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Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 52,871 bioRxiv papers from 244,990 authors.

Most tweeted bioRxiv papers, last 24 hours

347 results found. For more information, click each entry to expand.

1: High precision coding in mouse visual cortex
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Posted to bioRxiv 21 Jun 2019

High precision coding in mouse visual cortex
591 tweets neuroscience

Carsen Stringer, Michalis Michaelos, Marius Pachitariu

Single neurons in visual cortex provide unreliable measurements of visual features due to their high trial-to-trial variability. It is not known if this "noise" extends its effects over large neural populations to impair the global encoding of sensory stimuli. We recorded simultaneously from ~20,000 neurons in mouse visual cortex and found that the neural population had discrimination thresholds of 0.3 degrees in an orientation decoding task. These thresholds are ~100 times smaller than those reported behaviorally in mice. The discrepancy between neural and behavioral discrimination could not be explained by the types of stimuli we used, by behavioral states or by the sequential nature of trial-by-trial perceptual learning tasks. These results imply that the limits of sensory perception in mice are not set by neural noise in sensory cortex, but by the limitations of downstream decoders.

2: The effect of bioRxiv preprints on citations and altmetrics
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Posted to bioRxiv 22 Jun 2019

The effect of bioRxiv preprints on citations and altmetrics
309 tweets scientific communication and education

Nicholas Fraser, Fakhri Momeni, Philipp Mayr, Isabella Peters

A potential motivation for scientists to deposit their scientific work as preprints is to enhance its citation or social impact, an effect which has been empirically observed for preprints in physics, astronomy and mathematics deposited to arXiv. In this study we assessed the citation and altmetric advantage of bioRxiv, a preprint server for the biological sciences. We retrieved metadata of all bioRxiv preprints deposited between November 2013 and December 2017, and matched them to articles that were subsequently published in peer-reviewed journals. Citation data from Scopus and altmetric data from Altmetric.com were used to compare citation and online sharing behaviour of bioRxiv preprints, their related journal articles, and non-deposited articles published in the same journals. We found that bioRxiv-deposited journal articles received a sizeable citation and altmetric advantage over non-deposited articles. Regression analysis reveals that this advantage is not explained by multiple explanatory variables related to the article and its authorship. bioRxiv preprints themselves are being directly cited in journal articles, regardless of whether the preprint has been subsequently published in a journal. bioRxiv preprints are also shared widely on Twitter and in blogs, but remain relatively scarce in mainstream media and Wikipedia articles, in comparison to peer-reviewed journal articles.

3: High genetic diversity can contribute to extinction in small populations
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Posted to bioRxiv 21 Jun 2019

High genetic diversity can contribute to extinction in small populations
80 tweets evolutionary biology

Christopher C. Kyriazis, Robert K Wayne, Kirk E Lohmueller

Human-driven habitat fragmentation and loss has led to a proliferation of small and isolated plant and animal populations that may be threatened with extinction by genetic factors. The prevailing approach for managing these populations is to maintain high genetic diversity, which is often equated with fitness. Increasingly, this is being done using genetic rescue, where individuals from populations with high genetic diversity are translocated to small populations with high levels of inbreeding. However, the potentially negative consequences of this approach have recently been highlighted by the demise of the gray wolf population on Isle Royale, which only briefly recovered after genetic rescue by a migrant from the large mainland wolf population and then declined to the brink of extinction. Here, we use ecologically-motivated population genetic simulations to show that extinction risk in small populations is often increased by maximizing genetic diversity but is consistently decreased by minimizing deleterious variation. Surprisingly, we find that small populations that are founded or rescued by individuals from large populations with high genetic diversity have an elevated risk of extinction due to the high levels of recessive deleterious variation harbored by large populations. By contrast, we show that genetic rescue or founding from small or moderate-sized populations leads to decreased extinction risk due to greater purging of strongly deleterious variants. Our findings challenge the traditional conservation paradigm that focuses on genetic diversity in assessing extinction risk in favor of a new view that emphasizes minimizing deleterious variation. These insights have immediate implications for managing small and isolated populations in the increasingly fragmented landscape of the Anthropocene.

