Science current issue 
  • The story behind COVID-19 vaccines 
  • News at a glance 
  • Biden, Congress roll out big plans to expand NSF 
  • For a change, a hint of new physics does not fade away 
  • When modern humans met Neanderthals 
  • Latest Russian vaccine comes with a big dose of mystery 
  • Top German psychologist found to have fabricated data 
  • A star is torn 
  • The enigmatic origins of the human brain 
  • Preshaping clear glass at low temperatures 
  • Epigenetic nucleotides enhance therapy 
  • The push and pull of DNA methylation 
  • Recruiting T cells in cancer immunotherapy 
  • Limits on superconductivity in flatland 
  • Concrete steps to diversify the scientific workforce 
  • Rethinking Alexander Graham Bell's legacy 
  • Refracted reality 
  • Prevent bottom trawling in southern Brazil 
  • Assess before changing Brazil's shipping policy 
  • Northeast Brazil's imperiled Cerrado 
  • Competing signal peptides hold the key 
  • Repairing the fish heart 
  • Slipping boron into alkyl ethers 
  • Dating the ipsilateral visual pathway 
  • X-rays from giant radio pulses 
  • Seeding 2D crystals 
  • Cabbage blue boosted 
  • MPO in myeloid cells mitigates melanoma 
  • Shaping silica like a polymer 
  • Recruiting T cells 
  • Enhancing liquid biopsies 
  • intMEMOIR traces cell lineages 
  • Screen identifies demethylation regulator 
  • Dynamic activation of a GPCR 
  • Light makes light work of fatty acids 
  • UK variant transmission 
  • Three strikes to knock cancer out 
  • Brain evolution in early Homo 
  • Inducing a crossover 
  • Targeting huntingtin in pigs 
  • Touched by a plasmacytoid dendritic cell 
  • Fire in the flooded forest 
  • Conformational ensembles 
  • Chromatin coordinates stemness 
  • A metasurface performance enhancer 
  • It's a wrap(pER) 
  • Wet winters awaiting 
  • Hard, soft, hot, cold 
  • Bilateral visual projections exist in non-teleost bony fish and predate the emergence of tetrapods 

    In most vertebrates, camera-style eyes contain retinal ganglion cell neurons that project to visual centers on both sides of the brain. However, in fish, ganglion cells were thought to innervate only the contralateral side, suggesting that bilateral visual projections appeared in tetrapods. Here we show that bilateral visual projections exist in non-teleost fishes and that the appearance of ipsilateral projections does not correlate with terrestrial transition or predatory behavior. We also report that the developmental program that specifies visual system laterality differs between fishes and mammals, as the Zic2 transcription factor, which specifies ipsilateral retinal ganglion cells in tetrapods, appears to be absent from fish ganglion cells. However, overexpression of human ZIC2 induces ipsilateral visual projections in zebrafish. Therefore, the existence of bilateral visual projections likely preceded the emergence of binocular vision in tetrapods.

  • Targeting the nucleotide salvage factor DNPH1 sensitizes BRCA-deficient cells to PARP inhibitors 

    Mutations in the BRCA1 or BRCA2 tumor suppressor genes predispose individuals to breast and ovarian cancer. In the clinic, these cancers are treated with inhibitors that target poly(ADP-ribose) polymerase (PARP). We show that inhibition of DNPH1, a protein that eliminates cytotoxic nucleotide 5-hydroxymethyl-deoxyuridine (hmdU) monophosphate, potentiates the sensitivity of BRCA-deficient cells to PARP inhibitors (PARPi). Synthetic lethality was mediated by the action of SMUG1 glycosylase on genomic hmdU, leading to PARP trapping, replication fork collapse, DNA break formation, and apoptosis. BRCA1-deficient cells that acquired resistance to PARPi were resensitized by treatment with hmdU and DNPH1 inhibition. Because genomic hmdU is a key determinant of PARPi sensitivity, targeting DNPH1 provides a promising strategy for the hypersensitization of BRCA-deficient cancers to PARPi therapy.

