Biology subjects

Liu, K.

Publications and source records attributed to Liu, K..

At least 145 records · Page 8Linked to original sources

bioRxiv2024

CRISPR-mediated chromosome deletion facilitates genetic mapping of Vip3Aa resistance gene within complex genomic region in an invasive global pest

Connecting genetic variation to phenotypes and understanding the underlying biological mechanisms has been a fundamental goal of biological genetics. Here, we used the association analysis to identify a Vip3Aa resistance-associated genomic region in a strain of fall armyworm, JC-R, which exhibits >5000-fold resistance to the Bt toxin Vip3Aa. However, through various analytical approaches and fine-scale mapping across different populations, we demonstrated that this genomic region exhibits strong genetic linkage. The chromosome-level genome of JC-R and its parent strain JC-S were assembled, and extensive structural variations in the linkage regions were identified, which could be responsible for maintaining the linkage. To identify the causal variation within this linked region, a chromosome fragment stepwise knockout strategy based on CRISPR/Cas9 was developed. By crossing with the resistant strain and phenotyping segregating offspring on Vip3Aa-containing diet, we identified a chromosomal segment, KO8, containing the resistant gene. Subsequently, we conducted a comprehensive analysis of the variations in the KO8 region using multi-omics approaches, including genomic data, RNA-seq, proteomic, PacBio long read Iso-seq, and phosphoproteomic data. This analysis identified multiple variations in the chitin synthase gene CHS2, including amino acid substitution, alternative splicing, and changes in phosphorylation sites. After knocking out the CHS2, larvae exhibited over 6777-fold resistance to Vip3Aa. These results demonstrate that the chromosome fragment stepwise knockout strategy is a viable approach for studying complex genomic regions, and highlight the value of comprehensive analysis of genetic variations using multi-omics data. The identified candidate gene could potentially advance monitoring and management of pest resistance to Vip3Aa.

genetics↗

bioRxiv2024

In-vitro Metabolite Identification for MEDI7219, an Oral GLP-1 Peptide, using LC-MS/MS with CID and EAD Fragmentation

Oral peptide therapeutics typically suffer from short half-lives as they are readily degraded by digestive enzymes. Systematic peptide engineering along with formulation optimization led to the development of a clinical candidate MEDI7219, an orally-bioavailable GLP-1 peptide, that is much more stable than wild type GLP-1 or semaglutide. In this study, we elucidated peptide biotransformation products using in vitro pancreatin assay that employed both collision-induced dissociation (CID) and electron-activated dissociation (EAD) LC-MS/MS methods. Using this approach, we have confidently identified a total of 13 metabolites. Relative quantification of these metabolites over time showed sequential cleavage pattern as peptides were further digested to smaller fragments. These 13 metabolites mapped to 8 cleavage sites on MEDI7219 structure. Most of these cleavage sites can be explained by the specificity of digestive enzymes, e.g. ,trypsin, pepsin and elastase. -methyl-L-phenylalanine appeared to be well protected from chymotrypsin and pepsin digestion since no cleavage peptides ending with -methyl-L-phenylalanine were observed. These study results expand upon previously published stability data and provide new insights on potential GLP1 proteolytic liabilities for future engineering. Furthermore, this study exemplifies the application of pancreatin in vitro system methodology as a valuable tool for understanding metabolism of oral peptide therapeutics in vitro. Additionally, orthogonal MS fragmentation modes offered improved confidence in identification for peptide unknown metabolites. Significance StatementIn vitro metabolite identification of oral GLP1 peptide that uncovers potential proteolytic hotspots that can inform future oral peptide engineering.

