Biology subjects

Shi, X.

Publications and source records attributed to Shi, X..

At least 199 records · Page 11Linked to original sources

bioRxiv2020

Pluripotent stem cell derived models of neurological diseases reveal early transcriptional heterogeneity

BackgroundMany neurodegenerative diseases (NDs) develop only later in life, when cells in the nervous system lose their structure or function. In genetic forms of NDs, this late onset phenomenon remains largely unexplained. ResultsAnalyzing single cell RNA sequencing (scRNA-seq) from Alzheimers disease (AD) patients, we find increased transcriptional heterogeneity in AD excitatory neurons. We hypothesized that transcriptional heterogeneity precedes ND pathologies. To test this idea experimentally, we used juvenile forms (72Q; 180Q) of Huntingtons disease (HD) iPSCs, differentiated them into committed neuronal progenitors, and obtained single cell expression profiles. We show a global increase in gene expression variability in HD. Autophagy genes become more stable, while energy and actin-related genes become more variable in the mutant cells. Knocking-down several differentially-variable genes resulted in increased aggregate formation, a pathology associated with HD. We further validated the increased transcriptional heterogeneity in CHD8+/- cells, a model for autism spectrum disorder. ConclusionsOverall, our results suggest that although NDs develop over time, transcriptional regulation imbalance is present already at very early developmental stages. Therefore, an intervention aimed at this early phenotype may be of high diagnostic value.

molecular biology↗

bioRxiv2020

Potent SARS-CoV-2 neutralizing antibodies selected from a human antibody library constructed decades ago

Combinatorial antibody libraries not only effectively reduce antibody discovery to a numbers game, but enable documentation of the history of antibody responses in an individual. The SARS-CoV-2 pandemic has prompted a wider application of this technology to meet the public health challenge of pandemic threats in the modern era. Herein, we used a combinatorial human antibody library constructed 20 years before the COVID-19 pandemic to discover three highly potent antibodies that selectively bind SARS-CoV-2 spike protein and neutralize authentic SARS-CoV-2 virus. Compared to neutralizing antibodies from COVID-19 patients with generally low somatic hypermutation (SHM), these antibodies contain over 13-22 SHMs, many of which are involved in specific interactions in crystal structures with SARS-CoV-2 spike RBD. The identification of these somatically mutated antibodies in a pre-pandemic library raises intriguing questions about the origin and evolution of human immune responses to SARS-CoV-2.

microbiology↗

bioRxiv2020

Synergy and allostery in ligand binding by HIV-1 Nef

The Nef protein of human and simian immunodeficiency viruses (HIV and SIV, respectively) boosts viral pathogenicity through its interactions with host cell proteins. Nef has a folded core domain and large flexible regions, each carrying several protein interaction sites. By combining the polyvalency intrinsic to unstructured regions with the binding selectivity and strength of a 3D folded domain, Nef can bind to many different host cell proteins, perturbing their cellular functions. For example, the combination of a linear proline-rich motif and a hydrophobic core domain surface allows Nef to increase affinity and selectivity for particular Src family SH3 domains. Here we investigated whether the interplay between Nefs flexible regions and its core domain can allosterically influence ligand selection. We found that the flexible regions can bind back to the core domain in different ways, producing distinct conformational states that alter the SH3 domain selectivity and availability of Nefs functional motifs. The resulting cross-talk might help synergising certain subsets of ligands while excluding others, promoting functionally coherent Nef-bound protein ensembles. Further, we combined proteomic and bioinformatic analyses to identify human proteins that select SH3 domains in the same way as does Nef. We found that only 2-3% of clones from a whole human fetal library displayed a Nef-like SH3 selectivity. However, in most cases this selectivity appears to be achieved by a canonical linear interaction rather than a Nef-like tertiary interaction. This analysis suggests that Nefs SH3 recognition surface has no (or marginally few) cellular counterparts, validating the Nef tertiary binding surface as a promising unique drug target.

biophysics↗

bioRxiv2020

The RNA Structurome in the Asexual Blood Stages of Malaria Pathogen Plasmodium falciparum

