Biology subjects

Chen, M.

Publications and source records attributed to Chen, M..

At least 469 records · Page 26Linked to original sources

bioRxiv2020

Tumor genotype dictates radiosensitization after Atm deletion in brainstem gliomas

Diffuse intrinsic pontine glioma (DIPG) kills more children than any other type of brain tumor. Despite clinical trials testing many chemotherapeutic agents, radiotherapy remains the standard treatment. Here, we utilized Cre/loxP technology to show that deleting Ataxia telangiectasia mutated (Atm) in primary mouse models of DIPG can enhance tumor radiosensitivity. Genetic deletion of Atm improved survival of mice with p53 deficient but not p53 wild-type gliomas following radiotherapy. Similar to patients with DIPG, mice with p53 wild-type tumors had improved survival after radiotherapy independent of Atm deletion. p53 wild-type tumor cell lines induced proapoptotic genes after radiation and repressed the NRF2 target, Nqo1. Tumors lacking p53 and Ink4a/Arf expressed the highest level of Nqo1 and were most resistant to radiation, but deletion of Atm enhanced the radiation response. These results suggest that tumor genotype may determine whether inhibition of ATM during radiotherapy will be an effective clinical approach to treat DIPGs.

cancer biology↗

bioRxiv2020

A dynamic regulatory interface on SARS-CoV-2 RNA polymerase

The RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 is the core machinery responsible for the viral genome replication and transcription and also a major antiviral target. Here we report the cryo-electron microscopy structure of a post-translocated SARS-CoV-2 RdRp core complex, comprising one nsp12, one separate nsp8(I) monomer, one nsp7-nsp8(II) subcomplex and a replicating RNA substrate. Compared with the recently reported SARS-CoV-2 RdRp complexes, the nsp8(I)/nsp7 interface in this RdRp complex shifts away from the nsp12 polymerase. Further functional characterizations suggest that specific interactions between the nsp8(I) and nsp7, together with the rearrangement of nsp8(I)/nsp7 interface, ensure the efficient and processive RNA synthesis by the RdRp complex. Our findings provide a mechanistic insight into how nsp7 and nsp8 cofactors regulate the polymerase activity of nsp12 and suggest a potential new intervention interface, in addition to the canonical polymerase active center, in RdRp for antiviral design. Author summarySince it was first discovered and reported in late 2019, the coronavirus disease 2019 (COVID-19) pandemic caused by highly contagious SARS-CoV-2 virus is wreaking havoc around the world. Currently, no highly effective and specific antiviral drug is available for clinical treatment. Therefore, the threat of COVID-19 transmission necessitates the discovery of more effective antiviral strategies. Viral RNA-dependent RNA polymerase (RdRp) is an important antiviral drug target. Here, our cryo-EM structure of a SARS-CoV-2 RdRp/RNA replicating complex reveals a previously uncharacterized overall shift of the cofactor nsp8(I)/nsp7 interface, leading to its rearrangement. Through in vitro functional test, we found that the specific interactions on the interface are important to the efficient RNA polymerase activity of SARS-CoV-2 RdRp. These observations let us to suggest this interface as a potential new drug intervention site, outside of the canonical polymerase active center, in RdRp for antiviral design. Our findings would provide new insights into regulatory mechanism of this novel SARS-CoV-2 RdRp, contribute to the design of antiviral drugs against SARS-CoV-2, and benefit the global public health.

molecular biology↗

bioRxiv2020

Pharmacological prevention of neonatal opioid withdrawal in a pregnant guinea pig model.

Newborns exposed to prenatal opioids often experience intense postnatal withdrawal after cessation of the opioid, called neonatal opioid withdrawal syndrome (NOWS), with limited pre- and postnatal therapeutic options available. In a prior study in pregnant mice we demonstrated that the peripherally selective neutral opioid antagonist, 6{beta}-naltrexol (6BN), is a promising drug candidate for preventive prenatal treatment of NOWS. Here, we have developed methadone (MTD) treated pregnant guinea pigs as a physiologically more suitable model, enabling detection of robust spontaneous neonatal withdrawal. Prenatal MTD significantly aggravates two classic maternal separation stress behaviors in newborn guinea pigs: calling (vocalizing) and searching (locomotion) - natural attachment behaviors thought to be controlled by the endogenous opioid system. In addition, prenatal MTD significantly increases the levels of plasma cortisol in newborns, showing that cessation of MTD at birth engages the hypothalamic-pituitary-adrenal (HPA) axis. We find that co-administration of 6BN with MTD prevents these withdrawal symptoms in newborn pups with extreme potency (ID50 [~]0.02 mg/kg), at doses unlikely to induce maternal or fetal withdrawal or to interfere with opioid antinociception based on many prior studies. Furthermore, we demonstrate a similarly high potency of 6BN in preventing opioid withdrawal in adult guinea pigs (ID50 = 0.01 mg/kg). This suggests a novel receptor mechanism to account for the selectively high potency of 6BN to suppress opioid dependence as compared to its low potency as a classical opioid antagonist. In conclusion, 6BN is an attractive compound for development of a preventive therapy for NOWS.