4: A receptor for herbivore-associated molecular patterns mediates plant immunity
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Posted to bioRxiv 22 Jun 2019

A receptor for herbivore-associated molecular patterns mediates plant immunity
70 tweets plant biology

Adam D Steinbrenner, Maria Munoz-Amatriain, Jessica Montserrat Aguilar Venegas, Sassoum Lo, Da Shi, Nicholas Holton, Cyril Zipfel, Ruben Abagyan, Alisa Huffaker, Timothy J Close, Eric A. Schmelz

Plant-herbivore interactions are ubiquitous across nature and drive major agricultural losses. Inducible defense responses triggered through immune recognition aid in host plant protection; however, specific ligand-receptor pairs mediating the initial perception of herbivory remain unknown. Plants in the subtribe Phaseolinae detect herbivore-associated peptides in caterpillar oral secretions and the defined ligands are proteolytic fragments of chloroplastic ATP synthase termed inceptins. Using forward genetic mapping of inceptin-induced responses, we identify a cowpea (Vigna unguiculata) leucine-rich repeat receptor-like protein as an inceptin receptor (INR) sufficient for elicitor-induced responses and enhanced defense against armyworms (Spodoptera exigua). INR defines a receptor by which plants perceive herbivore-associated molecular patterns (HAMPs) and expands the paradigm of surface immune recognition to attack with mandibles.

5: Motility induced fracture reveals a ductile to brittle crossover in the epithelial tissues of a simple animal
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Posted to bioRxiv 19 Jun 2019

Motility induced fracture reveals a ductile to brittle crossover in the epithelial tissues of a simple animal
64 tweets biophysics

Vivek N. Prakash, Matthew Storm Bull, Manu Prakash

Animals are characterized by their movement, and their tissues are continuously subjected to dynamic force loading while they crawl, walk, run or swim [1]. Tissue mechanics fundamentally determine the ecological niches that can be endured by a living organism [2]. While epithelial tissues provide an important barrier function in animals, they are subjected to extreme strains during day to day physiological activities, such as breathing [1], feeding [3], and defense response [4]. However, failure or inability to withstand to these extreme strains can result in epithelial fractures [5, 6] and associated diseases [7,8]. From a materials science perspective, how properties of living cells and their interactions prescribe larger scale tissue rheology and adaptive response in dynamic force landscapes remains an important frontier [9]. Motivated by pushing tissues to the limits of their integrity, we carry out a multi-modal study of a simple yet highly dynamic organism, the Trichoplax Adhaerens [10,11,12], across four orders of magnitude in length (1um to 10 mm), and six orders in time (0.1 sec to 10 hours). We report the discovery of abrupt, bulk epithelial tissue fractures (10 sec) induced by the organisms own motility. Coupled with rapid healing (10 min), this discovery accounts for dramatic shape change and physiological asexual division in this early divergent metazoan. We generalize our understanding of this phenomena by codifying it in a heuristic model, highlighting the fundamental questions underlying the debonding/bonding criterion in a soft active living material by evoking the concept of an epithelial alloy. Using a suite of quantitative experimental and numerical techniques, we demonstrate a force driven ductile to brittle material transition governing the morphodynamics of tissues pushed to the edge of rupture. This work contributes to an important discussion at the core of developmental biology [13,14,15,16,17], with important applications to an emerging paradigm in materials and tissue engineering [5,18,19,20], wound healing and medicine [8,21,22].

6: Super-resolution Imaging Reveals 3D Structure and Organizing Mechanism of Accessible Chromatin
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Posted to bioRxiv 21 Jun 2019

Super-resolution Imaging Reveals 3D Structure and Organizing Mechanism of Accessible Chromatin
63 tweets molecular biology

Liangqi Xie, Peng Dong, Yifeng Qi, Margherita De Marzio, Xingqi Chen, Sambashiva Banala, Wesley R Legant, Brian P English, Anders Hansen, Anton Schulmann, Luke D. Lavis, Eric Betzig, Rafael Casellas, Howard Y. Chang, Bin Zhang, Robert Tjian, Zhe Liu

Access to cis-regulatory elements packaged in chromatin is essential for directing gene expression and cell viability. Here, we report a super-resolution imaging strategy, 3D ATAC-PALM, that enables direct visualization of the entire accessible genome. We found that active chromosomal segments are organized into spatially-segregated accessible chromatin domains (ACDs). Rapid depletion of CTCF or Cohesin (RAD21 subunit) induced enhanced ACD clustering, reduced physical separation between intrachromosomal ACDs, and differentially regulated ACD compaction. Experimental perturbations and polymer modeling suggest that dynamic protein-protein and protein-DNA interactions within ACDs couple with loop extrusion to organize ACD topology. Dysorganization of ACDs upon CTCF or Cohesin loss alters transcription factor binding and target search dynamics in living cells. These results uncover fundamental mechanisms underpinning the formation of 3D genome architecture and its pivotal function in transcriptional regulation.

