Biology subjects

Fang, X.

Publications and source records attributed to Fang, X..

At least 55 records · Page 3Linked to original sources

bioRxiv2025

Personalized Brain Morphometric Feature as a Transdiagnostic Predictor of Psychopathology: Insights from Dual Systems Models

BackgroundAdolescents are particularly vulnerable to developing psychopathological symptoms, yet neurobiological markers that can identify these vulnerabilities in a personalized and interpretable manner remain limited. Dual Systems Models suggest that this vulnerability may result from asynchronous development of neural systems subserving cognitive-control and socioemotional functions. Given that rigorous empirical evidence is sparse, this study aimed to quantify developmental imbalances and evaluate their predictive value for psychopathology. MethodsBased on Dual Systems Models, the dorsolateral prefrontal cortex (DLPFC) and ventral striatum (VS) were selected as key regions for the two brain systems, respectively. Using longitudinal data from the Adolescent Brain Cognitive Development (ABCD) study (baseline: n=11,238, ages 9.92{+/-}0.625 years; 2-year follow-up: n=7,870, ages 12.2{+/-}0.652 years; 4-year follow-up: n=2972, ages 14.1{+/-}0.693 years), we derived a personalized imbalance score based on brain morphometric features, including surface area, thickness and gray-matter volume. Nested linear mixed models were employed to assess associations between the imbalance scores and psychopathology. Additionally, generalized additive models were used to capture developmental trajectories of the imbalance scores and explore potential non-linear associations with psychopathology. To examine reproducibility, data from the Lifespan Human Connectome Project in Development study (HCP-D, N=652, ages 8-21 years) were interrogated. ResultsThe imbalance score, quantified as the difference between VS volume and DLPFC surface area, exhibited strong reliability and validity. During adolescence, the score exhibited a declining trend, with decreasing growth rates and variability between individuals. The score was positively associated with externalizing symptoms and showed a U-shaped relationship with internalizing symptoms. These findings were replicated in the HCP-D sample. ConclusionsThe novel neuroanatomical imbalance score empirically supports Dual Systems Models and may function as a transdiagnostic marker for internalizing and externalizing psychopathology. These findings enhance understanding of the neurodevelopmental mechanisms underlying adolescent psychopathology and offer potential implications for precision prevention and intervention strategies.

developmental biology↗

bioRxiv2025

Deciphering of single-cell chromatin accessibility and transcriptome reveals the discrepancy for ex vivo human erythropoiesis

BackgroundErythroid cells can be generated from hematopoietic stem and progenitor cells (HSPC) derived from various sources; however, few studies decode ex vivo human erythropoiesis for the discrepancies at single-cell multi-omics resolution and uncover the underlying restraints for erythrocyte regeneration. ResultsWe deciphered ex vivo human erythropoiesis at two differentiation states from three sources at single-cell chromatin accessibility and transcriptomes level. We identified detrimental myeloid differentiation tendencies during early differentiation. These tendencies were linked to low glutamine activity in cord blood- and iPSC-derived erythropoiesis. The erythroid progenitor differentiation is restricted by cell cycle and hypoxia signaling deficiencies, which are pronounced in the iPSC-derived erythropoiesis. We delineated the erythroid differentiation trajectory of various ex vivo erythropoiesis systems, and revealed a distinct roadmap from HSC to orthochromatic erythroblast with unprecedented resolution. The integrative analysis of single-cell chromatin accessibility and transcriptome across developmental stages uncovered a dynamic coordination, and highlighted the pivotal role of chromatin accessibility and associated enhancers in regulating ex vivo erythropoiesis. Cell-cell communications in the ex vivo erythropoiesis system were not as well established as those in the BM, suggesting that modulating cell-cell communication signals in distinct ex vivo erythropoiesis system may facilitate erythrocyte regeneration. ConclusionsThis study comprehensively characterized the discrepancies and constraints in ex vivo human erythropoiesis at single-cell multi-omics resolution, offering novel strategies to overcome these constraints. These insights are critical for advancing functional erythrocyte generation and have significant implications for clinical applications.

