This Week in Science

Science  15 Sep 2017:
Vol. 357, Issue 6356, pp. 1108
  1. Plant Science

    Managing gene silencing through replication

    1. Pamela J. Hines

    Winter chilling promotes flowering epigenetically.

    PHOTO: BKSRUS/ISTOCK PHOTO

    Vernalization is the process in plants by which wintertime chill stimulates springtime flowering. Yang et al. and Jiang and Berger show how chill is recorded in Arabidopsis epigenetically by methylation of histones. Specialized components of the Polycomb group of proteins remodel DNA to establish the methylation marks and are linked to DNA replication. Long-term stable epigenetic status follows rapid establishment of metastable epigenetic marks. This epigenetic strategy may be key to the developmental requirement of both secure and nimble fate decisions, allowing plant cells to change fates.

    Science, this issue p. 1142 and p. 1146

  2. Cancer

    Debugging a cancer therapy

    1. Paula A. Kiberstis

    Microbes contribute not only to the development of human diseases but also to the response of diseases to treatment. Geller et al. show that certain bacteria express enzymes capable of metabolizing the cancer chemotherapeutic drug gemcitabine into an inactive form. When bacteria were introduced into tumors growing in mice, the tumors became resistant to gemcitabine, an effect that was reversed by antibiotic treatment. Interestingly, a high percentage of human pancreatic ductal adenocarcinomas, a tumor type commonly treated with gemcitabine, contain the culprit bacteria. These correlative results raise the tantalizing possibility that the efficacy of an existing therapy for this lethal cancer might be improved by cotreatment with antibiotics.

    Science, this issue p. 1156

  3. Solid-State Cooling

    A solid way to keep cool

    1. Brent Grocholski

    Refrigeration relies on vapor compression that is noisy, takes up space, and is mechanically complex. Solid-state cooling requires changing an external field to drive cooling, but devices produced so far have not been efficient enough for practical applications. Ma et al. constructed a lightweight and flexible device using a thin electrocaloric polymer film, where toggling it in an electric field between a heat source and sink drives the cooling process (see the Perspective by Zhang and Zhang). The device rapidly cools down an overheated smartphone battery and has potential application for developing compact, low-profile electronics.

    Science, this issue p. 1130; see also p. 1094

  4. Biological Materials

    More than just a cotton shirt

    1. Marc S. Lavine

    Cotton can be engineered for functional fabrics.

    PHOTO: FILIPE NATALIO

    Responsive or functional fabrics include coatings or secondary materials with properties such as changing color with temperature or generating electricity with movement. The challenge is that anything added to a fabric can get washed or worn away. Hence, Natalio et al. opted to build the functionality directly into cotton grown in vitro, through the addition of glucose modified at the C2 position to the culture medium. By this process, fibers can be made that naturally fluoresce or have magnetic properties, for instance.

    Science, this issue p. 1118

  5. Neuroscience

    Thirst-quenching neural mechanisms

    1. Peter Stern

    To maintain homeostasis, physiological imbalances produce motivational drives. Thirst is one of the strongest drives. Allen et al. identified a distinct population of neurons in a brain region called the median preoptic nucleus that are activated during thirst (see the Perspective by Gizowski and Bourque). The activity of these neurons integrates the recent history of water intake and adaptively regulates goal-directed behavior. When thirsty, animals consume water, which in turn reduces the aversive activity of the neurons. This action is repeated until the level of aversion falls below the threshold necessary to evoke this behavior.

    Science, this issue p. 1149; see also p. 1092

  6. Human Genetics

    Genetic history of Papua New Guinea peoples

    1. Laura M. Zahn

    Papua New Guinea was likely a stepping stone for human migration from Asia to Australia. Bergström et al. analyzed genome-wide autosomal data from several peoples in Papua New Guinea and determined population structure, divergence, and temporal size changes on the island. A sharp genetic divide is evident between the highlands and lowlands that appears to have occurred 10,000 to 20,000 years ago, concurrent with the spread of crop cultivation and the trans-New Guinea language family.