RNA as an effector of biological functions often adopts secondary and tertiary structural folds. Plasmodium falciparum is a deadly human pathogen responsible for the devastating disease called malaria. In this study, we measured the differential accumulation of RNA secondary structures in coding and noncoding transcripts from the asexual developmental cycle in P. falciparum in human red blood cells. Our comprehensive analysis, combining high-throughput nuclease mapping of RNA structures by duplex RNA-seq, immunoaffinity purification and RNA analysis, collectively measured differentially base-paired RNA regions during the parasite development. Our mapping data not only aligned to a diverse pool of RNAs with known structures but also enabled us to identify new structural RNA regions in the malaria genome. On average, ~71% of the genes with secondary structures are found to be protein coding mRNAs. Mapping pattern of these base-paired RNAs corresponded to all parts of protein-coding mRNAs, including 5 UTR, CDS and 3 UTR. In addition to histone family genes which are known to form secondary structures in their mRNAs, transcripts from genes which are important for transcriptional and post-transcriptional control, such as unique plant-like transcription factor family, ApiAP2, DNA/RNA binding protein family, Alba, ribosomal proteins and eukaryotic initiation factors involved in translational control and the ones important for RBC invasion and cytoadherence also show strong accumulation of duplex RNA reads in various asexual stages. Intriguingly, our study determined a positive relationship between mRNA structural contents and translation efficiency in P. falciparum asexual blood stages, suggesting an essential role of RNA structural changes in malaria gene expression programs.

molecular biology↗

bioRxiv2020

Neuronal Activity-Induced BRG1 Phosphorylation Regulates Enhancer Activation

Neuronal activity-induced enhancers drive the gene induction in response to stimulation. Here, we demonstrate that BRG1, the core subunit of SWI/SNF-like BAF ATP-dependent chromatin remodeling complexes, regulates neuronal activity-induced enhancers. Upon stimulation, BRG1 is recruited to enhancers in an H3K27Ac-dependent manner. BRG1 regulates enhancer basal activities and inducibility by affecting cohesin binding, enhancer-promoter looping, RNA polymerase II recruitment, and enhancer RNA expression. Furthermore, we identified a serine phosphorylation site in BRG1 that is induced by neuronal activities and is sensitive to CaMKII inhibition. BRG1 phosphorylation affects its interaction with several transcription co-factors, possibly modulating BRG1 mediated transcription outcomes. Using mice with knock-in mutations, we showed that non-phosphorylatable BRG1 fails to efficiently induce activity-dependent genes, whereas phosphomimic BRG1 increases the enhancer activities and inducibility. These mutant mice displayed anxiety-like phenotypes and altered responses to stress. Therefore, our data reveal a mechanism connecting neuronal signaling to enhancer activities through BRG1 phosphorylation.

molecular biology↗

bioRxiv2020

Maternal factor PABPN1L is essential for maternal mRNA degradation during maternal-to-zygotic transition

Infertility affects 10% - 15% of families worldwide. However, the pathogenesis of female infertility caused by abnormal early embryonic development is not clear. We constructed a mouse model (Pabpn1l -/-) simulating the splicing abnormality of human PABPN1L and found that the female was sterile and the male was fertile. The Pabpn1l -/- oocytes can be produced, ovulated and fertilized normally, but cannot develop beyond the 2-cell stage. Using RNA-Seq, we found a large-scale upregulation of RNA in Pabpn1l -/- MII oocytes. Of the 2401 transcripts upregulated in Pabpn1l-/- MII oocytes, 1523 transcripts (63.4%) were also upregulated in Btg4 -/- MII oocytes, while only 53 transcripts (2.2%) were upregulated in Ythdf2 -/- MII oocytes. We documented that transcripts in zygotes derived from Pabpn1l -/- oocytes have a longer poly(A) tail than the control group, a phenomenon similar to that in Btg4-/- mice. Surprisingly, the poly(A) tail of these mRNAs was significantly shorter in the Pabpn1l -/- MII oocytes than in the Pabpn1l +/+. These results suggest that PABPN1L is involved in BTG4-mediated maternal mRNA degradation, and may antagonize poly(A) tail shortening in oocytes independently of its involvement in maternal mRNA degradation. Thus, PABPN1L variants could be a genetic marker of female infertility.

genetics↗

bioRxiv2020

TISCH: a comprehensive web resource enabling interactive single-cell transcriptome visualization of tumor microenvironment

