Biology subjects

Wright, S.

Publications and source records attributed to Wright, S..

At least 37 records · Page 2Linked to original sources

bioRxiv2023

Spatial and single-nucleus transcriptomic analysis of genetic and sporadic forms of Alzheimer's Disease

The pathogenesis of Alzheimers disease (AD) depends on environmental and heritable factors, with remarkable differences evident between individuals at the molecular level. Here we present a transcriptomic survey of AD using spatial transcriptomics (ST) and single-nucleus RNA-seq in cortical samples from early-stage AD, late-stage AD, and AD in Down Syndrome (AD in DS) donors. Studying AD in DS provides an opportunity to enhance our understanding of the AD transcriptome, potentially bridging the gap between genetic mouse models and sporadic AD. Our analysis revealed spatial and cell-type specific changes in disease, with broad similarities in these changes between sAD and AD in DS. We performed additional ST experiments in a disease timecourse of 5xFAD and wildtype mice to facilitate cross-species comparisons. Finally, amyloid plaque and fibril imaging in the same tissue samples used for ST enabled us to directly link changes in gene expression with accumulation and spread of pathology.

neuroscience↗

bioRxiv2022

The microbial community dynamics of cocaine sensitization in two behaviorally divergent strains of collaborative cross mice

The gut-brain axis is increasingly recognized as an important pathway involved in cocaine use disorder. Microbial products of the murine gut have been shown to affect striatal gene expression, and depletion of the microbiome by antibiotic treatment alters cocaine-induced behavioral sensitization in C57BL/6J male mice. Some reports suggest that cocaine-induced behavioral sensitization is correlated with drug self-administration behavior in mice. Here we profile the composition of the naive microbiome and its response to cocaine sensitization in two Collaborative Cross (CC) strains. These strains display extremely divergent behavioral responses to cocaine sensitization. A high-responding strain, CC004/TauUncJ (CC04), has a gut microbiome that contains a greater amount of Lactobacillus than the cocaine-nonresponsive strain CC041/TauUncJ (CC41). The gut microbiome of CC41 is characterized by an abundance of Eisenbergella, Robinsonella and Ruminococcus. In response to cocaine, CC04 has an increased Barnsiella population, while the gut microbiome of CC41 displays no significant changes. PICRUSt functional analysis of the functional potential of the gut microbiome in CC04 shows a significant number of potential gut-brain modules altered after exposure to cocaine, specifically those encoding for tryptophan synthesis, glutamine metabolism, and menaquinone synthesis (vitamin K2). Depletion of the microbiome by antibiotic treatment revealed an altered cocaine-sensitization response following antibiotics in female CC04 mice. Depleting the microbiome by antibiotic treatment in males revealed increased infusions for CC04 during a cocaine intravenous self-administration dose-response curve. Together these data suggest that genetic differences in cocaine-related behaviors may involve the microbiome. FUNDINGU01DA043809 to JAB, GMW P50DA039841 to EJC

animal behavior and cognition↗

bioRxiv2022

Microbial glutamate metabolism predicts intravenous cocaine self-administration in Diversity Outbred mice

