This Week in Science

Science  01 Jul 2016:
Vol. 353, Issue 6294, pp. 39
  1. Carbon Cycle

    Fungi relieve nitrogen limitation

    1. H. Jesse Smith

    Mycorrhizal symbiosis as shown by a circle of fungi on the outskirts of a tree's roots.

    PHOTO: © BIOSPHOTO/ALAMY STOCK PHOTO

    Rising concentrations of atmospheric CO2 stimulate plant growth; an effect that could reduce the pace of anthropogenic climate change. But plants also need nitrogen for growth. So far, experimental nitrogen addition has had equivocal effects on the magnitude of CO2 fertilization. Terrer et al. explain that the impact of nitrogen on plant growth depends on the relationship between nitrogen availability and symbioses with mycorrhizal soil fungi. Only plants with ectomycorrhizal fungi associated with their roots can overcome nitrogen limitation.

    Science, this issue p. 72

  2. Chemical Biology

    Mapping ADP-ribosylation by PARPs

    1. Beverly A. Purnell

    During many cell processes, ADP-ribose is transferred from NAD+ onto protein substrates by poly(ADP-ribose) polymerases (PARPs). Gibson et al. developed a method to track ribose transfer events and mapped hundreds of sites of ADP-ribosylation for PARPs 1, 2, and 3 across the proteome and genome. One PARP-1 target is NELF, a protein complex that regulates pausing by RNA polymerase II. If NELF is ribosylated, pausing is released and productive transcription elongation resumes.

    Science, this issue p. 45

  3. Evolutionary Biology

    Scales, feathers, and hair have a lot in common

    1. Shahid Naeem

    Placodes (dark blue) indicate the development of crocodile scales.

    PHOTO: COPYRIGHT UNIGE 2016 (TZIKA, DI-POÏ, MILINKOVITCH)

    The skin appendages of reptiles, birds, and mammals are so extraordinarily different from one another that they have been hypothesized to have arisen independently, but this turns out not to be the case. Di-Poï and Milinkovitch examined scale development in crocodiles, lizards, and snakes and in a scaleless, mutant lizard. They found that scales, like feathers and hair follicles, develop from localized thickened regions in the embryo, called placodes, and all follow similar molecular developmental pathways.

    Sci. Adv. 2, 10.1126.sciadv.1600708 (2016).

  4. Solar Cells

    Better in a flash of perovskite

    1. Phil Szuromi

    Performance efficiencies of inorganic-organic perovskite solar cells exceeding 20% have been reported for areas typically of 0.1 cm2 or less. If larger areas of the same materials are tried, defects limit charge carrier transport, and efficiency drops. Li et al. induced rapid crystallization by vacuum-flash evaporation of solvents to obtain high-quality films and obtained efficiencies of ∼20% for illuminated areas exceeding 1 cm2 centimeter.

    Science, this issue p. 58

  5. Organic Chemistry

    Adding two fluorines to just one carbon

    1. Jake Yeston

    Fluorine has emerged as a versatile substituent in drug discovery research. Its incorporation into molecular frameworks modifies spatial and electronic properties, as well as solubility. Banik et al. added two fluorines selectively to a single carbon center in phenyl-substituted olefins. The reaction proceeds by a migratory mechanism whereby the fluorine additions shift the phenyl group to the adjacent carbon. This creates a chiral center, from which a simple chiral iodine catalyst can generate gram quantities of difluoromethylated building blocks.

    Science, this issue p. 51

  6. Martian Geology

    Unexpected forms of sand dunes on Mars

    1. Keith T. Smith

    On Earth, wind and water passing over sand result in the formation of large dunes or small ripples, collectively called bedforms. Lapotre et al. analyzed images of bedforms on Mars, taken from orbit and from the Curiosity rover on the surface. They found a third size of bedform on the planet—between ripples and dunes—which is caused by the differing atmospheric conditions. Because bedforms can be preserved in sedimentary rock, in principle their traces can be used to determine the past evolution of Mars' atmosphere.

