This Week in Science

Science  13 Dec 2019:
Vol. 366, Issue 6471, pp. 1324
  1. Martian Atmosphere

    Mapping winds in Mars' upper atmosphere

    1. Keith T. Smith

    Computer-generated view of Mars at dawn reveals the surface topography

    PHOTO: NASA/JPL

    The atmospheric loss processes that stripped Mars of most of its ancient atmosphere are poorly understood. Benna et al. analyzed atmospheric measurements collected by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft as it repeatedly dipped into the red planet's upper atmosphere. Combining multiple observing modes allowed the authors to derive wind speeds and map the global circulation of the atmosphere at altitudes of ∼150 kilometers. In some locations, winds followed the slope of the surface topography far below. Such insights into the upper levels of planetary atmospheres are limited, even for Earth.

    Science, this issue p. 1363

  2. Molecular Biology

    Cohesin extrudes DNA loops

    1. Steve Mao

    DNA is folded into loops in eukaryotic cells by a process that depends on a ring-shaped adenosine triphosphatase complex called cohesin. Davidson et al. and Kim et al. now show that in the presence of the NIPBLMAU2 protein complex, the human cohesin complex can function as a molecular motor that extrudes DNA loops with high speed in vitro. In contrast to how it mediates sister chromatid cohesion, cohesin does not appear to entrap DNA topologically during loop extrusion. The results provide direct evidence for the loop extrusion model of chromatin organization and suggest that genome architecture is highly dynamic.

    Science, this issue p. 1338, p. 1345

  3. Ancient Atmosphere

    Stepping to an internal beat

    1. H. Jesse Smith

    What caused the stepwise nature of the rise of molecular oxygen in Earth's atmosphere since it appeared in large quantities more than 2 billion years ago? Alcott et al. argue that a set of internal feedbacks involving the global phosphorus, carbon, and oxygen cycles, not individual external forces, could be responsible. Their model, which depends only on a gradual shift from reducing to oxidizing surface conditions over time, produces the same three-step pattern observed in the geological record.

    Science, this issue p. 1333

  4. High-Pressure Physics

    Diamond-based sensors

    1. Jelena Stajic

    Material properties can change dramatically under pressure. Typically, to achieve high-pressure conditions, researchers place their samples in diamond anvil cells (DACs). However, monitoring the properties of the sample inside a DAC is tricky (see the Perspective by Hamlin and Zhou). Hsieh et al., Lesik et al., and Yip et al. developed monitoring techniques based on nitrogen-vacancy (NV) centers in diamond. The NV centers can act as sensors because their energy levels and the associated spectra are sensitive to strain and magnetic fields. This enabled optical readout of a spatially resolved signal.

    Science, this issue p. 1349, p. 1359, p. 1355; see also p. 1312

  5. Polymers

    Strong and tough fibers

    1. Marc S. Lavine

    Dragline spider silk is known for its combination of strength and toughness, but this combination has been hard to replicate in synthetic fibers. Liao et al. electrospun polyacrylonitrile-co-methyl acrylate fibers modified with a small amount of poly(ethylene glycol) bisazide (PEG-BA) (see the Perspective by Fox). After collecting the electrospun yarn, it was annealed under tension that both aligned the small fibers and cross-linked them together via the PEG-BA. As hoped, the overall properties were comparable to those of spider silk.

    Science, this issue p. 1376; see also p. 1314

  6. Neuroscience

    Cell-type identification in neural circuits

    1. Peter Stern

    In many cases, a single molecular marker is insufficient to define a specific cell type and may label a few, or a few hundred, physiologically distinguishable cell types. Lee et al. developed a high-throughput technique, called physiological optical tagging sequencing (PhOTseq), for identifying the expression profile of cells that exhibit a particular physiological profile (see the Perspective by Renninger). They used PhOTseq to identify genes encoding vomeronasal receptors in mice, which detect pheromones and subserve social communication.

    Science, this issue p. 1384; see also p. 1311

  7. Neuroscience

    Sleep disruption in cognitive decline

    1. Kevin S. LaBar

    Dementia affects nearly 36 million people worldwide, a number that is expected to double within the next two decades. Sleep disruption is thought to underlie some aspects of cognitive decline and neurodegeneration. Kaneshwaran et al. assessed sleep disruption in two cohort studies of older persons—the Rush Memory and Aging Project and the Religious Orders Study. In the subjects, greater sleep fragmentation was associated with higher neocortical expression of genes characteristic of microglial aging and activation. This valuable human data may provide therapeutic pointers for the treatment of neurodegenerative disorders.