developmental biology↗

bioRxiv2025

Exploring Population Differences in the Human Gut Microbiome: from Microbial Abundance to Single Nucleotide Polymorphisms

The human gut microbiota exhibits significant diversity across populations, influenced by factors such as geography, diet, and lifestyle, particularly between the Han Chinese and non-Chinese populations. While previous studies have predominantly focused on the taxonomic abundance of the gut microbiome, the impact of single nucleotide polymorphisms (SNPs) in driving population-specific differences remains largely underexplored. In this study, we systematically investigated gut microbial differences between the Han Chinese and non-Chinese populations using the Human Gut Microbiome Reference Genome Catalog (HGMRGC). HGMRGC includes 271,480 non-redundant genomes from 5,785 prokaryotic species, which was generated by metagenomic sequencing data from 9,320 publicly available samples across 22 countries and 3,584 newly sequenced samples from Han Chinese individuals across 29 provinces and regions in China. We observed geography was the primary driver of microbial variation of abundance and SNPs. We identified 625 novel population-specific genome clusters from HGMRGC with functional differences in carbohydrate utilization and 126 species exhibiting distinct prevalence related to vitamin biosynthesis, antibiotic resistance, and carbohydrate metabolism. Beta diversity analysis highlighted significant inter-population differences in both microbial abundance and SNPs, while alpha diversity analysis revealed that non-Chinese populations exhibited higher diversity in microbial abundance, and Han Chinese populations displayed greater diversity in SNPs. These results provide valuable insights into population-specific microbial diversity, laying the groundwork for future research on its functional and health implications.

microbiology↗

bioRxiv2025

Mechanistic basis for protection against fatty liver disease by CIDEB loss-of-function mutations

Background & AimsSomatic and germline CIDEB mutations are associated with protection from chronic liver diseases. The mechanistic basis and whether CIDEB suppression would be an effective therapy against fatty liver disease remain unclear. Methods21 CIDEB somatic mutations were introduced into cells to assess functionality. In vivo screening was used to trace Cideb mutant clones in mice fed normal chow, western (WD), and choline-deficient, L-amino acid-defined, high-fat (CDA-HFD) diets. Constitutive and conditional Cideb knockout mice were generated to study Cideb in liver disease. Isotope tracing was used to evaluate fatty acid oxidation and de novo lipogenesis. Transcriptomics, lipidomics, and metabolic analyses were utilized to explore molecular mechanisms. Double knockout models (Cideb/Atgl and Cideb/Ppara) tested mechanisms underlying Cideb loss. ResultsMost CIDEB mutations showed that they impair function, and lineage-tracing showed that loss-of-function clones were positively selected with some, but not all fatty liver inducing diets. Cideb KO mice were protected from WD, CDA-HFD, and alcohol diets, but had the greatest impact on CDA-HFD induced liver disease. Hepatocyte-specific Cideb deletion could ameliorate disease after MASLD establishment, modeling the impact of therapeutic siRNAs. Cideb loss protected livers via increased {beta}-oxidation, specifically through ATGL and PPARa activation. ConclusionsCideb deletion is more protective in some types of fatty liver disease. {beta}-oxidation is an important component of the Cideb protective mechanism. CIDEB inhibition represents a promising approach, and somatic mutations in CIDEB might predict the patient populations that might benefit the most.

physiology↗

bioRxiv2025

Stochastically Emergent Tumors offer in vivo whole genome interrogation of cancer evolution from non-malignant precursors

Interrogating the stochastic events underlying tumor evolution from non-malignant precursors is crucial for understanding therapy resistance. Current methods are complicated by chromosomal instability, obscuring driver identification and yielding non-representative genetics. Inspired by patient tumors that evolve without chromosomal instability, we developed Stochastically Emergent Tumors (SETs) by inducing mismatch repair deficiency in non-malignant precursors, then engrafting in mice. Barcoded SETs exhibited increased tumoral and drug target heterogeneity over current models. SETs delineated the stochastic contributions, mutational landscapes, and selective pressures distinguishing tumorigenesis from non-malignant precursor in vitro growth. SETs are an unlimited source for diverse Stochastically Emergent cell Lines (SELs), bolstering under-represented cancers. Since SETs composition dynamically reflects therapy exposure, they are a whole-genome platform for precision oncology. We identified three novel genetic drivers (ZFHX3, CIC, KMT2D) of differential prostate cancer therapy responses. These alterations are enriched in patients of African and Chinese ancestry and correlate with significant differences in survival.

