Transcription-mediated supercoiling regulates genome folding and loop formation.

The chromatin fiber folds into loops, but the mechanisms controlling loop extrusion are still poorly understood. Using super-resolution microscopy, we visualize that loops in intact nuclei are formed by a scaffold of cohesin complexes from which the DNA protrudes. RNA polymerase II decorates the top of the loops and is physically segregated from cohesin. Augmented looping upon increased loading of cohesin on chromosomes causes disruption of Lamin at the nuclear rim and chromatin blending, a homogeneous distribution of chromatin within the nucleus. Altering supercoiling via either transcription or topoisomerase inhibition counteracts chromatin blending, increases chromatin condensation, disrupts loop formation, and leads to altered cohesin distribution and mobility on chromatin. Overall, negative supercoiling generated by transcription is an important regulator of loop formation in vivo.

Genomic characterization of infectious bursal disease virus in Argentina provides evidence of the recent transcontinental spread of Chinese genotype A2dB1b.

The infectious bursal disease virus (IBDV) is a significant pathogen affecting the poultry industry worldwide. Its epidemiological history has been marked by the emergence of strains with different antigenic, pathogenic, and genetic features, some of which have shown notable spread potential. The A2dB1b genotype, also known as novel variant, has become widespread and gained increased relevance in IBDV epidemiology. This genotype was described in China in the 2010s and rapidly spread in Asia and Africa. The present study describes the circulation of the A2dB1b genotype in Argentina. Applying a next-generation sequencing approach, we obtained the complete coding sequence of 18 Argentine viruses. The high level of genomic homogeneity observed amongst these viruses, their monophyletic clustering in both partial and complete segments A and B derived phylogenies, and their close relatedness to some Chinese strains suggest that a unique transcontinental spread event from China to Argentina occurred recently. The apparent success of the A2dB1b genotype spreading throughout Asia, Africa, and South America may partially be due to specific amino acid characteristics. Novel residues in the hypervariable region of VP2 may help A2dB1b IBDVs evade the protection elicited by the applied commercial vaccines. Our findings underscore the importance of continuous characterization of field samples and evaluation of the control measures currently applied to fight against this specific IBDV genotype.

A molecular view of DNA flexibility.

DNA dynamics can only be understood by taking into account its complex mechanical behavior at different length scales. At the micrometer level, the mechanical properties of single DNA molecules have been well-characterized by polymer models and are commonly quantified by a persistence length of 50 nm (~150 bp). However, at the base pair level (~3.4 Å), the dynamics of DNA involves complex molecular mechanisms that are still being deciphered. Here, we review recent single-molecule experiments and molecular dynamics simulations that are providing novel insights into DNA mechanics from such a molecular perspective. We first discuss recent findings on sequence-dependent DNA mechanical properties, including sequences that resist mechanical stress and sequences that can accommodate strong deformations. We then comment on the intricate effects of cytosine methylation and DNA mismatches on DNA mechanics. Finally, we review recently reported differences in the mechanical properties of DNA and double-stranded RNA, the other double-helical carrier of genetic information. A thorough examination of the recent single-molecule literature permits establishing a set of general 'rules' that reasonably explain the mechanics of nucleic acids at the base pair level. These simple rules offer an improved description of certain biological systems and might serve as valuable guidelines for future design of DNA and RNA nanostructures.

A multiplex-NGS approach to identifying respiratory RNA viruses during the COVID-19 pandemic.

A methodological approach based on reverse transcription (RT)-multiplex PCR followed by next-generation sequencing (NGS) was implemented to identify multiple respiratory RNA viruses simultaneously. A convenience sampling from respiratory surveillance and SARS-CoV-2 diagnosis in 2020 and 2021 in Montevideo, Uruguay, was analyzed. The results revealed the cocirculation of SARS-CoV-2 with human rhinovirus (hRV) A, B and C, human respiratory syncytial virus (hRSV) B, influenza A virus, and metapneumovirus B1. SARS-CoV-2 coinfections with hRV or hRSV B and influenza A virus coinfections with hRV C were identified in adults and/or children. This methodology combines the benefits of multiplex genomic amplification with the sensitivity and information provided by NGS. An advantage is that additional viral targets can be incorporated, making it a helpful tool to investigate the cocirculation and coinfections of respiratory viruses in pandemic and post-pandemic contexts.

A ribonuclease III involved in virulence of Mucorales fungi has evolved to cut exclusively single-stranded RNA.