pharmacology and toxicology↗

bioRxiv2024

Alpine lakes harbor diverse, endemic and structurally unique RNA viruses

Alpine lakes, characterized by isolation, low temperatures, oligotrophic conditions, and intense ultraviolet radiation, remain a poorly explored ecosystem for RNA viruses. Here, we present the first comprehensive metatranscriptomic study of RNA viruses in Lake Nam Co, a high-altitude alkaline saline lake on the Tibetan Plateau. Using a combination of sequence- and structure-based homology searches, we identified 742 RNA virus species, including 383 novel genus-level groups and 84 novel family-level groups exclusively found in Lake Nam Co. These findings significantly expand the known diversity of the Orthornavirae, uncovering evolutionary adaptations such as permutated RNA-dependent RNA polymerase (RdRP) motifs and distinct RNA secondary structures. Notably, 14 previously unknown RNA virus families potentially infecting prokaryotes were predicted, broadening the known host range of RNA viruses and questioning the traditional assumption that RNA viruses predominantly target eukaryotes. The presence of auxiliary metabolic genes (AMGs) in viral genomes suggested that RNA viruses (families f.0102 and Nam-Co_family_51) exploit host energy production mechanisms in energy-limited alpine lakes. Low nucleotide diversity, SNP frequencies, and pN/pS ratios indicate strong purifying selection in Nam Co viral populations. Our findings offer insights into RNA virus evolution and ecology, highlighting the importance of extreme environments in uncovering hidden viral diversity, and further shed light into their potential ecological implications, particularly in the context of climate change. Significance StatementThis study unveils the hidden diversity and complexity of RNA viruses in the high-altitude ecosystem of Lake Nam Co, significantly expanding the known RNA virome. The discovery of novel viral clades, expanded potential host ranges, and unique evolutionary adaptations emphasizes the importance of exploring extreme environments to uncover viral diversity and evolutionary pathways. Our findings offer critical insights into viral evolution, host-virus interactions, and the ecological roles of RNA viruses, particularly in the context of climate change and environmental resilience.

microbiology↗

bioRxiv2024

The m6A reader IGF2BP3 promotes gastric cancer progression via increasing the expression of FBXO32 protein

N6-methyladenosine (m6A) represents the most prevalent chemical modification on eukaryotic mRNA, with an accumulating body of literature indicating its pivotal significance in the pathogenesis of human cancers. Nevertheless, the precise molecular interplay between the m6A reader protein IGF2BP3 and gastric cancer remains to be thoroughly delineated. Our study uncovered that the expression of IGF2BP3 in gastric cancer tissues is markedly elevated in comparison to adjacent normal tissues, and this upregulation is tightly correlated with the incidence of lymph node metastasis, more advanced TNM stages, and deeper invasion depth of tumor in patients. In vitro experiments demonstrated that IGF2BP3 potentiates the proliferative, migratory, and invasive capacities of gastric cancer cells, while concurrently inhibiting apoptosis and augmenting the intracellular levels of aerobic glycolysis. In vivo experiments revealed that IGF2BP3 contributes to the growth of gastric cancer. Mechanistically, IGF2BP3 can increase the expression of FBXO32 protein by recognizing and binding to the m6A binding site on FBXO32 mRNA and further activate the downstream cGMP-PKG signaling pathway, thereby modulating various biological functions of gastric cancer cells and ultimately promoting the progression of gastric cancer. In summary, our findings suggest that IGF2BP3 upregulates the expression of FBXO32 protein in an m6A dependent manner and subsequently activates the cGMP-PKG signaling pathway, ultimately leading to the onset and progression of gastric cancer. Consequently, the targeting of the IGF2BP3/FBXO32/cGMP-PKG axis emerges as a promising therapeutic modality for the treatment of gastric cancer.

cancer biology↗

bioRxiv2024

RNA-ligand interaction scoring via data perturbation and augmentation modeling

RNA-targeting drug discovery is undergoing an unprecedented revolution. Despite recent advances in this field, developing data-driven deep learning models remains challenging due to the limited availability of validated RNA-small molecule interactions and the scarcity of known RNA structures. In this context, we introduce RNAsmol, a novel sequence-based deep learning framework that incorporates data perturbation with augmentation, graph-based molecular feature representation and attention-based feature fusion modules to predict RNA-small molecule interactions. RNAsmol employs perturbation strategies to balance the bias between true negative and unknown interaction space thereby elucidating the intrinsic binding patterns between RNA and small molecules. The resulting model demonstrates accurate predictions of the binding between RNA and small molecules, outperforming other methods with average improvements of [~]8% (AUROC) in 10-fold cross-validation, [~]16% (AUROC) in cold evaluation (on unseen datasets), and [~]30% (ranking score) in decoy evaluation. Moreover, we use case studies to validate molecular binding hotspots in the prediction of RNAsmol, proving the models interpretability. In particular, we demonstrate that RNAsmol, without requiring structural input, can generate reliable predictions and be adapted to many RNA-targeting drug design scenarios.