cancer biology↗

bioRxiv2025

Spike inference from calcium imaging data acquired with GCaMP8 indicators

For neuroscience to be reproducible, its key methods must be quantitative and interpretable. Calcium imaging is such a key method, but it records neuronal activity only indirectly and is therefore difficult to interpret. These difficulties arise from the kinetics, nonlinearity, and sensitivity of calcium indicators, but also from the methods used for signal analysis. Here, we evaluate how methods for spike inference can be optimized to interpret data with the recently developed calcium indicator GCaMP8. We find that the indicator linearity of GCaMP8 enables more accurate recovery of high-frequency spiking events and the detection of single action potentials. Ground truth recordings from mouse neocortex show that the most linear calcium variants, GCaMP8s and GCaMP8m - but not GCaMP6, GCaMP7f, or GCaMP8f - robustly detect isolated spikes in pyramidal neurons under realistic noise conditions. In addition, we fine-tune and benchmark existing algorithms for spike inference (CASCADE, OASIS, MLSpike) with GCaMP8 data, investigate spike inference for interneurons, and demonstrate how the fast rise time of GCaMP8 enables low-latency real-time detection of neuronal activity. Together, our study provides tools and guidelines to optimally process calcium signals with GCaMP8 and highlights the key role of linearity in improving the interpretability of calcium imaging.

neuroscience↗

bioRxiv2025

Particular Amino Acid on Lateral Interface Maintains FtsZ Function Under Acid Stress in Streptococcus mutans

FtsZ is the core protein for cell division in bacteria that can polymerize into Z-rings and drive cytokinesis. Understanding how bacteria maintain the correct function of FtsZ under various environmental stresses is crucial for novel antibacterial drug discovery. Our previous study revealed that the FtsZ in S. mutans has higher self-assembly and GTPase activity under acidic stress, which may be responsible for the cariogenesis of S. mutans. However, the mechanism is still unknown. Here, we further reported the crystal structure of S. mutans FtsZ, revealing a unique lateral interface. Through protein polymerization and GTPase ability assay, we experimentally demonstrated that mutation of Arg68 on this lateral interface significantly reduced the functional activity of FtsZ in an acidic environment. The phenotype assay and rat caries model further showed that mutation of Arg68 effectively inhibited the acid resistance of S. mutans and the occurrence and progress of dental caries in vivo. By employing a molecular dynamics simulation analysis, we conclude that mutation of Arg68 disrupts the conformation change necessary for SmFtsZ polymerization under acidic conditions. Our study proposes a novel mechanism to maintain FtsZ function in bacteria and could be a potential target for antimicrobial drugs to inhibit the growth of S. mutans in an acidic environment. Significance StatementFtsZ is the core protein that drives cytokinesis. Maintaining the self-assembly and GTPase activity of FtsZ plays a critical role in cell growth under environmental stress. Currently, research on FtsZ function maintenance under stress mainly focuses on model organisms, with less on other pathogenic bacteria. This study reveals a novel structural mechanism for the acidic tolerance of FtsZ in S. mutans which survives in strongly acidic surroundings. Meanwhile, Arg68 on the lateral interface of SmFtsZ may be a potential therapeutic target to regulate microecology and combat S. mutans-associated dental caries.

microbiology↗

bioRxiv2025

Simultaneous Targeting of KRAS and CDK4 Synergistically Suppresses Pancreatic Cancer Cells