    Science, this issue p. 1160

  7. Space Sciences

    Surface water on the Moon

    1. Kip Hodges

    Recent research has fueled debate regarding the abundance of water in the Moon's interior and its implications for lunar evolution, but surface water is known to occur in the lunar regolith. Using data from NASA's Moon Mineralogy Mapper—an imaging spectrometer that was included on India's first mission to the Moon, Chandrayaan-1—Li and Milliken present a globally comprehensive map of these deposits. The upper meter of the lunar regolith is estimated to contain roughly 0.1 petagrams of water. Higher latitudes have more water ice than lower latitudes. Most of the ice was implanted by solar wind, with some local input from the lunar interior.

    Sci. Adv. 10.1126/sciadv.1701471 (2017).

  8. Cancer

    Unintentional immunotherapy inhibition

    1. Lindsey Pujanandez

    Metastatic spread depends on lymphangiogenesis, and mediators of this pathway are targeted clinically for cancer treatment. Fankhauser et al. used mouse models of melanoma to show that blocking lymphangiogenesis disrupted recruitment of naïve T cells and subsequent antitumor immunity. Data from patients enrolled in clinical trials confirmed that indicators of lymphangiogenesis were associated with robust T cell responses. These findings have important implications for using and predicting responses to immunotherapy.

    Sci. Transl. Med. 9, eaal4712 (2017).

  9. Attosecond Physics

    A quick glimpse of the x-ray aftermath

    1. Jake Yeston

    X-rays pass through your skin to reveal the inner workings below. At the atomic scale, x-rays skip past valence electrons to grab hold of the core electrons closer to the nucleus. Moulet et al. used two successive, extremely short laser pulses (lasting less than a quadrillionth of a second) to initiate and then track this process in a sample of silica. This study uncovered the angular momentum character and relaxation dynamics of the excitons, or electron-hole pairs, ensuing from the x-ray absorption.

    Science, this issue p. 1134

  10. Environment

    Global transport of microbes

    1. Julia Fahrenkamp-Uppenbrink

    Through dissemination in wastewater, travel by humans and animals, and transport of goods, microbial species can be spread at an unprecedented scale. In a Perspective, Zhu et al. argue that human activities are having similar effects on microbial species as on animal and plant species—for example, causing extinctions of endemic organisms and homogenization around the globe. As a result, antibiotic resistance genes are spreading rapidly, and biogeochemical processes are being affected at a landscape scale in currently unpredictable ways.

    Science, this issue p. 1099

  11. Optogenetics

    From biophysics to neuroscience tools

    1. Peter Stern

    The channelrhodopsins and their distinctive light-activated ion channels have emerged as major tools in modern biological research. Deisseroth and Hegemann review the structural and functional properties of these protein photoreceptors. Mutagenesis and modeling studies, coupled with the reintroduction of modified channels into living systems, offer a profound understanding of how these channels work. The insights into the underlying basic science provide foundations for developing further applications in biology and medicine.

    Science, this issue p. eaan5544

  12. Nanotechnology

    Sorting molecules with DNA robots

    1. Phil Szuromi

    Single-stranded DNA robots can move over the surface of a DNA origami sheet and sort molecular cargoes. Thubagere et al. developed a simple algorithm for recognizing two types of molecular cargoes and their drop-off destinations on the surface (see the Perspective by Reif). The DNA robot, which has three modular functional domains, repeatedly picks up the two types of molecules and then places them at their target destinations. No additional power is required because the DNA robot does this by random walking across the origami surface.

    Science, this issue p. eaan6558; see also p. 1095

  13. Materials Science

    Getting a hold with DNA

    1. Marc S. Lavine

    Stimuli-responsive materials can respond to physical or chemical cues to trigger changes in color, shape, or other properties. Cangialosi et al. used photolithography to define multilayer planar soft machines from polyacrylamide coupled to single strands of DNA. When presented with the complementary strands, the machines can change shape in complicated and programmable ways, including stepwise or sequential shape changes.