Cancer immunotherapy targeting co-inhibitory pathways by checkpoint blockade shows remarkable efficacy in a variety of cancer types. However, only a minority of patients respond to treatment due to the stochastic heterogeneity of tumor microenvironment (TME). Recent advances in single-cell RNA-seq technologies enabled comprehensive characterization of the immune system heterogeneity in tumors, but also posed computational challenges on how to integrate and utilize the massive published datasets to inform immunotherapy. Here, we present Tumor Immune Single Cell Hub (TISCH, http://tisch.comp-genomics.org), a large-scale curated database that integrates single-cell transcriptomic profiles of nearly two million cells from 76 high-quality tumor datasets across 28 cancer types. All the data were uniformly processed with a standardized workflow, including quality control, batch effect removal, malignant cell classification, cell clustering, cell-type annotation, differential expression analysis, and functional enrichment analysis. TISCH provides interactive gene expression visualization across multiple datasets at the single-cell level or cluster level, allowing systematic comparison between different cell-types, patients, tissue origins, treatment and response groups, and even different cancer-types. In summary, TISCH provides a user-friendly interface for systematically visualizing, searching, and downloading gene expression atlas in the TME from multiple cancer types, enabling fast, flexible and comprehensive exploration of the TME.

bioinformatics↗

bioRxiv2020

Differential Privacy Protection Against Membership Inference Attack on Machine Learning for Genomic Data

Machine learning is powerful to model massive genomic data while genome privacy is a growing concern. Studies have shown that not only the raw data but also the trained model can potentially infringe genome privacy. An example is the membership inference attack (MIA), by which the adversary, who only queries a given target model without knowing its internal parameters, can determine whether a specific record was included in the training dataset of the target model. Differential privacy (DP) has been used to defend against MIA with rigorous privacy guarantee. In this paper, we investigate the vulnerability of machine learning against MIA on genomic data, and evaluate the effectiveness of using DP as a defense mechanism. We consider two widely-used machine learning models, namely Lasso and convolutional neural network (CNN), as the target model. We study the trade-off between the defense power against MIA and the prediction accuracy of the target model under various privacy settings of DP. Our results show that the relationship between the privacy budget and target model accuracy can be modeled as a log-like curve, thus a smaller privacy budget provides stronger privacy guarantee with the cost of losing more model accuracy. We also investigate the effect of model sparsity on model vulnerability against MIA. Our results demonstrate that in addition to prevent overfitting, model sparsity can work together with DP to significantly mitigate the risk of MIA.

bioinformatics↗

bioRxiv2020

Soluble corn fiber reduces ovalbumin-induced sinonasal inflammation via the gut microbiota-airway axis

Asthma is a chronic airway inflammatory disease that affects approximately 300 million people worldwide, causing a substantial healthcare burden. Although there is a large degree of heterogeneity in the inflammatory response of asthmatics, a subset of patients are characterized by type-2 inflammation, which is in part mediated by TH2 cells in both the upper and lower airways. Asthma prevalence is increased in low-socioeconomic-status populations, where disparities in health behavior exist, including a shift toward a western diet characterized by low dietary fiber. Gut microbes metabolize fiber into short chain fatty acids that can reduce type-2 inflammation in peripheral organs, such as the airways. We hypothesized that soluble fiber can reduce ovalbumin (OVA)-induced upper airway inflammation in the context of the unified airway hypothesis, in mice maintained on ingredient-matched western (WD) and control diets (CD) through production of short chain fatty acids. Our results show that soluble fiber reduces IL-4 and IL-13 gene expression (p<0.05, Mann Whitney) in the sinonasal cavity of CD-fed mice, but this effect was lost in WD-fed mice. This loss of protection in WD-fed mice parallels compositional changes of the cecal and fecal microbiota. Mice fed a soluble fiber supplement while being maintained on a WD had altered microbial communities characterized by lower abundance of fiber fermentering bacteria. This work can be used to develop effective microbiome-based therapeutics as a low-cost method to reduce asthma morbidity. IMPORTANCEPrevious research has supported that western-style diets, typically high-fat and low-fiber, are associated with changes in the gut microbiome and increased inflammation. Western diets are accessible and prominent in low-socioeconomic-status populations, where asthma rates are highest; however, there has yet to be a low-cost asthma therapeutic. For the first time, we investigated whether supplementation with a physiologically relevant quantity of soluble corn fiber can reduce allergic airway inflammation. Our study supports that soluble corn fiber supplementation is associated with compositional shifts of the gut microbiota and reduced airway inflammation, promoting the use of fiber as a low-cost microbiome modifying therapy to reduce asthma-associated inflammation. However, soluble corn fiber in conjunction with a western diet resulted in an alternate gut microbiome composition and loss of protection against allergic airway inflammation. These findings further support the importance of the gut microbiota in host health.