Mutant Ras oncoproteins, particularly KRAS, are among the most prevalent drivers of cancer. Small-molecule inhibitors of KRAS have been developed, bearing high potential for cancer therapy but considerable risk of resistance development. To avoid cancer cell adaptation, effective combinatorial partners for increasing immediate efficacy remain to be explored. Here, we demonstrate that combining the KRAS inhibitor Sotorasib with the CDK4/6 inhibitor Palbociclib synergistically eliminates pancreatic ductal adenocarcinoma (PDAC) cells and organoids harboring KRAS G12C mutations. This synergy was particularly pronounced after drug washout, indicating a durable impact. Similar effects were observed in non-small-cell lung cancer (NSCLC) cells. Additionally, MRTX1133, a KRAS G12D inhibitor, synergized with Palbociclib to suppress KRAS G12D-mutant PDAC-derived cells. Mechanistically, these combinations induced sustained cell cycle arrest through reduced RB phosphorylation, decreased E2F1 levels, and increased CDKN1B/p27 expression. Deletion of CDKN1B largely rescued tumor cell proliferation, underscoring its critical role in mediating the observed synergy. These findings support the therapeutic potential of combining KRAS and CDK4/6 inhibitors for treating PDAC and other Ras-driven cancers.

cancer biology↗

bioRxiv2025

Intracellular tension relaxation engineered through D-enantiomeric hydrogel maneuvers neurogenesis and immunomodulation to facilitate spinal cord repair

Microenvironmental mechanics regulate morphogenesis and post-injury inflammation, however, the fragile mechanical strength and oxidative physiological environment hinder precise and consistent mechanical management after spinal cord injury (SCI). Here, we engineered self-assembling hydrogels of enantiomeric peptides with neural tissue- matching mechanical properties to persistently manipulate mechanosensing and mechanotransduction through stereo conformational recognition and consequent protein affinity difference. While hindering proliferation and morphogenesis in non-neural cells, D-hydrogel-induced intracellular tension relaxation triggered neurogenesis and ECM remolding in astrocytes, while simultaneously suppressing pro-inflammation and promoting pro-regeneration in microglia, which together enable neuroprotection from degeneration and enhance functional recovery in severe SCI rat models. These effects are mediated through neurogenic morphology changes resulting from cytoskeletal tension relaxation, leading to the opening of mechanosensitive ion channels in the cellular membrane, chromatin unfolding, and YAP nuclear translocation. This exclusive D- hydrogel-dependent neurogenesis, triggered by intracellular tension relaxation, revealed a neural-specific response to mechanical cues and provided a targeted tissue repair strategy for nerve injury. TeaserIntracellular tension relaxion activates morphogenesis specifically in neural cells through reversing neurogenic cellular morphology.

neuroscience↗

bioRxiv2025

Ether Rhodamines with Enhanced Hydrophilicity, Fluorogenicity, and Brightness for Super-Resolution Imaging

Rhodamine dyes are widely used fluorophores in super-resolution fluorescence imaging due to their exceptional optical properties and "aggregation-disaggregation" induced fluorogenic activation. However, their excessive lipophilicity often reduces brightness in aqueous environments and causes off-target staining, limiting their effectiveness in high-resolution imaging. To address these challenges, we introduce an ether-decorated N-terminal modification strategy for rhodamine and silicon-rhodamine (Si-rhodamine), replacing conventional N-alkyl groups. The ether chains enhance water solubility, decrease aggregate size, and improve fluorogenicity across a wide concentration range. Their flexible, hydrophilic structure forms a protective shield around the xanthene core, minimizing dye-water interactions and reducing fluorescence quenching. Additionally, the inductive effect of the ether chains decreases the electron-donating strength of the amino groups, suppressing quenching caused by twisted intramolecular charge transfer (TICT). These modifications collectively increase the quantum yields of ER and ESiR in water from 0.35 and 0.19 (for tetraethyl-substituted analogs) to 0.70 and 0.41, respectively. Probes derived from ER and ESiR exhibit outstanding fluorogenicity, enhanced signal-to-noise ratios, and improved resolution in complex aqueous environments, demonstrating superior performance in advanced super-resolution imaging techniques such as structured illumination microscopy (SIM), stimulated emission depletion (STED) microscopy, and single-molecule localization microscopy (SMLM). This work introduces an innovative strategy for fluorophore design, offering significant advancements for super-resolution imaging applications.