The gut microbiome is thought to play a critical role in the onset and development of psychiatric disorders, including depression and substance use disorder (SUD). To test the hypothesis that the microbiome affects addiction predisposing behaviors and cocaine intravenous self-administration (IVSA) and to identify specific microbes involved in the relationship, we performed 16S rRNA gene sequencing on feces from 228 diversity outbred mice. Twelve open field measures, two light-dark assay measures, one hole board and novelty place preference measure significantly differed between mice that acquired cocaine IVSA (ACQ) and those that failed to acquire IVSA (FACQ). We found that ACQ mice are more active and exploratory and display decreased fear than FACQ mice. The microbial abundances that differentiated ACQ from FACQ mice were an increased abundance of Barnesiella, Ruminococcus, and Robinsoniella and decreased Clostridium IV in ACQ mice. There was a sex-specific correlation between ACQ and microbial abundance, a reduced Lactobacillus abundance in ACQ male mice, and a decreased Blautia abundance in female ACQ mice. The abundance of Robinsoniella was correlated, and Clostridium IV inversely correlated with the number of doses of cocaine self-administered during acquisition. Functional analysis of the microbiome composition of a subset of mice suggested that gut-brain modules encoding glutamate metabolism genes are associated with the propensity to self-administer cocaine. These findings establish associations between the microbiome composition and glutamate metabolic potential and the ability to acquire cocaine IVSA thus indicating the potential translational impact of targeting the gut microbiome or microbial metabolites for treatment of SUD. HIGHLIGHTSO_LICorrelational analysis of novelty behaviors to IVSA acquisition shows that mice that acquire cocaine IVSA are more active and exploratory and have decreased fear than those that failed-to-acquire IVSA. C_LIO_LIThe gut microbiome profiling of 228 diversity outbred mice indicates the relative abundances of Barnesiella, Ruminococcus, Robinsoniella and Clostridium IV are associated with the ability to self-administer cocaine. C_LIO_LIAssociations between the gut microbiome and IVSA acquisition are sex-specific. Decreased relative abundances of Lactobacillus and Blautia are associated with IVSA in male and female mice, respectively. C_LIO_LIThe relative abundances of Robinsoniella and Clostridium IV were correlated with the number of infusions of self-administered cocaine. C_LIO_LIFunctional potential analysis of the gut microbiome supports a role for microbiomes encoding glutamate metabolism in the ability to self-administer cocaine. C_LI

neuroscience↗

bioRxiv2021

Genetic evidence that uptake of the fluorescent analog 2NBDG occurs independently of known glucose transporters

The fluorescent derivative of glucose, 2-Deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)-amino]-D-glucose (2NBDG), is a widely used surrogate reagent to visualize glucose uptake in live cells at single cell resolution. Using a model of CRISPR-Cas9 gene editing in 5TGM1 myeloma cells, we demonstrate that ablation of the glucose transporter gene Slc2a1 abrogates radioactive glucose uptake but has no effect on the magnitude or kinetics of 2NBDG import. Extracellular 2NBDG, but not NBD-fructose was transported by plasma cells into the cytoplasm suggesting specific activity that is unlinked to glucose import and that of chemically similar compounds. RNA-Seq analysis of primary plasma cells and the 5TGM1 myeloma cell line revealed expression of other candidate glucose transporters. Yet, deletion of these transporters individually or in combination with one another also had no impact on 2NBDG uptake. Ablation of the genes in the Slc29 and Slc35 families of nucleoside and nucleoside sugar transporters as well as the ATP-binding cassette (ABC) transporter family also failed to impact 2NBDG import. Thus, cellular uptake of 2NBDG is promoted by an unknown mechanism and is not a faithful indicator of glucose transport.

immunology↗

bioRxiv2021

Developmental and environmental plasticity in opsin gene expression in Lake Victoria cichlid fish

In many organisms, sensory abilities develop and evolve according to the changing demands of navigating, foraging and communication across different environments and life stages. Teleost fish inhabit heterogeneous light environments and exhibit a large diversity in visual system properties among species. Cichlids are a classic example of this diversity, generated by different tuning mechanisms that involve both genetic factors and phenotypic plasticity. Here, we document the developmental progression of visual pigment gene expression in Lake Victoria cichlids and test if these patterns are influenced by variation in light conditions. We reared two sister species of Pundamilia to adulthood in two distinct visual conditions that resemble the two light environments that they naturally inhabit in Lake Victoria. We also included interspecific first-generation hybrids. We then quantified (using RT-qPCR) the expression of the four Pundamilia opsins (SWS2B, SWS2A, RH2A and LWS) at 14 time points. We find that opsin expression profiles progress from shorter-wavelength sensitive opsins to longer-wavelength sensitive opsins with increasing age, in both species and their hybrids. The developmental trajectories of opsin expression also responded plastically to the visual conditions. Finally, we found subtle differences between reciprocal hybrids, possibly indicating parental effects and warranting further investigation. Developmental and environmental plasticity in opsin expression may provide an important stepping stone in the evolution of cichlid visual system diversity. Research highlightsIn Lake Victoria cichlid fish, expression levels of opsin genes (encoding visual pigments) differ between developmental stages and between experimental light treatments. This plasticity may contribute to the evolution of cichlid visual system diversity.