pharmacology and toxicology↗

bioRxiv2020

Transposable Element-Gene Splicing Modulates the Transcriptional Landscape of Human Pluripotent Stem Cells

Transposable elements (TEs) occupy nearly 50% of mammalian genomes and are both potential dangers to genome stability and functional genetic elements. TEs can be expressed and exonised as part of a transcript, however, their full contribution to the transcript splicing remains unresolved. Here, guided by long and short read sequencing of RNAs, we show that 26% of coding and 65% of non-coding transcripts of human pluripotent stem cells (hPSCs) contain TEs. Different TE families have unique integration patterns with diverse consequences on RNA expression and function. We identify hPSC-specific splicing of endogenous retroviruses (ERVs) as well as LINE L1 elements into protein coding genes that generate TE-derived peptides. Finally, single cell RNA-seq reveals that proliferating hPSCs are dominated by ERV-containing transcripts, and subpopulations express SINE or LINE-containing transcripts. Overall, we demonstrate that TE splicing modulates the pluripotency transcriptome by enhancing and impairing transcript expression and generating novel transcripts and peptides.

genomics↗

bioRxiv2020

Wireless AI-Powered IoT Sensors for Laboratory Mice Behavior Recognition

According to the U.S. Department of Agriculture in 2018, there are more than 100 million animals used in research, education, and testing per year. Of the laboratory animals used for research, 95 percent are mice and rats as reported by the Foundation for Biomedical Research (FBR). We present here our work in developing wireless Artificial Intelligent (AI)-powered IoT Sensors (AIIS) for laboratory mice motion recognition utilizing embedded micro-inertial measurement units (uIMUs). Based on the AIIS, we have demonstrated a small-animal motion tracking and recognition system that could recognize 5 common behaviors of mice in cages with accuracy of ~76.23%. The key advantage of this AIIS-based system is to enable high throughput behavioral monitoring of multiple to a large group of laboratory animals, in contrast to traditional video tracking systems that usually track only single or a few animals at a time. The system collects motion data (i.e., three axes linear accelerations and three axes angular velocities) from the IoT sensors attached to different mice, and classifies these data into different behaviors using machine learning algorithms. One of the challenging problems for data analysis is that the distribution of behavior samples is extremely imbalanced. Behaviors such as sleeping and walking dominate the entire sample set from different mice. However, machine learning algorithms often require a balanced sample set to achieve optimal performance. Thus, several methods are proposed to solve the imbalanced sample problem. Data processing methods for data segmentation, feature extraction, feature selection, imbalanced learning, and machine learning are explored to process motion data including sleeping, walking, rearing, digging, shaking, grooming, drinking and scratching. For example, by tuning the parameters of a machine-learning algorithm (i.e., Support Vector Machine (SVM)), the average accuracy of classifying five behaviors (i.e., sleeping, walking, rearing, digging and shaking) is 48.07% before solving the imbalance sample issue. To address this problem, an iteration of sample and feature selection is applied to improve the SVM performance. A combination of oversampling and undersampling is used to handle imbalanced classes, and feature selection provides the optimal number of features. The accuracy increases from 48.07% to 76.23% when the optimized combination is used. We further obtained an average accuracy of 86.46% by removing shaking, which is proved to have a negative effect on the overall performance, out of these five behaviors. Furthermore, we were able to classify less frequent behaviors including rearing, digging, grooming, drinking and scratching at an average accuracy of 96.35%.