Members of the ribonuclease III (RNase III) family regulate gene expression by processing double-stranded RNA (dsRNA). This family includes eukaryotic Dicer and Drosha enzymes that generate small dsRNAs in the RNA interference (RNAi) pathway. The fungus Mucor lusitanicus, which causes the deadly infection mucormycosis, has a complex RNAi system encompassing a non-canonical RNAi pathway (NCRIP) that regulates virulence by degrading specific mRNAs. In this pathway, Dicer function is replaced by R3B2, an atypical class I RNase III, and small single-stranded RNAs (ssRNAs) are produced instead of small dsRNA as Dicer-dependent RNAi pathways. Here, we show that R3B2 forms a homodimer that binds to ssRNA and dsRNA molecules, but exclusively cuts ssRNA, in contrast to all known RNase III. The dsRNA cleavage inability stems from its unusual RNase III domain (RIIID) because its replacement by a canonical RIIID allows dsRNA processing. A crystal structure of R3B2 RIIID resembles canonical RIIIDs, despite the low sequence conservation. However, the groove that accommodates dsRNA in canonical RNases III is narrower in the R3B2 homodimer, suggesting that this feature could be responsible for the cleavage specificity for ssRNA. Conservation of this activity in R3B2 proteins from other mucormycosis-causing Mucorales fungi indicates an early evolutionary acquisition.

Detection and genome characterisation of SARS-CoV-2 P.6 lineage in dogs and cats living with Uruguayan COVID-19 patients.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in domestic animals have occurred from the beginning of the pandemic to the present time. Therefore, from the perspective of One Health, investigating this topic is of global scientific and public interest. OBJECTIVES: The present study aimed to determine the presence of SARS-CoV-2 in domestic animals whose owners had coronavirus disease 2019 (COVID-19). METHODS: Nasopharyngeal and faecal samples were collected in Uruguay. Using quantitative polymerase chain reaction (qPCR), we analysed the presence of the SARS-CoV-2 genome. Complete genomes were obtained using ARTIC enrichment and Illumina sequencing. Sera samples were used for virus neutralisation assays. FINDINGS: SARS-CoV-2 was detected in an asymptomatic dog and a cat. Viral genomes were identical and belonged to the P.6 Uruguayan SARS-CoV-2 lineage. Only antiserum from the infected cat contained neutralising antibodies against the ancestral SARS-CoV-2 strain and showed cross-reactivity against the Delta but not against the B.A.1 Omicron variant. MAIN CONCLUSIONS: Domestic animals and the human SARS-CoV-2 P.6 variant comparison evidence a close relationship and gene flow between them. Different SARS-CoV-2 lineages infect dogs and cats, and no specific variants are adapted to domestic animals. This first record of SARS-CoV-2 in domestic animals from Uruguay supports regular surveillance of animals close to human hosts.

Dental caries prevalence and severity positively associate with AMY1 gene copy number.

OBJECTIVE: To establish the possible relation between total caries (TC) and caries severity (CS) with the AMY1 gene copy number (AMY1GCN). MATERIALS AND METHODS: This was an observational, cross-sectional, population-based, and association study with 303 participants. Each participant underwent a complete anamnesis and stomatological check-up, and peripheral blood was obtained to extract gDNA. TC and CS were determined as the number of caries at the dental exploration and the number of dental surfaces affected by caries, respectively, and AMY1GCN was determined by qPCR. RESULTS: We found an elevated caries prevalence (92.7%); TC and CS were 8 ± 10 and 10 ± 13 (median ± IR). There were higher TC and CS in those participants with AMY1GCN above the mean value (0.02 and 0.01 p values, respectively). A positive correlation between TC and CS with AMY1GCN (0.11 and 0.125 r values, 0.03 and 0.01 p values, respectively) was found, in addition to an association between TC and CS with AMY1GCN (1.5 and 1.6 OR values, 0.48 and 0.26 p values, respectively). CONCLUSION: TC and CS were positively related to the AMY1GCN. CLINICAL RELEVANCE: Dental caries has a high prevalence and a multifactorial etiology and has been related to a genetic component. Indeed, the salivary enzyme alpha-amylase could play a significant role in caries susceptibility, considering that its codifying gene (AMY1) can show variation in its gene copy number. This can be considered an important factor for the development of caries at a genetic level.

Entomopathogenic Nematode Compatibility with Vineyard Fungicides.

