This Week in Science

Science  06 Apr 2018:
Vol. 360, Issue 6384, pp. 44
  1. Evolutionary Biology

    On the evolution of baleen whales

    1. Jeremy Jackson

    Gene flow among baleen whales is complex.


    Baleen whales include the largest animals that have ever lived, but their evolutionary history has been difficult to decipher because of conflicting evidence from genes and morphology. Árnason et al. conducted whole-genome sequencing of the blue whale and five other baleen species to reconstruct their evolutionary history in detail. All existing species originated within the past 10 million years as global climates progressively cooled toward the poles. Taxonomic relationships are complicated by evidence of gene flow and hybridization among species facilitated by the absence of geographic barriers. Speciation occurred within an interwoven network of co-occurring lineages, rather than the classical Darwinian pattern of bifurcating trees that is characteristic of most animals.

    Sci. Adv. 10.1126/sciadv.aap9873 (2018).

  2. Emerging Infections

    Postnatal perturbation by Zika virus

    1. Lindsey Pujanandez

    Much of the concern surrounding Zika virus infections focuses on fetuses infected in utero. Mavigner et al. reasoned that this neurotropic virus may have deleterious effects even after birth. They found that infant rhesus macaques infected with Zika virus had peripheral and central nervous system pathology. The infected animals had structural and functional brain abnormalities and altered emotional responses. These differences persisted months after the virus had been cleared. Thus, infants and young children exposed to Zika virus should perhaps undergo more than just routine monitoring.

    Sci. Transl. Med. 10, eaao6975 (2018).

  3. Solar Cells

    Light relaxes hybrid perovskites

    1. Phil Szuromi

    Ion migration in organic-inorganic perovskite solar cells limits device stability and performance. Tsai et al. found that a cesium-doped lead triiodide perovskite with mixed organic cations underwent a uniform lattice expansion after 180 min of exposure at 1 sun of illumination. This structural change reduced the energy barriers for charge carriers at the contacts of solar cells. The resulting increase in power conversion efficiency from 18.5 to 20.5% was maintained for more than 1500 hours of illumination.

    Science, this issue p. 67

  4. Stem Cells

    Signaling hematopoietic stem cells from afar

    1. Beverly A. Purnell

    Throughout our entire life span, hematopoietic stem cells (HSCs) generate all of our blood cells. The bone marrow microenvironment, or niche, is key to activating stem cell activity. Decker et al. now show that thrombopoietin generated in the liver, but not from the local bone marrow niche, maintains HSCs in vivo in mice. Thus, systemic endocrine factors are needed to maintain somatic stem cells from a distance. These findings may be important when considering how to stimulate HSCs for therapeutic use.

    Science, this issue p. 106

  5. Topological Matter

    Beyond fractional quantum Hall

    1. Jelena Stajic

    Unlike most electronic topological phenomena, the fractional quantum Hall effect requires correlations among electrons. Spanton et al. describe a class of related but even more unusual states, the fractional Chern insulators (see the Perspective by Repellin and Regnault). They observed these states in samples of bilayer graphene, where one of the graphene layers was misaligned by a small angle with respect to an adjoining layer of hexagonal boron nitride. The misalignment created a superlattice potential and topologically nontrivial bands, which had a fractional filling, thanks to strong electronic interactions. The findings expand the class of correlated topological states, which have been predicted to harbor exotic excitations.

    Science, this issue p. 62; see also p. 31

  6. Molecular Biology

    Live imaging of DNA loop extrusion

    1. Steve Mao

    To spatially organize chromosomes, ring-shaped protein complexes including condensin and cohesin have been hypothesized to extrude DNA loops. Condensin has been shown to exhibit a DNA-translocating motor function, but extrusion has not been observed directly. Using single-molecule imaging, Ganji et al. visualized in real time a condensin-mediated, adenosine triphosphate–dependent, fast DNA loop extrusion process. Loop extrusion occurred asymmetrically, with condensin reeling in only one end of the DNA. These data provide unambiguous evidence of a loop extrusion mechanism for chromosome organization.

    Science, this issue p. 102

  7. Ancient Genomes

    Revisiting the origins of modern horses

    1. Laura M. Zahn

    The domestication of horses was very important in the history of humankind. However, the ancestry of modern horses and the location and timing of their emergence remain unclear. Gaunitz et al. generated 42 ancient-horse genomes. Their source samples included the Botai archaeological site in Central Asia, considered to include the earliest domesticated horses. Unexpectedly, Botai horses were the ancestors not of modern domestic horses, but rather of modern Przewalski's horses. Thus, in contrast to current thinking on horse domestication, modern horses may have been domesticated in other, more Western, centers of origin.