microbiology↗

bioRxiv2020

NAD+ Redox Imbalance in the Heart Exacerbates Diabetic Cardiomyopathy

BackgroundDiabetes is a risk factor of heart failure and promotes cardiac dysfunction. Diabetic tissues are associated with NAD+ redox imbalance; however, the hypothesis that NAD+ redox imbalance leads to dysfunction of diabetic hearts has not been tested. In this study, we employed mouse models with altered NAD+ redox balance to test the hypothesis. Methods and ResultsDiabetes was induced in C57BL/6 mice by streptozotocin injections, and diabetic cardiomyopathy (DCM) was allowed to develop for 16 weeks. Diabetic stress led to cardiac dysfunction and lowered NAD+/NADH ratio. This diabetogenic regimen was administered to cardiac-specific knockout mice of complex I subunit Ndufs4 (cKO), a model with lowered cardiac NAD+/NADH ratio without baseline dysfunction. Cardiac NAD+ redox imbalance in cKO hearts exacerbated systolic and diastolic dysfunction of diabetic mice in both sexes. Collagen levels and transcript analyses of fibrosis and extracellular matrix-dependent pathways did not show change in diabetic cKO hearts, suggesting that the exacerbated cardiac dysfunction was likely due to cardiomyocyte dysfunction. We found that cardiac NAD+ redox imbalance promoted superoxide dismutase 2 (SOD2) acetylation, protein oxidation, induced troponin I S150 phosphorylation and impaired energetics in diabetic cKO hearts. Importantly, elevation of cardiac NAD+ levels by nicotinamide phosphoribosyltransferase (NAMPT) normalized NAD+ redox balance, over-expression alleviated cardiac dysfunction and reversed pathogenic mechanisms in diabetic mice. ConclusionOur results show that NAD+ redox imbalance to regulate protein acetylation and phosphorylation is a critical mediator of the progression of DCM, and suggest the therapeutic potential of harnessing NAD+ metabolism in DCM.

physiology↗

bioRxiv2020

In situ structure of the AcrAB-TolC efflux pump at subnanometer resolution

In Gram-negative bacteria, tripartite efflux pump AcrAB-TolC plays a prominent role in antibiotic resistance. We have used high resolution cryo-ET to visualize the structure of Escherichia coli AcrAB-TolC at a 7 [A] resolution in intact cells. The resulting structures show the detailed architecture of the assembled complex embedded into cell envelope. Interactions with the inner membrane enable crosstalk between AcrB and TolC through AcrA, suggesting that assembly in the native cellular environment is critical for the pump activation mechanism, where the allosteric activating signal is triggered by the alternate binding of AcrA to the lipid membrane and AcrB porter domain. We establish a platform for high resolution in situ structural studies of bacteria efflux pump, which can yield critical information in understanding complex assemblies function. One sentence summaryA 7 [A] in situ structure of the AcrAB-TolC pump from bacteria by cryo-ET reveals mechanisms for active efflux.

biophysics↗

bioRxiv2020

Cascade Diversification Directs the Generation of Neuronal Diversity in Hypothalamus

