News & Views |
Featured
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Article |
Cell signalling by microRNA165/6 directs gene dose-dependent root cell fate
A fundamental question in developmental biology is how cells communicate positional information to pattern the tissues of an organ. Here, the patterning of a plant's xylem tubes, which transport water and solutes from root to shoot, is studied. A new bidirectional signalling pathway is discovered, whereby a transcription factor moves from cell to cell in one direction, and microRNAs move in the other direction. The result is a differential distribution of target mRNA in the vascular cylinder, determining xylem cell types.
- Annelie Carlsbecker
- , Ji-Young Lee
- & Philip N. Benfey
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Letter |
The scaffold protein Ste5 directly controls a switch-like mating decision in yeast
Before mating, a yeast cell must detect a partner cell that is close enough and expresses sufficiently large amounts of a sex pheromone. The mating decision is an all-or-none, switch-like response to pheromone concentration. It is now shown that this decision involves the competition of one kinase and one phosphatase enzyme for multiple phosphorylation sites on a 'scaffold' protein. The results should prompt a re-evaluation of the role of related signalling molecules that have been implicated in cancer.
- Mohan K. Malleshaiah
- , Vahid Shahrezaei
- & Stephen W. Michnick
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Letter |
Native GABAB receptors are heteromultimers with a family of auxiliary subunits
GABAB receptors are the G-protein-coupled receptors for γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain. Here, functional proteomics is used to show that GABAB receptors in the brain are complexes of GABAB1, GABAB2 and members of a subfamily of KCTD proteins. The KCTD proteins increase the potency of agonists and markedly alter the G-protein signalling of the receptors, suggesting that they determine the pharmacology and kinetics of the receptor response.
- Jochen Schwenk
- , Michaela Metz
- & Bernhard Bettler
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Letter |
Functional genomic screen for modulators of ciliogenesis and cilium length
Primary cilia are tiny hair-like structures expressed on the surface of eukaryotic cells. They participate in a range of processes, such as sensing the extracellular environment and regulating signalling pathways during development. Here, a functional genomic screen is presented that used RNA interference to identify human genes involved in controlling ciliogenesis. Several positive and negative ciliogenesis modulators with broad-ranging functions were found.
- Joon Kim
- , Ji Eun Lee
- & Joseph G. Gleeson
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Letter |
APCDD1 is a novel Wnt inhibitor mutated in hereditary hypotrichosis simplex
Hereditary hypotrichosis simplex is a rare form of hereditary hair loss in humans, where the hair follicle is miniaturized. Now, the gene involved has been identified, using genetic linkage analysis in three affected families. The gene, APCDD1, is expressed in human hair follicles. It encodes a previously unknown membrane-bound glycoprotein that inhibits signalling through the Wnt protein and functions upstream of β-catenin.
- Yutaka Shimomura
- , Dritan Agalliu
- & Angela M. Christiano
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Letter |
Control of mammary stem cell function by steroid hormone signalling
The ovarian hormones oestrogen and progesterone increase breast cancer risk but the cellular mechanisms are unclear. Here it is shown that the size of the mammary stem cell pool in mice is regulated by steroid hormone signalling, although these cells lack the receptors for oestrogen and progesterone. The augmented pool could lead to clonal expansion of a mutated cell, possibly accounting for the increased incidence of breast cancer associated with pregnancy.
- Marie-Liesse Asselin-Labat
- , François Vaillant
- & Jane E. Visvader
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Letter |
MicroRNA-mediated integration of haemodynamics and Vegf signalling during angiogenesis
During embryonic development, blood vessels remodel in response to blood flow. Here, a genetic pathway is described through which this mechanosensory stimulus is integrated with early developmental signals to remodel vessels of the aortic arch in zebrafish. It is found that the flow-induced transcription factor klf2a is required to induce the expression of an endothelial-specific microRNA, activating signalling through the growth factor Vegf.
