Biology subjects

Petersen, A.

Publications and source records attributed to Petersen, A..

At least 19 recordsLinked to original sources

bioRxiv2026

Synonymous HTT CAA/CCA-loss variants associated with early Huntington disease onset enhance toxicity beyond somatic instability

Huntington disease is a fatal neurodegenerative disorder caused by CAG repeat expansion encoding polyglutamine in the HTT gene. Recent studies have shown that loss of CAA/CCA interruptions within polyglutamine-coding CAG tracts and adjacent polyproline-coding region are linked to earlier disease onset. It has been hypothesized that somatic repeat instability, influenced by these interrupted CAG tracts, may mediate this effect. Here we demonstrate that HTT CAA/CCA-loss variant linked to early disease onset exacerbates mutant HTT toxicity in cellular models through mechanisms independent of somatic repeat instability. The CAA/CCA-loss variant exhibits significantly higher toxicity than canonical HTT sequences in both transient expression and stable cell line models. Notably, this enhanced toxicity persists in knockout cells of the mismatch repair gene MSH3 where somatic instability is blunted, with a consistent toxicity hierarchy (CAA/CCA-loss > CCA-loss > CAA-loss > canonical HTT) in both wildtype and MSH3 knockout cells. Furthermore, the CAA/CCA-loss variant generates elevated levels of repeat-associated non-AUG (RAN) translation products. In HEK293-based cellular models, these results suggest that the disease-accelerating effects of HTT CAA/CCA-loss variants involve intrinsic properties of the altered sequence context, highlighting the importance of understanding sequence-specific mechanisms in HD pathogenesis beyond polyglutamine length and somatic instability.

genetics↗

bioRxiv2026

Detrimental effects of atomoxetine on visual signal detection in rats: Comparison with ADHD psychomotor stimulant drugs

RationaleAttention-deficit/hyperactivity disorder (ADHD) is associated with executive dysfunction involving inattention and impulsivity, with evidence of disrupted functional expression of the dopamine and noradrenaline transporters. ObjectiveWe investigated the dose-dependent modulation of anti-ADHD drugs on selective and sustained visual attention in low-, mid-and high-attention phenotypes. Two mathematical approaches, signal detection theory and theory of visual attention were applied to further characterise the effects and mechanisms. MethodsRats were trained to detect and respond to the presence or absence of a visual target to obtain food reward on a signal detection task. After attentional performance stabilised, the indirect catecholamine agonist, d-amphetamine (0.1; 0.2; 0.4 mg/kg), the dopamine (DA) and noradrenaline (NA) reuptake inhibitor methylphenidate (0.3; 1; 3 mg/kg), and the NA reuptake inhibitor atomoxetine (0.1; 0.3; 1 mg/kg), were administered systemically. ResultsLow-dose d-amphetamine produced baseline-dependent effects on attention, improving target discrimination only in rats with lower attentive performance, whereas methylphenidate did not significantly improve attention but increased guessing. In contrast, low-dose atomoxetine selectively impaired attention in low-attentive subjects, whereas high-dose atomoxetine generally impaired discrimination performance. All three drugs had expected effects on motor response output. ConclusionsAs well as demonstrating baseline-dependent effects of amphetamine on visual attention, the findings for methylphenidate and atomoxetine suggest important, apparently opposing effects on visual signal detection performance produced via blockade of the DA and NA transporters. The deleterious effects of atomoxetine on performance were especially noteworthy in view of its use as a treatment in ADHD.

animal behavior and cognition↗

bioRxiv2026

A mechanism-aware stoichiometry platform resolves functional viral thresholds and induces antiviral hypersensitivity

Antiviral discovery is frequently hindered by a stoichiometric blind spot--a lack of resolution regarding the functional density of viral enzymes required for replication. Traditional screening pipelines rely on target-based or phenotypic assays that cannot distinguish between simple molecular binding and the crossing of a functional stoichiometric cliff. Here, we present a mechanism-aware platform that resolves these enzymatic requirements with single-virion precision. By integrating quantitative cryo-electron microscopy and genomic validation with Monte Carlo modeling, we map the stoichiometric landscapes of HIV-1 Protease (PR) and Reverse Transcriptase (RT). We uncover a striking disparity in enzymatic demand: a high-redundancy buffering capacity for PR ([~]40 monomers) contrasted with a high-threshold requirement for RT ([~]95 subunits). We demonstrate that by systematically de-buffering the virion, our platform induces a state of antiviral hypersensitivity, enabling the detection of therapeutic activity in novel and clinical inhibitors that remain invisible to traditional workflows. Furthermore, this multiplexed profiling enables de novo target identification, as inhibitors trigger failure exclusively on their respective stoichiometric arms. This platform provides a deterministic roadmap for de-risking drug discovery and identifying viral sub-stoichiometric vulnerabilities.