biochemistry↗

bioRxiv2024

State-specific Peptide Design Targeting G Protein-coupled Receptors

G protein-coupled receptors (GPCRs) play critical roles in various physiological processes and serve as pivotal targets for drug discovery. Peptides are particularly compelling therapeutic agents for targeting GPCRs, as they frequently exhibit superior affinity, selectivity, and potency compared to small-molecule drugs. However, the states (active and inactive) of GPCRs profoundly influence their interactions with ligands, highlighting the need for state-specific strategies in peptide design. To address this, we developed an efficient state-specific peptide design pipeline targeting GPCRs. This framework enables the tailored design of agonists or antagonists based on the active or inactive conformational states of GPCR structures. A state-specific folding model, optimized for GPCR-peptide complexes, was used to select high-potential peptides from the pool of designed candidates. Using this approach, we successfully identified both agonist and antagonist peptides for the Apelin Receptor (APJR) and the Growth Hormone Secretagogue Receptor (GHSR), as well as a competitive inhibitor for the Glucagon-Like Peptide-1 Receptor (GLP-1R).

bioinformatics↗

bioRxiv2024

BioLLM: A Standardized Framework for Integrating and Benchmarking Single-Cell Foundation Models

The application and evaluation of single cell foundational models (scFMs) present significant challenges stemming from the heterogeneity of architectural frameworks and coding standards. To address these issues, we introduce BioLLM, a framework facilitating the integration and application of scFMs in single-cell RNA sequencing data analysis. BioLLM provides a universal interface, bridging diverse scFMs into a seamless ecosystem. By mitigating architectural disparities and coding conventions, it empowers researchers with streamlined access to scFMs. With standardized APIs and comprehensive documentation, BioLLM streamlines model switching and comparative analyses, while incorporating best practices for consistent model evaluation. Our comprehensive evaluation of scFMs revealed distinct strengths and limitations, highlighting scGPTs robust performance across all tasks, both in zero-shot and fine-tuning scenarios. Geneformer and scFoundation also demonstrated strong capabilities in gene-level tasks, benefiting from effective pretraining strategies. In contrast, scBERT underperformed relative to other models, likely attributable to its considerably smaller parameter count and the limited size of the training dataset. Ultimately, BioLLM aims to empower the scientific community to leverage the full potential of foundational models, advancing our understanding of complex biological systems through enhanced single-cell analysis.

bioinformatics↗

bioRxiv2024

Inhibition of Soluble Epoxide Hydrolase Ameliorates Cerebral Blood Flow Autoregulation and Cognition in Alzheimer's Disease and Diabetes-Related Dementia Rat Models

Alzheimers Disease and Alzheimers Disease-related dementias (AD/ADRD) pose major global healthcare challenges, with diabetes mellitus (DM) being a key risk factor. Both AD and DM-related ADRD are characterized by reduced cerebral blood flow, although the exact mechanisms remain unclear. We previously identified compromised cerebral hemodynamics as early signs in TgF344-AD and type 2 DM-ADRD (T2DN) rat models. Genome-wide studies have linked AD/ADRD to SNPs in soluble epoxide hydrolase (sEH). This study explored the effects of sEH inhibition with TPPU on cerebral vascular function and cognition in AD and DM-ADRD models. Chronic TPPU treatment improved cognition in both AD and DM-ADRD rats without affecting body weight. In DM-ADRD rats, TPPU reduced plasma glucose and HbA1C levels. Transcriptomic analysis of primary cerebral vascular smooth muscle cells from AD rats treated with TPPU revealed enhanced pathways related to cell contraction, alongside decreased oxidative stress and inflammation. Both AD and DM-ADRD rats exhibited impaired myogenic responses and autoregulation in the cerebral circulation, which were normalized with chronic sEH inhibition. Additionally, TPPU improved acetylcholine-induced vasodilation in the middle cerebral arteries (MCA) of DM-ADRD rats. Acute TPPU administration unexpectedly caused vasoconstriction in the MCA of DM-ADRD rats at lower doses. In contrast, higher doses or longer durations were required to induce effective vasodilation at physiological perfusion pressure in both control and ADRD rats. Additionally, TPPU decreased reactive oxygen species production in cerebral vessels of AD and DM-ADRD rats. These findings provide novel evidence that chronic sEH inhibition can reverse cerebrovascular dysfunction and cognitive impairments in AD/ADRD, offering a promising avenue for therapeutic development.