evolutionary biology↗

bioRxiv2021

Substrate, temperature, and geographical patterns among nearly 2,000 natural yeast isolates

Yeasts have broad importance as industrially and clinically relevant microbes and as powerful models for fundamental research, but we are only beginning to understand the roles yeasts play in natural ecosystems. Yeast ecology is often more difficult to study compared to other, more abundant microbes, but growing collections of natural yeast isolates are beginning to shed light on fundamental ecological questions. Here we used environmental sampling and isolation to assemble a dataset of 1,962 isolates collected from throughout the contiguous United States of America (USA) and Alaska, which were then used to uncover geographic patterns, along with substrate and temperature associations among yeast taxa. We found some taxa, including the common yeasts Torulaspora delbrueckii and Saccharomyces paradoxus, to be repeatedly isolated from multiple sampled regions of the US, and we classify these as broadly distributed cosmopolitan yeasts. A number of yeast taxon - substrate associations were identified, some of which were novel and some of which support previously reported associations. Further, we found a strong effect of isolation temperature on the phyla of yeasts recovered, as well as for many species. We speculate that substrate and isolation temperature associations reflect the ecological diversity of and niche partitioning by yeast taxa. Take AwayO_LIAnalysis of environmental metadata of nearly 2,000 yeast isolates. C_LIO_LIIndividual yeast taxa associate with specific substrates and plant genera. C_LIO_LIOptimal yeast isolation temperature differs depending on taxonomic rank. C_LIO_LISubstrate type and isolation temperatures affect isolated yeast diversity. C_LI

ecology↗

bioRxiv2021

Encephalitis patient derived monoclonal GABAA receptor antibodies cause catatonia and epileptic seizures

Autoantibodies targeting the GABAA receptor (GABAAR) hallmark an autoimmune encephalitis presenting with frequent seizures and psychomotor abnormalities. Their pathogenic role is still not well-defined, given the common overlap with further autoantibodies and the lack of patient derived monoclonal antibodies (mAbs). We cloned and recombinantly produced five affinity-maturated GABAAR IgG1 mAbs from cerebrospinal fluid cells, which bound to various epitopes involving 1 and {gamma}2 receptor subunits, with variable binding strength and partial competition. mAbs selectively reduced GABAergic currents in neuronal cultures without causing receptor internalization. Cerebroventricular infusion of GABAAR mAbs and Fab fragments into rodents induced a severe phenotype with catatonia, seizures and increased mortality, reminiscent of encephalitis patients symptoms. Our results prove direct functional effects of autoantibodies on GABAARs and provide an animal model for GABAAR encephalitis. They further provide the scientific rationale for clinical treatments using antibody depletion and pave the way for future antibody-selective immunotherapies.

neuroscience↗

bioRxiv2020

Phenotypic plasticity, population structure and adaptation in a young weed species with a worldwide distribution

The colonization success of a species depends on phenotypic plasticity, adaptive potential and population structure. Assessing their relative contributions during a colonization process is challenging, and a large-scale experiment had yet to be done. In this study, we attempted to tease apart their effects on the fitness of one of the most common plant on Earth, the shepherds purse (Capsella bursa-pastoris), a self-fertilizing and allopolyploid weed, with a worldwide distribution. The overarching goal is to eventually understand how the shepherds purse extensive distribution range was established so rapidly. To do so, we carried out three common gardens, located in Europe, Asia and North America, and measured several life-history traits on field-collected accessions belonging to three distinct genetic clusters (Middle East, Europe, and Asia). Our experiment showed that (i) the success of C. bursa-pastoris is mainly due to its high degree of phenotypic plasticity; and (ii), genetic cluster effect reflected a classic pattern observed in core vs marginal populations, with the Middle Eastern cluster (putative core population) outperforming the European and Asian clusters. This study therefore revealed, in a model species, different relative contributions of plasticity and adaptation to fitness, depending on the population and the time since colonization occurred.