- Stefania Nicoli
- , Clive Standley
- & Nathan D. Lawson
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Article |
Dendritic organization of sensory input to cortical neurons in vivo
Many sensory neurons in the mammalian cortex are tuned to specific stimulus features — for example, some fire only when horizontal bars move from top to bottom in the visual field. But it has been unclear whether such tuning is encoded in a neuron's inputs, or whether the neuron itself computes its response. Here, a new technique for visualizing and mapping sensory inputs to the dendrites of neurons in the mouse visual cortex has shown that each neuron makes its own 'decision' as to the orientation preference of its output.
- Hongbo Jia
- , Nathalie L. Rochefort
- & Arthur Konnerth
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Letter |
Control of cortical GABA circuitry development by Nrg1 and ErbB4 signalling
Although several synaptic adhesion proteins have been identified as genetic risk factors in schizophrenia, it is unclear as to what role they play in disease progression. Here, it is shown that two such proteins — neuregulin 1 and its receptor ErbB4 — function to regulate the connectivity of specific cortical circuits. The study not only implicates these proteins in the wiring of inhibitory synapses, about which little is known, but also provides a new perspective on their involvement in schizophrenia.
- Pietro Fazzari
- , Ana V. Paternain
- & Beatriz Rico
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Article |
Phenotypic profiling of the human genome by time-lapse microscopy reveals cell division genes
High-throughput microscopy combined with gene silencing by RNA interference is a powerful method for studying gene function. Here, a genome-wide method is presented for phenotypic screening of each of the ∼21,000 human protein-coding genes, using two-day imaging of dividing cells with fluorescently labelled chromosomes. The method enabled the identification of hundreds of genes involved in biological functions such as cell division, migration and survival.
- Beate Neumann
- , Thomas Walter
- & Jan Ellenberg
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Article |
Adiponectin and AdipoR1 regulate PGC-1α and mitochondria by Ca2+ and AMPK/SIRT1
Adiponectin is a protein with anti-diabetic properties; its levels are decreased in obesity, insulin resistance and type 2 diabetes. It is shown here that mice with a muscle-specific disruption of adiponectin receptor 1 (AdipoR1) are insulin resistant and less able to endure exercise. The pathway downstream of receptor activation is delineated; the findings suggest that the decreased levels of adiponectin and AdipoR1 seen in obesity may have causal roles in the mitochondrial dysfunction and insulin resistance seen in diabetes.
- Masato Iwabu
- , Toshimasa Yamauchi
- & Takashi Kadowaki
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Letter |
NINJA connects the co-repressor TOPLESS to jasmonate signalling
In plants, the hormone jasmonoyl-isoleucine (JA-Ile) regulates growth, development and defence against pathogens. Proteins of the JAZ family repress JA-Ile-dependent gene expression, but the mechanism has been unclear. Here, an adaptor protein, NINJA, has been identified, which recruits co-repressor proteins that are known to mediate auxin-responsive gene expression as well. Hence these co-repressors are part of general repression complexes that are recruited to several different signalling pathways.
- Laurens Pauwels
- , Gemma Fernández Barbero
- & Alain Goossens
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News & Views |
Genome-wide view of mitosis
An exceptionally large-scale project aimed at assigning function to all protein-coding genes in the human genome is reported on page 721 by Neumann et al.
1 . Here are two complementary views on the experimental design and analysis, and on how useful the findings will be to cell biologists.- Jason R. Swedlow
- , Cecilia Cotta-Ramusino
- & Stephen J. Elledge
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Letter |
Chemoprevention of colorectal cancer by targeting APC-deficient cells for apoptosis
Cancer 'chemoprevention' uses substances to reverse, suppress or prevent the initial phase of carcinogenesis or the progression of neoplastic cells to cancer cells. Here it is shown that treatment with TRAIL proteins and all-trans-retinyl acetate can cause the death, in vitro and in vivo, of premalignant cells deficient in the adenomatous polyposis coli gene. Normal cells are unaffected. Selectively eliminating premalignant tumour cells in this way is thus an effective method for chemoprevention.
- Ling Zhang
- , Xiaoyang Ren
- & Xiangwei Wu
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Letter |
Haploid plants produced by centromere-mediated genome elimination
Making haploid plants — which inherit chromosomes from only one parent — is useful for genetic research and also, crucially, for plant breeding. A new method for generating haploid Arabidopsis plants is now described, involving the manipulation of a single centromeric protein, CENH3. When cenh3 null plants are crossed with wild-type plants, the mutant chromosomes are eliminated, producing haploid progeny.