biophysics↗

bioRxiv2025

Environmental identification of novel enzymes against heteroatomic plastics

Better enzymes are needed to develop sustainable methods to recycle plastics with C-X heterobonds such as polyurethane (PUR) and nylon, for which no industrial-scale solutions exist. Current methods rely largely on sequence mining based on a small number of known enzymes. Here we expand the pool of PURases and nylonases by bioprospecting legacy plastic waste with fluorophore plastic mimics combined with FACS. We identify 29 plastic-degrading bacteria, from which 12 enzymes are identified by mass spectrometry and homology searches. Compared to existing enzymes, these enzymes are superior in thermostability and the ability to hydrolyse different high-molecular weight PUR oligomers and nylon textiles. To our knowledge, this is the first reported example of enzymes capable of hydrolysing longer chains of PUR and nylon. This study significantly increases the number of known PURases and nylonases and provides starting points for optimization campaigns through protein engineering and for in silico discovery.

biochemistry↗

bioRxiv2025

Receptor agonist of NFκB signaling ligand directs lung epithelial cell expansion through RANK signaling

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally, with progressive emphysema driven by repeated epithelial damage and impaired repair. Recently, we found that secretion of the osteokine "receptor agonist of nuclear factor {kappa}B signaling ligand" (RANKL) is higher in lung fibroblasts from patients with COPD compared to control and that RANKL represses lung epithelial cell death. However, the underlying mechanism, its cross-species conservation and the involved epithelial cell types remain unclear. To investigate how RANKL affects lung epithelial cells, we used primary lung organoids from human and mouse epithelial cells and showed that RANKL supplementation increased alveolar organoid forming capacity in these cultures compared to vehicle-treated controls. In elastase-treated mice, RANKL was able to rescue the elastase-induced loss of epithelial cells compared to vehicle-treated controls and it augmented the proportion of epithelial cells in transitional states expressing Krt8 and MHCII. Using A549 epithelial cells to investigate whether RANK or the alternative receptor for RANKL, "leucine-rich repeat-containing G-protein coupled receptor 4" (LGR4) were responding to RANKL treatment, we found that RANKL most likely acts through RANK These results suggest that RANKL may enhance stem cell survival of primarily alveolar epithelial cells in both mice and humans. We therefore conclude that RANKL is another osteokine, in addition to periostin, osteopontin, osteoglycin, and osteoprotegerin, that has a role in lung tissue repair and that its signaling pathway could be explored for therapeutic applications. New & NoteworthyRANKL enhances human and murine alveolar epithelial cell expansion. Using organoids and an elastase injury model, we show RANKL promotes alveolar epithelial type II cell expansion and rescues transitional cell type loss. RANKL/RANK signaling therefore emerges as a conserved lung regenerative pathway and may be a potential therapeutic target for diseases like COPD with impaired epithelial repair.

cell biology↗

bioRxiv2024

Competitive assembly resolves the stoichiometry of essential proteins in infectious HIV-1 virions.