evolutionary biology↗

bioRxiv2020

The genetic architecture and genomic context of glyphosate resistance

Much of what we know about the genetic basis of herbicide resistance has come from detailed investigations of monogenic adaptation at known target-sites, despite the increasingly recognized importance of polygenic resistance. Little work has been done to characterize the broader genomic basis of herbicide resistance, including the number and distribution of genes involved, their effect sizes, allele frequencies, and signatures of selection. In this work, we implemented genome-wide association (GWA) and population genomic approaches to examine the genetic architecture of glyphosate resistance in the problematic agricultural weed, Amaranthus tuberculatus. A GWA was able to correctly identify the gene targeted by glyphosate, but when we statistically controlled for two target-site genetic mechanisms, we found an additional 250 genes across all 16 chromosomes associated with non-target site resistance (NTSR). The encoded proteins had functions that have been linked to non-target site resistance (NTSR), the most significant of which is response to chemicals, but also showed pleiotropic roles in reproduction and growth. The architecture of NTSR was enriched for large effect sizes and low allele frequencies, suggesting the role of pleiotropic constraints on its evolution. The enrichment of rare alleles also suggested that the genetic architecture of NTSR may be population-specific and heterogeneous across the range. Despite their rarity, we found signals of recent positive selection on NTSR-alleles by both window- and haplotype-based statistics, and an enrichment of amino-acid changing variants. In our samples, genome-wide SNPs explain a comparable amount of the total variation in glyphosate resistance to monogenic mechanisms, even in a collection of individuals where 80% of resistant individuals have large-effect TSR mutations, indicating an underappreciated polygenic contribution to the evolution of herbicide resistance in weed populations.

evolutionary biology↗

bioRxiv2020

Barbadin selectively modulates FPR2-mediated neutrophil functions independent of receptor endocytosis

Formyl peptide receptor 2 (FPR2), a member of the family of G protein-coupled receptors (GPCRs), mediates neutrophil migration, a response that has been linked to {beta}-arrestin recruitment. {beta}-Arrestin regulates GPCR endocytosis and can also elicit non-canonical receptor signaling. To determine the poorly understood role of {beta}-arrestin in FPR2 endocytosis and in NADPH-oxidase activation in neutrophils, Barbadin was used as a research tool in this study. Barbadin has been shown to bind the clathrin adaptor protein (AP2) and thereby prevent {beta}- arrestin/AP2 interaction and {beta}-arrestin-mediated GPCR endocytosis. In agreement with this, AP2/{beta}-arrestin interaction induced by an FPR2-specific agonist was inhibited by Barbadin. Unexpectedly, however, Barbadin did not inhibit FPR2 endocytosis, indicating that a mechanism independent of {beta}-arrestin/AP2 interaction may sustain FPR2 endocytosis. This was confirmed by the fact, that FPR2 also underwent agonist-promoted endocytosis in {beta}-arrestin deficient cells, albeit at a diminished level as compared to wild type cells. Dissection of the Barbadin effects on FPR2-mediated neutrophil functions including NADPH-oxidase activation mediated release of reactive oxygen species (ROS) and chemotaxis reveled that Barbadin had no effect on chemotactic migration whereas the release of ROS was potentiated/primed. The effect of Barbadin on ROS production was reversible, independent of {beta}-arrestin recruitment, and similar to that induced by latrunculin A. Taken together, our data demonstrate that endocytic uptake of FPR2 occurs independently of {beta}-arrestin, while Barbadin selectively augments FPR2-mediated neutrophil ROS production independently of receptor endocytosis. Given that Barbadin binds to AP2 and prevents the AP2/{beta}-arrestin interaction, our results indicate a role for AP2 in FPR2-mediated ROS release from human neutrophils.

