This Week in Science

Science  26 Jun 2020:
Vol. 368, Issue 6498, pp. 1443
  1. Ecology

    Easier polar plunge for penguins

    1. Barbara Block

    Sea-ice loss in the Antarctic has led to greater success in foraging and breeding for Adélie penguins.

    CREDIT: NATURE PICTURE LIBRARY/ALAMY STOCK PHOTO

    In polar regions affected by a warming climate, it is increasingly important to understand what effect yearly variations in sea ice have on animal foraging and reproductive success. Watanabe et al. instrumented 175 Adélie penguins—a sentinel species for Southern Ocean ecosystems—with activity monitors and video cameras during four Antarctic field seasons with variable amounts of ice. During ice-free years, penguins traveled more by swimming rather than walking, lowering their energetic cost per unit distance traveled. Forage area increased in ice-free years, and more krill were captured per unit dive time, increasing foraging efficiency, growth rates, and breeding success. Adélie penguin populations in the continental Antarctic region are thus likely to grow in the coming decades as sea ice declines.

    Sci. Adv. 10.1126/sciadv.aba4828 (2020).

  2. Chromatin Sequencing

    Primary architecture of chromatin fibers

    1. Laura M. Zahn

    The organization of chromosomal DNA, including the positioning of nucleosomes and nucleosome-free regions harboring regulatory proteins along single chromatin fibers, is fundamental to genome function. However, most sequencing methods cannot elucidate this organization at the nucleotide level. Stergachis et al. present an approach, Fiber-seq, that maps chromatin fibers onto the underlying DNA template using methyltransferases to create a kind of stencil in fly and human cells. This method identifies chromatin structure at nearly a single-molecule level and can monitor the position of nucleosomes. Using Fiber-seq, the authors identify how regulatory DNA activation is related to nucleosome positioning and DNA variation.

    Science, this issue p. 1449

  3. Plasmonic Materials

    Groovy chiral gold particles

    1. Phil Szuromi

    Electron tomography reconstructions of a gold nanorod grown with a chiral surfactant

    CREDIT: GONZÁLEZ-RUBIO ET AL.

    Although plasmonic optical activity can arise from chiral assemblies of gold and silver nanoparticles, there are few examples of gold nanoparticles with intrinsic chirality and high optical activity. González-Rubio et al. show that morphological chirality can be induced during the seeded growth of gold nanoparticles, particularly for highly anisotropic nanorods. Chiral additives as cosurfactants formed helical micelles that directed the seeded growth to create grooves that maintained a chiral morphology. The resulting particles displayed high-intensity circular dichroism with anisotropy factors near 0.2 at near-infrared wavelengths.

    Science, this issue p. 1472

  4. Solar Physics

    The flow of plasma inside the Sun

    1. Keith T. Smith

    The activity of the Sun, including the occurrence of sunspots, is driven by magnetic fields that originate from the motion of charged plasma beneath the surface. Helioseismology uses acoustic oscillations to probe the Sun's interior, analogous to seismology's use of earthquakes to investigate Earth's interior. Gizon et al. analyzed helioseismology data from 1996 to 2019, covering two 11-year solar cycles. They measured the latitudinal and radial flow of plasma as a function of depth within the Sun and how it varies with time. The results support magnetic flux-transport dynamo models, which can explain the distribution of sunspots over each solar cycle.

    Science, this issue p. 1469

  5. Quantum Optics

    Metalens-array–based quantum source

    1. Ian S. Osborne

    Spontaneous down-conversion is an exotic optical process in a nonlinear crystal in which a high-energy photon splits into two lower-energy photons that are quantum mechanically entangled. These entangled pairs are valuable commodities for quantum information processing and quantum communications. Because the experimental setup is usually performed with bulk optical components, there is a need to decrease the size scale for application. Li et al. combined an array of specialized metalenses with a nonlinear crystal and show that the scale of the process can be shrunk substantially. The approach should prove useful for developing miniaturized integrated quantum optical technologies.

    Science, this issue p. 1487

  6. Coronavirus

    Who and what next?

    1. Caroline Ash

    The coronavirus 2019 (COVID-19) pandemic has brought tighter restrictions on the daily lives of millions of people, but we do not yet understand what measures are the most effective. Zhang et al. modeled virus transmission in Wuhan, China, in February 2020, investigating the effects of interventions ranging from patient management to social isolation. Age-mixing patterns were estimated by contact surveys conducted in Wuhan and Shanghai at the beginning of February 2020. Once people reduced their average daily contacts from 14 to 20 down to 2, transmission rapidly fell below the epidemic threshold. The model also showed that preemptive school closures helped to reduce transmission, although alone they would not prevent a COVID-19 outbreak. Limiting human mixing to within households appeared to be the most effective measure.