During assembly on the plasma membrane, HIV-1 virions incorporate Gag-Pol as well as gp120/gp41 trimers. The Pol region consists of protease, reverse transcriptase and integrase precursors which are essential enzymes required for maturation, reverse transcription, and integration of the viral genome in the next host. gp120/gp41 trimers catalyze the fusion of the virion with its next host. Only a fraction of released virions are infectious. The stoichiometry of gp120/gp41 and Gag-Pol proteins in HIV virions was previously measured using cryotomography and ratiometric protein analysis, but what is the stoichiometry of these proteins in infectious virions remained to be determined. Here we developed a method based on competition between infectious HIV backbones with noninfectious mutants and measured 100 {+/-} 10 Gag-Pol and 15 {+/-} 3 gp120/gp41 proteins incorporated in infectious virions assembled in HEK293 cells from NL4.3 HIV-1 backbone. Our measurements are in broad agreement with cryotomography and ratiometric protein analysis and therefore stoichiometry of gp120/gp41 and Gag-Pol in infectious virions is the same as all released virions. With the development of appropriate mutants and infectivity assays, our method is applicable to other infectious viruses. Statement of significanceThere are 30 million people who have succumbed to the AIDS pandemic with 600,000 additional deaths per year. HIV has an accelerated rate of mutational accumulation with the virus mutating out of neutralizing antibodies within the same patient making development of vaccines challenging. Like most enveloped viruses, only a fraction of released virions are infectious and the question of what selects these virions has remained a mystery. The method developed in this article will allow stoichiometric measurements on infectious virions and therefore allows further studies of causes of infectivity.

biophysics↗

bioRxiv2023

Modeling cellular self-organization in strain-stiffening hydrogels

We develop a three-dimensional mathematical model framework for the collective evolution of cell populations by an agent-based model (ABM) that mechanically interacts with the surrounding extra-cellular matrix (ECM) modeled as a hydrogel. We derive effective two-dimensional models for the geometrical set-up of a thin hydrogel sheet to study cell-cell and cell-hydrogel mechanical interactions for a range of external conditions and intrinsic material properties. We show that without any stretching of the hydrogel sheets, cells show the well-known tendency to form long chains with varying orientations. Our results further show that external stretching of the sheet produces the expected nonlinear strain-softening or stiffening response, with, however, little qualitative variation of the over-all cell dynamics for all the materials considered. The behavior is remarkably different when solvent is entering or leaving from strain softening or stiffening hydrogels, respectively.

bioengineering↗

bioRxiv2023

Endogenous Staphylococcus aureus CRISPR-cas system limits phage proliferation and efficiently excises from the genome as part of the SCCmec cassette

CRISPR-Cas is an adaptive immune system that allows bacteria to inactivate mobile genetic elements. Approximately 50% of bacteria harbor CRISPR-cas, however in the human pathogen Staphylococcus aureus, CRISPR-cas loci are less common and often studied in heterologous systems. We analyzed the prevalence of CRISPR-cas in genomes of methicillin resistant Staphylococcus aureus (MRSA) isolated in Denmark. Only 2.9 % of the strains carried CRISPR-cas systems, but for strains of sequence type ST630 over half were positive. All CRISPR-cas loci were type III-A and located within the staphylococcal chromosomal cassette (SCCmec) type V(5C2&5) conferring {beta}-lactam resistance. Curiously, only 23 different CRISPR spacers were identified in 69 CRISPR-positive strains and almost identical SCCmec cassettes, CRISPR arrays and cas genes, are present in staphylococcal species other than aureus, suggesting that these were transferred horizontally. For the ST630 strain 110900, we demonstrate that the SCCmec cassette containing CRISPR-cas excises from the chromosome at high frequency. However, the cassette was not transferable under the conditions investigated. One of the CRISPR spacers targets a late gene in the lytic bacteriophage (phage) virus philPLA-RODI, and we show that the system protects against phage infection by reducing phage burst size. However, CRISPR-Cas can be overloaded or bypassed by CRISPR escape mutants. Our results imply that the endogenous type III-A CRISPR-Cas system in S. aureus is active against targeted phages, albeit with low efficacy. This suggests native S. aureus CRISPR-Cas offers only partial immunity, and in nature may work in tandem with other defense systems. ImportanceCRISPR-Cas is an adaptive immune system enabling bacteria and archaea to protect themselves against mobile genetic elements such as phages. In strains of Staphylococcus aureus, CRISPR-cas is rare, but when present, it is located within the SCCmec element encoding resistance to methicillin and other {beta}-lactam antibiotics. We show that the entire module is excisable, with almost identical versions found in different species of non-aureus staphylococci suggesting that the system only rarely acquires new spacers in S. aureus. Additionally, we show that in its endogenous form, the S. aureus CRISPR-Cas is active but inefficient against lytic phages, with phages being able to form escape mutants or overload the system. This leads us to propose that CRISPR-Cas in S. aureus offers only partial immunity in native systems, and so may work together with other defense systems to prevent phage-mediated killing.