bioinformatics↗

bioRxiv2024

Vaccine-elicited and naturally elicited antibodies differ in their recognition of the HIV-1 fusion peptide

Broadly neutralizing antibodies have been proposed as templates for HIV-vaccine design, but it has been unclear how similar vaccine-elicited antibodies are to their naturally elicited templates. To provide insight, here we compare the recognition of naturally elicited and vaccine-elicited antibodies targeting the HIV-1-fusion peptide, which comprises envelope (Env) residues 512-526, with the most common sequence being AVGIGAVFLGFLGAA. Naturally elicited antibodies bound peptides with negative-charge substitutions around residues 517-520 substantially better than the most common sequence, despite these substitutions rarely appearing in HIV; by contrast, vaccine-elicited antibodies were less tolerant of sequence variation, with no substitution of residues 512-516 showing increased binding. Molecular dynamics analysis and cryo-EM structure of the naturally elicited ACS202 antibody in complex with HIV-Env trimer with A517E suggested enhanced binding to result from electrostatic interactions with positively charged antibody residues. Overall, vaccine-elicited antibodies appeared to be more fully optimized to bind the most common fusion peptide sequence. HIGHLIGHTSPeptide substitution scan reveals naturally elicited antibodies against fusion peptide (FP) can bind select non-canonical FP sequences with high affinity. Peptide substitution scan data for FP antibodies correlates significantly with their differential selection indicating variation in binding relates to neutralization tolerance. Structure and energetic analysis of naturally elicited ACS202 with HIV-Env trimer reveals basis for improved recognition of A517E mutant. Atomic level interactions from MD simulation analysis corroborate trends observed with peptide substitutions. verall, peptide substitution scans reveal vaccine-elicited antibodies against FP to be less permissive to FP-sequence variability than naturally elicited antibodies.

immunology↗

bioRxiv2024

Skeletal Muscle Specific PolG Dysfunction Activates the Integrated Stress Response and Promotes a Cachexia like Phenotype

During mitochondrial damage, information is relayed between the mitochondria and nucleus to coordinate precise responses to preserve cellular health. One such pathway is the mitochondrial integrated stress response (mtISR), which is specifically activated by mitochondrial DNA (mtDNA) damage. However, the causal molecular signals responsible for this activation remain elusive. A gene often associated with mtDNA mutations/deletions is Polg1, which encodes the mitochondrial DNA Polymerase {gamma} (PolG). Here, we describe what is to our knowledge the first conditional muscle specific model of PolG mutation, and demonstrate a rapid development of mitochondrial dysfunction and cachexia in these animals from [~]5 months of age. Detailed molecular profiling of muscles demonstrated robust activation of the mtISR, likely mediated upstream by the HRI/DELE1 stress pathway. This was accompanied by striking alterations to the mitochondrial folate cycle and its metabolites, strongly implying imbalanced folate intermediates as a previously unrecognised pathology driving the mtISR in mitochondrial disease.

physiology↗

bioRxiv2024

Semaphorin Receptors Antagonize Wnt Signaling Through Beta-Catenin Degradation

Precise control of morphogen signaling levels is essential for proper development. An outstanding question is: what mechanisms ensure proper morphogen activity and correct cellular responses? Previous work has identified Semaphorin (SEMA) receptors, Neuropilins (NRPs) and Plexins (PLXNs), as positive regulators of the Hedgehog (HH) signaling pathway. Here, we provide evidence that NRPs and PLXNs antagonize Wnt signaling in both fibroblasts and epithelial cells. Further, Nrp1/2 deletion in fibroblasts results in elevated baseline Wnt pathway activity and increased maximal responses to Wnt stimulation. Notably, and in contrast to HH signaling, SEMA receptor-mediated Wnt antagonism is independent of primary cilia. Mechanistically, PLXNs and NRPs act downstream of Dishevelled (DVL) to destabilize {beta}-catenin (CTNNB1) in a proteosome-dependent manner. Further, NRPs, but not PLXNs, act in a GSK3b/CK1-dependent fashion to antagonize Wnt signaling, suggesting distinct repressive mechanisms for these SEMA receptors. Overall, this study identifies SEMA receptors as novel Wnt pathway antagonists that may also play larger roles integrating signals from multiple inputs.