  • The primitive brain of early Homo 

    The brains of modern humans differ from those of great apes in size, shape, and cortical organization, notably in frontal lobe areas involved in complex cognitive tasks, such as social cognition, tool use, and language. When these differences arose during human evolution is a question of ongoing debate. Here, we show that the brains of early Homo from Africa and Western Asia (Dmanisi) retained a primitive, great ape–like organization of the frontal lobe. By contrast, African Homo younger than 1.5 million years ago, as well as all Southeast Asian Homo erectus, exhibited a more derived, humanlike brain organization. Frontal lobe reorganization, once considered a hallmark of earliest Homo in Africa, thus evolved comparatively late, and long after Homo first dispersed from Africa.

  • Pollen PCP-B peptides unlock a stigma peptide-receptor kinase gating mechanism for pollination 

    Sexual reproduction in angiosperms relies on precise communications between the pollen and pistil. The molecular mechanisms underlying these communications remain elusive. We established that in Arabidopsis, a stigmatic gatekeeper, the ANJEA–FERONIA (ANJ–FER) receptor kinase complex, perceives the RAPID ALKALINIZATION FACTOR peptides RALF23 and RALF33 to induce reactive oxygen species (ROS) production in the stigma papillae, whereas pollination reduces stigmatic ROS, allowing pollen hydration. Upon pollination, the POLLEN COAT PROTEIN B-class peptides (PCP-Bs) compete with RALF23/33 for binding to the ANJ–FER complex, leading to a decline of stigmatic ROS that facilitates pollen hydration. Our results elucidate a molecular gating mechanism in which distinct peptide classes from pollen compete with stigma peptides for interaction with a stigmatic receptor kinase complex, allowing the pollen to hydrate and germinate.

  • Boron insertion into alkyl ether bonds via zinc/nickel tandem catalysis 

    Mild methods to cleave the carbon-oxygen (C–O) bond in alkyl ethers could simplify chemical syntheses through the elaboration of these robust, readily available precursors. Here we report that dibromoboranes react with alkyl ethers in the presence of a nickel catalyst and zinc reductant to insert boron into the C–O bond. Subsequent reactivity can effect oxygen-to-nitrogen substitution or one-carbon homologation of cyclic ethers and more broadly streamline preparation of bioactive compounds. Mechanistic studies reveal a cleavage-then-rebound pathway via zinc/nickel tandem catalysis.

  • High-throughput injection molding of transparent fused silica glass 

    Glass is one of the most relevant high-performance materials that has the benefit of a favorable environmental footprint compared with that of other commodity materials. Despite the advantageous properties of glasses, polymers are often favored because they can be processed using scalable industrial replication techniques like injection molding (IM). Glasses are generally processed through melting, which is both energy intensive and technologically challenging. We present a process for glassworks using high-throughput IM of an amorphous silicon dioxide nanocomposite that combines established process technologies and low-energy sintering. We produce highly transparent glass using classical IM and sintering, allowing for a potentially substantial reduction in energy consumption. Our strategy merges polymer and glass processing, with substantial implications for glass utilization.

  • Enhanced x-ray emission coinciding with giant radio pulses from the Crab Pulsar 

    Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars that last a few microseconds and are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside of radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percentage points during GRPs. We observed the Crab Pulsar simultaneously at x-ray and radio wavelengths, finding enhancement of the x-ray emission by 3.8 ± 0.7% (a 5.4 detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts.

  • Gate-controlled BCS-BEC crossover in a two-dimensional superconductor 

    Bardeen-Cooper-Schrieffer (BCS) superfluidity and Bose-Einstein condensation (BEC) are the two extreme limits of the ground state of the paired fermion systems. We report crossover behavior from the BCS limit to the BEC limit realized by varying carrier density in a two-dimensional superconductor, electron-doped zirconium nitride chloride. The phase diagram, established by simultaneous measurements of resistivity and tunneling spectra under ionic gating, demonstrates a pseudogap phase in the low-doping regime. The ratio of the superconducting transition temperature and Fermi temperature in the low–carrier density limit is consistent with the theoretical upper bound expected in the BCS-BEC crossover regime. These results indicate that the gate-doped semiconductor provides an ideal platform for the two-dimensional BCS-BEC crossover without added complexities present in other solid-state systems.