    Sci. Adv. 10.1126/sciadv.aax7331 (2019).

  8. Psychiatric Diseases

    Dissecting the effects of ecstasy

    1. Mattia Maroso

    Owing to its prosocial effects, MDMA (commonly known as ecstasy) is being evaluated for the treatment of psychiatric disorders. Unfortunately, MDMA's rewarding addictive properties hinder its therapeutic use. Heifets et al. investigated the mechanisms mediating the effects of MDMA in mice. They found that the prosocial and rewarding effects were mediated by independent mechanisms: The prosocial effects were mediated by the serotoninergic system, whereas the rewarding effects required dopaminergic signaling. The results offer hope for the development of more specific therapeutics with fewer side effects.

    Sci. Transl. Med. 11, eaaw6435 (2019).

  9. Body Size

    It's the prey that matters

    1. Sacha Vignieri

    Although many people think of dinosaurs as being the largest creatures to have lived on Earth, the true largest known animal is still here today—the blue whale. How whales were able to become so large has long been of interest. Goldbogen et al. used field-collected data on feeding and diving events across different types of whales to calculate rates of energy gain (see the Perspective by Williams). They found that increased body size facilitates increased prey capture. Furthermore, body-size increase in the marine environment appears to be limited only by prey availability.

    Science, this issue p. 1367; see also p. 1316

  10. Climate Change

    Measuring mitigation and adaptation

    1. Caroline Ash

    As more and more carbon dioxide is emitted into the atmosphere, humans and the natural world are beset by the damaging consequences of a rapidly changing climate. Natural and seminatural ecosystems are likely to be the best starting place for immediate adaptation and mitigation solutions. First, though, many natural environments need restoration to maximize their own resilience to climate change. In reviewing our options, Morecroft et al. point out that we can directly observe the success of mitigation strategies by quantifying atmospheric carbon dioxide. Successful adaptation is more challenging because it involves a range of social and biodiversity measures. However, we could make matters worse if we do not constantly monitor the effects of the interventions we devise and react flexibly as changing conditions unfold.

    Science, this issue p. eaaw9256

  11. Global Conservation

    The time is now

    1. Sacha Vignieri

    For decades, scientists have been raising calls for societal changes that will reduce our impacts on nature. Though much conservation has occurred, our natural environment continues to decline under the weight of our consumption. Humanity depends directly on the output of nature; thus, this decline will affect us, just as it does the other species with which we share this world. Díaz et al. review the findings of the largest assessment of the state of nature conducted as of yet. They report that the state of nature, and the state of the equitable distribution of nature's support, is in serious decline. Only immediate transformation of global business-as-usual economies and operations will sustain nature as we know it, and us, into the future.

    Science, this issue p. eaax3100

  12. Agriculture

    Mobile farming advice

    1. Caroline Ash

    Mobile phones are almost universally available, and the costs of information transmission are low. They are used by smallholder farmers in low-income countries, largely successfully, to optimize markets for their produce. Fabregas et al. review the potential for boosting mobile phone use with smartphones to deliver not only market information but also more sophisticated agricultural extension advice. GPS-linked smartphones could provide locally relevant weather and pest information and video-based farming advice. But how to support the financial requirements of such extension services is less obvious, given the unwieldiness of government agencies and the vested interests of commercial suppliers.

    Science, this issue p. eaay3038

  13. Structural Biology

    Revised view of anticancer drug mechanism

    1. L. Bryan Ray

    A crystal structure of the active form of cyclin-dependent kinase 4 (CDK4) provides insight into regulation of the cell cycle and the mechanism of action of a drug used for breast cancer therapy. The protein p27 has been thought to act as a CDK inhibitor. Guiley et al. performed a structural analysis of active complexes of CDK4 with cyclin D1 (CycD1) and p27 (see the Perspective by Sherr). The results showed that p27 actually remodels the active site of CDK4 to allow full activation when p27 is phosphorylated on tyrosine (phosp27). Furthermore, they found that the breast cancer drug palbociclib, a CDK4 inhibitor, doesn't actually interact with active phosp27-CDK4-CycD1 trimers. Instead, it appears that the drug, which shows promise in the clinic, binds to inactive CDK4 monomers and prevents interaction with p27.

