This Week in Science

Science  05 Jul 2019:
Vol. 365, Issue 6448, pp. 40
  1. Marine Ecology

    The biggest bloom

    1. H. Jesse Smith

    Underwater photograph taken near Key Largo, Florida, of a Sargassum mat from below

    CREDIT: CHRIS GUG/ALAMY STOCK PHOTO

    Floating mats of Sargassum seaweed in the center of the North Atlantic were first reported by Christopher Columbus in the 15th century. These mats, although abundant, have until recently been limited and discontinuous. However, Wang et al. report that, since 2011, the mats have increased in density and aerial extent to generate a 8850-kilometer-long belt that extends from West Africa to the Caribbean Sea and Gulf of Mexico (see the Perspective by Gower and King). This represents the world's largest macroalgal bloom. Such recurrent blooms may become the new normal.

    Science, this issue p. 83; see also p. 27

  2. CRISPR Biology

    Beyond adaptive immunity

    1. Steve Mao

    Prokaryotic CRISPR-Cas systems defend bacterial cells from phage and plasmid infection. Strecker et al. characterized a CRISPR-Cas system that functions beyond adaptive immunity (see the Perspective by Hou and Zhang). Type V-K CRISPR-Cas from cyanobacteria was associated with a Tn7-like transposon and a natural nuclease–deficient effector Cas12k. Cas12k directed the insertion of Tn7-like transposons into target sites via RNA-guided Tn7 transposition. This system was reprogrammed to efficiently and specifically insert DNA both in vitro and into the Escherichia coli genome.

    Science, this issue p. 48; see also p. 25

  3. Restoration Ecology

    The potential for global forest cover

    1. Andrew M. Sugden

    The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Bastin et al. used direct measurements of forest cover to generate a model of forest restoration potential across the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9 billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more than 200 gigatonnes of additional carbon at maturity. Such a change has the potential to store an equivalent of 25% of the current atmospheric carbon pool.

    Science, this issue p. 76; see also p. 24

  4. Protein Dynamics

    Refilling the proton pump

    1. Michael A. Funk

    Proteins are dynamic. Rearrangements of side chains, secondary structure, and entire domains gate functional transitions on time scales ranging from picoseconds to milliseconds. Weinert et al. used time-resolved serial crystallography to study large conformational changes in the proton pump bacteriorhodopsin that allow for redistribution of protons during the pumping cycle. They adapted methods used for x-ray free electron lasers to synchrotron x-ray sources. Large loop movements and a chain of water molecules were central to regenerating the starting state of bacteriorhodopsin.

    Science, this issue p. 61

  5. Light Metals

    Smaller but more ductile

    1. Brent Grocholski

    Poor ductility is one limiting factor in widespread use of strong but lightweight magnesium alloys in cars, trains, and planes. The usual way to try to circumvent this poor ductility is by adding other elements, which can be costly. Liu et al. show that very small samples of pure magnesium are much more ductile than previously believed (see the Perspective by Proust). The small samples suppress the deformation twinning that causes fractures in larger samples. Avoiding this mechanism should allow development of high-ductility magnesium and other metal alloys.

    Science, this issue p. 73; see also p. 30

  6. Behavioral Economics

    Honesty and selfishness across cultures

    1. Tage S. Rai

    Rationalist approaches to economics assume that people value their own interests over the interests of strangers. Cohn et al. wanted to examine the trade-off between material self-interest and more altruistic behaviors (see the Perspective by Shalvi). They distributed more than 17,000 wallets containing various sums of money in 355 cities across 40 countries. In contrast to what rationalist theories of economics predict, citizens were more likely to return wallets that contained more money. The findings also reveal a high level of civic honesty across nations.