Vineyards, covering over seven million hectares worldwide, hold significant socio-cultural importance. Traditionally reliant on conventional practices and agrochemicals, this agroecosystem faces environmental challenges, including soil and water pollution. Sustainable viticulture, driven by eco-friendly practices and cost reduction, has gained prominence, underlining the importance of biological control agents such as entomopathogenic nematodes (EPNs). EPNs naturally occurr in vineyard soils and play a crucial role in controlling pest damage. Ensuring compatibility between EPNs and the commonly used vineyard fungicides is critical, as these applications constitute the predominant pest-management practice during the productive grapevine cycle. This study assessed the impact of authorized grapevine fungicides on EPNs, focusing on the survival of populations and sublethal effects on their virulence. We investigated the compatibility of two EPN populations (Steinernema feltiae 107 and S. carpocapsae 'All') with three organic production-approved products (Bacillus pumilus, sulfur, and copper oxychloride) and two synthetic chemicals (Trifloxystrobin and Mancozeb). Our findings revealed that the viability of S. feltiae 107 was reduced when exposed to sulfur and copper oxychloride, and its virulence was affected by copper oxychloride and Mancozeb, although only two days after exposure and with no significant differences for larval mortality at five days. In contrast, S. carpocapsae 'All' exhibited full compatibility with all five fungicides, with no impact on its viability or virulence. Consequently, our results suggested that the evaluated fungicides could be co-applied on both EPN populations if they were employed on the same day. However, further research on multi-target interactions is needed to ensure the successful implementation of this kind of co-application.

Flexible Superlubricity Unveiled in Sidewinding Motion of Individual Polymeric Chains.

A combination of low temperature atomic force microcopy and molecular dynamic simulations is used to demonstrate that soft designer molecules realize a sidewinding motion when dragged over a gold surface. Exploiting their longitudinal flexibility, pyrenylene chains are indeed able to lower diffusion energy barriers via on-surface directional locking and molecular strain. The resulting ultralow friction reaches values on the order of tens of pN reported so far only for rigid chains sliding on an incommensurate surface. Therefore, we demonstrate how molecular flexibility can be harnessed to realize complex nanomotion while retaining a superlubric character. This is in contrast with the paradigm guiding the design of most superlubric nanocontacts (mismatched rigid contacting surfaces).

Reduced nicotinamide mononucleotide is a new and potent NAD+ precursor in mammalian cells and mice.

Nicotinamide adenine dinucleotide (NAD+ ) homeostasis is constantly compromised due to degradation by NAD+ -dependent enzymes. NAD+ replenishment by supplementation with the NAD+ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) can alleviate this imbalance. However, NMN and NR are limited by their mild effect on the cellular NAD+ pool and the need of high doses. Here, we report a synthesis method of a reduced form of NMN (NMNH), and identify this molecule as a new NAD+ precursor for the first time. We show that NMNH increases NAD+ levels to a much higher extent and faster than NMN or NR, and that it is metabolized through a different, NRK and NAMPT-independent, pathway. We also demonstrate that NMNH reduces damage and accelerates repair in renal tubular epithelial cells upon hypoxia/reoxygenation injury. Finally, we find that NMNH administration in mice causes a rapid and sustained NAD+ surge in whole blood, which is accompanied by increased NAD+ levels in liver, kidney, muscle, brain, brown adipose tissue, and heart, but not in white adipose tissue. Together, our data highlight NMNH as a new NAD+ precursor with therapeutic potential for acute kidney injury, confirm the existence of a novel pathway for the recycling of reduced NAD+ precursors and establish NMNH as a member of the new family of reduced NAD+ precursors.

QUAM-AFM: A Free Database for Molecular Identification by Atomic Force Microscopy.

This paper introduces Quasar Science Resources-Autonomous University of Madrid atomic force microscopy image data set (QUAM-AFM), the largest data set of simulated atomic force microscopy (AFM) images generated from a selection of 685,513 molecules that span the most relevant bonding structures and chemical species in organic chemistry. QUAM-AFM contains, for each molecule, 24 3D image stacks, each consisting of constant-height images simulated for 10 tip-sample distances with a different combination of AFM operational parameters, resulting in a total of 165 million images with a resolution of 256 × 256 pixels. The 3D stacks are especially appropriate to tackle the goal of the chemical identification within AFM experiments by using deep learning techniques. The data provided for each molecule include, besides a set of AFM images, ball-and-stick depictions, IUPAC names, chemical formulas, atomic coordinates, and map of atom heights. In order to simplify the use of the collection as a source of information, we have developed a graphical user interface that allows the search for structures by CID number, IUPAC name, or chemical formula.