    Science, this issue p. eaaw2106; see also p. 1315

  14. Microbiota

    Clostridial metabolite production

    1. Caroline Ash

    The clostridia are Firmicute bacterial commensals commonly found in the mammalian gut. Clostridia produce a range of metabolites that diffuse into the host's circulation and have been difficult to manipulate genetically, but Guo et al. successfully developed a CRISPR-Cas9 deletion system in Clostridium sporogenes (see the Perspective by Henke and Clardy). The authors used deletion mutants and mass spectrometry to elucidate clostridial synthesis of several different branched short-chain fatty acids (SCFAs), including isobutyrate, 2-methylbutyrate, and isovalerate. Germ-free mice colonized with mutants incapable of synthesizing SCFAs showed altered immunoglobulin A production. This finding potentially links bacterial SCFA production and host responses to the presence of the clostridia.

    Science, this issue p. eaav1282; see also p. 1309

  15. Microbiota

    Prospecting for drugs in the microbiome

    1. Caroline Ash

    The microbiome is an important source of natural products that can profoundly influence health and disease in the host. Sugimoto et al. constructed a modular, probabilistic strategy called MetaBGC to uncover biosynthetic gene clusters (BGCs) in human microbiome samples (see the Perspective by Henke and Clardy). The authors found geographic and strain-specific distributions of BGCs. By zeroing in on two type II aromatic polyketides, the native organisms were identified, the BGCs were reconstructed in Streptomyces, and the products were characterized. When expressed in Bacillus subtilis, the products resembled currently used anticancer drugs and antibiotics. These polyketides were not cytotoxic but had inhibitory activity against oral Gram-positive bacteria, which may reflect the niche and ecology of the originating organisms.

    Science, this issue p. eaax9176; see also p. 1309

  16. Glycobiology

    A division of labor for glycosylation

    1. Michael A. Funk

    Glycosylation is a ubiquitous modification of eukaryotic secreted proteins. Asparagine-linked chains of sugars are appended to many substrates as they are translocated into the endoplasmic reticulum. Ramírez et al. solved cryo–electron microscopy structures of two human oligosaccharyltransferase complexes, OST-A and OST-B. The catalytic subunits bind partner proteins that direct glycosylation of specific substrates either cotranslationally (OST-A) or on fully folded proteins (OST-B). High-resolution views of the active site and bound substrates in one of the complexes reveal important features of the human enzymes.

    Science, this issue p. 1372

  17. Nanomaterials

    Single-layer porphyrin polymerization

    1. Phil Szuromi

    Two-dimensional polymers can be made as monolayer sheets through controlled synthesis at an interface. However, it is often difficult to create intact sheets over large areas that can be transferred onto substrates. Zhong et al. polymerized derivatized porphyrin molecules during laminar flow at a sharp pentane-water interface to form sheets that are 5 centimeters in diameter (see the Perspective by MacLean and Rosei). The authors used electron microscopy and spectroscopy to confirm that they had produced intact monolayers. These films were then transferred onto monolayer sheets of molybdenum disulfide to form superlattices for use as capacitors.

    Science, this issue p. 1379; see also p. 1308

  18. Mucosal Immunology

    Protecting intestinal stem cells

    1. Anand Balasubramani

    The intestinal epithelium is replaced every week. Thus, maintenance of this tissue requires rapid self-renewal driven by intestinal stem cells. This homeostasis is disrupted in a number of settings, including allogeneic bone marrow transplantation. After bone marrow transplantation, allogeneic T cells often attack and kill intestinal cells in an interferon-γ (IFN-γ)–dependent manner. Takashima et al. used in vivo transplant models and in vitro organoid systems to define the targets of IFN-γ in the mouse intestine. They found that IFN-γ directly targets intestinal stem cells. Furthermore, inhibitors of JAK-STAT signaling could be used to protect the intestinal stem cell compartment from T cell–mediated damage.

    Sci. Immunol. 4, eaay8556 (2019).

  19. Physiology

    Metabolic changes under pressure

    1. Wei Wong

    Chronic hypertension causes irreversible damage to the kidneys. Rinschen et al. performed multiomics analyses of kidney tissue from rats that spontaneously develop hypertension when fed a high-salt diet. At early disease stages, kidney glomeruli showed metabolic changes. The alterations in kinase activity and metabolic enzyme abundance that occurred at later disease stages appeared to be triggered by the initial metabolic changes. Thus, metabolic interventions could potentially be useful in treating hypertension-induced kidney disease.

    Sci. Signal. 12, eaax9760 (2019).

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