microbiology↗

bioRxiv2023

Novel determinant of antibiotic resistance: a clinically selected Staphylococcus aureus clpP mutant survives daptomycin treatment by reducing binding of the antibiotic and adapting a rod-shaped morphology

Daptomycin is a last-resort antibiotic used for treatment of infections caused by Gram-positive antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). Treatment failure is commonly linked to accumulation of point mutations, however, the contribution of single mutations to resistance and the mechanisms underlying resistance remain incompletely understood. Here we show that a single nucleotide polymorphism (SNP) selected during daptomycin therapy inactivates the highly conserved ClpP protease and is causing reduced susceptibility of MRSA to daptomycin, vancomycin, and {beta}-lactam antibiotics as well as decreased expression of virulence factors. Super-resolution microscopy demonstrated that the improved survival of the clpP mutant strain during daptomycin treatment was associated with reduced binding of daptomycin to the septal site and diminished membrane damage. In both the parental strain and the clpP strain, daptomycin inhibited the inward progression of septum synthesis eventually leading to lysis and death of the parental strain while surviving clpP cells were able to continue synthesis of the peripheral cell wall in the presence of 10 x MIC daptomycin resulting in a rod-shaped morphology. To our knowledge, this is the first demonstration that synthesis of the outer cell wall continues in the presence of daptomycin. Collectively, our data provide novel insight into the mechanisms behind bacterial killing and resistance to this important antibiotic. Also, the study emphasizes that treatment with last-line antibiotics is selective for mutations that, like the SNP in clpP, favor antibiotic resistance over virulence gene expression. IMPORTANCEThe bacterium Staphylococcus aureus is a leading cause of life-threatening infections and treatment is challenged by the worldwide dissemination of methicillin-resistant Staphylococcus aureus (MRSA) that are multi-drug resistant. Daptomycin, a cell membrane-targeting cationic lipopeptide, is one of the few antibiotics with activity against MRSA, however, the killing mechanism of daptomycin and the mechanisms leading to resistance are not fully understood. Here we show than an MRSA strain, isolated from the blood of a patient treated with daptomycin, has acquired a mutation that inactivates the ClpXP protease resulting in increased resistance to several antibiotics and diminished expression of virulence genes. Super resolution microscopy showed that the mutant avoids daptomycin-elicited killing by preventing the binding of the antibiotic to the septal site and by growing into a rod-shaped morphology. In summary, this study discloses new perspectives on the mechanism of killing and the mechanism of resistance to an antibiotic of last resort.

microbiology↗

bioRxiv2023

Mutant huntingtin expression in the hypothalamus promotes ventral striatal neuropathology

Huntingtons disease is a fatal neurodegenerative disorder caused by an expanded CAG triplet repeat in the huntingtin (HTT) gene. Previous research focused on neuropathology in the striatum and its association with a typical movement disorder. Direct effects of mutant HTT (mHTT) in the striatum may cause neuropathology, although non-cell autonomous effects have also been suggested. Important non-motor features of HD include psychiatric symptoms and metabolic dysfunction, which may be linked to hypothalamic neuropathology. As hypothalamic neurons project to the ventral striatum, we hypothesized that expression of mHTT in the hypothalamus leads to disrupted neurotransmission in the ventral striatum and causes pathology. The overall aim of this study was to investigate the impact of mHTT expression in the hypothalamus on ventral striatal neuropathology and its contribution to non-HD motor symptoms. We demonstrate that selective expression of mHTT in the hypothalamus leads to the loss of dopamine and cAMP-regulated phosphoprotein (DARPP-32) immunopositive neurons in the ventral striatum in mice. Contrary to the effects of direct expression of mHTT in the hypothalamus, selective overexpression of mHTT in the ventral striatum does not affect body weight. Selective expression of mHTT in the ventral striatum leads to mHTT inclusion formation and loss of DARPP-32 neurons without affecting motor activity or anxiety-like behavior. We show that DARPP-32 neuron loss in the ventral striatum is recapitulated in the R6/2 mouse model of HD. Chemogenetic activation of hypothalamic neurons projecting to the ventral striatum had a blunted response in the R6/2 mice compared to wild-type mice, indicating a disrupted hypothalamus-ventral striatal circuitry. In summary, the expression of mHTT in the hypothalamus may impact the development of ventral striatal pathology in mice. This opens the possibility that non-cell-autonomous effects in the reward circuitry play a role in HD.