pharmacology and toxicology↗

bioRxiv2020

Interacting evolutionary pressures drive mutation dynamics and health outcomes in aging blood

A small population of self-renewing, hematopoietic stem cells continuously reconstitutes our immune system. As we age, these cells, or their pluripotent descendants, accumulate somatic mutations; some of these mutations provide selection advantages and increase in frequency in the peripheral blood cell population. This process of positive selection, deemed age-related clonal hematopoiesis (ARCH), is associated with increased risk for cardiac disease and blood malignancies, like acute myeloid leukemia (AML). However, it remains unclear why some people with ARCH do not progress to AML, even when their blood cells harbor well-known AML driver mutations. Here, we examine whether negative selection can play a role in determining AML progression by modelling the complex interplay of positive and negative selective processes. Using a novel approach combining deep learning and population genetic models, we detect pervasive negative selection in targeted sequence data from the blood of 92 pre-AML individuals and 385 healthy controls. We find that the relative proportion of passenger to driver mutations is critical in determining if the selective advantage conferred to a cell by a known driver mutation is able to overwhelm negative selection acting on passenger mutations and allow clones harbouring disease-predisposing mutations to rise to dominance. We find that a subset of non-driver genes is enriched for mildly damaging mutations in healthy individuals fitting purifying models of evolution suggesting that mutations in these genes might confer a protective role against disease-predisposing clonal expansions. Through exploring non drivercentric models of evolution, we show how different classes of evolution act to shape hematopoietic dynamics and subsequent health outcome which may better inform disease prediction and unveil novel therapeutic targets. We anticipate that our results and modelling techniques can be broadly applied to identify both driver mutations and those mildly damaging passenger mutations, as well as help understand the early evolution of cancer in other cells and tissues.

cancer biology↗

bioRxiv2020

Mechanical and signaling mechanisms that guide pre-implantation embryo movement.

How a mammalian embryo determines and arrives at its site of attachment is a mystery that has puzzled researchers for decades. Additionally, in multiparous species, embryos face a unique challenge of achieving adequate spacing to avoid competition for maternal resources. Using our enhanced confocal imaging and 3D image reconstruction technology, we evaluate murine embryo location in the uterus along the longitudinal oviductal-cervical axis. Our analysis reveals three distinct pre-implantation stages: a) Embryo entry; b) Unidirectional movement of embryo clusters; and c) Bidirectional scattering and spacing of embryos. We show that unidirectional movement of embryo clusters is facilitated by a mechanical stimulus of the embryo as a physical object and is regulated by adrenergic uterine smooth muscle contractions. Embryo scattering, on the other hand, relies on embryo-uterine communication reliant on the LPAR3 signaling pathway and is independent of adrenergic muscle contractions. We propose that the presence of embryo clusters in the uterine horn provides an opportunity for the uterus to sense and count the embryos, followed by scattering and spacing these embryos along the given length of the horn. Thus, uterine implantation sites in mice are neither random nor predetermined but are guided by the number of embryos entering the uterine lumen. These studies have implications for understanding how embryo-uterine communication is key to determining an optimal implantation site, which is necessary for the success of a pregnancy. Significance StatementIn mammals that carry multiple offspring in one gestation, embryos seemingly acquire even embryo spacing. Such even distribution would imply a guided interaction between the mother and the fetus very early on in pregnancy to allow favorable pregnancy outcomes. Thus, it is essential to understand quantitatively if and when such a uniform distribution of embryos is established. Further, uncovering the physical and biological mechanisms that allow for such equal distribution of embryos, will improve our understanding of early pregnancy events and provide for novel targets for improving pregnancy success in case of infertility and artificial reproductive technologies as well as to develop non-hormonal therapies for contraception.

developmental biology↗

bioRxiv2020

Sleep and Diurnal Rest-Activity Rhythm Disturbances in a Mouse Model of Alzheimer's Disease

