This Week in Science

Science  26 Jun 2015:
Vol. 348, Issue 6242, pp. 1440
  1. Coral Reefs

    Some like it hot

    1. Sacha Vignieri

    Corals inherit heat tolerance in northern Great Barrier Reef

    IMAGE: BLIOKH ET AL.

    Coral reefs are threatened by increasing temperatures. Acute temperature increases stress and damage corals. However, more gradual temperature changes can result in adaptation and subsequent tolerance for higher temperatures. Dixon et al. show that the heat tolerance that currently exists across coral populations from different latitudes can be inherited. Thus, natural variation in temperature tolerance may facilitate rapid adaptation among corals as our climate warms.

    Science, this issue p. 1460

  2. 3D Lithography

    Complex shapes from chemical lithography

    1. Marc S. Lavine

    Lithographic printing of semi-conductors builds up complex patterns one layer at a time. The process involves multiple steps to mask, print, and etch each layer. Luo et al. tweaked the same process used to grow silicon nanowires to pattern them into complex three-dimensional (3D) shapes. Gold acted as a catalyst to grow and elongate silicon nanowires from the vapor phase. Varying the pressure of the growth process altered the rate of gold diffusion along the surface of the wire. Upon etching the wires, the non-uniform coating of gold acted as a lithographic mask. The authors were thus able to make complex-shaped silicon spicules with a series of ridges and notches by strictly chemical means.

    Science, this issue p. 1451

  3. Materials Chemistry

    A green way to clean up an oil spill

    1. Zakya H. Kafafi

    Cleaning thin films of light crude oil from the marine environment is a herculean task. Currently, silicone-based compounds are used, which can leave a permanent residue. Inspired by the natural pigments in plants, John et al. developed a plant-based oil-cleaning agent. The product functions as a “green” chemical herder to retract thin oil layers into a thickened mass suitable for recovery or burning. The biodegradable agent was as good as synthetic chemicals at corraling oil and left no residual contamination.

    Sci. Adv. 10.1126. sciadv.1400265 (2015)

  4. Gene Regulation

    Multitasking around the clock

    1. Paula A. Kiberstis

    Chronic disruption of our circadian rhythms—for example, through shift work—may increase the risk of metabolic disease. Zhang et al. found that a multitasking transcription factor called Rev-erb-α regulates expression of both clock and metabolic genes through distinct mechanisms. At clock genes, it binds directly to a specific DNA sequence, displacing a competing transcription factor. At metabolic genes, it interacts not with DNA but with other transcription factors that regulate metabolic gene expression in a tissue-specific manner.

    Science, this issue p. 1488

  5. Brain Circuits

    Looming in on the threat-response circuit

    1. Peter Stern

    Avoidance pathways identified in the brain

    IMAGE: LINE K. BAY/AUSTRALIAN INSTITUTE OF MARINE SCIENCE; SHANG ET AL.

    What are the neural elements that transmit threat-relevant inputs in the brain? Shang et al. systematically identified the key neuronal subtypes in the mouse superior colliculus underlying active avoidance and defensive-like behaviors. They found a pathway that responded to looming objects, linking input from the retina to the fear center in the brain.

    Science, this issue p. 1472

  6. Dermatology

    B12 boosts acne via the microbiota

    1. Angela Colmone

    Low doses of vitamin B12 supplements can help acne, but in higher doses the same supplement can cause acne flare-ups. Why? Kang et al. show that transcriptional changes in the resident microbes of the skin enhance B12-induced acne. Supplementing patients with the vitamin reduced the expression of B12-synthesis genes in Propionibacterium acnes. This altered the transcriptome of the skin microbiota, driving production of inflammation-inducing porphyrins.

    Sci. Transl. Med. 7, 293ra103 (2015).

  7. Structural Biology

    An RNA seed poised to meet its target

    1. Guy Riddihough

    The CRISPR-Cas system in prokaryotes precisely identifies infecting parasitic DNAs and viruses and destroys them. The CRISPR-Cas system has been adapted for facile genome editing, heralding a new age in molecular biology. Jiang et al. show that the Cas9 nuclease adopts a distinct confirmation when it binds to the targeting guide RNA. The guide RNA then assumes a preordered shape. This RNA “seed region” is thus poised to initiate recognition of the DNA target sequence.

