This Week in Science

Science  23 May 2014:
Vol. 344, Issue 6186, pp. 868
  1. Evolution

    Ruffling ancient ratite feathers

    1. Laura M. Zahn

    An adult kiwi and an elephant bird egg.


    Biologists have often pointed to the breakup of the supercontinent Gondwana to explain how related species ended up on far-flung continents, but as new research shows, that explanation doesn't fly with ratite birds. Ratite birds are a lineage of large, mostly flightless birds including the African ostrich, the Australian emu, the South American rhea, the diminutive New Zealand kiwi, and the extinct Madagascar elephant bird. Mitchell et al. examined the phylogeny of these birds, adding ancient mitochondrial DNA sequences from the extinct elephant bird. It seems that ratites originated from flighted ancestors who evolved large sizes and loss of flight only after flying to their new homes.

    Science, this issue p. 898.

  2. Subsurface Microbes

    Mapping sub–sea-floor communities

    1. Nicholas S. Wigginton

    The sea floor is teeming with microbes, whose sheer numbers produce a major effect on the global biogeochemical cycles of carbon, sulfur, and other important nutrients. Bowles et al. constructed a map showing how deeply sulfates penetrate marine sediments worldwide and how quickly that sulfate is chemically reduced by microbes in the sub–sea-floor. Globally, almost a third of the organic carbon that reaches the sea floor is consumed during sulfate reduction, and the vast majority of microbial cells in the sub–sea-floor at continental margins get their energy through the biochemical processes of fermentation and methanogenesis.

    Science, this issue p. 889.

  3. Deep Earth

    Delving deeper into the lower mantle

    1. Nicholas S. Wigginton

    Earth's lower mantle is an enigmatic region, a transition zone between slowly churning solids and a liquid outer core. Large seismic structures and discontinuities in this region are probably due to sharp gradients in temperature, composition, or mineralogy. Teasing apart the precise effects of these factors requires experiments at lower mantle temperatures and pressures (see the Perspective by Williams). Zhang et al. found that the major mineral phase of the lower mantle decomposes into two minerals. Andrault et al. show how the melting of subducted basalt from the oceanic crust will form pile-like structures on top of the core/mantle boundary.

    Science, this issue p. 877, p. 892; see also p. 800.

  4. Cosmology

    Confirming cosmic dual conjecture

    1. Ian S. Osborne

    Quantum mechanics and gravity can seem to contradict each other. Superstring theory may provide a route to reconcile the two, thanks to the gauge/gravity duality conjecture, which allows the system to be described mathematically. However, this conjecture has yet to be formally confirmed. Hanada et al. (see the Perspective by Maldacena) performed a simulation of the dual gauge theory in the parameter regime that corresponds to a quantum black hole. Their results agree with a prediction for an evaporating black hole, including quantum gravity corrections, confirming that the dual gauge theory indeed provides a complete description of the quantum nature of the evaporating black hole.

    Science, this issue p. 882; see also p. 806.

  5. Corals and Climate

    Hot and bothered corals can cope

    1. Caroline Ash

    How well can corals adapt to temperature extremes? Better than anticipated, it turns out. Corals from reef pools with wide temperature fluctuations resist stress better than corals from less extreme pools. Nevertheless, corals transplanted into the hotter and more variable conditions soon acquired thermal tolerance. Palumbi et al. (see the Perspective by Eakin) found that the tougher specimens produced more of certain proteins, such as the tumor necrosis factor receptor superfamily, which protected them from the effects of heat. Ramping up heat shock and transport proteins yielded heat tolerance far more rapidly than mutation and adaptation. Hopefully, this ability will allow some mitigation of climate change on coral reefs.

    Science, this issue p. 895; see also p. 798.

  6. Gut Microbiota

    Bacteria breach intestinal barriers

    1. Orla M. Smith

    In an ironic complication of liver cirrhosis, beneficial microbes can escape from the gut and cause serious infections—or even death. Balmer et al. now show that the blood vessels of the healthy liver form a barrier to runaway gut bacteria. However, in animal models of liver disease and gut dysfunction and in patients with nonalcoholic liver disease, the liver is unable to capture these escapees. The bacteria then leak into the blood system, activating immune responses that break down the mutualistic relationship between the gut microbes and the host. This type of breakdown is an important complication of liver disease.

    Sci. Transl. Med. 6, 237ra66 (2014).

  7. Bone Physiology

    Another way of growing strong bones

    1. John F. Foley

    Thyroid hormones increase the number of cells (blue) in trabecular bone.


    To stay strong, bones are constantly rebuilding themselves. Thyroid hormones regulate this process by entering cells and binding to nuclear receptors, which travel to the nucleus, where they change gene expression. However, these hormones also stimulate rapid cellular changes that do not require gene regulation. Kalyanaraman et al. found a different form of nuclear receptor in bone cells. When bound to thyroid hormones, this receptor increased the numbers of bone cells and protected them from death. When the researchers treated mice lacking thyroid hormones with a compound that mimicked the effects of this receptor, their bone cells grew normally.