The female mouse is resistant to mild vitamin B3 deficiency.

PURPOSE: Vitamin B3 provides nicotinamide adenine dinucleotide (NAD+), an essential coenzyme in oxidoreductase reactions. Severe vitamin B3 deficiency leads to the disease Pellagra, while mild vitamin B3 deficiency has been linked to age-related and metabolic diseases. Mild vitamin B3 deficiency is understudied, especially in females. Therefore, we examined how female mice responded to a diet that induced mild vitamin B3 deficiency in male mice. METHODS: Female C57BL/6RccHsd mice were subjected for 18 weeks to a diet without vitamin B3 and low but sufficient tryptophan (0.115%) (0NR) and were compared to control female mice on the same diet with the reference dose of vitamin B3 (30NR, 30 mg nicotinamide riboside/ kg diet). RESULTS: In the female mice, no differences between the two dietary groups were found in liver nicotinamide mononucleotide (NMN) levels, body composition, whole body energy and substrate metabolism measured by indirect calorimetry, or liver triacylglycerol metabolism. Expression of seven genes that previously were shown to respond to mild vitamin B3 deficiency in male white adipose tissue were not differentially expressed between the female dietary groups, neither was insulin sensitivity. CONCLUSION: We concluded that the female 0NR mice were not vitamin B3 deficient; the role of age, sex and health status is discussed. Demonstrated by clear differences between females and males, the latter showing mild deficiency under the same conditions, this study highlights the importance of studying both sexes.

The Chemokine Receptors Ccr5 and Cxcr6 Enhance Migration of Mesenchymal Stem Cells into the Degenerating Retina.

Cell therapy approaches hold great potential for treating retinopathies, which are currently incurable. This study addresses the problem of inadequate migration and integration of transplanted cells into the host retina. To this end, we have identified the chemokines that were most upregulated during retinal degeneration and that could chemoattract mesenchymal stem cells (MSCs). The results were observed using a pharmacological model of ganglion/amacrine cell degeneration and a genetic model of retinitis pigmentosa, from both mice and human retinae. Remarkably, MSCs overexpressing Ccr5 and Cxcr6, which are receptors bound by a subset of the identified chemokines, displayed improved migration after transplantation in the degenerating retina. They also led to enhanced rescue of cell death and to preservation of electrophysiological function. Overall, we show that chemokines released from the degenerating retinae can drive migration of transplanted stem cells, and that overexpression of chemokine receptors can improve cell therapy-based regenerative approaches.

Double-stranded RNA bending by AU-tract sequences.

Sequence-dependent structural deformations of the DNA double helix (dsDNA) have been extensively studied, where adenine tracts (A-tracts) provide a striking example for global bending in the molecule. However, in contrast to dsDNA, sequence-dependent structural features of dsRNA have received little attention. In this work, we demonstrate that the nucleotide sequence can induce a bend in a canonical Watson-Crick base-paired dsRNA helix. Using all-atom molecular dynamics simulations, we identified a sequence motif consisting of alternating adenines and uracils, or AU-tracts, that strongly bend the RNA double-helix. This finding was experimentally validated using atomic force microscopy imaging of dsRNA molecules designed to display macroscopic curvature via repetitions of phased AU-tract motifs. At the atomic level, this novel phenomenon originates from a localized compression of the dsRNA major groove and a large propeller twist at the position of the AU-tract. Moreover, the magnitude of the bending can be modulated by changing the length of the AU-tract. Altogether, our results demonstrate the possibility of modifying the dsRNA curvature by means of its nucleotide sequence, which may be exploited in the emerging field of RNA nanotechnology and might also constitute a natural mechanism for proteins to achieve recognition of specific dsRNA sequences.

Understanding the paradoxical mechanical response of in-phase A-tracts at different force regimes.

A-tracts are A:T rich DNA sequences that exhibit unique structural and mechanical properties associated with several functions in vivo. The crystallographic structure of A-tracts has been well characterized. However, the mechanical properties of these sequences is controversial and their response to force remains unexplored. Here, we rationalize the mechanical properties of in-phase A-tracts present in the Caenorhabditis elegans genome over a wide range of external forces, using single-molecule experiments and theoretical polymer models. Atomic Force Microscopy imaging shows that A-tracts induce long-range (∼200 nm) bending, which originates from an intrinsically bent structure rather than from larger bending flexibility. These data are well described with a theoretical model based on the worm-like chain model that includes intrinsic bending. Magnetic tweezers experiments show that the mechanical response of A-tracts and arbitrary DNA sequences have a similar dependence with monovalent salt supporting that the observed A-tract bend is intrinsic to the sequence. Optical tweezers experiments reveal a high stretch modulus of the A-tract sequences in the enthalpic regime. Our work rationalizes the complex multiscale flexibility of A-tracts, providing a physical basis for the versatile character of these sequences inside the cell.