    Science, this issue p. 70; see also p. 29

  7. Cancer

    Putting CAR T cells in idle

    1. Yevgeniya Nusinovich

    Chimeric antigen receptor T (CAR T) cells can be an effective cell therapy for cancer. Unfortunately, excessive activation of CAR T cells can occasionally cause severe, even lethal, toxicity. Existing approaches can suppress overactive CAR T cells, but these generally kill the CAR T cells, which abrogates both their toxicity and their antitumor effects. In contrast, Mestermann et al. identified dasatinib as a drug that can temporarily inactivate CAR T cells. This helps reduce acute toxicity and allows the T cells to recover their anti-tumor effects after the drug is removed.

    Sci. Transl. Med. 11, eaau5907 (2019).

  8. Gut Microbiome

    Inheriting microbiome variation

    1. Erin Williams

    In mice, the bacterial species in the gut microbiome are maternally inherited. Yardeni et al. found reduced gut microbiome species diversity in mice with variations in mitochondrial DNA (mtDNA) that were associated with increased reactive oxygen species (ROS) production. When pups were cross-fostered, the gut microbiome species after weening reflected not the microbiota community of the nursing mother but rather the inherited mtDNA variation. Pharmacological or genetic reductions in mitochondrial ROS levels increased microbiome diversity.

    Sci. Signal. 12, eaaw3159 (2019).

  9. Chemical Physics

    A panoramic view of photodissociation

    1. Jake Yeston

    As light pulses get shorter in time, they correspondingly get broader in frequency. Kobayashi et al. take advantage of both properties of attosecond pulses to elucidate iodine monobromide (IBr) photodissociation by detecting ultrafast bromine and iodine spectral shifts simultaneously. A preliminary burst of light weakens the I–Br bond. Then, as the atoms fly apart, they reach a configuration where the bond vibration can couple ground and excited electronic states. The broadband probe pulse reveals rapid changes in each atom's electronic structure at this juncture.

    Science, this issue p. 79

  10. Metasurfaces

    A metasurface polarization camera

    1. Ian S. Osborne

    Imaging the polarization of light scattered from an object provides an additional degree of freedom for gaining information from a scene. Conventional polarimeters can be bulky and usually consist of mechanically moving parts (with a polarizer and analyzer setup rotating to reveal the degree of polarization). Rubin et al. designed a metasurface-based full-Stokes compact polarization camera without conventional polarization optics and without moving parts. The results provide a simplified route for polarization imaging.

    Science, this issue p. eaax1839

  11. African Genetics

    East African genetics and pastoralism

    1. Laura M. Zahn

    The origin and spread of domestic animals across the globe also affected the underlying genetic composition of human populations. In Africa, however, it has been difficult to identify the impact of interactions among migrating food producers and local hunter-gatherers. Prendergast et al. wanted to discern the timing and movement of husbandry and pastoralism and its effects on foraging communities in Africa. They sequenced 41 ancient eastern African human genomes from individuals that lived approximately 100 to 4000 years ago. Surprisingly, relatively little genetic mixture occurred at the same time as the spread of pastoralism.

    Science, this issue p. eaaw6275

  12. Protein Stability

    Glycine N-degron regulation revealed

    1. Stella M. Hurtley

    For more than 30 years, N-terminal sequences have been known to influence protein stability, but additional features of these N-end rule, or N-degron, pathways continue to be uncovered. Timms et al. used a global protein stability (GPS) technology to take a broader look at these pathways in human cells. Unexpectedly, glycine exposed at the N terminus could act as a potent degron; proteins bearing N-terminal glycine were targeted for proteasomal degradation by two Cullin-RING E3 ubiquitin ligases through the substrate adaptors ZYG11B and ZER1. This pathway may be important, for example, to degrade proteins that fail to localize properly to cellular membranes and to destroy protein fragments generated during cell death.

    Science, this issue p. eaaw4912

  13. Neurodevelopment

    Temporal code underlies circuit formation

    1. Pamela J. Hines

    Olfactory neurons respond to various odorants according to which olfactory receptors, of many, they express. During development, axons from olfactory neurons that express the same olfactory receptor converge to share the same glomeruli. Nakashima et al. now show that, in mice, the neurons build these connections according to shared patterns of activity. When the olfactory receptor is triggered, it causes its cell not simply to fire but to fire in specific patterns. Neurons that speak the same code end up connected at the same glomerulus.