    Science, this issue p. 55

  7. Transcription

    Spatial structure of RNA expression

    1. Laura M. Zahn

    RNA-seq and similar methods can record gene expression within and among cells. Current methods typically lose positional information and many require arduous single-cell isolation and sequencing. Ståhl et al. have developed a way of measuring the spatial distribution of transcripts by annealing fixed brain or cancer tissue samples directly to bar-coded reverse transcriptase primers, performing reverse transcription followed by sequencing and computational reconstruction, and they can do so for multiple genes.

    Science, this issue p. 78

  8. Bird Flight

    Cloud-gliding frigate birds

    1. Sacha Vignieri

    Frigate birds are among the highest fliers in the avian world. Wiermirskirch et al. show that great frigate birds stay aloft for months at a time, using a variety of strategies that take advantage of atmospheric conditions (see the Perspective by Huey and Deutsch). Locally, they exploit uplift and favorable winds, but for long-distance transoceanic travel, frigate birds fly up to 4000 m to exploit low-pressure conditions within clouds for gliding. Understanding the strategies of these impressive voyagers increases our understanding of long-distance migration and our appreciation for the extremes that flight adaptations can reach.

    Science, this issue p. 74 see also p. 26

  9. Cancer Immunology

    Building the route to metastasis

    1. Leslie K. Ferrarelli

    Dying tumor cells release the phospholipid S1P, which stimulates proinflammatory responses in tumor-associated macrophages, including secretion of the protein lipocalin-2. Jung et al. discovered that in the context of breast cancer, this pathway causes lymphatic endothelial cells to release a factor that promotes the formation of new lymphatic vessels. The problem is that breast cancer cells can metastasize via lymphatic vessels. If the S1P-lipocalin-2 pathway is inhibited in mice, then metastasis is suppressed. Likewise, infection can trigger the release of S1P and thus could also enhance metastasis (see the Focus by Rodvold and Zanetti).

    Sci. Signal. 9, ra64 and fs13 (2016).

  10. Anthropology

    Evolutionary lessons from hominin teeth

    1. Julia Fahrenkamp-Uppenbrink

    Evolution may take the path of least resistance to arrive at a solution that is not optimal but can be reached more quickly. In a Perspective, Ungar and Hlusko compare the teeth of hominins that lived over a million years ago with those of gorillas. Despite a similar diet of tough plant foods, the hominins have flat teeth with thick enamel, rather than the crested teeth that gorillas have and that are better for chewing these foods. The authors argue that the enamel cap can expand without causing other phenotypic changes that could affect the fitness of the individual; in contrast, changes in tooth cusp patterning are genetically complex and take much longer to evolve.

    Science, this issue p. 29

  11. Proteostasis

    Making and maintaining a healthy proteome

    1. Stella M. Hurtley

    The cytoplasm is crowded with proteins that must be made and then maintained to keep the cell healthy. Balchin et al. review how proteins are folded and kept folded correctly within cells. A network of molecular chaperones monitors folding and assembly, but the capacity of our cells to keep the proteome healthy declines with age. Such a loss of capacity might be a common mechanism in neurodegeneration and certain chronic diseases.

    Science, this issue p. 42

  12. Retinal Repair

    MANF enough for tissue repair

    1. Stella M. Hurtley

    Stem cell-based regenerative therapies are being developed to treat several disease conditions. A common complication is poor engraftment of such replacement cells because of the hostile microenvironments created by many degenerative and inflammatory diseases. Neves et al. found that mesencephalic astrocyte-derived neurotrophic factor (MANF) modulates immune cells and has an effect on damaged retinal photoreceptors in fruit flies and mice (see the Perspective by Cameron and Goldberg). In mice, MANF also improved photoreceptor integration after transplantation to treat retinal degeneration and helped to restore vision.