    Science, this issue p. 1477

  8. Photosynthesis

    Protection from too much light

    1. Nicholas S. Wigginton

    Photosynthetic organisms protect themselves from too much light using pigment photoswitches that absorb excess energy. Leverenz et al. analyzed the structure of an active, energy-dissipating form of the orange carotenoid protein (OCP) from a cyanobacterium. When activated by excess light, OCP moves its hydrophobic carotenoid pigment 12 Å within the protein to accommodate nonphotochemical quenching by the broader photosynthetic antenna complex.

    Science, this issue p. 1463

  9. Climate Change

    Walking back talk of the end of warming

    1. H. Jesse Smith

    Previous analyses of global temperature trends during the first decade of the 21st century seemed to indicate that warming had stalled. This allowed critics of the idea of global warming to claim that concern about climate change was misplaced. Karl et al. now show that temperatures did not plateau as thought and that the supposed warming “hiatus” is just an artifact of earlier analyses. Warming has continued at a pace similar to that of the last half of the 20th century, and the slowdown was just an illusion.

    Science, this issue p. 1469

  10. Applied Optics

    Getting around the capacity crunch

    1. Ian S. Osborne

    The growing appetite for an ever-faster Internet and enhanced long-haul communication requires the pumping of more light down optic fibers. However, light-induced nonlinearities limit how much light can be pumped into the fiber without compromising the signal. This limitation has led to the prospect of a “capacity crunch.” Temprana et al. eliminated the effects of nonlinearity by using digital back-propagation methods with mutually coherent laser pulses from a single frequency comb.

    Science, this issue p. 1445

  11. Embryo Development

    BMP mophogens direct growth and fate

    1. Beverly A. Purnell

    As shown in classic fate-mapping studies, tissues and organs arise from specific regions of the embryo. Work over the past few decades has identified molecular players directing this choreographed development. Bone morphogenetic proteins (BMPs) and their antagonists establish domains in developing embryos. Bier and De Robertis review historical events for key discoveries in this area. They go on to lay out the current understanding of how diffusible morphogens form gradients to subdivide germ layers into distinct territories and organize body axes, regulate growth, and maintain stem cell niches.

    Science, this issue 10.1126/science.aaa5838

  12. Heart Development

    Making cardiomyocytes

    1. Beverly A. Purnell

    In the heart, multiple cell types work together. Cardiac progenitor cells give rise to cardiomyocyte, endothelial, or smooth muscle lineages. However, the identity of a marker specific to cardiomyocyte formation has been elusive. Jain et al. now identify a specialized progenitor population that is committed exclusively to forming cardiomyocytes. They also identify the niche signals that promote lineage commitment and the mechanisms involved in making cardiomyocytes. The findings may help in the development of future cell-based regenerative therapeutics for heart disease.

    Science, this issue 10.1126/science.aaa6071

  13. Optics

    A quantum twist on classical optics

    1. Ian S. Osborne

    Interpreting recent experimental results of light interactions with matter shows that the classical Maxwell theory of light has intrinsic quantum spin Hall effect properties even in free space. Complex effects in condensed-matter systems can often find analogs in cleaner optical systems. Bliokh et al. argue that the optical systems exhibiting such complex phenomena should also be simpler (see the Perspective by Stone). Their theoretical study shows that free-space light has a nonzero topological spin Chern number and thus should have counterpropagating surface modes. Such modes are actually well known and can be described as evanescent modes of Maxwell equations.

    Science, this issue p. 1448; see also p. 1432

  14. High-Pressure Physics

    Driving liquid deuterium into metal

    1. Brent Grocholski

    Quick and powerful compression can force materials to change their properties dramatically. Knudson et al. compressed liquid deuterium to extreme temperatures and pressures using high-energy magnetic pulses at the Sandia Z-machine (see the Perspective by Ackland). Deuterium began to reflect like a mirror during compression, as the electrical conductivity sharply increased. The observed conditions for metallization of deuterium and hydrogen help us to build theoretical models for the universe's most abundant element. This a our understanding of the internal layering of gas giant planets such as Jupiter and Saturn.