7: Brain state stability during working memory is explained by network control theory, modulated by dopamine D1/D2 receptor function, and diminished in schizophrenia
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Posted to bioRxiv 23 Jun 2019

Brain state stability during working memory is explained by network control theory, modulated by dopamine D1/D2 receptor function, and diminished in schizophrenia
58 tweets neuroscience

Urs Braun, Anais Harneit, Giulio Pergola, Tommaso Menara, Axel Schaefer, Richard F Betzel, Zhenxiang Zang, Janina I. Schweiger, Kristina Schwarz, Junfang Chen, Giuseppe Blasi, Alessandro Bertolino, Daniel Durstewitz, Fabio Pasqualetti, Emanuel Schwarz, Andreas Meyer-Lindenberg, Danielle S. Bassett, Heike Tost

Dynamical brain state transitions are critical for flexible working memory but the network mechanisms are incompletely understood. Here, we show that working memory entails brain-wide switching between activity states. The stability of states relates to dopamine D1 receptor gene expression while state transitions are influenced by D2 receptor expression and pharmacological modulation. Schizophrenia patients show altered network control properties, including a more diverse energy landscape and decreased stability of working memory representations.

8: Genetic screens in isogenic mammalian cell lines without single cell cloning
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Posted to bioRxiv 23 Jun 2019

Genetic screens in isogenic mammalian cell lines without single cell cloning
50 tweets genetics

Peter C DeWeirdt, Kendall R Sanson, Ruth E Hanna, Mudra Hegde, Annabel K Sangree, Christine Strand, Nicole S Persky, John G. Doench

Isogenic pairs of cell lines, which differ by a single genetic modification, are powerful tools for understanding gene function. Generating such pairs for mammalian cells, however, is labor-intensive, time-consuming, and impossible in some cell types. Here we present an approach to create isogenic pairs of cells and screen them with genome-wide CRISPR-Cas9 libraries to generate genetic interaction maps. We queried the anti-apoptotic genes BCL2L1 and MCL1, and the DNA damage repair gene PARP1, via 25 genome-wide screens across 4 cell lines. For all three genes, we identify a rich set of both expected and novel buffering and synthetic lethal interactions. Further, we compare the interactions observed in genetic space to those found when targeting these genes with small molecules and identify hits that may inform the clinical uses for these inhibitors. We anticipate that this methodology will be broadly useful to comprehensively study genes of interest across many cell types.

9: There is no single functional atlas even for a single individual: Parcellation of the human brain is state dependent
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Posted to bioRxiv 01 Oct 2018

There is no single functional atlas even for a single individual: Parcellation of the human brain is state dependent
30 tweets neuroscience

Mehraveh Salehi, Abigail S. Greene, Amin Karbasi, Xilin Shen, Dustin Scheinost, R Todd Constable

The goal of human brain mapping has long been to delineate the functional subunits in the brain and elucidate the functional role of each of these brain regions. Recent work has focused on whole-brain parcellation of functional Magnetic Resonance Imaging (fMRI) data to identify these subunits and create a functional atlas. Functional connectivity approaches to understand the brain at the network level require such an atlas to assess connections between parcels and extract network properties. While no single functional atlas has emerged as the dominant atlas to date, there remains an underlying assumption that such an atlas exists. Using fMRI data from a highly sampled subject as well as two independent replication data sets, we demonstrate that functional parcellations based on fMRI connectivity data reconfigure substantially and in a meaningful manner, according to brain state.

10: Stop codon-proximal 3′UTR introns in vertebrates can elicit EJC-dependent Nonsense-Mediated mRNA Decay
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Posted to bioRxiv 21 Jun 2019

Stop codon-proximal 3′UTR introns in vertebrates can elicit EJC-dependent Nonsense-Mediated mRNA Decay
25 tweets molecular biology

Pooja Gangras, Thomas L Gallagher, Robert D Patton, Zhongxia Yi, Michael A Parthun, Kiel T Tietz, Natalie C Deans, Ralf Bundschuh, Sharon L Amacher, Guramrit Singh