The hypothalamus contains an astounding heterogeneity of neurons to achieve its role in regulating endocrine, autonomic and behavioral functions. Despite previous progress in deciphering the gene regulatory programs linked to hypothalamus development, its molecular developmental trajectory and origin of neuronal diversity remain largely unknown. Here we combine transcriptomic profiling of 43,261 cells derived from Rax+ hypothalamic neuroepithelium with lineage tracing to map a developmental landscape of mouse hypothalamus and delineate the developmental trajectory of radial glial cells (RGCs), intermediate progenitor cells (IPCs), nascent neurons and peptidergic neurons in the lineage hierarchy. We show that RGCs adopt a conserved strategy for multipotential differentiation but generate both Ascl1+ and Neurog2+ IPCs, which display regionally differential origins in telencephalon. As transit-amplifying cells, Ascl1+ IPCs differ from their telencephalic counterpart by displaying fate bifurcation to produce both glutamatergic and GABAergic neurons. After classifying the developing neurons into 29 subtypes coded by diverse transcription factors, neurotransmitters and neuropeptides, we identified their molecular determinants via regulon analysis and further found that postmitotic neurons at nascent state possess the potential to resolve into more diverse subtypes of peptidergic neurons. Together, our study offers a single-cell framework for hypothalamus development and reveals that multiple cell types along the order of lineage hierarchy contribute to the fate diversification of hypothalamic neurons in a stepwise fashion, suggesting that a cascade diversifying model can deconstruct the origin of neuronal diversity.

developmental biology↗

bioRxiv2020

The autophagy adaptor NDP52 and the FIP200 coiled-coil allosterically activate ULK1 complex membrane recruitment

The selective autophagy pathways of xenophagy and mitophagy are initiated when the adaptor NDP52 recruits the ULK1 complex to autophagic cargo. Hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) was used to map the membrane and NDP52 binding sites of the ULK1 complex to unique regions of the coiled coil of the FIP200 subunit. Electron microscopy of the full-length ULK1 complex shows that the FIP200 coiled coil projects away from the crescent-shaped FIP200 N-terminal domain dimer. NDP52 allosterically stimulates membrane-binding by FIP200 and the ULK1 complex by promoting a more dynamic conformation of the membrane-binding portion of the FIP200 coiled coil. Giant unilamellar vesicle (GUV) reconstitution confirmed that membrane recruitment by the ULK1 complex is triggered by NDP52 engagement. These data reveal how the allosteric linkage between NDP52 and the ULK1 complex could drive the first membrane recruitment event of phagophore biogenesis in xenophagy and mitophagy.

biochemistry↗

bioRxiv2020

Polarized endosome dynamics engage cytosolic Par-3 and dynein during asymmetric division

Asymmetric cell division (ACD), which produces two daughters with different fates, is fundamental for generating cellular diversity. In the developing embryos of both invertebrates and vertebrates, asymmetrically dividing progenitors generate daughter cells with differential activity of Notch signaling1-7, a key regulator of cell fate decisions8,9. The cell polarity regulator Par-3 is critical for establishing this Notch asymmetry1,4,6, but the underlying mechanisms are not understood. Here, employing in vivo time-lapse imaging in the developing zebrafish forebrain during the mitotic cycle of radial glia, the principal vertebrate neural stem cells10,11, we show that during ACD, endosomes containing the Notch ligand Delta D (Dld) undergo convergent movement toward the cleavage plane, followed by preferential segregation into the posterior (and subsequently basal) Notchhi daughter. This asymmetric segregation requires the activity of Par-3 and the dynein motor complex. Employing label-retention expansion microscopy, we further detect Par-3 in the cytosol in association with the dynein light intermediate chain 1 (DLIC1) on Dld endosomes, suggesting a direct involvement of Par-3 in dynein-mediated polarized transport of Notch signaling endosomes. Our data reveal an unanticipated mechanism by which Par-3 regulates cell fate decision by directly polarizing Notch signaling components during ACD.

cell biology↗

bioRxiv2020

Heterologous expression and cell membrane localization of dinoflagellate rhodopsins in mammalian cells

Rhodopsins are now found in all domains of life, and are classified into two large groups: type II, found in animals and type I found in microbes including Bacteria, Archaea, and Eukarya. While type II rhodopsin functions in many photodependent signaling processes including vision, type I among others contains rhodopsins that function as a light-driven proton pump to convert light into ATP as in proteobacteria (named proteorhodopsin). Proteorhodopsin homologs have been documented in dinoflagellates, but their subcellular localizations and functions are still poorly understood. Even though sequence analyses suggest that it is a membrane protein, experimental evidence that dinoflagellate rhodopsins are localized on the plasma membrane or endomembranes is still lacking. As no robust dinoflagellate gene transformation tool is available, we used HEK 293T cells to construct a mammalian expression system for two dinoflagellate rhodopsin genes. The success of expressing these genes in the system shows that this mammalian cell type is suitable for expressing dinoflagellate genes. Immunofluorescence of the expressed protein locates these dinoflagellate rhodopsins on the cell membrane. This result indicates that the protein codons and membrane targeting signal of the dinoflagellate genes are compatible with the mammalian cells, and the proteins subcellular localization is consistent with proton pump rhodopsins.