    Science, this issue p. 111

  8. Neuroscience

    A small molecule for stroke therapy

    1. Peter Stern

    Better therapies for motor impairments after stroke are greatly needed. In mice and nonhuman primates, Abe et al. found that edonerpic maleate enhanced synaptic plasticity and functional recovery after a traumatic insult to the brain (see the Perspective by Rumpel). This recovery of motor function was accompanied by functional reorganization of the cortex.

    Science, this issue p. 50; see also p. 30

  9. Nitrogen Cycle

    Freed from a rocky embrace

    1. H. Jesse Smith

    Nitrogen availability is a central controller of terrestrial plant growth and, thereby, of the carbon cycle and global climate change. It has been widely assumed that the atmosphere is the main source of terrestrial nitrogen input. Surprisingly, Houlton et al. now show that bedrock is just as large a nitrogen source across major sectors of the global terrestrial environment. They used three diverse and largely independent assessments of the nitrogen mobility and reactivity of rocks in the surface environment. These approaches yielded convergent estimates pointing to the equal importance of the atmosphere and bedrock as nitrogen sources.

    Science, this issue p. 58

  10. Structural Biology

    Focusing in on herpesvirus

    1. Valda Vinson

    The herpesvirus family includes herpes simplex virus type 1 (HSV-1), which causes cold sores, and type 2 (HSV-2), which causes genital herpes. Herpesviruses comprise a large DNA genome enclosed in a large and complex protein cage called a capsid (see the Perspective by Heldwein). Dai and Zhou used electron microscopy to determine a high-resolution structure of the HSV-1 capsid bound to the tegument proteins that occupy the space between the capsid and the nuclear envelope. The structure suggests how these components may play a role in viral transport. Yuan et al. describe a higher-resolution structure of an HSV-2 capsid, providing insight into how the shell assembles and is stabilized.

    Science, this issue p. eaao7298, p. eaao7283; see also p. 34

  11. Cell Biology

    A quick fix for leaky endosomes

    1. Stella M. Hurtley

    Cells internalize diverse material through various forms of endocytosis into an extensive endolysosomal network. Protecting the integrity of endolysosomal membranes in both physiological and pathophysiological contexts is critical to cell health. Skowyra et al. describe a role for the ESCRT (endosomal sorting complex required for transport) machinery on endolysosomal organelles during membrane repair (see the Perspective by Gutierrez and Carlton). The ESCRTs act as first responders to repair limited membrane damage and thereby restore compartmental integrity and function. This ESCRT activity is distinct from organelle disposal pathways. These findings will be important in understanding cellular responses to invading pathogens and potentially disruptive proinflammatory particulates.

    Science, this issue p. eaar5078; see also p. 33

  12. Biocatalysis

    Double rings made with heme

    1. Michael A. Funk

    Cyclic organic structures with adjacent three-carbon rings—bicyclobutanes—are useful starting materials for chemical and materials synthesis owing to their extreme ring strain. Constructing these molecules is a challenging task for organic chemists, especially if a single stereoisomer is desired. Chen et al. engineered a heme-containing enzyme to catalyze sequential carbene insertion reactions using an alkyne substrate. Starting with an enzyme that could only catalyze a single carbene insertion, a series of mutations led to variants that catalyzed efficient, stereoselective production of bicyclobutanes. By using a less reactive alkyne substrate and screening more variants with active site mutations, the authors found enzymes that stop at either enantiomer of the intermediate cyclopropene.

    Science, this issue p. 71

  13. Organic Chemistry

    A sulfur matchmaker for fluorous coupling

    1. Jake Yeston

    Fluorination is a burgeoning technique for fine-tuning the properties of pharmaceutical compounds. Unfortunately, the cross-coupling reactions widely used to make carbon-carbon bonds in drug research can be tripped up by fluorine substituents. Merchant et al. report a class of easily prepared, solid sulfone compounds that engage in nickel-catalyzed coupling of their fluoroalkyl groups with aryl zinc reagents. These sulfones considerably simplify the synthetic routes to fluorinated analogs that would previously have required multistep strategies focused strictly on the fluorination protocol.