    Science, this issue p. 1455; see also p. 1429

  15. Marine Sulfur Cycle

    Sourcing the smell of the seaside

    1. Nicholas S. Wigginton

    Marine phytoplankton plays a critical role in the global sulfur cycle. Algae, for instance, are the main source of the aromatic compound dimethylsulfide (DMS) released from the oceans into the atmosphere. Alcolombri et al. identified the lyase enzyme responsible for DMS production in the bloom-forming marine phytoplankton Emiliania huxleyi (see the Perspective by Johnston). The presence of this gene in other globally distributed phytoplankton and corals suggests that it may serve as a reliable indicator of DMS production across diverse phyla. Because DMS gets oxidized to sulfur aerosols, which act as cloud condensation nuclei, this enzyme is a key global biogeochemical catalyst.

    Science, this issue p. 1466; see also p. 1430

  16. Gene Silencing

    Keeping quiet one gene at a time

    1. Stella M. Hurtley

    Chromosomal DNA comes in two flavors—euchromatin, which contains most of the expressed genes, and heterochromatin, which usually remains quiet. But what keeps genes within heterochromatin silent? Tchasovnikarova et al. examined the basis for this type of silencing in mammalian cells (see the Perspective by Brummelkamp). They identified a complex of proteins in human cells they called HUSH that kept particular parts of the genome silent by changing associated histone methylation marks.

    Science, this issue p. 1481, see also p. 1433

  17. RNA Biochemistry

    Unwinding RNA for protein synthesis

    1. Guy Riddihough

    During the first steps of protein synthesis, the small subunit of the ribosome scans the 5′ end of the mRNA, looking for the protein start codon. This process involves one of the translation initiation factors, eIF4A, which helps to remove any RNA structures that might impede the ribosome's search. García-García et al. used single-molecule optical trap assays to show that eIF4A, in combination with two other translation initiation factors, is able to continuously and directionally unwind a double-stranded RNA hairpin. The factors unwound RNA in steps roughly equal to a turn of the RNA double helix.

    Science, this issue p. 1486

  18. Synthetic Ecology

    More than the sum of its parts

    1. Julia Fahrenkamp-Uppenbrink

    How do microbial strains and species interact and survive in microbial communities? The answer may help scientists to devise biotechnological processes; e.g., for creating biofuels from biomass. In a Perspective, Fredrickson highlights recent insights into the cooperative mechanisms that help microbial communities to thrive. Different species often share the work of producing essential compounds such as amino acids. Cooperating cells can evolve to outcompete cheaters that exploit such common goods without reciprocation. Spatial organization is also important; for example, in helping mixed biofilms to resist antimicrobials.

    Science, this issue p. 1425

  19. Microbiota

    Benefits of breastfeeding

    1. Lisa Chong

    Dietary changes that boost good microflora in our gut are of great health interest, but it is unclear how to best sculpt this microbial community to our benefit. In a Perspective, Hinde and Lewis take an evolutionary view of the infant gut microbiome and breastfeeding for insights into optimizing interventions. Bifidobacterium is the major microbial clade in the healthy infant gut. These bacteria metabolize the oligosaccharides most prevalent in human milk, generating byproducts that aid the developing gut and immune system. Natural selection may have favored the coevolution of human milk and a healthy gut microbiota in response to regimes that exerted pressure on immunity and digestion

    Science, this issue p. 1427

  20. Drug Discovery

    Finding better immunosuppressants

    1. John F. Foley

    The immunosuppressant cyclosporin A (CsA) prevents organ rejection in transplant patients. CsA inhibits the phosphatase calcineurin and prevents the activation of the NFAT transcription factors, both of which are required for T cell proliferation. However, CsA also prevents calcineurin from binding to other targets, leading to many side effects. Matsoukas et al. identified compounds that displaced NFAT from calcineurin-NFAT complexes without inhibiting the activity of the phosphatase. Four of these compounds blocked the expression of NFAT target genes and inhibited the proliferation of human CD4+ T cells, and may be good leads for further testing as immunosuppressants.

    Sci. Signal. 8, ra63 (2015).

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