    Sci. Signal. 7, ra48 (2014).

  8. Cancer Immunology

    Origins of tumor macrophages

    1. Kristen L. Mueller

    To help the immune system fight cancer, it is important to understand the origins and functions of immune cells in tumors and the surrounding tissues. One type of immune cells, macrophages, is present both in tumors and in nearby noncancerous tissue, but the relationship between these two cell populations is unclear. Franklin et al. found that tumor-associated macrophages in mouse mammaries differed in form, function, and origin from macrophages found in nearby noncancerous mammary tissue. Moreover, when they removed macrophages from the tumors but not the other mammary tissue, tumors shrank and cytotoxic T cells—another kind of immune cell that kills tumor cells—infiltrated the tumors. Tumor-associated macrophages may thus be an important therapeutic target.

    Science, this issue p. 921.

  9. Neuroscience

    Decisions, decisions, decisions…

    1. Peter Stern

    Flies, like humans, deliberate before making perceptual judgments: They ponder difficult decisions longer than they do easy ones. DasGupta et al. measured reaction times in flies choosing between different smells. Mutations in a particular gene, they found, could cause indecision. Mutations in the same gene are implicated in intellectual disability, learning deficits, and language impairment.

    Science, this issue p. 901.

  10. Surface Science

    Probing bonding profiles with a CO tip

    1. Phil Szuromi

    Greater resolution has been achieved in atomic force microscopy by terminating the tip with a sharper probe: an adsorbed CO molecule. Chiang et al. now show that the adsorbed CO tip can reveal the bonding within cobalt phthalocyanine molecules absorbed on silver or gold surfaces. Inelastic tunneling spectroscopy reveals variations in the vibration excitation of the CO molecule that can map out the internal bonding of the molecules, as well as hydrogen bonding between molecules.

    Science, this issue p. 885

  11. Infectious Disease

    Progress toward an effective malaria vaccine

    1. Caroline Ash

    The history of efforts to develop a malaria vaccine has been long and difficult. Raj et al. probed for molecules produced by this blood parasite that are recognized by natural immune responses of people living in malaria-endemic areas of Africa. One, PfSEA-1, blocked parasite exit from red blood cells. Vaccination experiments with mouse malaria showed almost fourfold reduction in parasitemia; moreover, passive transfer of PfSEA-1 antibodies transferred protection from mouse to mouse. Encouragingly, the presence of PfSEA-1 antibodies correlates with significant protection from severe malaria in children and adolescents from Kenya and Tanzania.

    Science, this issue p. 871

  12. Microbial Genomics

    In translation, sometimes stop can mean go

    1. Laura M. Zahn

    The genetic code appears to be largely conserved across all domains of life. Although limited deviations have been reported, Ivanova et al. used metagenomics to survey the prevalence of stop codon reassignment in naturally occurring microbial populations. Certain bacteria and bacteriophages exhibited lineage-specific recoding of their stop codons. In one specific phage, the genome was restructured into two genetic sets. One set of genes was encoded in a way that didn't gel with the host genome and probably helped with infection. A second set of more host-compatible sequences encoded proteins expressed in the later stages of infection.

    Science, this issue p. 909

  13. Neuroscience

    Firing, wiring, and Hebbian remodeling

    1. Peter Stern

    Correlated neuronal activity is generally thought to drive circuit remodeling in the central nervous system. This model, first proposed by Hebb, is strongly supported by several lines of evidence, though it has been difficult to directly observe such changes in real time. Munz et al. developed an experimental approach to watch structural remodeling of neuronal axons in vivo at high temporal resolution. They measured changes in synaptic efficacy while presenting specific patterned stimuli to test the Hebb model. Although the key predictions of Hebbian developmental plasticity were upheld, the mechanistic details of how this occurred were unexpected.

    Science, this issue p. 904

  14. Cancer Genomics

    Candidate Cushing's culprit identified

    1. Laura M. Zahn

    Cushing's syndrome is a rare condition resulting from the excess production of cortisol. About 15% of Cushing's syndrome cases are associated with an adrenocortical tumor. However, the genetic etiology of these adrenocortical tumors is ill defined (see the Perspective by Kirschner). Cao et al. and Sato et al. both performed whole-exome sequencing of tumors from individuals with adrenal Cushing's syndrome and compared it with the patient's own matched non-tumor DNA and identified recurrent mutations in the protein kinase A catalytic subunit alpha (PRKACA) gene, as well as less frequent mutations in other putative pathological genes. The most common recurrent mutation activated the kinase, which may suggest a potential therapeutic target.

    Science, this issue p. 913, p. 917; see also p. 804