- Maruthachalam Ravi
- & Simon W. L. Chan
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Review Article |
Linking functional decline of telomeres, mitochondria and stem cells during ageing
- Ergün Sahin
- & Ronald A. DePinho
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Review Article |
Neural mechanisms of ageing and cognitive decline
- Nicholas A. Bishop
- , Tao Lu
- & Bruce A. Yankner
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Article |
Zscan4 regulates telomere elongation and genomic stability in ES cells
Zscan4 is shown to be involved in maintaining telomeres in embryonic stem (ES) cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once within nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis–specific homologous recombination genes. Knocking down Zscan4 shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages.
- Michal Zalzman
- , Geppino Falco
- & Minoru S. H. Ko
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Article |
Molecular mechanism of multivesicular body biogenesis by ESCRT complexes
Here, multivesicular body (MVB) biogenesis is reconstituted using giant unilamellar vesicles and all of the ESCRT complexes. ESCRT-0 is required for clustering of cargo proteins, whereas ESCRT-I and -II in combination deform the membrane into buds, in which cargo is confined. ESCRT-III subunits localize to the bud neck and are required for scission of the membrane to form intraluminal vesicles. These results explain how ESCRT complexes sequester cargo proteins into MVBs.
- Thomas Wollert
- & James H. Hurley
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Letter |
Identification of two evolutionarily conserved genes regulating processing of engulfed apoptotic cells
In multicellular organisms, apoptotic cells are removed from tissues by phagocytes, which recognize and engulf the dying cells. The molecular mechanisms underlying the subsequent degradation of the cells have been unclear. Here, two evolutionarily conserved genes have been identified that are required for such processing in Caenorhabditis elegans and mammals. An understanding of these events could lead to new treatments for diseases associated with poor engulfment and destruction of dying cells.
- Jason M. Kinchen
- & Kodi S. Ravichandran
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Article |
Skp2 targeting suppresses tumorigenesis by Arf-p53-independent cellular senescence
Cellular senescence — an irreversible cell-cycle arrest — has been implicated in suppressing tumour formation or growth. A new cellular signalling pathway that drives senescence has now been identified. This pathway does not involve most known mediators of senescence, and instead signals via the proteins Atf4, p27 and p21. Inactivating the proto-oncogene Skp2 in the context of oncogenic signalling can induce senescence through this new pathway, indicating that drugs that target Skp2 might be useful in cancer treatment.
- Hui-Kuan Lin
- , Zhenbang Chen
- & Pier Paolo Pandolfi
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News & Views |
Actin filaments up against a wall
The front of motile cells is thought to be pushed out by branched filaments of actin protein abutting the cell membrane. New work challenges this textbook view, showing that actin branches grow away from, or obliquely to, a surface.
- Cécile Sykes
- & Julie Plastino
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News & Views |
A lower bar for senescence
Cellular senescence is a physiological mechanism for thwarting the proliferation of tumour cells. Encouraging cancer-prone cells to senesce might therefore be a way to nip this disease in the bud.
- Manuel Serrano
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Letter |
Phosphorylation of histone H3T6 by PKCβI controls demethylation at histone H3K4
The amino-terminal tails of histone proteins are subject to a variety of post-translational modifications; addition or removal of these 'marks' facilitates gene activation or silencing. Here, a mechanism is defined that modulates the activity of the dual-specificity histone demethylase LSD1 during androgen-dependent transcription. Androgen-dependent signalling through protein kinase C beta I leads to phosphorylation of a histone amino acid, which prevents demethylation of an adjacent amino acid by LSD1.
- Eric Metzger
- , Axel Imhof
- & Roland Schüle
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Research Highlights |
Neuroscience: Nerve cell talk
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Research Highlights |
Cancer biology: Arsenic activation
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Letter |
Spatial control of EGF receptor activation by reversible dimerization on living cells
Signalling through the epidermal growth factor receptor (EGFR) is preceded by its dimerization, which has typically been thought to occur through a ligand-induced conformational change. Here, the dimerization dynamics of individual EGFR molecules have been determined in living cells in real time, using a quantum-dot-based approach. Unliganded EGFR molecules undergo spontaneous and reversible dimerization; these pre-formed dimers are primed for ligand binding and signalling and are enriched at the cell periphery.