neuroscience↗

bioRxiv2023

Circular mitochondrial-encoded mRNAs are a distinct subpopulation of mitochondrial mRNA in Trypanosoma brucei

Since the first identification of circular RNA (circRNA) in viral-like systems, reports of circRNAs and their functions in various organisms, cell types, and organelles have greatly expanded. Here, we report the first evidence of circular mRNA in the mitochondrion of the eukaryotic parasite, Trypanosoma brucei. While using a circular RT-PCR technique developed to sequence mRNA tails of mitochondrial transcripts, we found that some mRNAs are circularized without an in vitro circularization step normally required to produce PCR products. Starting from total in vitro circularized RNA and in vivo circRNA, we high-throughput sequenced three transcripts from the 3 end of the coding region, through the 3 tail, to the 5 start of the coding region. We found that fewer reads in the circRNA libraries contained tails than in the total RNA libraries. When tails were present on circRNAs, they were shorter and less adenine-rich than the total population of RNA tails of the same transcript. Additionally, using hidden Markov modelling we determined that enzymatic activity during tail addition is different for circRNAs than for total RNA. Lastly, circRNA UTRs tended to be shorter and more variable than those of the same transcript sequenced from total RNA. We propose a revised model of Trypanosome mitochondrial tail addition, in which a fraction of mRNAs is circularized prior to the addition of adenine-rich tails and may act as a new regulatory molecule or in a degradation pathway.

molecular biology↗

bioRxiv2022

Competitive HIV budding suggests that a self-packaging gRNA:Gag-Pol complex directs HIV assembly and enforces infectivity.

To resolve the assembly mechanism of infectious HIV virions, we tested the ability of HIV to assemble infectious virions in the presence of a titrated mix of infectious/ non-infectious proviral genomes. The analysis of our assembly competitions shows that during translation, 15 {+/-} 5 Gag-Pols bind back to their parental gRNA creating a gRNA1: Gag-Pol15 complex. This complex initiates the infectious virion assembly through interactions mediated by cis packaged Gag/Gag-pols and the plasma membrane. Our analysis also shows the number of Gag-Pol and Env proteins packaged in an infectious HIV virion and the minimum functional units of these proteins required for viral infectivity. We suggest that aside from orchestrating the infectious virion assembly the gRNA1: Gag-Pol15 complex plays a major role in HIV evolution and likely hampers effectiveness of antiviral therapies. One-Sentence SummaryCompetitive HIV budding reveals gRNA1: Gag-Pol15 complex orchestrating viral assembly.

microbiology↗

bioRxiv2021

TCAIM controls effector T cell generation by preventing Mitochondria-Endoplasmic Reticulum Contact Site-initiated Cholesterol Biosynthesis

T cells need to adapt their cellular metabolism for effector cell differentiation. This relies on alterations in mitochondrial physiology. Which signals and molecules regulate those alterations remains unclear. We recently reported, that the mitochondrial protein TCAIM inhibits activation-induced changes in mitochondrial morphology and function and thus, CD4+ effector T cell formation. Using conditional TCAIM knock-in (KI) and knockout (KO) mice, we now show that it also applies to CD8+ T cells and more importantly, delineate the molecular processes in mitochondria by which TCAIM controls effector cell differentiation. TCAIM KI resulted in reduced activation-induced HIF1 protein expression. Metabolomics and transcriptional data in combination with mathematical flux modeling revealed an impaired induction of anabolic pathways, especially of the mevalonate pathway and cholesterol biosynthesis in TCAIM KI CD8+ T cells. Addition of cholesterol completely rescued HIF1 protein expression, activation and proliferation of TCAIM KI CD8+ T cells. At the molecular level, TCAIM delayed activation-induced mitochondria-ER contact (MERC) formation by binding to MERC promoting proteins such as RMD3 and VDAC2. In summary, we demonstrate that TCAIM suppresses effector cell differentiation by inhibiting MERC formation, which induce HIF1-mediated increase in cellular metabolism and cholesterol biosynthesis.