  • Seeded 2D epitaxy of large-area single-crystal films of the van der Waals semiconductor 2H MoTe2 

    The integration of two-dimensional (2D) van der Waals semiconductors into silicon electronics technology will require the production of large-scale, uniform, and highly crystalline films. We report a route for synthesizing wafer-scale single-crystalline 2H molybdenum ditelluride (MoTe2) semiconductors on an amorphous insulating substrate. In-plane 2D-epitaxy growth by tellurizing was triggered from a deliberately implanted single seed crystal. The resulting single-crystalline film completely covered a 2.5-centimeter wafer with excellent uniformity. The 2H MoTe2 2D single-crystalline film can use itself as a template for further rapid epitaxy in a vertical manner. Transistor arrays fabricated with the as-prepared 2H MoTe2 single crystals exhibited high electrical performance, with excellent uniformity and 100% device yield.

  • Krüppel-like factor 1 is a core cardiomyogenic trigger in zebrafish 

    Cardiac regeneration requires dedifferentiation and proliferation of mature cardiomyocytes, but the mechanisms underlying this plasticity remain unclear. Here, we identify a potent cardiomyogenic role for Krüppel-like factor 1 (Klf1/Eklf), which is induced in adult zebrafish myocardium upon injury. Myocardial inhibition of Klf1 function does not affect heart development, but it severely impairs regeneration. Transient Klf1 activation is sufficient to expand mature myocardium in uninjured hearts. Klf1 directs epigenetic reprogramming of the cardiac transcription factor network, permitting coordinated cardiomyocyte dedifferentiation and proliferation. Myocardial expansion is supported by Klf1-induced rewiring of mitochondrial metabolism from oxidative respiration to anabolic pathways. Our findings establish Klf1 as a core transcriptional regulator of cardiomyocyte renewal in adult zebrafish hearts.

  • New Products 
  • A risk worth taking 
  • QSER1 protects DNA methylation valleys from de novo methylation 

    DNA methylation is essential to mammalian development, and dysregulation can cause serious pathological conditions. Key enzymes responsible for deposition and removal of DNA methylation are known, but how they cooperate to regulate the methylation landscape remains a central question. Using a knockin DNA methylation reporter, we performed a genome-wide CRISPR-Cas9 screen in human embryonic stem cells to discover DNA methylation regulators. The top screen hit was an uncharacterized gene, QSER1, which proved to be a key guardian of bivalent promoters and poised enhancers of developmental genes, especially those residing in DNA methylation valleys (or canyons). We further demonstrate genetic and biochemical interactions of QSER1 and TET1, supporting their cooperation to safeguard transcriptional and developmental programs from DNMT3-mediated de novo methylation.

  • Comment on "Tumor-initiating cells establish an IL-33-TGF-{beta} niche signaling loop to promote cancer progression" 

    Taniguchi et al. (Research Articles, 17 July 2020, p. 269) claim that the cytokine interleukin-33 induces accumulation of tumor-associated macrophages expressing the immunoglobulin E receptor FcRI. Although these findings hold great therapeutic promise, we provide evidence that the anti-FcRI antibody used in this study is not specific for FcRI on macrophages, which raises concerns about the validity of some of the conclusions.

  • Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England 

    A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant, VOC 202012/01 (lineage B.1.1.7), emerged in southeast England in September 2020 and is rapidly spreading toward fixation. Using a variety of statistical and dynamic modeling approaches, we estimate that this variant has a 43 to 90% (range of 95% credible intervals, 38 to 130%) higher reproduction number than preexisting variants. A fitted two-strain dynamic transmission model shows that VOC 202012/01 will lead to large resurgences of COVID-19 cases. Without stringent control measures, including limited closure of educational institutions and a greatly accelerated vaccine rollout, COVID-19 hospitalizations and deaths across England in the first 6 months of 2021 were projected to exceed those in 2020. VOC 202012/01 has spread globally and exhibits a similar transmission increase (59 to 74%) in Denmark, Switzerland, and the United States.