animal behavior and cognition↗

bioRxiv2020

Protein Structure Refinement Guided by Atomic Packing Frustration Analysis

1Recent advances in machine learning, bioinformatics and the understanding of the folding problem have enabled efficient predictions of protein structures with moderate accuracy, even for targets when there is little information from templates. All-atom molecular dynamics simulations provide a route to refine such predicted structures, but unguided atomistic simulations, even when lengthy in time, often fail to eliminate incorrect structural features that would allow the structure to become more energetically favorable owing to the necessity of making large scale motions and overcoming energy barriers for side chain repacking. In this study, we show that localizing packing frustration at atomic resolution by examining the statistics of the energetic changes that occur when the local environment of a site is changed allows one to identify the most likely locations of incorrect contacts. The global statistics of atomic resolution frustration in structures that have been predicted using various algorithms provide strong indicators of structural quality when tested over a database of 20 targets from previous CASP experiments. Residues that are more correctly located turn out to be more minimally frustrated than more poorly positioned sites. These observations provide a diagnosis of both global and local quality of predicted structures, and thus can be used as guidance in all-atom refinement simulations of the 20 targets. Refinement simulations guided by atomic packing frustration turn out to be quite efficient and significantly improve the quality of the structures.

biophysics↗

bioRxiv2020

Cell Type Aware analysis of RNA-seq data(CARseq) reveals difference and similarities ofthe molecular mechanisms of Schizophrenia andAutism

Most tissue samples are composed of different cell types. Differential expression analysis without accounting for cell type composition cannot separate the changes due to cell type composition or cell type-specific expression. We propose a computational framework to address these limitations: Cell Type Aware analysis of RNA-seq (CARseq). CARseq employs a negative binomial distribution that appropriately models the count data from RNA-seq experiments. Simulation studies show that CARseq has substantially higher power than a linear model-based approach and it also provides more accurate estimate of the rankings of differentially expressed genes. We have applied CARseq to compare gene expression of schizophrenia/autism subjects versus controls, and identified the cell types underlying the difference and similarities of these two neuron-developmental diseases. Our results are consistent with the results from differential expression analysis using single cell RNA-seq data.

bioinformatics↗

bioRxiv2020

SMPD3-mediated extracellular vesicle biogenesis inhibits oligodendroglioma growth

Isocitrate dehydrogenase (IDH) mutant gliomas, including oligodendroglioma (IDH-O) and astrocytoma (IDH-A), have signature slow-growth rates that are poorly understood. Here, we reveal that SMPD3, a ceramide-producing sphingomyelinase implicated as a tumor suppressor gene and involved in extracellular vesicle biogenesis, suppresses IDH-mutant tumor growth via autocrine and paracrine actions. In patients with IDH-mutant gliomas, higher SMPD3 expression levels correlate with longer survival, consistent with ceramide acting as an anti-oncometabolite. SMPD3 knock-down in patient-derived IDH-O cells enhances proliferation cell-autonomously in 2D-culture and 3D-human cerebral organoids, and accelerates tumor growth in mouse orthotopic xenografts. Supporting paracrine actions, IDH-O-derived extracellular vesicles, enriched in ribosomal proteins, induce astrocytic death in vitro. Furthermore, non-neoplastic glia in IDH-O tumors proliferate abnormally yet undergo apoptosis, concomitant with the acquisition of a translation-enriched transcriptional signature by tumor-associated oligodendrocytes. SMPD3 thus suppresses IDH-mutant glioma growth cell-autonomously and phenotypically alters normal glia via extracellular vesicle biogenesis and paracrine actions.

cancer biology↗

bioRxiv2020

Genomic and TCR Repertoire Intratumor Heterogeneity of Small-cell Lung Cancer and its Impact on Survival

Small-cell lung cancer (SCLC) is speculated to harbor complex genomic intratumor heterogeneity (ITH) associated with high recurrence rate and suboptimal response to immunotherapy. Here, we revealed a rather homogeneous mutational landscape but extremely suppressed and heterogeneous T cell receptor (TCR) repertoire in SCLCs. Higher mutational burden, lower chromosomal copy number aberration (CNA) burden, less CNA ITH and less TCR ITH were associated with longer overall survival of SCLC patients. Compared to non-small cell lung cancers (NSCLCs), SCLCs had similar predicted neoantigen burden and mutational ITH, but significantly more suppressed and heterogeneous TCR repertoire that may be associated with higher CNA burden and CNA ITH in SCLC. Novel therapeutic strategies targeting CNA could potentially improve the tumor immune microenvironment and response to immunotherapy in SCLC.

genomics↗

bioRxiv2020

Single-cell in vivo brain optogenetic stimulation by two-photon excitation fluorescence transfer

Optogenetic manipulation with single-cell resolution can be achieved by two-photon excitation; however, this frequently requires relatively high laser powers or holographic illumination. Here we developed a practical strategy to improve the efficiency of two-photon stimulation by positioning fluorescent proteins or small fluorescent molecules with high two-photon cross-sections in the vicinity of opsins. This generates a highly localized source of endogenous single-photon illumination that can be tailored to match the optimal opsin absorbance. Through neuronal and vascular stimulation in the live mouse brain, we demonstrate the utility of this technique to achieve more efficient opsin stimulation, without loss of cellular resolution. We also provide a theoretical framework for understanding the potential advantages and constrains of this methodology, with suggestions for future improvements. Altogether, this fluorescence transfer illumination method allows experiments difficult to implement in the live brain such as all-optical neural interrogation and control of regional cerebral blood flow.