immunology↗

bioRxiv2021

Effects of excitotoxicity in the hypothalamus in transgenic mouse models of Huntington disease

Huntington disease (HD) is a fatal neurodegenerative movement disorder caused by an expanded CAG repeat in the huntingtin gene (HTT). The mutant huntingtin protein is ubiquitously expressed, but only certain brain regions are affected. The hypothalamus has emerged as an important area of pathology with selective loss of neurons expressing the neuropeptides orexin (hypocretin), oxytocin and vasopressin in human postmortem HD tissue. Hypothalamic changes in HD may have implications for early disease manifestations affecting the regulation of sleep, emotions and metabolism. The underlying mechanisms of selective vulnerability of certain neurons in HD are not fully understood, but excitotoxicity has been proposed to play a role. Further understanding of mechanisms rendering neurons sensitive to mutant huntingtin may reveal novel targets for therapeutic interventions. In the present study, we wanted to examine whether transgenic HD mice display altered sensitivity to excitotoxicity in the hypothalamus. We first assessed effects of hypothalamic injections of the excitotoxin quinolinic acid (QA) into wild-type (WT) mice. We show that neuronal populations expressing melanin-concentrating hormone (MCH) and cocaine and amphetamine-regulated transcript (CART) display a dose-dependent sensitivity to QA. In contrast, neuronal populations expressing orexin, oxytocin, vasopressin as well as tyrosine hydroxylase in the A13 area are resistant to QA-induced toxicity. We demonstrate that the R6/2 transgenic mouse model expressing a short fragment of mutant HTT displays hypothalamic neuropathology with discrete loss of the neuronal populations expressing orexin, MCH, CART, and orexin at 12 weeks of age. The BACHD mouse model expressing full-length mutant HTT does not display any hypothalamic neuropathology at 2 months of age. There was no effect of hypothalamic injections of QA on the neuronal populations expressing orexin, MCH, CART or oxytocin in neither HD mouse model. In conclusion, we find no support for a role of excitotoxicity in the loss of hypothalamic neuronal populations in HD.

neuroscience↗

bioRxiv2021

IKKβ signaling mediates metabolic changes in the hypothalamus of a Huntington's disease mouse model

BackgroundHuntingtons disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, and underlying mechanisms are not fully known. As the IKK{beta}/NF-{kappa}B pathway is an essential regulator of metabolism, we investigated the involvement of IKK{beta}, the upstream activator of NF-{kappa}B in hypothalamus-specific HD metabolic changes. MethodsUsing viral vectors, we expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) fragments in the hypothalamus of mice without IKK{beta} in the CNS (IKK{beta}-/-) and control mice (IKK{beta}+/+). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology. ResultsHypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKK{beta} prohibited weight gain in females, which was independent of neuroprotection and microglial activation. ConclusionsThe expression of mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKK{beta} pathway attenuates the obese phenotype.

neuroscience↗

bioRxiv2020

Bioarchaeological analysis of one of the earliest Islamic burials in the Levant

The Middle East plays a central role in human history harbouring a vast diversity of ethnic, cultural and religious groups. However, much remains to be understood about past and present genomic diversity in this region. Here, we present for the first time, a multidisciplinary bioarchaeological analysis of two individuals dated to late 7th and early 8th centuries from Tell Qarassa, an open-air site in modern-day Syria. Radiocarbon dates, religious and cultural burial evidence indicate that this site represents one of the earliest Islamic Arab burials in the Levant during the Late Antiquity period. Interestingly, we found genomic similarity to a genotyped group of modern-day Bedouins and Saudi rather than to most neighbouring Levantine groups. This is highlighted through substantial Neolithic Levant ancestry in our samples, inviting an alternative scenario of long-term continuity in this region. This raises questions about the influence of ancient populations and historical migrations to genetic structure in the Middle East. As our study represents the first genomic analysis of an early Islamic burial in the Levant, we discuss our findings and possible historic scenarios in light of forces such as genetic drift and their possible interaction with religious and cultural processes.

genetics↗

bioRxiv2019

The Sle1 Cell Wall Amidase Controls Daughter Cell Splitting, Cell Size, and β-Lactam Resistance in Community Acquired Methicillin Resistant Staphylococcus aureus USA300