The Exon Junction Complex (EJC) regulates many steps in post-transcriptional gene expression and is essential for cellular function and organismal development; however, EJC-regulated genes and genetic pathways during development remain largely unknown. To study EJC function during zebrafish development, we first established that zebrafish EJCs mainly bind ~24 nucleotides upstream of exon-exon junctions, and are also detected at more distant non-canonical positions. We then generated mutations in two zebrafish EJC core genes, rbm8a and magoh, and observed that homozygous mutant embryos show paralysis, muscle disorganization, neural cell death, and motor neuron outgrowth defects. Coinciding with developmental defects, mRNAs subjected to Nonsense-Mediated mRNA Decay (NMD) due to translation termination ≥ 50 nts upstream of the last exon-exon junction are upregulated in EJC mutant embryos. Surprisingly, several transcripts containing 3′UTR introns (3′UI) < 50 nts downstream of a stop codon are also upregulated in EJC mutant embryos. These proximal 3′UI-containing transcripts are also upregulated in NMD-compromised zebrafish embryos, cultured human cells, and mouse embryonic stem cells. Loss of function of foxo3b, one of the upregulated proximal 3′UI-containing genes, partially rescues EJC mutant motor neuron outgrowth. In addition to foxo3b, 166 other genes contain a proximal 3′UI in zebrafish, mouse and humans, and these genes are enriched in nervous system development and RNA binding functions. A proximal 3′UI-containing 3′UTR from one of these genes, HNRNPD, is sufficient to reduce steady state transcript levels when fused to a β-globin reporter in HeLa cells. Overall, our work shows that genes with stop codon-proximal 3′UIs encode a new class of EJC-regulated NMD targets with critical roles during vertebrate development.

11: Enhancer-dependence of gene expression increases with developmental age
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Posted to bioRxiv 21 Jun 2019

Enhancer-dependence of gene expression increases with developmental age
25 tweets molecular biology

Wenqing Cai, Jialiang Huang, Qian Zhu, Bin E Li, Davide Seruggia, Pingzhu Zhou, Minh Nguyen, Yuko Fujiwara, Huafeng Xie, Zhenggang Yang, Danni Hong, Pengfei Ren, Jian Xu, William T. Pu, Guocheng Yuan, Stuart H Orkin

How overall principles of gene regulation (the "logic") may change during ontogeny is largely unexplored. We compared transcriptomic, epigenomic and topological profiles in embryonic (EryP) and adult (EryD) erythroblasts. Despite reduced chromatin accessibility compared to EryP, distal chromatin of EryD is enriched in H3K27ac, Gata1 and Myb occupancy. In contrast to EryP-specific genes, which exhibit promoter-centric regulation through Gata1, EryD-specific genes employ distal enhancers for long-range regulation through enhancer-promoter looping, confirmed by Gata1 HiChIP. Genome editing demonstrated distal enhancers are required for gene expression in EryD but not in EryP. Applying a metric for enhancer-dependence of transcription, we observed a progressive reliance on enhancer control with increasing age of ontogeny among diverse primary cells and tissues of mouse and human origin. Our findings highlight fundamental and conserved differences in regulatory logic at distinct developmental stages, characterized by simpler promoter-centric regulation in embryonic cells and combinatorial enhancer-driven control in adult cells.

12: CD49f is a novel marker to purify functional human iPSC-derived astrocytes
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Posted to bioRxiv 21 Jun 2019

CD49f is a novel marker to purify functional human iPSC-derived astrocytes
23 tweets neuroscience

Lilianne Barbar, Tanya Jain, Matthew Zimmer, Ilya Kruglikov, Suzanne Burstein, Tomasz Rusielewicz, Madhura Nijsure, Gist Croft, Minghui Wang, Bin Zhang, Shane Liddelow, Valentina Fossati

Astrocytes play a central role in the central nervous system (CNS), maintaining brain homeostasis, providing metabolic support to neurons, regulating connectivity of neural circuits, and controlling blood flow as an integral part of the blood-brain barrier. They have been increasingly implicated in the mechanisms of neurodegenerative diseases, prompting a greater need for methods that enable their study. The advent of human induced pluripotent stem cell (iPSC) technology has made it possible to generate patient-specific astrocytes and CNS cells using protocols developed by our team and others as valuable disease models. Yet isolating astrocytes from primary specimens or from in vitro mixed cultures for downstream analyses has remained challenging. To address this need, we performed a screen for surface markers that allow FACS sorting of astrocytes. Here we demonstrate that CD49f is an effective marker for sorting functional human astrocytes. We sorted CD49f+ cells from a protocol we previously developed that generates a complex culture of oligodendrocytes, neurons and astrocytes from iPSCs. CD49f-purified cells express all canonical astrocyte markers and perform characteristic functions, such as neuronal support and glutamate uptake. Of particular relevance to neurodegenerative diseases, CD49f+ astrocytes can be stimulated to take on an A1 neurotoxic phenotype, in which they secrete pro-inflammatory cytokines and show an impaired ability to support neuronal maturation. This study establishes a novel marker for isolating functional astrocytes from complex CNS cell populations, strengthening the use of iPSC-astrocytes for the study of their regulation and dysregulation in neurodegenerative diseases.