Study ObjectivesAccumulating evidence suggests a strong association between sleep, amyloid-beta (A{beta}) deposition, and Alzheimers disease (AD). We sought to determine if: (1) deficits in rest-activity rhythms and sleep are significant phenotypes in J20 AD mice, (2) metabotropic glutamate receptor 5 inhibitors (mGluR5) could rescue deficits in rest-activity rhythms and sleep, and (3) A{beta} levels are responsive to treatment with mGluR5 inhibitors. MethodsDiurnal rest-activity levels were measured by actigraphy and sleep-wake patterns by electroencephalography (EEG), while animals were chronically treated with mGluR5 inhibitors. Behavioral tests were performed, and A{beta} levels measured in brain lysates. ResultsJ20 mice exhibited a 4.5 hour delay in the acrophase of activity levels compared to wild-type littermates, and spent less time in REM sleep during the second half of the light period. J20 mice also exhibited decreased NREM delta power but increased NREM sigma power. The mGluR5 inhibitor CTEP rescued the REM sleep deficit and improved NREM delta and sigma power but did not correct rest-activity rhythms. No statistically significant differences were observed in A{beta} levels, rotarod performance or the passive avoidance task following chronic mGluR5 inhibitor treatment. ConclusionsJ20 mice have disruptions in rest-activity rhythms and reduced homeostatic sleep pressure (reduced NREM delta power). NREM delta power was increased following treatment with an mGluR5 inhibitor. Drug bioavailability was poor. Further work is necessary to determine if mGluR5 is a viable target for treating sleep phenotypes in AD. Statement of SignificanceSleep disruption is evolving as an important risk factor as well as phenotype of neurological diseases including Alzheimers disease. This study is novel in determining alterations in the rest-activity rhythm and sleep-wake pattern of J20 Alzheimers disease mice and wild type littermates. Specifically, there is a delay in acrophase with prolonged hyperactivity during the dark cycle, and reduced sleep pressure that was improved by treatment with mGluR5 inhibitor. Critical remaining knowledge gaps and future directions include testing the effects of Alzheimers disease drugs on rescue of sleep and rest-activity patterns in other Alzheimers disease models. These studies are relevant to human Alzheimers disease as monitoring sleep phenotypes may predict disease risk, and therapies that normalize sleep patterns may slow progression.

neuroscience↗

bioRxiv2019

Common genetic variants shape broad patterns of within-population variation in gene expression.

Understanding the persistence of genetic variation within populations has long been a goal of evolutionary biology. One promising route towards achieving this goal is using population genetic approaches to describe how selection acts on the loci associated with trait variation. Gene expression provides a model trait for addressing the challenge of the maintenance of variation because it can be measured genome-wide without information about how gene expression affects traits. Previous work has shown that loci affecting the expression of nearby genes (local or cis-eQTLs) are under negative selection, but we lack a clear understanding of the selective forces acting on variants that affect the expression of genes in trans. Here, we identify loci that affect gene expression in trans using genomic and transcriptomic data from one population of the obligately outcrossing plant, Capsella grandiflora. The allele frequencies of trans-eQTLs are consistent with stronger negative selection acting on trans-eQTLs than cis-eQTLs, and even more strongly on trans-eQTLs associated with the expression of multiple genes. However, despite this general pattern, we still observe the presence of a trans-eQTL at intermediate frequency that affects the expression of a large number of genes in the same coexpression module. Overall, our work highlights the different selective pressures shaping variation in cis- and trans- gene regulation.