- Inhee Chung
- , Robert Akita
- & Ira Mellman
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News |
How the cell's powerhouses turn deadly
Mitochondria can trigger a lethal immune response after injuries.
- Heidi Ledford
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Article |
Systems survey of endocytosis by multiparametric image analysis
A new strategy is presented to accurately profile the activity of human genes in endocytosis by combining genome-wide RNAi, automated high-resolution confocal microscopy and quantitative multi-parametric image analysis. Several novel components of endocytosis and endosome trafficking were uncovered; a systems analysis further revealed that the cell regulates the number, size and concentration of cargo within endosomes.
- Claudio Collinet
- , Martin Stöter
- & Marino Zerial
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Research Highlights |
Cell biology: Lost in the mail
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News & Views |
A brake on lipid synthesis
Although sphingolipids are vital cellular components, the path to their production is paved with toxic intermediates. Orm proteins allow cells to form these lipids without killing themselves in the process.
- Fikadu G. Tafesse
- & Joost C. M. Holthuis
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Letter |
Compensatory evolution in mitochondrial tRNAs navigates valleys of low fitness
Evolution from one fitness peak to another must involve either transitions through intermediates of low fitness or skirting round the fitness valley through compensatory mutations elsewhere. Here, the base pairs in mitochondrial tRNA stems is used as a model to show that deep fitness valleys can be traversed. Transitions between AU and GC pairs have occurred during mammalian evolution without help from genetic drift or mutations elsewhere.
- Margarita V. Meer
- , Alexey S. Kondrashov
- & Fyodor A. Kondrashov
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Letter |
An intrinsic vasopressin system in the olfactory bulb is involved in social recognition
Peptide hormones such as oxytocin and vasopressin influence social behaviour in several mammalian species. Here it is shown that a population of interneurons in the rat olfactory bulb releases vasopressin, and that vasopressin signalling is required in the olfactory system for proper social recognition in rats. Although vasopressin may not work in exactly the same way in humans, social recognition mediated by experience-dependent vasopressin release may be common.
- Vicky A. Tobin
- , Hirofumi Hashimoto
- & Mike Ludwig
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Letter |
RAF inhibitors transactivate RAF dimers and ERK signalling in cells with wild-type BRAF
The RAS–RAF signalling pathway is an attractive target for drug development in oncology, and several RAF inhibitors are being tested in clinical trials. Here and in an accompanying paper, RAF inhibitors are shown to have opposing roles, functioning as either inhibitors or activators of RAF depending on the cellular context and mutational status of RAF. The mechanistic basis for these opposing roles is dissected. The results have implications for the clinical use of these inhibitors and for the design of kinase inhibitors.
- Poulikos I. Poulikakos
- , Chao Zhang
- & Neal Rosen
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Letter |
Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards
The existence of all-female species of whiptail lizard, formed as a hybrid between sexual species, has been known since 1962; however, how the meiotic program is altered to produce diploid eggs while maintaining heterozygosity has remained unclear. Here it is shown in parthenogenetic species that meiosis initiates with twice the number of chromosomes compared to sexual species, and that pairing and recombination takes place between genetically identical sister chromosomes instead of between homologues.
- Aracely A. Lutes
- , William B. Neaves
- & Peter Baumann
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Letter |
Rere controls retinoic acid signalling and somite bilateral symmetry
The vertebrate body plan shows marked bilateral symmetry, although this can be disrupted in conditions such as scoliosis. Here, a mutation in Rere is found that leads to the formation of asymmetrical somites in mouse embryos; furthermore, Rere is shown to control retinoic acid signalling, which is required to maintain somite symmetry by interacting with Fgf8. The results provide insight into how bilateral symmetry is maintained.