neuroscience↗

bioRxiv2020

The influence of axial length upon the retinal ganglion cell layer of the human eye

PurposeWe examined the relationship between axial length and the thickness and volume of the ganglion cell layer (GCL) of the retina, and related these measures to the size of the optic chiasm. MethodsWe used optical coherence tomography to measure the thickness of the GCL over a 50{degrees} extent of the horizontal meridian in 50 normally-sighted participants with a wide range of axial lengths. Using a model eye informed by individual biometry, we converted GCL thickness to tissue volume per square degree. The volume of the optic chiasm was measured for 40 participants using magnetic resonance imaging. ResultsWhile GCL thickness decreases with increasing axial length, there is a positive relationship between GCL tissue volume and axial length, leading us to conclude that increasing axial length is associated with decreased retinal ganglion cell packing, increased cell size, or both. We characterize how retinal ganglion cell tissue varies systematically in volume and spatial distribution as a function of axial length. This model allows us to remove the effect of axial length from individual difference measures of GCL volume. We find that variation in GCL volume correlates well with the size of the optic chiasm as measured using magnetic resonance imaging. ConclusionsOur results provide the volume of ganglion cell tissue in the retina, adjusted for the effects of axial length upon ganglion cell size and/or packing. The resulting volume measure accounts for individual differences in the size of the optic chiasm, supporting its use to characterize the post-retinal visual pathway.

neuroscience↗

bioRxiv2020

Bio-JOIE: Joint Representation Learning of Biological Knowledge Bases

The widespread of Coronavirus has led to a worldwide pandemic with a high mortality rate. Currently, the knowledge accumulated from different studies about this virus is very limited. Leveraging a wide-range of biological knowledge, such as gene on-tology and protein-protein interaction (PPI) networks from other closely related species presents a vital approach to infer the molecular impact of a new species. In this paper, we propose the transferred multi-relational embedding model Bio-JOIE to capture the knowledge of gene ontology and PPI networks, which demonstrates superb capability in modeling the SARS-CoV-2-human protein interactions. Bio-JOIE jointly trains two model components. The knowledge model encodes the relational facts from the protein and GO domains into separated embedding spaces, using a hierarchy-aware encoding technique employed for the GO terms. On top of that, the transfer model learns a non-linear transformation to transfer the knowledge of PPIs and gene ontology annotations across their embedding spaces. By leveraging only structured knowledge, Bio-JOIE significantly outperforms existing state-of-the-art methods in PPI type prediction on multiple species. Furthermore, we also demonstrate the potential of leveraging the learned representations on clustering proteins with enzymatic function into enzyme commission families. Finally, we show that Bio-JOIE can accurately identify PPIs between the SARS-CoV-2 proteins and human proteins, providing valuable insights for advancing research on this new disease.

bioinformatics↗

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

Quantification of proteins, protein complexes and mRNA in single cells by proximity-sequencing

Multiplexed analysis of single-cells enables accurate modeling of cellular behaviors, classification of new cell types, and characterization of their functional states. Here we present proximity-sequencing (Prox-seq), a method for simultaneous measurement of an individual cells proteins, protein complexes and mRNA. Prox-seq utilizes deep sequencing and barcoded proximity assays to measure proteins and their complexes from all pairwise combinations of targeted proteins, in thousands of single-cells. The number of measured protein complexes scales quadratically with the number of targeted proteins, providing unparalleled multiplexing capacity. We developed a high-throughput experimental and computational pipeline and demonstrated the potential of Prox-Seq for multi-omic analysis with a panel of 13 barcoded proximity probes, enabling the measurement of 91 protein complexes, along with thousands of mRNA molecules in single T-cells and B-cells. Prox-seq provides access to an untapped yet powerful measurement modality for single-cell phenotyping and can discover new protein interactions in signaling and drug studies.

bioengineering↗

bioRxiv2020

Probing the functions of microglial cyclin-dependent kinase 5 under physiological and pathological conditions