molecular biology↗

bioRxiv2024

SciMind: A Multimodal Mixture-of-Experts Model for Advancing Pharmaceutical Sciences

Large language models (LLMs) have made substantial strides, but their use in reliably tackling issues within specialized domains, particularly in interdisciplinary areas like pharmaceutical sciences, is hindered by data heterogeneity, knowledge complexity, unique objectives, and a spectrum of constraint conditions. In this area, diverse modalities such as nucleic acids, proteins, molecular structures, and natural language are often involved. We designed a specialized token set and introduced a new Mixture-of-Experts (MoEs) pre-training and fine-tuning strategy to unify these modalities in one model. With this strategy, weve created a multi-modal mixture-of-experts foundational model for pharmaceutical sciences, named SciMind. This model has undergone extensive pre-training on publicly accessible datasets including nucleic acid sequences, protein sequences, molecular structure strings, and biomedical texts, and delivers good performance on biomedical text comprehension, promoter prediction, protein function prediction, molecular description, and molecular generation.

bioinformatics↗

bioRxiv2024

Spatial organization of PI3K-PI(3,4,5)P3-AKT signaling by focal adhesions

The class I PI3K-AKT signaling pathway is the master regulator of cell survival, growth, and proliferation, and among the most frequently mutated pathways in cancer. However, where and how the PI3K-AKT signaling is spatially activated and organized in mammalian cells remain poorly understood. Here, we identified focal adhesions (FAs) as the subcellular signaling hubs organizing the activation of PI3K-PI(3,4,5)P3-AKT signaling in mammalian cells. We found that class IA PI3Ks are preferentially and dynamically recruited to FAs for activation, resulting in localized production of the critical signaling lipid PI(3,4,5)P3 around FAs. As the effector protein of PI(3,4,5)P3, AKT molecules are dynamically recruited around FAs for activation. Mechanistically, the spatial recruitment/activation of PI3K-PI(3,4,5)P3-AKT cascade are regulated by the activated FAK. Furthermore, combined inhibition of class I PI3K and FAK results in a more potent inhibitory effect on cancer cells. Thus, our results unveil a growth-factor independent, compartmentalized organization mechanism for PI3K-PI(3,4,5)P3-AKT signaling.

cell biology↗

bioRxiv2024

The genomic and epigenomic dynamics of hemizygous genes across crops with contrasting mating systems

Hemizygous genes, which present on only one of the two homologous chromosomes of diploid organisms, have been mainly studied in the context of sex chromosomes and sex-linked genes. However, structural variants (SVs), such as a deletion/insertion of one allele, can lead to hemizygous genes, a phenomenon largely unexplored in plants. Here, we investigated the genomic and epigenomic landscapes of hemizygous genes across 22 genomes with varying propagation histories: eleven clonal lineages, seven outcrossed samples and four inbred and putatively homozygous genomes. We identified SVs leading to genic hemizygosity. As expected, very few genes (0.01%-1.2%) were hemizygous in the homozygous genomes, representing negative controls. Hemizygosity was appreciable among outcrossed lineages, averaging 8.7% of genes, but consistently elevated for the clonal samples at 13.8% genes, likely reflecting heterozygous SVs accumulation during clonal propagation. Compared to diploid genes, hemizygous genes were more often situated in centromeric than telomeric regions and underlying weaker purifying selection. They also had reduced levels of expression, averaging [~]20% of the expression levels of diploid genes, violating the evolutionary model of dosage compensation. We also detected higher DNA methylation levels, in hemizygous genes and transposable elements, which may contribute to the reduced expression of hemizygous genes. Finally, expression profiles showed that hemizygous genes were more specifically expressed in contexts related to fruit development, organ differentiation and stress responses. Overall, hemizygous genes accumulate in clonally propagated lineages and display distinct genetic, and epigenetic features compared to diploid genes, shedding new insights on genetic studies and breeding programs of clonal crops.