    Science, this issue p. 75

  14. Neurodevelopment

    Embryonic hints of adult diversity

    1. Pamela J. Hines

    The adult brain contains dozens of different types of interneurons that control and refine neuronal circuits. Mi et al. used single-cell transcriptomics to investigate when these subtypes emerge during interneuron development in the mouse. Transcriptomes of embryonic interneurons showed similarities to adult classes of differentiated interneurons, thus dividing the immature embryonic interneurons themselves into classes. Nearly a dozen classes of embryonic neurons could be identified soon after their last mitosis by transcriptomic similarity with known classes of adult cortical interneurons. Thus, the fate of embryonic interneurons can be read in their transcriptomes well before the neurons migrate and reach their final sites of differentiation and circuit integration.

    Science, this issue p. 81

  15. Paleoanthropology

    The Middle Stone Age in Africa

    1. Andrew M. Sugden

    The Olorgesailie basin in the southern Kenya rift valley contains sediments dating back to 1.2 million years ago, preserving a long archaeological record of human activity and environmental conditions. Three papers present the oldest East African evidence of the Middle Stone Age (MSA) and elucidate the system of technology and behavior associated with the origin of Homo sapiens. Potts et al. present evidence for the demise of Acheulean technology that preceded the MSA and describe variations in late Acheulean hominin behavior that anticipate MSA characteristics. The transition to the MSA was accompanied by turnover of large mammals and large-scale landscape change. Brooks et al. establish that ∼320,000 to 305,000 years ago, the populations in eastern Africa underwent a technological shift upon procurement of distantly sourced obsidian for toolmaking, indicating the early development of social exchange. Deino et al. provide the chronological underpinning for these discoveries.

    Science, this issue p. 86, p. 90, p. 95

  16. Stem Cells

    Staging quiescent cells

    1. Beverly A. Purnell

    Tissue-specific stem cells either divide or wait in a quiescent state until needed by the body. Quiescent stem cells have been thought to reside in the G0 stage before activating to reenter the cell cycle. However, Otsuki and Brand now show that most quiescent stem cells in the Drosophila brain are arrested in G2. Cells in the two phases display differences; for example, G2 stem cells awaken more quickly than G0 stem cells, with the conserved pseudokinase Tribbles playing a regulatory role. Elucidating the different pathways and mechanisms underlying quiescence could help to inform regenerative drug design.

    Science, this issue p. 99

  17. Pollution

    Microplastics everywhere

    1. Julia Fahrenkamp-Uppenbrink

    Over the past decade and a half, numerous studies have shown that marine environments are contaminated with small pieces of plastic (microplastics) that are finding their way into sea salt and seafood. In a Perspective, Rochman highlights recent work into microplastic pollution of freshwater and land environments. Microplastic contamination is just as ubiquitous in these environments as in the ocean, yet knowledge is much more limited. Research on freshwater and land contamination with microplastics will be crucial for understanding the sources and transport of microplastics to the sea, as well as for elucidating the distinct processes and impacts in these environments themselves.

    Science, this issue p. 28

  18. Neurodegeneration

    A target in Parkinson's disease?

    1. Gemma Alderton

    The kinase LRRK2 is activated by mutation in a subset of patients with Parkinson's disease, making it a possible therapeutic target. In a Perspective, Alessi and Sammler discuss the possible mechanisms leading to Parkinson's disease in patients with LRRK2 activation. In particular, the authors describe the role of LRRK2 in regulating diverse RAB guanosine triphosphatases, which are important in intracellular vesicular transport. Furthermore, the role of LRRK2 in inflammation is discussed as a possible common pathogenic mechanism in Parkinson's disease.

    Science, this issue p. 36

  19. Neuroscience

    From Nogo to go

    1. Wei Wong

    Recovery of motor function after spinal cord injury is limited by multiple inhibitors of axonal regeneration, such as the myelin-associated protein Nogo. Sekine et al. found that ORL1, a receptor for the opioid peptide nociceptin, also blocked axonal regeneration through mechanisms that partially depended on the Nogo receptor NgR1. In mice, an ORL1 antagonist improved motor function recovery and axonal regeneration after spinal cord injury. These effects were accentuated in Ngr1-deficient mice, suggesting a possible clinical benefit to using a combination of ORL1 and NgR1 blockers to treat spinal cord injury.

    Sci. Signal. 11, eaao4180 (2018).