13: Cellular and Molecular Probing of Intact Transparent Human Organs
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Posted to bioRxiv 21 May 2019

Cellular and Molecular Probing of Intact Transparent Human Organs
21 tweets cell biology

Shan Zhau, Mihail Ivilinov Todorov, Ruiyao Cai, Hanno Steinke, Elisabeth Kemter, Eckhard Wolf, Jan Lipfert, Ingo Bechmann, Ali Erturk

Optical tissue transparency permits cellular and molecular investigation of complex tissues in 3D, a fundamental need in biomedical sciences. Adult human organs are particularly challenging for this approach, owing to the accumulation of dense and sturdy molecules in decades-aged human tissues. Here, we introduce SHANEL method utilizing a new tissue permeabilization approach to clear and label stiff human organs. We used SHANEL to generate the first intact transparent adult human brain and kidney, and perform 3D histology using antibodies and dyes in centimeters depth. Thereby, we revealed structural details of the sclera, iris and suspensory ligament in the human eye, and the vessels and glomeruli in the human kidney. We also applied SHANEL on transgenic pig organs to map complex structures of EGFP expressing beta cells in >10 cm size pancreas. Overall, SHANEL is a robust and unbiased technology to chart the cellular and molecular architecture of intact large mammalian organs.

14: Reaction mechanisms of Pol IV, RDR2 and DCL3 drive RNA channeling in the siRNA-directed DNA methylation pathway
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Posted to bioRxiv 22 Jun 2019

Reaction mechanisms of Pol IV, RDR2 and DCL3 drive RNA channeling in the siRNA-directed DNA methylation pathway
20 tweets biochemistry

Jasleen Singh, Vibhor Mishra, Feng Wang, Hsiao-Yun Huang, Craig Pikaard

In eukaryotes with multiple small RNA pathways the mechanisms that channel RNAs within specific pathways are unclear. Here, we reveal the reactions that account for channeling in the siRNA biogenesis phase of the Arabidopsis RNA-directed DNA methylation pathway. The process begins with template DNA transcription by NUCLEAR RNA POLYMERASE IV (Pol IV) whose atypical termination mechanism, induced by nontemplate DNA basepairing, channels transcripts to the associated RNA-dependent RNA polymerase, RDR2. RDR2 converts Pol IV transcripts into double-stranded RNAs then typically adds an extra untemplated 3' terminal nucleotide to the second strands. The dicer endonuclease, DCL3 cuts resulting duplexes to generate 24 and 23nt siRNAs. The 23nt RNAs bear the untemplated terminal nucleotide of the RDR2 strand and are underrepresented among ARGONAUTE4-associated siRNAs. Collectively, our results provide mechanistic insights into Pol IV termination, Pol IV-RDR2 coupling and RNA channeling from template DNA transcription to siRNA guide strand/passenger strand discrimination.

15: Aging-Associated Decrease in the Histone Acetyltransferase KAT6B Causes Myeloid-Biased Hematopoietic Stem Cell Differentiation
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Posted to bioRxiv 22 Jun 2019

Aging-Associated Decrease in the Histone Acetyltransferase KAT6B Causes Myeloid-Biased Hematopoietic Stem Cell Differentiation
19 tweets cell biology

Eraj Shafiq Khokhar, Sneha Borikar, Elizabeth Eudy, Tim Stearns, Kira Young, Jennifer Trowbridge

Aged hematopoietic stem cells (HSCs) undergo biased lineage priming and differentiation toward production of myeloid cells. A comprehensive understanding of gene regulatory mechanisms causing HSC aging is needed to devise new strategies to sustainably improve immune function in aged individuals. Here, a focused shRNA screen of epigenetic factors reveals that the histone acetyltransferase Kat6b regulates myeloid cell production from hematopoietic progenitor cells. Within the stem and progenitor cell compartment, Kat6b is most highly expressed in long-term (LT)-HSCs and is significantly decreased with aging at the transcript and protein levels. Knockdown of Kat6b in young LT-HSCs causes skewed production of myeloid cells both in vitro and in vivo. Transcriptome analysis identifies enrichment of aging and macrophage-associated gene signatures alongside reduced expression of self-renewal and multilineage priming signatures. Together, our work identifies KAT6B as an epigenetic regulator of LT-HSC aging and a novel target to improve aged immune function.