developmental biology↗

bioRxiv2024

Tonotopy is not preserved in a descending stage of auditory cortex

Previous studies based on layer specificity suggest that ascending signals from the thalamus to the sensory neocortex preserve spatially organized information, but it remains unknown whether sensory information descending from sensory neocortex to the thalamus also maintains such spatial organization pattern. By focusing on projection specificity, we mapped the tone response properties of two groups of cortical neurons in the primary auditory cortex (A1), based on the relationship between their specific connections to other regions and their function in ascending (thalamocortical recipient, TR neurons) or descending (corticothalamic, CT neurons) auditory information. A clear tonotopic gradient was observed among TR neurons, but not CT neurons. Additionally, CT neurons exhibited markedly higher heterogeneity in their frequency tuning and had broader bandwidth than TR neurons. These results reveal that the information flow descending from A1 to the thalamus via CT neurons is not arrange tonotopically, suggesting that the descending information flow possibly contributes to higher-order feedback processing of diverse auditory inputs.

neuroscience↗

bioRxiv2024

Production and functional verification of 8-gene (GGTA1, CMAH, β4GalNT2, hCD46, hCD55, hCD59, hTBM, hCD39)-edited donor pigs for xenotransplantation

Gene-edited pig-to-human xenotransplantation continues to make breakthroughs and is expected to enter clinic to solve the global shortage of donor organs. However, which gene combination is suitable for which organ transplantation remains unclear. In this study, we utilized CRISPR/Cas9 gene editing technology, PiggyBac transposon system and somatic cell cloning to construct GTKO/CMAHKO/{beta}4GalNT2KO/hCD46/hCD55/hCD59/hCD39/hTBM 8 gene-edited cloned (GEC) donor pigs, and performed pig to non-human primate (NHP) transplantation to evaluate the effectiveness of these GEC pigs. The multiple vectors were co-transfected into fetal fibroblasts of Diannan miniature pig with O blood type, and 25 colonies were screened out, and one of them carried GGTA1, CMAH and {beta}4GalNT2 biallelic knockout and integration of hCD46, hCD55, hCD59, hTBM and hCD39 genes, which was used as a donor cell for cloning, and a 33-day-old viable fetus was obtained. The fetus was identified and confirmed for normal karyotype and the absence of three xenogeneic antigens -Gal, Neu5Gc and Sda, and expression of hCD46, hCD55, hCD59, hTBM and hCD39 genes, then the recloning was carried out and 28 cloned piglets were obtained by natural delivery. Molecular identification at DNA, mRNA and protein levels showed that 8 gene editing (GE) was successful in these GEC piglets. Moreover, antigen-antibody binding assay and complement-dependent cytotoxicity assay demonstrated that 8GE effectively reduced the immune incompatibility and kidney xenograft survived up to 15 and 17 days into two NHPs, respectively. During this period, the recipient serum antibodies IgA and IgM, complements C3 and C4, coagulation indicators PT, APTT, TT and FIB, as well as most electrolytes and liver function indicators remained relatively stable. The 24-hour urine output and serum creatinine remained normal at a period of post-transplantation. These results indicated that the 8GEC pigs effectively alleviated immune rejection and exerted life-supporting kidney function in the recipient.

genetics↗

bioRxiv2024

Comparison of therapeutic effects between pulsed field ablation and cryoballoon ablation in the treatment of atrial fibrillation: a systematic review and me-ta-analysis