molecular biology↗

bioRxiv2020

Immunoglobulin fragment F(ab')2 against RBD potently neutralizes SARS-CoV-2 in vitro

COVID-19 caused by the emerging human coronavirus, SARS-CoV-2, has become a global pandemic, leading a serious threat to human health. So far, there is none vaccines or specific antiviral drugs approved for that. Therapeutic antibodies for SARS-CoV-2, was obtained from hyper immune equine plasma in this study. Herein, SARS-CoV-2 RBD with gram level were obtained through Chinese hamster ovary cells high-density fermentation. The binding of RBD to SARS-CoV-2 receptor, human ACE2, was verified and the efficacy of RBD in vivo was tested on mice and then on horses. As a result, RBD triggered high-titer neutralizing antibodies in vivo, and immunoglobulin fragment F(ab)2 was prepared from horse antisera through removing Fc. Neutralization test demonstrated that RBD-specific F(ab)2 inhibited SARS-CoV-2 with EC50 at 0.07 g/ml, showing a potent inhibitory effect on SARS-CoV-2. These results highlights as RBD-specific F(ab)2 as therapeutic candidate for SARS-CoV-2.

pharmacology and toxicology↗

bioRxiv2020

Potent human neutralizing antibodies elicited by SARS-CoV-2 infection

The pandemic caused by emerging coronavirus SARS-CoV-2 presents a serious global public health emergency in urgent need of prophylactic and therapeutic interventions. SARS-CoV-2 cellular entry depends on binding between the viral Spike protein receptor-binding domain (RBD) and the angiotensin converting enzyme 2 (ACE2) target cell receptor. Here, we report on the isolation and characterization of 206 RBD-specific monoclonal antibodies (mAbs) derived from single B cells of eight SARS-CoV-2 infected individuals. These mAbs come from diverse families of antibody heavy and light chains without apparent enrichment for particular families in the repertoire. In samples from one patient selected for further analyses, we found coexistence of germline and germline divergent clones. Both clone types demonstrated impressive binding and neutralizing activity against pseudovirus and live SARS-CoV-2. However, the antibody neutralizing potency is determined by competition with ACE2 receptor for RBD binding. Surprisingly, none of the SARS-CoV-2 antibodies nor the infected plasma cross-reacted with RBDs from either SARS-CoV or MERS-CoV although substantial plasma cross-reactivity to the trimeric Spike proteins from SARS-CoV and MERS-CoV was found. These results suggest that antibody response to RBDs is viral species-specific while that cross-recognition target regions outside the RBD. The specificity and neutralizing characteristics of this plasma cross-reactivity requires further investigation. Nevertheless, the diverse and potent neutralizing antibodies identified here are promising candidates for prophylactic and therapeutic SARS-CoV-2 interventions.

immunology↗

bioRxiv2020

A quasi-paired cohort strategy reveals the impaired detoxifying function of microbes in the gut of autistic children

Growing evidence suggests that autism spectrum disorder (ASD) is highly associated with dysbiosis in the gut microbiome. However, results of metagenome-based microbiome studies are not always consistent due to great individual diversity that overwhelms disease-associated alterations. Here, we proposed a novel analysis strategy--quasi-paired cohort and applied it to a metagenomic study of ASD microbiomes. By comparing the paired samples of ASD and neurotypical subjects, we identified significant deficiencies in ASD children in detoxifying enzymes and pathways, which showed strong correlations to mitochondrial damage. Diagnostic models with these detoxifying enzymes accurately discriminated ASD individuals from controls, and the dysfunction score inferred from the model increased with the clinical rating scores of ASD. Conclusively, our findings suggest a previously undiscovered mechanism in which impaired microbial detoxification leads to toxicant accumulation and mitochondrion damage contributes to the pathogenesis of ASD. This novel mechanism points to future therapeutic strategies of rebuilding microbial detoxification for ASD.

microbiology↗