16: Transcriptional Activation of Arabidopsis Zygotes Is Required for Their Initial Division
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Posted to bioRxiv 21 Jun 2019

Transcriptional Activation of Arabidopsis Zygotes Is Required for Their Initial Division
19 tweets developmental biology

Ping Kao, Michael Nodine

Commonly referred to as the maternal-to-zygotic transition, the shift of developmental control from maternal-to-zygotic genomes is a key event during animal and plant embryogenesis. Together with the degradation of parental gene products, the increased transcriptional activities of the zygotic genome remodels the early embryonic transcriptome during this transition. Although evidence from multiple flowering plants suggests that zygotes become transcriptionally active soon after fertilization, the timing and developmental requirements of zygotic genome activation in Arabidopsis thaliana (Arabidopsis) remained a matter of debate until recently. In this report, we optimized an expansion microscopy technique for robust immunostaining of Arabidopsis ovules and seeds. This enabled the detection of marks indicative of active transcription in zygotes before the first cell division. Moreover, we employed a live-imaging culture system together with transcriptional inhibitors to demonstrate that such active transcription is required in zygotes. Our results indicate that zygotic genome activation occurs soon after fertilization and is physiologically required prior to the initial zygotic division in Arabidopsis.

17: Aequorea victoria's secrets
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Posted to bioRxiv 19 Jun 2019

Aequorea victoria's secrets
18 tweets biochemistry

Gerard G Lambert, Hadrien Depernet, Guillaume Gotthard, Darrin T Schultz, lsabelle Navizet, Talley Lambert, Daphne S. Bindels, Vincent Levesque, Jennifer N Nero Moffatt, Anya Salih, Antoine Royant, Nathan C. Shaner

Using mRNA-Seq and de novo transcriptome assembly, we identified, cloned and characterized nine previously undiscovered fluorescent protein (FP) homologs from Aequorea victoria and a related Aequorea species, with most sequences highly divergent from avGFP. Among these FPs are the brightest GFP homolog yet characterized and a reversibly photochromic FP that responds to UV and blue light. Beyond green emitters, Aequorea species express purple- and blue-pigmented chromoproteins (CPs) with absorbances ranging from green to far-red, including two that are photoconvertible. X-ray crystallography revealed that Aequorea CPs contain a chemically novel chromophore with an unexpected crosslink to the main polypeptide chain. Because of the unique attributes of several of these newly discovered FPs, we expect that Aequorea will, once again, give rise to an entirely new generation of useful probes for bioimaging and biosensing.

18: Engineering bacteriocin-mediated resistance against plant pathogenic bacteria in plants
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Posted to bioRxiv 24 May 2019

Engineering bacteriocin-mediated resistance against plant pathogenic bacteria in plants
15 tweets plant biology

William M Rooney, Rhys Grinter, Annapaula Correia, Julian Parkhill, Daniel Walker, Joel J Milner

Pseudomonas syringae (Ps) and related plant pathogenic bacteria are responsible for losses in diverse crops such as tomato, kiwifruit, pepper, olive and soybean. Current solutions, involving the use of chemicals and the introduction of resistance genes, have enjoyed only limited success and may have adverse environmental impacts. Consequently, there is a pressing need to develop alternative technologies to address the problem of bacterial disease in crops. An alternative strategy is to utilise the narrow spectrum protein antibiotics (bacteriocins) used by diverse bacteria for competition against closely related species. Here, we demonstrate that active putidacin L1 (PL1) can be expressed at high levels in planta and expression of PL1 provides effective resistance against diverse pathovars of Ps. Furthermore, we found that strains which evolve to become insensitive to PL1; lose their O-antigen, exhibit reduced motility and are less virulent in PL1 transgenic plants. Our results provide proof-of-principle that transgene-mediated expression of a bacteriocin in planta is an effective strategy for providing disease resistance against bacterial pathogens. Genetically modified (GM) crops expressing insecticidal proteins have proved extremely successful as a strategy for pest management; expressing bacteriocins to control bacterial disease may have a similar potential. Crucially, nearly all genera of bacteria, including many plant pathogenic species, produce bacteriocins, providing an extensive source of these antimicrobial agents.