BackgroundPulmonary vein isolation (PVI) is the cornerstone of atrial fibrillation (AF) ablation surgery. Cryoballoon ablation (CBA), a conventional thermal ablation technique, enjoys widespread clinical application. In contrast, Pulsed field ablation (PFA) is a novel non thermal ablation technique for the treatment of atrial fibrillation (AF) patients, with safety comparable to traditional thermal ablation surgery. The present study aims to evaluate and compare the procedural efficiency and safety profiles of PFA and CBA in the management of AF. MethodWe performed a systematic search across PubMed, the Cochrane Library, and Embase databases, encompassing the literature up to February 2024, to inform our systematic review and meta-analysis. When assessing outcome indicators, the risk ratio (RR) and its corresponding 95% confidence interval (CI) were calculated for dichotomous variables. For continuous variables, the mean difference (MD) and the associated 95% CI were determined. In this context, an RR less than 1 and an MD less than 0 were considered advantageous for the PFA group. ResultIn this analysis, nine observational studies encompassing 2,875 patients with AF were included. Among these, 38% (n=1105) were treated with PFA, while 62% (n=1,770) received CBA. The results indicated that PFA was associated with a significantly shorter surgical duration compared to CBA, with a mean difference (MD) of -10.49 minutes (95% CI [-15.50, -5.49]; p<0.0001). Additionally, the PFA group exhibited a reduced risk of perioperative complications relative to the CBA group, with a risk ratio (RR) of 0.52 (95% CI 0.30-0.89; p=0.02). Nevertheless, no statistically significant differences were observed when comparing the two treatment cohorts concerning fluorescence irradiation time (MD 0.71; 95% CI [-0.45, 1.86]; p=0.23) and the recurrence of atrial arrhythmias during follow-up (RR 0.95; 95% CI 0.78-1.14; p=0.57). ConclusionThe outcomes of this investigation reveal that PFA holds a relative advantage over CBA in certain respects, notably by reducing both surgical duration and the incidence of perioperative complications. However, no significant distinction was identified between the two modalities concerning the duration of fluorescence irradiation or the rate of atrial arrhythmia recurrence. To enhance the robustness of these estimates, further research is needed, especially by incorporating additional randomized controlled trials.

physiology↗

bioRxiv2024

Redefining FLASH RT: the impact of mean dose rate and dose per pulse in the gastrointestinal tract

BackgroundThe understanding of how varying radiation beam parameter settings affect the induction and magnitude of the FLASH effect remains limited. PurposeWe sought to evaluate how the magnitude of radiation-induced gastrointestinal (GI) toxicity (RIGIT) depends on the interplay between mean dose rate (MDR) and dose per pulse (DPP). MethodsC57BL/6J mice were subjected to total abdominal irradiation (11-14 Gy single fraction) under conventional irradiation (low DPP and low MDR, CONV) and various combinations of DPP and MDR up to ultra-high-dose-rate (UHDR) beam conditions. The effects of DPP were evaluated for DPPs of 1-6 Gy while the total dose and MDR were kept constant; the effects of MDR were evaluated for the range 0.3- 1440 Gy/s while the total dose and DPP were kept constant. RIGIT was quantified in non-tumor-bearing mice through the regenerating crypt assay and survival assessment. Tumor response was evaluated through tumor growth delay. ResultsWithin each tested total dose using a constant MDR (>100 Gy/s), increasing DPP led to better sparing of regenerating crypts, with a more prominent effect seen at 12 and 14 Gy TAI. However, at fixed DPPs >4 Gy, similar sparing of crypts was demonstrated irrespective of MDR (from 0.3 to 1440 Gy/s). At a fixed high DPP of 4.7 Gy, survival was equivalently improved relative to CONV for all MDRs from 0.3 Gy/s to 104 Gy/s, but at a lower DPP of 0.93 Gy, increasing MDR produced a greater survival effect. We also confirmed that high DPP, regardless of MDR, produced the same magnitude of tumor growth delay relative to CONV using a clinically relevant melanoma mouse model. ConclusionsThis study demonstrates the strong influence that the beam parameter settings have on the magnitude of the FLASH effect. Both high DPP and UHDR appeared independently sufficient to produce FLASH sparing of GI toxicity, while isoeffective tumor response was maintained across all conditions.

cancer biology↗

bioRxiv2024

The robust, high-throughput, and temporally regulated roxCre and loxCre reporting systems for genetic modifications in vivo

Cre-loxP technology, a cornerstone in fate mapping and in vivo gene function studies, faces challenges in achieving precise and efficient conditional mutagenesis through inducible systems. This study introduces two innovative genetic tools designed to overcome these limitations. The first, roxCre, enables DreER-mediated Cre release, paving the way for intersectional genetic manipulation that permits increased precision and efficiency. The second, loxCre, facilitates conditional gene targeting by allowing CreER lines to induce Cre expression with significantly enhanced efficiency. These tools incorporate a fluorescent reporter for genetic lineage tracing, simultaneously revealing efficient gene knockout in cells marked by the reporter. These strategies hold great potential for precise and efficient exploration of lineage-specific gene functions, marking a significant advancement in genetic research methodologies.