  • Imaging cell lineage with a synthetic digital recording system 

    During multicellular development, spatial position and lineage history play powerful roles in controlling cell fate decisions. Using a serine integrase–based recording system, we engineered cells to record lineage information in a format that can be read out in situ. The system, termed integrase-editable memory by engineered mutagenesis with optical in situ readout (intMEMOIR), allowed in situ reconstruction of lineage relationships in cultured mouse cells and flies. intMEMOIR uses an array of independent three-state genetic memory elements that can recombine stochastically and irreversibly, allowing up to 59,049 distinct digital states. It reconstructed lineage trees in stem cells and enabled simultaneous analysis of single-cell clonal history, spatial position, and gene expression in Drosophila brain sections. These results establish a foundation for microscopy-readable lineage recording and analysis in diverse systems.

  • Response to Comment on "Tumor-initiating cells establish an IL-33-TGF-{beta} niche signaling loop to promote cancer progression" 

    Kamphuis et al. argue that macrophages accumulated in the proximity of tumor-initiating cells do not express the high-affinity immunoglobulin E receptor FcRIα. Although we cannot exclude the possibility of nonspecific binding of anti-FcRIα antibody (clone MAR-1), we provide evidence that macrophages in squamous cell carcinomas express FcRIα and that IL-33 induces FcRIα expression in bone marrow cell–derived macrophages.

  • Epigenetics, fragmentomics, and topology of cell-free DNA in liquid biopsies 

    Liquid biopsies that analyze cell-free DNA in blood plasma are used for noninvasive prenatal testing, oncology, and monitoring of organ transplant recipients. DNA molecules are released into the plasma from various bodily tissues. Physical and molecular features of cell-free DNA fragments and their distribution over the genome bear information about their tissues of origin. Moreover, patterns of DNA methylation of these molecules reflect those of their tissue sources. The nucleosomal organization and nuclease content of the tissue of origin affect the fragmentation profile of plasma DNA molecules, such as fragment size and end motifs. Besides double-stranded linear fragments, other topological forms of cell-free DNA also exist—namely circular and single-stranded molecules. Enhanced by these features, liquid biopsies hold promise for the noninvasive detection of tissue-specific pathologies with a range of clinical applications.

  • Mechanism and dynamics of fatty acid photodecarboxylase 

    Fatty acid photodecarboxylase (FAP) is a photoenzyme with potential green chemistry applications. By combining static, time-resolved, and cryotrapping spectroscopy and crystallography as well as computation, we characterized Chlorella variabilis FAP reaction intermediates on time scales from subpicoseconds to milliseconds. High-resolution crystal structures from synchrotron and free electron laser x-ray sources highlighted an unusual bent shape of the oxidized flavin chromophore. We demonstrate that decarboxylation occurs directly upon reduction of the excited flavin by the fatty acid substrate. Along with flavin reoxidation by the alkyl radical intermediate, a major fraction of the cleaved carbon dioxide unexpectedly transformed in 100 nanoseconds, most likely into bicarbonate. This reaction is orders of magnitude faster than in solution. Two strictly conserved residues, R451 and C432, are essential for substrate stabilization and functional charge transfer.

  • Structure and dynamics of the CGRP receptor in apo and peptide-bound forms 

    G protein–coupled receptors (GPCRs) are key regulators of information transmission between cells and organs. Despite this, we have only a limited understanding of the behavior of GPCRs in the apo state and the conformational changes upon agonist binding that lead to G protein recruitment and activation. We expressed and purified unmodified apo and peptide-bound calcitonin gene–related peptide (CGRP) receptors from insect cells to determine their cryo–electron microscopy (cryo-EM) structures, and we complemented these with analysis of protein conformational dynamics using hydrogen-deuterium exchange mass spectrometry and three-dimensional variance analysis of the cryo-EM data. Together with our previously published structure of the active, Gs-bound CGRP receptor complex, our work provides insight into the mechanisms of class B1 GPCR activation.