    Science, this issue p. 1126

  14. CRISPR Biology

    Host factor drives the big bend

    1. Steve Mao

    Bacteria have a highly adaptable DNA-detecting and -editing machine called CRISPR-Cas to ward off virus attack. The Cas1-Cas2 integrase, with the help of an accessory protein called IHF (integration host factor), captures foreign DNA motifs into bacterial CRISPR loci. These motifs then act as sensors of any further invaders. By analyzing the integrase complex structure, Wright et al. show how Cas1-Cas2 recognizes the CRISPR array for site-specific integration (see the Perspective by Globus and Qimron). IHF sharply bends DNA, which allows DNA to access two active sites within the integrase complex to ensure sequence specificity for the integration reaction. The features of the CRISPR integrase complex may explain the natural divergence of CRISPR arrays in bacteria and can be exploited for genome-tagging applications.

    Science, this issue p. 1113; see also p. 1096

  15. Neutrino Physics

    Nailing down an elusive process

    1. Jelena Stajic

    Detecting neutrinos—elementary particles that barely interact with other matter—usually requires detectors of enormous size. A particular interaction of neutrinos with atomic nuclei, called the coherent elastic neutrino-nucleus scattering (CEνNS), is predicted to occur with relatively high probability, and it could be used to drastically reduce the size of neutrino detectors. However, observing this interaction requires a source of low-energy neutrinos and detectors that contain nuclei of optimal mass. Akimov et al. observed CEνNS with a 6.7σ confidence by using a comparatively tiny, 14.6-kg sodium-doped CsI scintillator exposed to neutrinos from a spallation neutron facility (see the Perspective by Link). The discovery places tighter bounds on exotic, beyond-the-standard-model interactions involving neutrinos.

    Science, this issue p. 1123; see also p. 1098

  16. Materials Science

    Putting the pieces together

    1. Marc S. Lavine

    One route to improving the delivery of existing drugs is by encapsulation inside a protective but slowly degrading shell. Such slow-release capsules improve drug availability in vivo, reduce side effects, and allow for more constant dose delivery. McHugh et al. leverage a number of existing fabrication techniques to make tiny (∼400-µm), hollow injectable microparticles that can be filled with fluid containing the therapeutic agent. By adjusting the degradation rate of the microparticle material (in this case, a lactic/glycolic copolymer), the cargo in the internal reservoir can be released at a desired time, ranging from a few days to 2 months.

    Science, this issue p. 1138

  17. Immune Regulation

    Regulating the germinal center

    1. Angela Colmone

    Unregulated production of antibodies may contribute to the development of autoimmunity. In humans and mice, follicular regulatory T (Tfr) cells are thought to limit the germinal center reaction and reduce antibody production within B cell follicles. Yet how Tfr cells control the germinal center reaction is unclear. Ritvo et al. show that Tfr cells are a rare population of CD4+CXCR5+PD1+Foxp3+ cells that do not express CD25 and do not respond to interleukin-2. When compared to follicular helper T (Tfh) cells and regulatory T cells, Tfr cells clustered with the former. Moreover, Tfr cells expressed decoy molecules for the interleukin-1 signaling pathway, pointing to a mechanism for suppression of Tfh cells.

    Sci. Immunol. 2, eaan0368 (2017).

  18. Immunology

    Legitimizing a chemoattractant receptor

    1. John F. Foley

    The orphan receptor GPR15 mediates the trafficking of lymphocytes to the colon and skin and the recruitment of effector T cells to inflamed intestinal tissue. Using porcine colonic extracts, Suply et al. purified a ligand (GPR15L) that activated GPR15 but not other chemoattractant receptors. In mice, GPR15L recruited T cells to skin grafts, and loss of the ligand was associated with decreased graft rejection. Because GPR15L mRNA is abundant in psoriatic lesions, these results suggest that the GPR15-GPR15L axis could be targeted to treat inflammatory skin conditions.

    Sci. Signal. 10, eaal0180 (2017).