genetics↗

bioRxiv2024

Tumoroid-on-a-Plate (ToP): Physiologically Relevant Cancer Model Generation and Therapeutic Screening

Employing three-dimensional (3D) in vitro models, including tumor organoids and spheroids, stands pivotal in enhancing cancer therapy. These models bridge the gap between 2D cell cultures and complex in vivo environments, effectively mimicking the intricate cellular interplay and microenvironmental factors found in solid tumors. Consequently, they offer versatile tools for comprehensive studies into cancer progression, drug responses, and tailored therapies. In this study, we present a novel open-surface microfluidic-integrated platform called the Tumoroid-on-a-Plate (ToP) device, designed for generating intricate predictive 3D solid tumor models. By incorporating a tumor mass, stromal cells, and extracellular matrix components, we successfully replicate the complexity of glioblastoma (GBM) and pancreatic adenocarcinoma (PDAC) within our system. Using our advanced ToP model, we were able to successfully screen the effect of various GBM extracellular matrix compositions, such as Collagen and Reelin, on the invasiveness of the GBM cells with the ToP model. The ToP in vitro model also allowed for the screening of chemotherapeutic drugs such as temozolomide and iron-chelators in a single and binary treatment setting on the complex ECM-embedded tumoroids. This helped to investigate the toxic effect of different therapeutics on the viability and apoptosis of our in vitro GBM and PDAC cancer models. Additionally, by co-culturing human-derived fibroblast cells with PDAC tumoroids, the pro-invasive impact of the stromal component of the tumor microenvironment on growth behaviour and drug response of the tumoroids was revealed. This study underscores the transformative role of predictive 3D models in deciphering cancer intricacies and highlights the promise of ToP in advancing therapeutic understanding.

bioengineering↗

bioRxiv2024

Jumbo phages possess independent synthesis and utilization systems of NAD+

Jumbo phages, phages with genomes >200 kbp, contain some unique genes for successful reproduction in their bacterial hosts. Due to complex and massive genomes analogous to those of small-celled bacteria, how do jumbo phages complete their life cycle remain largely undefined. In this study, we assembled 668 high-quality jumbo phage genomes from over 15 TB of intestinal metagenomic data from 955 samples of five animal species (cow, sheep, pig, horse, and deer). Within them, we obtained a complete genome of 716 kbp in length, which is the largest phage genome so far reported in the gut environments. Interestingly, 174 out of the 668 jumbo phages were found to encode all genes required for synthesis of NAD+ by the salvage pathway or Preiss-Handler pathway, referred as NAD-jumbo phage. Besides synthesis genes of NAD+, these NAD-jumbo phages also encode at least 15 types of NAD+-consuming enzyme genes involved in DNA replication, DNA repair, and counterdefense, suggesting that these phages not only have the capacity to synthesize NAD+ but also redirect NAD+ metabolism towards phage propagation need in hosts. Phylogenetic analysis and environmental survey indicated NAD-jumbo phages are widely present in the Earths ecosystems, including the human gut, lakes, salt ponds, mine tailings, and seawater. In summary, this study expands our understanding of the diversity and survival strategies of phages, and in-depth study of the NAD-jumbo phages is crucial for understanding their role in ecological regulation.

microbiology↗

bioRxiv2024

Microglial-Mediated Prevention of Axonal Degeneration in the Injured Spinal Cord: Insights from an In Vivo Imaging Study

