Editors' Choice

Science  29 May 2015:
Vol. 348, Issue 6238, pp. 986
  1. Neurodevelopment

    Coordinating neurons with blood vessels

    1. Pamela J. Hines

    Neurons and blood vessels in the retina

    PHOTO: THOMAS DEERINCK/NCMIR/SCIENCE SOURCE

    The retina develops as interleaved layers of neurons and blood vessels. Usui et al. show that in mice, the development of blood vessel layers depends on signals from amacrine cells, a type of interneuron in the retina. Too much or too little signal resulted in too many or too few blood vessels, particularly affecting the intermediate vascular plexus (a network of blood vessels) embedded within the retina. This cellular crosstalk coordinates neuronal demand for oxygen with the blood's ability to supply it. With the intermediate vascular plexus poorly formed, photoreceptors (a type of neuron) degenerate, leading to deficits in vision.

    J. Clin. Invest. 10.1172/JCI80297 (2015).

  2. Physics

    Cooling a semiconductor with polaritons

    1. Jelena Stajic

    Shining light onto a solid to cool it may seem counterintuitive, because the light will temporarily increase the solid's energy. To go back to its low-energy state, the solid may then emit photons more energetic than the ones it absorbed initially, effectively lowering its temperature. Such cooling methods are well established, but place stringent requirements on the material being cooled. Klembt et al. show that exciton-polaritons, exotic part-photon, part-exciton quasi-particles, can be used to cool a semiconductor microcavity. The cooling mechanism depends on the ability of the polaritons to absorb the energy of lattice vibrations and shortly thereafter to leave the solid as light. At low enough laser power, this process overpowers a competing heating process in which two photons are absorbed simultaneously.

    Phys. Rev. Lett. 114, 186403 (2015).

  3. Microbiology

    A new role for nitrogen fixers

    1. Caroline Ash

    North American coniferous forests harbor large amounts of the bacteria called bradyrhizobia. This genus made its name as obligatory symbionts of legumes, able to snatch atmospheric nitrogen via the nif gene product and supply it as nitrate to the plant and to fertilize soils. In return, the bacterium's nod genes allow it to live within the safety of the plants' roots. But legumes are rare in coniferous forests. Nevertheless, VanInsberghe et al. discovered that diverse bradyrhizobia, all lacking nif and nod genes, occur abundantly in these forests' soils. They are not symbionts, but they have other metabolic talents, depending on their environment. The symbionts are instead the minority in the genus.

    ISME J. 10.1038/ismej.2015.54 (2015).

  4. Drug Trial Economics

    Surrogates stimulate cancer investments

    1. Brad Wible

    Allowing the use of surrogate (nonmortality) endpoints in clinical trials could lead drug companies to invest more in treatments for early-stage cancers and prevention. Long lags occur from when a drug patent is filed until it can be commercialized, a result of lengthy clinical trials that often have to demonstrate impacts on survival. Long lags leave less time for companies to recoup investments before patent expiration, skewing investment toward late-stage cancers for which shorter survival times lead to faster trials. Budish et al. compiled drug and trial data back to 1973 and show that the use of surrogate endpoints increased private drug research investments for cancers that otherwise would have long commercialization lags and diminished investment.

    Am. Econ. Rev. 10.1257/aer:20131176 (2015); final accepted version at http://economics.mit.edu/files/10363.

  5. Genome Editing

    Toward better control of genome editing

    1. Valda Vinson

    Thanks to the CRISPR-Cas system, scientists can now modify nearly any location in the genome. A stumbling block to therapeutic use, however, is that Cas9 (an endonuclease) cleaves DNA at areas of interest but often also at off-target sites. Scientists hope to overcome this by engineering versions of Cas9 with higher specificity for the target DNA. Zetsche et al. and Davis et al. explored regulating the activity of Cas9 through two different approaches, both of which relied on pharmacological activation of the enzyme. By restricting the amount of active Cas9, both strategies achieved increases in specificity. These and other specificity-enhancing approaches may give scientists the ability to better control genome modification.

    Nat. Biotechnol. 33, 139 (2015); Nat. Chem. Biol. 11, 316 (2015).

  6. Microbiology

    Cooperation causes van Gogh to appear

    1. Stella M. Hurtley

    Cell-cell interactions underlie many fundamental aspects of biology, even when those cells are normally considered autonomous, such as bacteria. Van Gestel et al. studied how Bacillus subtilis cooperate to allow a colony to move en bloc across a surface. The cells bundled themselves into so-called van Gogh bundles consisting of regimented rows of cells that generate looping strands at the outer edge of the colony. These loops then push themselves away, allowing the bacteria to move to pastures new. Two distinct types of cell are needed to form the bundles, one to form a sort of intercellular glue and the other to form a slippery track.

    B. subtilis divides the labor between two cell types (in red and green) to move across a solid surface

    CREDIT: J. VAN GESTEL ET AL., PLOS BIOL. (20 APRIL 2015)

    PLOS Biol. 10.1371/journal. pbio.1002141 (2015).

  7. Global Precipitation

    Where the hard rain is and will be falling

    1. H. Jesse Smith

    3D map of rainfall in Typhoon Phanfone

    CREDIT: NASA SVS

    Extreme precipitation events are rare, but they are very important in the global hydrological cycle. Accordingly, it is important to be able to characterize their distribution, frequencies, and magnitudes. Liu and Zipser report observations recovered over a full year by instruments on the Global Precipitation Mission Core Observatory satellite, which provide diurnal three-dimensional coverage of the entire subpolar world and categorize precipitation events by their area, depth, and convective intensity. These types of events are important to include in global climate models, in order for them to accurately describe the global water cycle.

    Geophys. Res. Lett. 10.1002/2015GL063776 (2015).

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