- Gonçalo C. Vilhais-Neto
- , Mitsuji Maruhashi
- & Olivier Pourquié
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Letter |
Telomere elongation in induced pluripotent stem cells from dyskeratosis congenita patients
Here, iPS cell technology is used to study the mechanisms underlying dyskeratosis congenita in humans. Reprogramming restores telomere elongation in dyskeratosis congenita cells despite genetic lesions affecting telomerase. The reprogrammed cells were able to overcome a critical limitation in telomerase RNA component (TERC) levels to restore telomere maintenance and self-renewal, and multiple telomerase components are targeted by pluripotency-associated transcription factors.
- Suneet Agarwal
- , Yuin-Han Loh
- & George Q. Daley
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Letter |
Differential innate immune signalling via Ca2+ sensor protein kinases
Plants and animals sense intruding pathogens by using proteins that recognize diverse microbe-associated molecular patterns (MAMPs) and initiate innate immune responses. Early signalling responses in the host include calcium influx, an oxidative burst and transcriptional reprogramming. Here, four calcium-dependent protein kinases are described that function as calcium sensors, act as convergence points for various MAMPs, and are crucial for transcriptional reprogramming and oxidative burst in plants.
- Marie Boudsocq
- , Matthew R. Willmann
- & Jen Sheen
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Letter |
Mical links semaphorins to F-actin disassembly
Semaphorins and their receptors, plexins, relay guidance information to neurons during development and regulate actin dynamics through an unknown mechanism. Recently, proteins of the Mical family of enzymes have been found to associate with plexins; here, Mical is reported to directly link semaphorins and their plexin receptors to the precise control of actin filament dynamics.
- Ruei-Jiun Hung
- , Umar Yazdani
- & Jonathan R. Terman
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Research Highlights |
Stem cells: Uneven divide
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News & Views |
Mitochondrial damage control
Defects in mitochondria are implicated in Parkinson's disease. Study of a quality-control pathway involving the proteins PINK1 and Parkin provides further clues about the mechanism involved.
- Asa Abeliovich
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Letter |
Enzyme-inhibitor-like tuning of Ca2+ channel connectivity with calmodulin
Ca2+ channels and calmodulin (CaM) are two prominent hubs of biological signalling networks, affecting functions such as cardiac excitability and gene transcription. The prevailing view has been that the ultrastrong affinity of channels for the Ca2+-free form of calmodulin (apoCaM) ensures their saturation with CaM and yields a form of concentration independence between Ca2+ channels and CaM. Here, however, significant exceptions to this autonomy are shown to exist.
- Xiaodong Liu
- , Philemon S. Yang
- & David T. Yue
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Article |
Plasmepsin V licenses Plasmodium proteins for export into the host erythrocyte
To survive and evade host responses, malaria parasites export several hundred proteins into the host cell on infection. A feature of these proteins is a conserved, pentameric motif that is cleaved by an unknown protease before export. This is one of two independent studies revealing the identity of the protease as plasmepsin V, an aspartic acid protease located in the endoplasmic reticulum. This enzyme is essential for parasite viability and is an attractive candidate for drug development.
- Ilaria Russo
- , Shalon Babbitt
- & Daniel E. Goldberg
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Article |
An aspartyl protease directs malaria effector proteins to the host cell
To survive and evade host responses, malaria parasites export several hundred proteins into the host cell on infection. A feature of these proteins is a conserved, pentameric motif that is cleaved by an unknown protease before export. This is one of two independent studies revealing the identity of the protease as plasmepsin V, an aspartic acid protease located in the endoplasmic reticulum. This enzyme is essential for parasite viability and is an attractive candidate for drug development.
- Justin A. Boddey
- , Anthony N. Hodder
- & Alan F. Cowman
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Letter |
TGF-β–FOXO signalling maintains leukaemia-initiating cells in chronic myeloid leukaemia
Chronic myeloid leukaemia is caused by a BCR-ABL fusion, a constitutively active tyrosine kinase that, it is believed, leads to suppression of the forkhead O transcription factors (FOXO). Although the use of the tyrosine kinase inhibitor imatinib is a breakthrough for CML therapy, imatinib does not deplete the leukaemia-initiating cells (LICs) that drive the recurrence of CML. Foxo3a is now shown to have an essential role in the maintenance of CML LICs in a mouse model.
- Kazuhito Naka
- , Takayuki Hoshii
- & Atsushi Hirao
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Research Highlights |
Imaging: Virus vision
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