Organic mulching modulated native populations of entomopathogenic nematode in vineyard soils differently depending on its potential to control outgrowth of their natural enemies.

The entomopathogenic nematodes (EPNs) are biological control agents that are widespread in crop soils. However, traditional agricultural management practices such as cultivation and agrochemical usage can alter the soil balance that enables their occurrence and activity. Alternative strategies like mulching are commonly employed to prevent weed growth, enhance below-ground biodiversity by improving soil, organic matter content, fertility, and moisture. We hypothesized that organic mulches would favor biotic conditions for nematofauna development in crop soil, including EPNs, compared to herbicide application or tillage. Traditional (insect baits) and molecular (qPCR analysis) tools were used in this study to assess the abundance and activity of native EPNs, and the abundance of potential natural enemies, such as free-living nematode (FLN) competitors, nematophagous fungi (NF), and ectoparasitic bacteria, in soils managed with different organic mulches or traditional practices. As a model agroecosystem, we selected the vineyard, one of the most intensively managed crop systems. We compared mulches of grape pruning debris (GPD-M), straw (Str-M), and spent mushroom compost (SMC-M) in two commercial vineyards, which employed either integrated or organic pest and disease management. Following a completely randomized design, we retrieved two composite samples per plot (n = 3 per treatment in each vineyard) in April, June, and October 2020. Numbers of EPNs and selected members of their soil food web were higher in the organic than the integrated managed vineyard. Supporting our hypothesis, organic mulching overall favored nematode occurrence in both vineyards. We found higher NF abundance for Str-M, and GPD-M in the organic vineyard, which plausibly explained the lower EPN activity and occurrence compared to SMC-M in both vineyards. We conclude that the organic mulches can provide appropriate conditions for increasing nematofauna numbers but, depending on the mulch type, may also adversely affect EPNs by increasing their natural enemies. Our findings highlight the need to explore alternative farming practices to unravel complex biotic interactions that affect beneficial soil organisms in agroecosystems.

Transmission cluster of COVID-19 cases from Uruguay: emergence and spreading of a novel SARS-CoV-2 ORF6 deletion.

BACKGROUND: Evolutionary changes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) include indels in non-structural, structural, and accessory open reading frames (ORFs) or genes. OBJECTIVES: We track indels in accessory ORFs to infer evolutionary gene patterns and epidemiological links between outbreaks. METHODS: Genomes from Coronavirus disease 2019 (COVID-19) case-patients were Illumina sequenced using ARTIC_V3. The assembled genomes were analysed to detect substitutions and indels. FINDINGS: We reported the emergence and spread of a unique 4-nucleotide deletion in the accessory ORF6, an interesting gene with immune modulation activity. The deletion in ORF6 removes one repeat unit of a two 4-nucleotide repeat, which shows that directly repeated sequences in the SARS-CoV-2 genome are associated with indels, even outside the context of extended repeat regions. The 4-nucleotide deletion produces a frameshifting change that results in a protein with two inserted amino acids, increasing the coding information of this accessory ORF. Epidemiological and genomic data indicate that the deletion variant has a single common ancestor and was initially detected in a health care outbreak and later in other COVID-19 cases, establishing a transmission cluster in the Uruguayan population. MAIN CONCLUSIONS: Our findings provide evidence for the origin and spread of deletion variants and emphasise indels' importance in epidemiological studies, including differentiating consecutive outbreaks occurring in the same health facility.

Anti-Adherence and Antimicrobial Activities of Silver Nanoparticles against Serotypes C and K of Streptococcus mutans on Orthodontic Appliances.