Cyclin dependent kinase 5 (Cdk5) regulates various developmental and physiological processes in the central nervous system. Deregulation of Cdk5 activity in neurons induces severe neurodegeneration and has been implicated in Alzheimers disease (AD) and other neurodegenerative conditions. A large fraction of AD risk genes are highly expressed in microglia, highlighting an important role for these cells in AD pathogenesis. While Cdk5 function in neurons is well characterized, our understanding of its roles in microglial function under physiological and neurodegenerative conditions remain rudimentary. Here, we investigate the roles of Cdk5 in microglia using myeloid-specific Cdk5 conditional knockout mice. Using microglia-specific transcriptome profiling, histological analyses, and behavioral assessments, we found that knockout of Cdk5 in microglia for 1 month induced transcriptional changes characterized by upregulation of cell cycle processes and type I interferon signaling genes in both physiological conditions and AD-related amyloidogenesis. In contrast to the robust transcriptional changes, conditional loss of microglial Cdk5 produced minimal effects on the density and morphology of microglia and their phagocytic activity toward myelin debris. Moreover, Cdk5cKO mice exhibited little change in synaptic density and tasks associated with locomotor, anxiety-like, and memory-related behaviors. Our findings indicate that the conditional loss of Cdk5 in microglia induces rapid alterations of microglial transcriptome with minimal or delayed effects on histological and behavioral responses.

neuroscience↗

bioRxiv2020

Elevated ACE2 expression in the olfactory neuroepithelium: implications for anosmia and upper respiratory SARS-CoV-2 entry and replication

The site of SARS-CoV-2 entry and replication critically impacts strategies for COVID-19 diagnosis, transmission mitigation, and treatment. We determined the cellular location of the SARS-CoV-2 target receptor protein, ACE2, in the human upper airway, finding striking enrichment (200-700 folds) in the olfactory neuroepithelium relative to nasal respiratory or tracheal epithelial cells. This cellular tropism of SARS-CoV-2 may underlie its high transmissibility and association with olfactory dysfunction, while suggesting a viral reservoir potentially amenable to intranasal therapy.

molecular biology↗

bioRxiv2020

Comparative proteomics analysis identifies L-FABP as a putative biomarker of graft injury during liver transplantation

BackgroundTo a large extent the success of liver transplantation depends on quality of allografts. The molecular basis of the susceptibility of different liver allografts to transplant injury remains undefined. MethodsTransplanted liver samples were collected and divided into three groups: the optimal graft (OG) group, early allograft dysfunction (EAD) group, and primary nonfunction (PNF) group. iTRAQ comparative quantitative proteomic analysis and multiple reaction monitoring (MRM) verification was performed. ResultsMore than 160 differentially expressed proteins were detected in the PNF group, compared to 54 and 36 proteins in the EAD and OG groups respectively. Liver-type fatty acid-binding protein (L-FABP) was found as differentially expressed in both cold preserved and reperfused liver. Serum L-FABP level in donors was higher in the PNF and EAD groups than in the OG group. A lower tissue expression of L-FABP was observed in the PNF groups than other groups after reperfusion, indicating incompetent liver donor quality. In mouse ischemia reperfusion injury (IRI) model, the serum levels and tissue expression of L-FABP corresponded to the ALT variation curve. ConclusionsSuboptimal donor livers are more sensitive to ischemia reperfusion injury. L-FABP might be an effective biomarker for evaluating donor quality in liver transplantation.

molecular biology↗

bioRxiv2020

Reference-free and de novo Identification of Circular RNAs

BackgroundEarly studies have unveiled multiple regulatory functions of circular RNAs (circRNAs); however, accurate detection and quantification of circRNAs, especially in understudied organisms, is unsolved yet. ResultsIn this study, we developed a new reference-free method, namely Cirit, to de novo detect circRNAs with sequence support from the next generation sequencing (NGS) transcriptome. The Cirit showed remarkable performance in accurate detection and quantification of circRNAs via comparing with current methods from different aspects. Using Cirit, we detected 28,813 nonredundant human circRNAs from 91 transcriptome datasets, as well as 2,385 circRNAs from four understudied organisms. Subsequent analyses found that the majority of human circRNAs expressed spatiotemporally; only a very small portion of circRNAs were back-splice junction (BSJ)-consistent (maximally 5.17%) or sequence-consistent (under 2%). Furthermore, circRNA genesis were relatively flexible that only about 60% of human circRNAs used the canonical GT-AG pattern for back-splice. The inconsistent expression of circRNAs challenges their roles as precise transcriptional regulators. ConclusionsIn summary, the reference-free method provides a straightforward and universal way for reliable circRNA research. It will largely boost the successful rate in designing highly specific probes to monitor circRNA behavior in cell. In particular, it brings circRNA research to the organisms that have no genome or draft genome.

bioinformatics↗