evolutionary biology↗

bioRxiv2019

The effects of losing sex on the molecular evolution of plant defense

It is hypothesized that the loss of sexual reproduction and reduced recombination rates decrease the ability for hosts to evolve in response to selection by parasites. Using transcriptomes from 32 species, we test whether repeated losses of sex in the plant genus Oenothera has resulted in changes to the evolution of defense genes against herbivores and pathogens. To achieve this, the function of 2,431 Oenothera orthologous genes was determined based on GO annotations from Arabidopsis thaliana. Phylogenetic Analysis by Maximum Likelihood (PAML) was then used to examine how the patterns of molecular evolution in 721 defense and 1,710 non-defense genes differ between sexual (16 spp.) and asexual (16 spp.) taxa. We test whether the relative rates of nonsynonymous to synonymous substitutions ({omega} = dN/dS) in proteins with defensive function were higher in lineages with sexual reproduction ({omega}sexual> {omega}a-sexual), and we asked if such patterns were exclusive for defense genes or not. We detected variability in the rate of amino acid replacements of proteins in >50% of genes and positive selection on 3% of the genes examined. Nevertheless, our results clearly show that on average, signatures of positive and purifying selection on defense and non-defense genes are similar and only a small number of specific genes related to plant immune function may be affected by a loss of sex.

evolutionary biology↗

bioRxiv2019

Population genomics of the facultatively asexual duckweed Spirodela polyrhiza

O_LIClonal propagation allows some plant species to achieve massive population sizes quickly but also reduces the evolutionary independence of different sites in the genome.\nC_LIO_LIWe examine genome-wide genetic diversity in Spirodela polyrhiza, a duckweed that reproduces primarily asexually.\nC_LIO_LIWe find that this geographically widespread and numerically abundant species has very low levels of genetic diversity. Diversity at nonsynonymous sites relative to synonymous sites is high, suggesting that purifying selection is weak. A potential explanation for this observation is that a very low frequency of sex renders selection in effective. However, there is a pronounced decay in linkage disequilibrium over 40 kb, suggesting that though sex may be rare at the individual level it is not too infrequent at the population level. In addition, neutral diversity is affected by the physical proximity of selected sites, which would be unexpected if sex was exceedingly rare at the population level.\nC_LIO_LIThe amount of genetic mixing as assessed by the decay in linkage disequilibrium is not dissimilar from selfing species such as Arabidopsis thaliana, yet selection appears to be much less effective in duckweed. We discuss alternative explanations for the signature of weak purifying selection.\nC_LI

evolutionary biology↗

bioRxiv2018

Long-term balancing selection drives evolution of immunity genes in Capsella

Genetic drift is expected to remove polymorphism from populations over long periods of time, with the rate of polymorphism loss being accelerated when species experience strong reductions in population size. Adaptive forces that maintain genetic variation in populations, or balancing selection, might counteract this process. To understand the extent to which natural selection can drive the retention of genetic diversity, we document genomic variability after two parallel species-wide bottlenecks in the genus Capsella. We find that ancestral variation preferentially persists at immunity related loci, and that the same collection of alleles has been maintained in different lineages that have been separated for several million years. Our data point to long term balancing selection as an important factor shaping the genetics of immune systems in plants and as the predominant driver of genomic variability after a population bottleneck.

evolutionary biology↗

bioRxiv2018

CRISPR-Cas9 ribonucleoprotein-mediated co-editing and counterselection in the rice blast fungus

The rice blast fungus Magnaporthe oryzae is the most serious pathogen of cultivated rice and a significant threat to global food security. To accelerate targeted mutation and specific gene editing in this species, we have developed a rapid plasmid-free CRISPR-Cas9-based gene editing method. It has previously been reported in M. oryzae that transformation with plasmids expressing Cas9 can generate specific mutations using sgRNAs, directing the endonuclease to specific genes. We show, however, that expression of Cas9 is highly toxic to M. oryzae, rendering this approach impractical. We demonstrate that using purified Cas9 pre-complexed to RNA guides to form ribonucleoproteins (RNPs), provides an alternative and very effective gene editing procedure. When used in combination with oligonucleotide or PCR-generated donor DNAs, generation of strains with specific base pair edits, in-locus gene replacements, or multiple gene edits, is very rapid and straightforward. Additionally, we report a novel counterselection strategy which allows creation of precisely edited fungal strains that contain no foreign DNA and are completely isogenic to the wild type. Together, these developments represent a scalable improvement in the precision and speed of genetic manipulation in M. oryzae and are likely to be broadly applicable to other fungal species.

microbiology↗