Background and Objectives: Streptococcus mutans (S. mutans) is the main microorganism associated with the presence of dental caries and specific serotypes of this bacteria have been related to several systemic diseases limiting general health. In orthodontics, white spot lesions (WSL), represent a great challenge for clinicians due to the great fluctuation of their prevalence and incidence during conventional orthodontic treatments. Although silver nanoparticles (AgNP) have been demonstrated to have great antimicrobial properties in several microorganisms, including S. mutans bacteria, there is no available information about anti adherence and antimicrobial properties of AgNP exposed to two of the most relevant serotypes of S. mutans adhered on orthodontic materials used for conventional therapeutics. The objective of this study was to determine anti-adherence and antimicrobial levels of AgNP against serotypes c and k of S. mutans on conventional orthodontic appliances. Materials and Methods: An AgNP solution was prepared and characterized using dispersion light scattering (DLS) and transmission electron microscopy (TEM). Antimicrobial and anti-adherence activities of AgNP were determined using minimal inhibitory concentrations (MIC) and bacterial adherence testing against serotypes c and k of S. mutans clinically isolated and confirmed by PCR assay. Results: The prepared AgNP had spherical shapes with a good size distribution (29.3 ± 0.7 nm) with negative and well-defined electrical charges (−36.5 ± 5.7 mV). AgNP had good bacterial growth (55.7 ± 19.3 µg/mL for serotype c, and 111.4 ± 38.6 µg/mL for serotype k) and adherence inhibitions for all bacterial strains and orthodontic wires (p < 0.05). The serotype k showed statistically the highest microbial adherence (p < 0.05). The SS wires promoted more bacterial adhesion (149.0 ± 253.6 UFC/mL × 104) than CuNiTi (3.3 ± 6.0 UFC/mL × 104) and NiTi (101.1 ± 108.5 UFC/mL × 104) arches. SEM analysis suggests CuNiTi wires demonstrated better topographical conditions for bacterial adherence while AFM evaluation determined cell wall irregularities in bacterial cells exposed to AgNP. Conclusions: This study suggests the widespread use of AgNP as a potential anti-adherent and antimicrobial agent for the prevention of WSL during conventional orthodontic therapies and, collaterally, other systemic diseases.

Visual authoring of virtual reality conversational scenarios for e-learning.

The COVID-19 pandemic has led to face-to-face activities being developed in a virtual format that often offers a poor experience in areas such as education. Virtual Learning Environments have improved in recent years thanks to new technologies such as Virtual Reality or Chatbots. However, creating Virtual Learning Environments requires advanced programming knowledge, so this work is aimed to enable teachers to create these new environments easily. This work presents a set of extensions for App Inventor that facilitate the authoring of mobile learning apps that use Chatbots in a Virtual Reality environment, while simultaneously monitoring of student activity. This proposal is based on integrating block-based languages and Business Process Model and Notation diagrams. The developed extensions were successfully implemented in an educational app called Let's date!. A quantitative analysis of the use of these extensions in App Inventor was also carried out, resulting in a significant reduction in the number of blocks required. The proposed contribution has demonstrated its validity in creating virtual learning environments through visual programming and modelling, reducing development complexity.

Acute Cerebrovascular Events With COVID-19 Infection.

BACKGROUND AND PURPOSE: Coronavirus disease 2019 (COVID-19) has been associated with an increased incidence of thrombotic events, including stroke. However, characteristics and outcomes of COVID-19 patients with stroke are not well known. METHODS: We conducted a retrospective observational study of risk factors, stroke characteristics, and short-term outcomes in a large health system in New York City. We included consecutively admitted patients with acute cerebrovascular events from March 1, 2020 through April 30, 2020. Data were stratified by COVID-19 status, and demographic variables, medical comorbidities, stroke characteristics, imaging results, and in-hospital outcomes were examined. Among COVID-19-positive patients, we also summarized laboratory test results. RESULTS: Of 277 patients with stroke, 105 (38.0%) were COVID-19-positive. Compared with COVID-19-negative patients, COVID-19-positive patients were more likely to have a cryptogenic (51.8% versus 22.3%, P<0.0001) stroke cause and were more likely to suffer ischemic stroke in the temporal (P=0.02), parietal (P=0.002), occipital (P=0.002), and cerebellar (P=0.028) regions. In COVID-19-positive patients, mean coagulation markers were slightly elevated (prothrombin time 15.4±3.6 seconds, partial thromboplastin time 38.6±24.5 seconds, and international normalized ratio 1.4±1.3). Outcomes were worse among COVID-19-positive patients, including longer length of stay (P<0.0001), greater percentage requiring intensive care unit care (P=0.017), and greater rate of neurological worsening during admission (P<0.0001); additionally, more COVID-19-positive patients suffered in-hospital death (33% versus 12.9%, P<0.0001). CONCLUSIONS: Baseline characteristics in patients with stroke were similar comparing those with and without COVID-19. However, COVID-19-positive patients were more likely to experience stroke in a lobar location, more commonly had a cryptogenic cause, and had worse outcomes.