Editors' Choice

Editors' Choice

Science  18 Nov 2016:
Vol. 354, Issue 6314, pp. 844
  1. Galaxies

    How many galaxies are in the universe?

    1. Keith T. Smith

    Hubble eXtreme Deep Field view of distant galaxies


    Counting the number of galaxies is a complicated problem because astronomical surveys are biased and incomplete: It is easier to detect a bright nearby galaxy than a faint distant one. Small galaxies are the most numerous, but a boundary must be drawn between them and large star clusters. Distant galaxies are seen as they were earlier in their lifetime, and galaxy numbers can fall through merging. Taking into account these effects and more, Conselice et al. combined and extrapolated results from numerous surveys to determine that there are 2.0 ± 0.6 trillion galaxies in the observable universe. The vast majority still await discovery.

    Astrophys. J. 830, 83 (2016).

  2. Urban Ecology

    C4 plants in the heat of the city

    1. Andrew M. Sugden

    Cities tend to have a warmer microclimate than their surroundings—the so-called “urban heat island” effect. The elevated temperature, along with other aspects of the urban environment, can have a marked influence on the organisms that live in cities. Duffy and Chown find that plants with C4 photosynthetic metabolism, a trait that is favored in warmer herbaceous communities, are more common in European cities than in adjacent nonurban habitats. They predict that under further climatic warming, C4 species may become generally more widespread in temperate habitats, compared with C3 species that are adapted to cooler conditions.

    Higher temperatures in cities select for C4 plants.


    J. Ecol. 104, 1618 (2016).

  3. Metabolism

    Small RNA regulates glucose homeostasis

    1. Beverly A. Purnell

    Noncoding RNAs, such as microRNAs, regulate gene expression through RNA silencing and posttranscriptional gene regulation. Lin et al. show that miR-155 is important for glucose homeostasis and insulin sensitivity. When miR-155 is overexpressed in mice, they become hypoglycemic, whereas if miR-155 is deleted, the result is hyperglycemia and insulin resistance. miR-155 does not seem to alter pancreas morphology or β-cell function; instead, it appears to act on negative regulators of insulin signaling, such as C/EPBb, HDAC4, and SOCS1. Patients with type 2 diabetes show reduced miR-155, suggesting that it may also be involved in human insulin signaling. The discovery of this microRNA function opens a window of opportunity for the treatment of diabetes through glycemic control.

    PLOS Genet. 10.1371/journal.pgen.1006308 (2016).

  4. Tissue Repair

    Getting one's joint out of nose

    1. Paula A. Kiberstis

    Articular cartilage lubricates joints and is essential for pain-free movement. Unlike other tissues, injured cartilage does not repair on its own. One common treatment involves harvesting cartilage-secreting cells called chondrocytes from the injured joint, expanding the cells in culture for a few weeks, and then implanting them back into the joint. Animal studies suggest that chondrocytes from a different tissue source, the nose, are better at regenerating articular cartilage. Mumme et al. tested this less invasive procedure in a pilot study of 10 patients with knee injuries. In all cases, they successfully produced cartilage tissue ex vivo by using chondrocytes taken from the nasal septum. All patients reported an improvement in clinical scores for pain, knee function, and quality of life.

    Lancet 388, 1985 (2016).

  5. Paleoanthropology

    Farmer-foragers went west

    1. Caroline Ash

    Humans began to settle and combine farming with foraging about 12,000 years ago. Over the next 2000 to 3000 years, they moved west from the Fertile Crescent into Anatolia, although it seems, from the distribution of obsidian flints, that the eastern and western populations kept in contact. Kılınç et al. obtained genome sequence data from nine Neolithic individuals from two ancient village sites in Anatolia. The settlers from the older site were distinct from their European forager counterparts but, like them, showed little genetic diversity, indicating a small population. The later farmer-settlers, who had acquired pottery-making skills, were genetically more diverse. These data point to an additional wave of migration from the Fertile Crescent or the Levant that brought new genes and promoted further westward expansion before the mobile hunter-gatherers of the northern steppes added their genes to the European mix.

    Curr. Biol. 26, 2659 (2016).

  6. Catalysis

    Longer lifetimes for a metal oxide

    1. Phil Szuromi

    Although heterogeneous molybdenum catalysts can convert cyclohexene to its epoxide with high conversion and selectivity, the catalysts deactivate quickly because the Mo species leach into solution. Noh et al. show that a more stable catalyst can be made by depositing Mo via a metallorganic complex onto the zirconium oxide nodes within the metal organic framework (MOF) NU-1000. After exposure to air to form the Mo oxide species, this catalyst showed activity comparable to that of epoxidation of Mo supported on ZrO2. However, the ZrO2 support lost 80% of its Mo after reaction, whereas no loss of Mo occurred for the MOF catalyst. Density functional theory calculations indicate that the loss of Mo(VI) from the MOF Zr node is energetically unfavorable.

    Fragment of a clay pot discovered at Tepecik Çiftlik, Turkey


    J. Am. Chem. Soc. 10.1021/jacs.6b08898 (2016).

  7. Antibiotic Resistance

    No silver bullet for wastewater treatment

    1. Julia Fahrenkamp-Uppenbrink

    The spread of antibiotic resistance is a major public health concern. Czekalski et al. investigate whether ozonation of wastewater can help to combat this spread by eliminating resistant bacteria. In laboratory experiments, ozone doses that can be used in full-scale applications disrupted intracellular resistance genes. However, ozonation of secondary effluent at a wastewater treatment plant did not affect the abundance of intracellular resistance genes, and multiresistant bacteria partly regrew after ozonation. The results have important implications for wastewater treatment plants that are planning to implement ozonation.

    Environ. Sci. Technol. 10.1021/acs.est.6b02640 (2016).