plant biology↗

bioRxiv2024

5-HT Neurons Integrate GABA and Dopamine Inputs to Regulate Meal Initiation

Obesity is a growing global health epidemic with limited effective therapeutics. Serotonin (5-HT) is one major neurotransmitter which remains an excellent target for new weight-loss therapies, but there remains a gap in knowledge on the mechanisms involved in 5-HT produced in the dorsal Raphe nucleus (DRN) and its involvement in meal initiation. Using a closed-loop optogenetic feeding paradigm, we showed that the 5-HTDRN{lozenge}arcuate nucleus (ARH) circuit plays an important role in regulating meal initiation. Incorporating electrophysiology and ChannelRhodopsin-2-Assisted Circuit Mapping, we demonstrated that 5-HTDRN neurons receive inhibitory input partially from GABAergic neurons in the DRN, and the 5-HT response to GABAergic inputs can be enhanced by hunger. Additionally, deletion of the GABAA receptor subunit in 5-HT neurons inhibits meal initiation with no effect on the satiation process. Finally, we identified the instrumental role of dopaminergic inputs via dopamine receptor D2 in 5-HTDRN neurons in enhancing the response to GABA-induced feeding. Thus, our results indicate that 5-HTDRN neurons are inhibited by synergistic inhibitory actions of GABA and dopamine, which allows for the initiation of a meal.

neuroscience↗

bioRxiv2024

CCQM-P199b: Interlaboratory comparability study of SARS-CoV-2 RNA copy number quantification

Nucleic acid amplification tests including reverse transcription quantitative PCR (RT-qPCR) are used to detect RNA from Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of the Coronavirus disease 2019 (COVID-19) pandemic. Standardized measurements of RNA can facilitate comparable performance of laboratory tests in the absence of existing reference measurement systems early on in a pandemic. Interlaboratory study CCQM P199b "SARS-CoV-2 RNA copy number quantification" was designed to test the fitness-for-purpose of developed candidate reference measurement procedures (RMPs) for SARS-CoV-2 genomic targets in purified RNA materials, and was conducted under the auspices of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) to evaluate the measurement comparability of national metrology institutes (NMIs) and designated institutes (DIs), thereby supporting international standardization. Twenty-one laboratories participated in CCQM P199b and were requested to report the RNA copy number concentration, expressed in number of copies per microliter, of the SARS-CoV-2 nucleocapsid (N) gene partial region (NC_045512.2: 28274-29239) and envelope (E) gene (NC_045512.2: 26245-26472) (optional measurements) in samples consisting of in vitro transcribed RNA or purified RNA from lentiviral constructs. Materials were provided in two categories: lower concentration ({approx} (101-104) /L in aqueous solution containing human RNA background) and high concentration ({approx} 109 /L in aqueous solution without any other RNA background). For the measurement of N gene concentration in the lower concentration study materials, the majority of laboratories (n = 17) used one-step reverse transcription-digital PCR (RT-dPCR), with three laboratories applying two-step RT-dPCR and one laboratory RT-qPCR. Sixteen laboratories submitted results for E gene concentration. Reproducibility (% CV or equivalent) for RT-dPCR ranged from 19 % to 31 %. Measurements of the high concentration study material by orthogonal methods (isotope dilution-mass spectrometry and single molecule flow cytometry) and a gravimetrically linked lower concentration material were in a good agreement, suggesting a lack of overall bias in RT-dPCR measurements. However methodological factors such as primer and probe (assay) sequences, RT-dPCR reagents and dPCR partition volume were found to be potential sources of interlaboratory variation which need to be controlled when applying this technique. This study demonstrates that the accuracy of RT-dPCR is fit-for-purpose as a RMP for viral RNA target quantification in purified RNA materials and highlights where metrological approaches such as the use of in vitro transcribed controls, orthogonal methods and measurement uncertainty evaluation can support standardization of molecular methods.

molecular biology↗