    Science, this issue p. 43; see also p. 30

  13. Ultrafast Dynamics

    Clocking electrons as they exit a metal

    1. Jake Yeston

    Einstein earned his Nobel Prize for a quantum-mechanical explanation of electron ejection from metals by light. More than a century later, attosecond spectroscopy has let researchers explore that process in real time. Tao et al. used attosecond pulse trains to distinguish the dynamics of electrons excited from a nickel surface into discrete states versus free space (see the Perspective by Bovensiepen and Liggues). They succeeded in resolving a time delay of ∼200 as that was associated with excitation into unoccupied band states.

    Science, this issue p. 62; see also p. 28

  14. Centrosomes

    Kicking out an unwanted centrosome

    1. Stella M. Hurtley

    Centrosomes are composed of a pair of centrioles, are the key microtubule-organizing center in animal cells, and are inherited solely from sperm. Pimenta-Marques et al. investigated the mechanism of centriole elimination during egg formation, or oogenesis, in the fruit fly. Loss or experimental knockdown of an enzyme called Polo kinase coincided with centriole loss. If Polo kinase was experimentally “tethered” to the centrioles during oogenesis, centriole elimination was prevented, which led to abnormal meiosis, embryonic defects, and female sterility.

    Science, this issue p. 44

  15. Malaria Mosquitoes

    Female-fatal product of the Yob gene

    1. Caroline Ash

    Mechanisms of sex determination are highly variable and complex in invertebrates. For vector-borne disease control strategies, it is important to understand the reproductive biology of the organisms involved. Krzywinska et al. have studied sex determination in species of Anopheles mosquitoes, whose females suck blood and can transmit malaria parasites (see the Perspective by Sinkins). One gene called Yob is found only on the Y chromosome of males. Yob is expressed in male embryos within 2 hours of eggs being laid, and transcription continues lifelong. If Yob is injected into embryos younger than 2 hours, only male mosquitoes emerge, because Yob's presence is lethal to female embryos.

    Science, this issue p. 67; see also p. 33

  16. Climate Change

    Changing sex ratios

    1. Sacha Vignieri

    Climate-warming temperatures might be expected to affect the sex ratio of species if sex determination is temperature-dependent. Petry et al. show that indirect climate effects could also alter sex ratios in species in which sex is genetically determined and damage reproductive fitness (see the Perspective by Etterson and Mazer). Over four decades, sex ratios in populations of a dioecious alpine plant have shifted toward females as a result of the different water needs of the male and female plants. The lack of males has reduced the reproductive success and fitness of the females. Similar subtle differences between sexes in environmental sensitivities could eventually lead to population declines.

    Science, this issue p. 69; see also p. 32

  17. Structural Biology

    Stargazin and the AMPA receptor

    1. Stella M. Hurtley

    AMPA-subtype ionotropic glutamate receptors (AMPARs) mediate fast excitatory neurotransmission and contribute to higher cognitive processes such as learning and memory. In the brain, AMPARs exist as protein-protein complexes with various auxiliary subunits that tightly control AMPAR trafficking, gating, and pharmacology. Disruption of these complexes is implicated in numerous psychiatric and neurodegenerative diseases. Twomey et al. used cryo-electron microscopy to solve the structure of an AMPAR complex with stargazin (STZ), the major representative of transmembrane AMPAR regulatory proteins. STZ controls AMPAR synaptic targeting, synaptic plasticity, compartment-specific activity, pharmacology, and gating.

    Science, this issue p. 83

  18. Cancer

    A new type of cancer cluster

    1. Megan Frisk

    Setting out to isolate circulating tumor cells (CTCs) in the blood of cancer patients, Cima et al. instead noticed that clusters, rather than single cells, abounded. But these clusters were not like CTCs: The cells did not express the epithelial cell marker EpCAM and they did not have the same mutations as the primary tumor. Instead, the clusters matched the genotype and phenotype of endothelial cells and were shed from tumors in mice and in humans as intact clusters, rather than forming by coagulation. In patients, the presence of endothelial cell clusters correlated with early-stage disease and might be a unique indicator of cancer before treatment starts.

    Sci. Transl. Med. 8, 345ra89 (2016).

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