Microglia, the primary immune cells in the central nervous system, play a critical role in regulating neuronal function and fate through their interaction with neurons. Despite extensive research, the specific functions and mechanisms of microglia-neuron interactions remain incompletely understood. In this study, we demonstrate that microglia establish direct contact with myelinated axons at Nodes of Ranvier in the spinal cord of mice. Under normal physiological conditions, microglia-node contact occurs in a random scanning pattern and is associated with neuronal activity. However, in response to axonal injury, microglia rapidly transform their contact into a robust wrapping form, preventing acute axonal degeneration from extending beyond the nodes. This neuroprotective wrapping behavior of microglia is dependent on the function of their P2Y12 receptors, which may be activated by ATP released through axonal volume-activated anion channels at the nodes. Additionally, voltage-gated sodium channels (NaV) contribute to the interaction between nodes and glial cells following injury, and inhibition of NaV delays axonal degeneration. Through in vivo imaging, our findings reveal a neuroprotective role of microglia during the acute phase of spinal cord injury, achieved through a novel form of neuron-glia interaction.

neuroscience↗

bioRxiv2024

Precision and Accuracy of Single-Cell/Nuclei RNA Sequencing Data

Single-cell and single-nucleus RNA sequencing (sc/snRNA-Seq) have become essential tools for profiling gene expression across different cell types in biomedical research. While factors like RNA integrity, cell count, and sequencing depth are known to influence data quality, quantitative benchmarks and actionable guidelines are lacking. This gap contributes to variability in study designs and inconsistencies in downstream analyses. In this study, we systematically evaluated quantitative precision and accuracy in expression measures across 23 sc/snRNA-Seq datasets comprising 3,682,576 cells from 339 samples. Precision was assessed using technical replicates based on pseudo-bulks created from subsampling. Accuracy was evaluated using sample-matched scRNA-Seq and pooled-cell RNA-Seq data of mononuclear phagocytes from four species. Our results show that precision and accuracy are generally low at the single-cell level, with reproducibility being strongly influenced by cell count and RNA quality. We establish data-driven thresholds for optimizing study design, recommending at least 500 cells per cell type per individual to achieve reliable quantification. Furthermore, we show that signal-to-noise ratio is a key metric for identifying reproducible differentially expressed genes. To support future research, we developed VICE (Variability In single-Cell gene Expressions), a tool that evaluates sc/snRNA-seq data quality and estimates the true positive rate of differential expression results based on sample size, observed noise levels, and expected effect size. These findings provide practical, evidence-based guidelines to enhance the reliability and reproducibility of sc/snRNA-seq studies.

genomics↗

bioRxiv2024

Electromagnetic Modeling within a Microscopically Realistic Brain - Implications for Brain Stimulation

Modeling brain stimulation at the microscopic scale may reveal new paradigms for various stimulation modalities. We present the largest map to date of extracellular electric field distributions within a layer L2/L3 mouse primary visual cortex brain sample. This was enabled by the automated analysis of serial section electron microscopy images with improved handling of image defects, covering a volume of 250 x 140 x 90 m3. The map was obtained by applying a uniform brain stimulation electric field at three different polarizations and accurately computing microscopic field perturbations using the boundary element fast multipole method. We used the map to identify the effect of microscopic field perturbations on the activation thresholds of individual neurons. Previous relevant studies modeled a macroscopically homogeneous cortical volume. Our result shows that the microscopic field perturbations - an electric field spatial noise with a mean value of zero - only modestly influence the macroscopically predicted stimulation field strengths necessary for neuronal activation. The thresholds do not change by more than 10% on average. Under the stated limitations and assumptions of our method, this result justifies the conventional theory of "invisible" neurons embedded in a macroscopic brain model for transcranial magnetic and transcranial electrical stimulation. However, our result is solely sample-specific and largely neglects the effect of the microcapillary network. Furthermore, we only considered the uniform impressed field and a single- pulse stimulation time course. Significance statementThis study is arguably the first attempt to model brain stimulation at the microscopic scale, enabled by automated analysis of modern scanning electron microscopy images of the brain. It concentrates on modeling microscopic perturbations of the extracellular electric field caused by the physical cell structure and is applicable to any type of brain stimulation. Data availability statementPost-processed cell CAD models (383, stl format), microcapillary CAD models (34, stl format), post-processed neuron morphologies (267, swc format), extracellular electric field and potential distributions at different polarizations (267x3, MATLAB format), *.ses projects files for biophysical modeling with Neuron software (267x2, Neuron format), and computed neuron activating thresholds at different conditions (267x8, Excel tables, without the sample polarization correction from Section 2.8) are made available online through BossDB, a volumetric open-source database for 3D and 4D neuroscience data.

neuroscience↗