claudin that reveals just how the toxin damages epithelial barriers (see the Perspective by Artursson and Knight).

    Science, this issue p. 775; see also p. 716

  15. Chemical Biology

    Toward drugging the undruggable in cancer

    1. Paula A. Kiberstis

    Many human cancers are characterized by inappropriate activity of transcription factors. These proteins are attractive drug targets in principle, but normalizing their function requires drugs that modulate specific protein-protein interactions, a goal that has been challenging. In acute myeloid leukemia, a chromosomal translocation creates an aberrant form of the transcription factor CBF-beta, which outcompetes “normal” CBF-beta for binding to another transcription factor called RUNX1, thereby deregulating its activity. Illendula et al. identified and chemically optimized a small molecule that selectively disrupts the interaction between the aberrant CBF-beta and RUNX1 (see the Perspective by Koehler and Chen). This molecule restored normal gene expression patterns and delayed leukemia progression in mice. Thus, transcription factors may not be as undruggable as once thought.

    Science, this issue p. 779; see also p. 713

  16. Centromeres

    The α-satellite arrays of human centromeres

    1. Ali Shilatifard

    Centromeres link sister chromatids and are central to chromosome segregation. Centromeres are found within the tandemly repetitive α-satellite DNA sequences. It has been difficult to define the molecular processes involved in the formation of centromeres. Henikoff et al. identified two sets of human α-satellite dimer sequences that are consistently associated with particular centromere-associated nucleosomes—the proteinaceous structures around which chromosomal DNA is wrapped. This finding may help to identify other tandem repeat arrays within the centromeres of other eukaryotes and should allow for a better molecular understanding of centromere evolution and function.

    Science Advances 10.1126/sciadv.00234 (2015).