Editors' Choice

Science  19 Jul 2013:
Vol. 341, Issue 6143, pp. 216
  1. Astronomy

    Merger Relics

    1. Maria Cruz

    Massive galaxies are thought to form through a succession of mergers between smaller galaxies. These interactions are expected to be more frequent in regions where there are fewer galaxies; in high-density regions, galaxies move faster and mergers are less likely. However, a recent study has revealed that 38% of massive galaxies in heavy clusters of galaxies show features that are consistent with the merging of galaxies (such as tidal tails). To try to explain this unexpected result, Yi et al. ran a cosmological-volume simulation to derive the merger history of dark-matter halos, then constructed semi-analytical models of galaxies to populate those halos, and finally performed hydrodynamical simulations of galaxy-galaxy mergers to estimate the lifetime of merger features. Merger features are expected to last very long in clusters of galaxies. Thus, when observed there, they may not be the result of recent in situ mergers but relics from interactions that happened when the galaxies were in a different environment.

    Astron. Astrophys. 554, A122 (2013).

  2. Signal Transduction

    Minute Regulation

    1. L. Bryan Ray

    A more thorough understanding of cellular signaling mechanisms depends on resolving the spatial and temporal characteristics of such signals in vivo. During the third hour of development of the fruit fly embryo, formation of the membranes that partition the syncytium into individual cells occurs with such regularity that it can be used as a marker of developmental age of the embryo with an accuracy of about 1 min. Lim et al. analyzed the kinetics of the effects of the mitogen-activated protein kinase ERK on transcription in dozens of stained and fixed embryos oriented on microfluidics chips. Activated ERK was known to reduce the nuclear localization of the transcriptional repressor protein Cic, thus increasing Cic's degradation. However, these more refined measurements showed that ERK has a faster regulatory effect on Cic, indicating that Cic degradation may be a consequence of an earlier signal.

    Proc. Natl. Acad. Sci. U.S.A. 110, 10330 (2013).

  3. Cancer

    Tumor Epigenetics

    1. Paula A. Kiberstis

    That human tumors display both genetic mutations and epigenetic alterations—for example, in DNA methylation—has been known for many years; with the completion of cancer genome sequencing projects, possible causal links between the two have come into sharper focus. The discovery of recurrent tumor-associated mutations in genes that encode chromatin-modifying enzymes or DNA methyltransferases represents a clear link between tumor genotype and “epigenotype.” Emerging evidence suggests that a link can be subtle, as illustrated by two studies describing consistent epigenetic alterations in tumors with mutations in the gene encoding the metabolic enzyme succinate dehydrogenase (SDH). Killian et al. find that gastrointestinal stromal tumors harboring SDH mutations are characterized by dramatic and widespread DNA hypermethylation, whereas Letouzé et al. report that SDH-mutant paragangliomas display DNA hypermethylation that is associated with the silencing of genes involved in neuroendocrine cell differentiation. Both groups hypothesize that the hypermethylation phenotype is due to the aberrant accumulation of an oncometabolite that inhibits DNA-demethylating enzymes, with succinate being a strong candidate.

    Cancer Discov. 3, 648 (2013); Cancer Cell 23, 739 (2013).

  4. Epidemiology

    Communicable Disease

    1. Barbara R. Jasny

    In the United States, states have the authority to grant exemptions so that children can begin to attend school without having been vaccinated against childhood diseases. Medical exemptions can be granted when a child has a history of allergic reactions or is immunocompromised. However, there has been a noticeable increase in the numbers of unvaccinated children resulting from nonmedical exemptions, based on religious or philosophical grounds; in 2011–2012, roughly 80% of all exemptions were nonmedical. Blank et al. have gathered information from public health officials, health departments, the Centers for Disease Control and Prevention, the National Conference of State Legislatures, and state legislature databases. Policies were characterized as easy, medium, or difficult, according to the level of effort they would pose for parents requesting exemptions. The lower the barrier, the more nonmedical exemptions were observed, with a twofold difference between the easiest and most difficult procedures. For 2011–2012, at least 21 bills were introduced at the state level to change the exemption procedures, and exemptions would have been made easier if bills in 10 states had passed. As of February 2013, three bills have been introduced in two states to tighten exemptions, and five bills have been introduced in four states to loosen them. The authors advocate social and policy efforts to promote parental education and to stem the spread of vaccine-preventable diseases.