    Science, this issue p. eaaw5030

  14. Cell Biology

    Linking protein misfolding and innate immunity

    1. Stella M. Hurtley

    Multiple innate immune sensors undergo rapid assembly into large complexes known as signalosomes. This is an essential step during cellular responses to microbes and danger signals. How this process is regulated to avoid accumulation of potentially toxic protein aggregates remains poorly understood. Abdel-Nour et al. identified a pathway, dependent on heme-regulated inhibitor, eukaryotic initiation factor 2α, activating transcription factor 4, and heat shock protein B8, which controls the folding and scaffolding of innate immune sensors, allowing optimal proinflammatory signaling (see the Perspective by Pierre). The pathway appears to mirror the endoplasmic reticulum unfolded protein response (UPR), and so was named the cytosolic UPR (cUPR). The cUPR may represent a general mechanism to control protein misfolding in cells.

    Science, this issue p. eaaw4144; see also p. 28

  15. Cell Biology

    ER-phagy keeps cells healthy

    1. Stella M. Hurtley

    In eukaryotic cells, about one-third of all proteins are targeted to the endoplasmic reticulum (ER), which serves as a hub for secretory protein traffic and quality control. Cui et al. studied a protein known as Lst1 in yeast and SEC24C in mammalian cells that is involved in loading secretory cargo into vesicles that are delivered to the Golgi complex. In response to stress caused by starvation or misfolded aggregate-prone secretory proteins, Lst1 acted to promote an additional function—ER-phagy. Together with autophagy receptors on the ER, Lst1 targeted ER domains for degradation to avert protein aggregation, thus preserving cellular health.

    Science, this issue p. 53

  16. Biochemistry

    Oxygen sensing across kingdoms

    1. Paula A. Kiberstis

    The ability to sense and respond to changes in oxygen levels is critical for most forms of life. To date, mechanistic studies of this process in mammals have focused on the oxygen-sensitive stability of a transcription factor called hypoxia-inducible factor. Masson et al. discovered an enzymatic oxygen sensor in humans that is functionally identical to plant cysteine oxidases, enzymes that control responses to hypoxia in plants. The human and plant enzymes convert the N-terminal cysteine in substrate proteins to cysteine sulfinic acid, a modification that ultimately targets the proteins for degradation. Oxygen sensing is impaired in many human diseases, and further study of the human enzyme could help in the development of strategies for therapeutic intervention.

    Science, this issue p. 65

  17. Neuroscience

    Brain immune cells in disease

    1. Gemma Alderton

    The microglia are brain-resident macrophages that are important for homeostasis. Recent studies show that microglia are also involved in various brain diseases, such as multiple sclerosis and Alzheimer's disease. In a Perspective, Priller and Prinz discuss how these disease-associated microglia exhibit alterations that are specific to the type of disease. This specificity suggests avenues by which microglia might be targeted to overcome brain pathology.

    Science, this issue p. 32

  18. Immunology

    Hypertension-induced alarm signal

    1. Ifor Williams

    Human hypertension is a highly prevalent disease known to be associated with chronic low-grade inflammation. Zhao et al. used mouse models to look for hypertension-induced proinflammatory molecules that contribute to T cell activation and inflammation. They found consistent elevations in plasma levels of the alarmin molecule adenosine triphosphate in hypertensive mice. Increased adenosine triphosphate (ATP) concentrations promoted T cell responses by enhancing expression of the CD86 costimulatory molecule on antigen-presenting cells, an effect mediated through the P2X7 purinergic receptor. Elevations of plasma ATP were also detected in a cohort of hypertensive human patients when compared with normotensive controls. Thus, ATP release and the ATP-P2X7 signaling axis represent potential targets to help rein in the proinflammatory sequelae associated with chronic hypertension.

    Sci. Immunol. 4, eaau6426 (2019).