    Science, this issue p. 1481

  7. Coronavirus

    A wrench in the works of COVID-19

    1. Valda Vinson

    Understanding the inner workings of the virus that causes coronavirus disease 2019 (COVID-19) may help us to disrupt it. Yin et al. focused on the viral polymerase essential for replicating viral RNA. They determined a structure of the polymerase bound to RNA and to the drug remdesivir. Remdesivir mimics an RNA nucleotide building block and is covalently linked to the replicating RNA, which blocks further synthesis of RNA. The structure provides a template for designing improved therapeutics against the viral polymerase.

    Science, this issue p. 1499

  8. Macrophages

    Sex, age, and the macrophage

    1. Christiana N. Fogg

    Peritoneal macrophages are known to contribute to pathology of peritonitis, endometriosis, and cancer, but the effects of age and sex on the biology of these cells are not well understood. Bain et al. show that replenishment of peritoneal macrophages from the bone marrow is much higher in male mice than in female mice. This disparity results in marked sexual dimorphisms in the phenotypic identity of peritoneal macrophages, including differential expression of a receptor involved in response to bacterial infection. These findings provide insight into the effects of sex and age on peritoneal inflammation and infection.

    Sci. Immunol. 5, eabc4466 (2020).

  9. Coronavirus

    Reducing airborne transmission

    1. Gemma Alderton

    Respiratory infectious diseases are thought to be transmitted mostly through contact with surfaces that are contaminated with virus-laden droplets produced from coughs and sneezes of infected individuals, but this is not the only transmission route. When people speak and breathe, they produce tiny droplets called aerosols, as well as larger droplets, which evaporate and become buoyant in airflows. In a Perspective, Prather et al. discuss the accumulating evidence that virus-containing aerosols could lead to airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19). Given the lengthy presymptomatic phase and asymptomatic infections, the authors argue that wearing well-fitted masks, especially in enclosed indoor spaces, is important to help prevent SARS-CoV-2 transmission.

    Science, this issue p. 1422

  10. Genomic Duplications

    The fate of genes after duplication

    1. Laura M. Zahn

    Gene duplication within an organism is a relatively common event during evolution. However, we cannot predict the fate of the duplicated genes: Will they be lost, evolve, or overlap in function within an organismal lineage or species? Kuzmin et al. explored the fate of duplicated gene function within the yeast Saccharomyces cerevisiae (see the Perspective by Ehrenreich). They examined how experimental deletions of one or two duplicated genes (paralogs) affected yeast fitness and were able to determine which genes have likely evolved new essential functions and which retained functional overlap, a condition the authors refer to as entanglement. On the basis of these results, they propose how entanglement affects the evolutionary trajectory of gene duplications.

    Science, this issue p. eaaz5667 ; see also p. 1424

  11. Developmental Biology

    Guiding regeneration

    1. Beverly A. Purnell

    Many adult organisms can regenerate neural circuits after injury. However, it is not clear which guidance mechanisms operate to promote axon path finding in the adult. Scimone et al. addressed this question by investigating regeneration of the planarian visual system (see the Perspective by Roberts-Galbraith). Distinct muscle cell populations were found in close association with photoreceptor axons that, together with a neuron class, facilitated visual system assembly after diverse injuries or eye transplantations. These cells exhibited features similar to embryonic guidepost cells and were specified independently of eyes in precise locations by the action of adult positional information cues. Absence of these guidepost-like cells was associated with defective neuronal wiring in regeneration.

    Science, this issue p. eaba3203; see also p. 1428

  12. Neuroscience

    The adaptive human frontal cortex

    1. Peter Stern

    Flexibly switching between different tasks is a fundamental human cognitive ability that allows us to make selective use of only the information needed for a given decision. Minxha et al. used single-neuron recordings from patients to understand how the human brain retrieves memories on demand when needed for making a decision and how retrieved memories are dynamically routed in the brain from the temporal to the frontal lobe. When memory was not needed, only medial frontal cortex neural activity was correlated with the task. However, when outcome choices required memory retrieval, frontal cortex neurons were phase-locked to field potentials recorded in the medial temporal lobe. Therefore, depending on demands of the task, neurons in different regions can flexibly engage and disengage their activity patterns.

    Science, this issue p. eaba3313

  13. Structural Biology

    Engaging the nucleosome

    1. Beverly A. Purnell

    Cell identity is defined by gene expression patterns that are established through the binding of specific transcription factors. However, nucleosomal units limit access of transcription factors to specific DNA motifs within the mammalian genome. To study how transcription factors bind such chromatinized, nucleosome-embedded motifs, Michael et al. focused on the pluripotency factors OCT4 and SOX2. They systematically quantified the relative affinities of these factors at different motif positions throughout the nucleosome, enabling structure determination of OCT4-SOX2–bound nucleosomes by cryo–electron microscopy. OCT4 and SOX2 bound cooperatively to strengthen DNA-binding affinity and resulted in DNA distortions that destabilized the nucleosome. This analysis reveals position-dependent binding modes that were validated in vivo, providing insights on how transcription factors read out chromatinized motifs.