    Health Affairs 32, 1282 (2013).

  5. Ocean Science

    Heating the Deep Ocean

    1. Julia Fahrenkamp-Uppenbrink

    As greenhouse gas concentrations in the atmosphere increase, the resulting heat warms not only the atmosphere but also the oceans. However, temperature increases at the sea surface and in the upper ∼700 m of the oceans stalled in the 2000s. Recent modeling and observational studies have suggested that the deep ocean has taken up the heat, particularly at depths between 700 and 2000 m. However, regular, spatially homogenous ocean temperature data are only available since 2003 from the Argo ocean observing system, complicating comparison with earlier data sets. Balmaseda et al. used a new observation-based reanalysis of the ocean to investigate how the heat content has changed over the period from 1958 to 2009. They provide evidence for an overall warming trend, punctuated by cooling episodes that can be attributed to volcanic eruptions. The massive 1997–1998 El Niño event also had a noticeable cooling impact. In the past decade, the deep ocean has continued to warm, whereas temperatures in the upper 300 m have stabilized; the ocean as a whole has continued to warm at an increasing rate. The qualitative warming patterns persisted when Argo data were removed. The authors attribute the changing heat distribution to changes in surface winds, particularly an intensification of the trade winds in subtropical gyres.

    Geophys. Res. Lett. 40, 1754 (2013).

  6. Geochemistry

    Oxidation Before Oxygen

    1. Nicholas S. Wigginton

    The emergence of oxygen-producing photosynthesis had a profound effect on Earth's surface environment. It eventually oxidized the oceans and atmosphere, paving the way for aerobic life. Determining the timing of photosynthesis and the subsequent transformation of biogeochemical cycles relies on analyzing clues in ancient buried sediments. Johnson et al. analyzed the mineralogy and isotopic signatures of carbon and sulfur in 2.4-billion-year-old drill cores from South Africa. Synchrotron-based x-ray absorption spectroscopy revealed that abundant Mn oxides were hosted in carbonate deposits, which were probably formed via oxidation of soluble Mn(II). Several lines of geochemical evidence based on redox-sensitive proxies, however, preclude oxygen as the primary oxidant acting on Mn. Moreover, because the rise of oxygen from oxygenic cyanobacteria would not occur for another 200 million years after the sediments were deposited, a primitive (or transitional) form of photosynthesis may have been responsible for forming the Mn oxides. In this scenario, the water-oxidizing complex in the early photosynthesizing enzyme machinery utilized Mn(II) as an electron donor.

    Proc. Natl. Acad. Sci. U.S.A. 110, 11238 (2013).

  7. Materials Science

    I Sense the Force

    1. Marc S. Lavine

    Although composite materials can show enhanced properties, understanding the way these materials deform and fail is not straightforward. Besides the individual properties of the matrix and the filler, one has to worry about the distribution of the filler particles, the strength of the interfacial bonding between the filler and matrix, and the way that the combined material will deform and debond. Raja et al. show that luminescent semiconductor nanocrystal tetrapods, composed of zinc-blend CdSe cores with epitaxially grown wurtzie CdS arms, can be used as stress sensors. The tetrapods were electrospun into a matrix of poly l-lactic acid at weight fractions ranging from 3.6 to 40%. During extension of the composite fibers, both the elastic and plastic deformation regions could be tracked through shifts in the fluorescence of the nanocrystals. The authors note that because the particles tend to clump and because there is incomplete stress transfer from the polymer to the nanocrystals, they do not deform plastically when the polymer does, thus giving greater reversibility to the stress measurements, as seen in comparing the fluorescence observations with traditional tensile measurements.

    Nano Lett. 10.1021/nl401999t (2013).