Most clinically relevant methicillin resistant Staphylococcus aureus (MRSA) strains have become resistant to {beta}-lactams antibiotics through horizontal acquisition of the mecA gene encoding PBP2a, a peptidoglycan transpeptidase with low affinity for {beta}-lactams. The level of resistance conferred by mecA is, however, strain dependent and the mechanisms underlying this phenomenon remain poorly understood. We here show that {beta}-lactam resistance correlates to expression of the Sle1 cell wall amidase in the fast spreading and highly virulent community-acquired MRSA USA300 clone. Sle1 is a substrate of the ClpXP protease, and while the high Sle1 levels in cells lacking ClpXP activity confer {beta}-lactam hyper-resistance, USA300 cells lacking Sle1 are as sensitive to {beta}-lactams as cells lacking mecA. This finding prompted us to assess the cellular roles of Sle1 in more detail, and we demonstrate that high Sle1 levels accelerate the onset of daughter cells splitting and decrease cell size. Vice versa, oxacillin decreases the Sle1 level, and imposes a cell-separation defect that is antagonized by high Sle1 levels, suggesting that high Sle1 levels increase tolerance to oxacillin by promoting cell separation. In contrast, increased oxacillin sensitivity of sle1 cells appears linked to a synthetical lethal effect on septum synthesis. In conclusion, this study demonstrates that Sle1 is a key factor in resistance to {beta}-lactam antibiotics in the JE2 USA300 model strain, and that PBP2a is required for expression of Sle1 in JE2 cells exposed to oxacillin.\n\nImportanceThe bacterium Staphylococcus aureus is a major cause of human disease, and the global spread of S. aureus resistant to {beta}-lactam antibiotics (MRSA) has made treatment increasingly difficult. {beta}-lactams interfere with cross-linking of the bacterial cell wall, however, the killing mechanism of this important class of antibiotics is still not fully understood. Here we provide novel insight into this topic by showing that {beta}-lactam resistance is controlled by the Sle1 cell wall amidase in the fast spreading and highly virulent MRSA USA300 clone. We show that Sle1 high levels accelerate the onset of daughter cells splitting and decrease cell size. Vice versa, oxacillin decreases the Sle1 level, and imposes a cell-separation defect that is antagonized Sle1. The key finding that resistance to {beta}-lactams correlates positively to expression of Sle1 indicates that, in S. aureus, the detrimental effects of {beta}-lactam antibiotics are linked to inhibition of daughter cells splitting.

microbiology↗

bioRxiv2019

TVA-based modeling of short-term memory capacity, speed of processing and perceptual threshold in chronic stroke patients: Case-control differences, reliability, and sensitivity to cognitive training

Attentional deficits following stroke are common and pervasive, and are important predictors for functional recovery. Attentional functions comprise a set of specific cognitive processes allowing to attend, filter and select among a continuous stream of stimuli. These mechanisms are fundamental for more complex cognitive functions such as learning, planning and cognitive control, all crucial for daily functioning, including social interactions. The distributed functional neuroanatomy of these processes is a likely explanation for the high prevalence of attentional impairments following stroke, and underscores the importance of a clinical implementation of computational approaches allowing for sensitive and specific modeling of attentional sub-processes. The Theory of Visual Attention (TVA) offers a theoretical, computational, neuronal and practical framework to assess the efficiency of visual selection performance and parallel processing of multiple objects. Here, using a whole-report experimental paradigm in a cross-sectional case-control comparison and in six repeated assessments over the course of a three-week intensive computerized cognitive training (CCT) intervention in chronic stroke patients (> 6 months since hospital admission, NIHSS < 7 at hospital discharge), we assessed the sensitivity and reliability of TVA parameters reflecting short-term memory capacity (K), processing speed (C) and perceptual threshold (t0). Cross-sectional group comparisons documented lower short-term memory capacity, slower processing speed and higher perceptual threshold in patients compared to age-matched healthy controls. Further, longitudinal analyses revealed high reliability of the TVA parameters in stroke patients, and higher processing speed at baseline was associated with larger cognitive benefits of the CCT. The results support the feasibility, reliability and sensitivity of TVA-based assessment of attentional functions in chronic stroke patients.

neuroscience↗