    Science, this issue p. 1460

  14. Structural Biology

    A blueprint to understand cohesin

    1. Valda Vinson

    Cohesin is a multiprotein complex that entraps sister chromatids for chromosome segregation and regulates transcription by extruding DNA loops to shape DNA organization. Shi et al. determined the structure of human cohesin bound to the protein NIBPL, which helps load cohesin onto DNA, and DNA at medium resolution by cryo–electron microscopy. Two adenosine triphosphatase domains play a key role in cohesin function. The structure explains how NIBPL and DNA synergistically activate these domains and gives insight into how DNA is trapped by cohesin.

    Science, this issue p. 1454

  15. Spectroscopy

    DNA circular dichroism in gas phase

    1. Jake Yeston

    Circular dichroism spectroscopy is widely used to distinguish between nonidentical mirror-image molecules. The technique relies on differential absorption of left versus right circularly polarized light and therefore tends to require solution-phase samples for adequate sensitivity. Daly et al. now report gas-phase circular dichroism spectra of DNA oligonucleotides based on detection of photodetached electrons rather than transmitted light (see the Perspective by Barran). The salient spectral features matched those in solution. Pairing the technique with mass spectrometry enables prior mass selection of particular molecules for analysis.

    Science, this issue p. 1465; see also p. 1426

  16. Exoplanets

    A nearby multiplanet system

    1. Keith T. Smith

    Exoplanets can interact gravitationally with other objects orbiting the same star, affecting their evolution and stability. Studying these effects requires locating systems with multiple planets. Monitoring the nearby red dwarf star GJ 887, Jeffers et al. detected periodic radial velocity signals, indicating the presence of two planets on orbits with periods of about 9 and 22 days and a further candidate planet (see the Perspective by Davies). The inclinations of the orbits are unknown, so only minimum masses could be determined, but those were consistent with both planets being super-Earths—more massive than Earth but less than Neptune. This system is only 3.3 parsecs from the Sun, which should facilitate follow-up with other techniques.

    Science, this issue p. 1477; see also p. 1432

  17. Photosynthesis

    Pairs of peaks stabilize output power

    1. Michael A. Funk

    A counterintuitive feature of photosynthesis is that the primary pigments involved in absorbing light—for example, chlorophyll a and b in plants—do not all absorb right at the peak of the spectrum but instead are offset from the peak and each other. Arp et al. formulated a network model that explains how using pigments with this absorption-peak pattern can mitigate internal and external fluctuations in energy transfer, minimizing noise in output power (see the Perspective by Duffy). The model accurately reproduces absorption peaks for three diverse photosynthetic systems from different spectral environments. Such a mechanism may provide an underlying robustness to biological photosynthetic processes that can be further tuned and tweaked to adapt to longer-scale fluctuations in light intensity.

    Science, this issue p. 1490; see also p. 1427

  18. Dog Genomics

    Sled dog arctic adaptations go far back

    1. Laura M. Zahn

    Dogs have been used for sledding in the Arctic as far back as ∼9500 years ago. However, the relationships among the earliest sled dogs, other dog populations, and wolves are unknown. Sinding et al. sequenced an ancient sled dog, 10 modern sled dogs, and an ancient wolf and analyzed their genetic relationships with other modern dogs. This analysis indicates that sled dogs represent an ancient lineage going back at least 9500 years and that wolves bred with the ancestors of sled dogs and precontact American dogs. However, gene flow between sled dogs and wolves likely stopped before ∼9500 years ago.

    Science, this issue p. 1495

  19. Calcium Signaling

    Lighting a spark from the lysosome

    1. Wei Wong

    Calcium ion (Ca2+) sparks in vascular smooth muscle cells are critical for blood vessel dilation and for regulating blood pressure. Thakore et al. showed that these Ca2+ sparks were initiated by Ca2+ released from lysosomes through the cation channel TRPML1 (see the Focus by Nieves-Cintron et al.). Lysosomes in contractile vascular smooth muscle cells were localized in close proximity to this ion channel. Vascular smooth muscle cells from mice deficient in TRPML1 did not generate Ca2+ sparks, and these mice were spontaneously hypertensive.

    Sci. Signal. 13, eaba1015, eabc0993 (2020).

  20. Cancer

    Intuitive CD8+ T cells sense DNA

    1. Lindsey Pujanandez

    Stimulator of interferon genes (STING) agonism is an area of active exploration for cancer immunotherapy. Li et al. examined a DNA-sensing cascade called cGAS-STING in antitumor CD8+ T cells. They observed dampened STING activity in CD8+ T cells from patients with cancer or mice implanted with tumors. By contrast, STING signaling in transferred T cells supported a stem-like memory phenotype, which is known to be beneficial for responses to immunotherapy. Cytosolic DNA was enriched in activated T cells, and STING agonism improved the efficacy of adoptive cell therapy in multiple mouse models. These results highlight that CD8+ T cell DNA sensing could be exploited for therapeutic benefit in immunotherapy.

    Sci. Transl. Med. 12, eaay9013 (2020).

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