19: Effector prediction and characterization in the oomycete pathogen Bremia lactucae reveal host-recognized WY domain proteins that lack the canonical RXLR motif
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Posted to bioRxiv 22 Jun 2019

Effector prediction and characterization in the oomycete pathogen Bremia lactucae reveal host-recognized WY domain proteins that lack the canonical RXLR motif
15 tweets plant biology

Kelsey Jordan Wood, Munir Nur, Juliana Gil, Kyle Fletcher, Kim Lakeman, Ayumi Gothberg, Tina Khuu, Jennifer Kopetzky, Archana Pandya, Mathieu Pel, Richard Michelmore

Pathogens infecting plants and animals use a diverse arsenal of effector proteins to suppress the host immune system and promote infection. Identification of effectors in pathogen genomes is foundational to understanding mechanisms of pathogenesis, for monitoring field pathogen populations, and for breeding disease resistance. We identified candidate effectors from the lettuce downy mildew pathogen, Bremia lactucae, using comparative genomics and bioinformatics to search for the WY domain. This conserved structural element is found in Phytophthora effectors and some other oomycete pathogens; it has been implicated in the immune-suppressing function of these effectors as well as their recognition by host resistance proteins. We predicted 54 WY domain containing proteins in isolate SF5 of B. lactucae that have substantial variation in both sequence and domain architecture. These candidate effectors exhibit several characteristics of pathogen effectors, including an N-terminal signal peptide, lineage specificity, and expression during infection. Unexpectedly, only a minority of B. lactucae WY effectors contain the canonical N-terminal RXLR motif, which is a conserved feature in the majority of cytoplasmic effectors reported in Phytophthora spp. Functional analysis effectors containing WY domains revealed eleven out of 21 that triggered necrosis, which is characteristic of the immune response on wild accessions and domesticated lettuce lines containing resistance genes. Only two of the eleven recognized effectors contained a canonical RXLR motif, suggesting that there has been an evolutionary divergence in sequence motifs between genera; this has major consequences for robust effector prediction in oomycete pathogens.

20: The genomic impact of European colonization of the Americas
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Posted to bioRxiv 21 Jun 2019

The genomic impact of European colonization of the Americas
14 tweets genomics

Linda Ongaro, Marilia O Scliar, Rodrigo Flores, Alessandro Raveane, Davide Marnetto, Stefania Sarno, Guido A Gnecchi-Ruscone, Marta E Alarcon-Riquelme, Etienne Patin, Pongsakorn Pongsakorn, Garrett Hellenthal, Miguel Gonzalez-Santos, Roy J King, Anastasia Kouvatsi, Oleg Balanovsky, Elena Balanovska, Lubov Atramentova, Shahlo Turdikulova, Sarabjit Mastana, Damir Marjanovic, Lejla Kovacevic, Andreja Leskovac, Maria F Lima-Costa, Alexandre C Pereira, Mauricio L Barreto, Bernardo L. Horta, Nédio Mabunda, Celia A May, Andrés Moreno-Estrada, Alessandro Achilli, Anna Olivieri, Ornella Semino, Kristiina Tambets, Toomas Kivisild, Donata Luiselli, Antonio Torroni, Cristian Capelli, Eduardo Tarazona-Santos, Mait Metspalu, Luca Pagani, Francesco Montinaro

The human genetic diversity of the Americas has been shaped by several events of gene flow that have continued since the Colonial Era and the Atlantic slave trade. Moreover, multiple waves of migration followed by local admixture occurred in the last two centuries, the impact of which has been largely unexplored. Here we compiled a genome-wide dataset of ~12,000 individuals from twelve American countries and ~6,000 individuals from worldwide populations and applied haplotype-based methods to investigate how historical movements from outside the New World affected i) the genetic structure, ii) the admixture profile, iii) the demographic history and iv) sex-biased gene-flow dynamics, of the Americas. We revealed a high degree of complexity underlying the genetic contribution of European and African populations in North and South America, from both geographic and temporal perspectives, identifying previously unreported sources related to Italy, the Middle East and to specific regions of Africa.

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