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Choi, J.

Publications and source records attributed to Choi, J..

At least 217 records · Page 12Linked to original sources

Investigating the genetic architecture of eye colour in a Canadian cohort

The main factors that determine eye colour are the amount of melanin concentrated in iris melanocytes, as well as the shape and distribution of melanosomes. Eye colour is highly variable in populations with European ancestry, in which eye colour categories cover a continuum of low to high quantities of melanin accumulated in the iris. A few polymorphisms in the HERC2/OCA2 locus in chromosome 15 have the largest effect on eye colour in these populations, although there is evidence of other variants in the locus and across the genome also influencing eye colour. To improve our understanding of the genetic loci determining eye colour, we performed a meta-analysis of genome-wide association studies in a Canadian cohort of European ancestry (N= 5,641) and investigated putative causal variants. Our fine-mapping results indicate that there are several candidate causal signals in the HERC2/OCA2 region, whereas other significant loci in the genome likely harbour a single causal signal (TYR, TYRP1, IRF4, SLC24A4). Furthermore, a short subset of the associated eye colour regions was colocalized with the gene expression or methylation profiles of cultured melanocytes (HERC2, OCA2), and transcriptome-wide association studies highlighted the expression of two genes associated with eye colour: SLC24A4 and OCA2. Finally, genetic correlations of eye and hair colour from the same cohort suggest high pleiotropy at the genome level, but locus-level evidence hints at several differences in the genetic architecture of both traits. Overall, we provide a better picture of how polymorphisms modulate eye colour variation, particularly in the HERC2/OCA2 locus, which may be a consequence of specific molecular processes in the iris melanocytes. Author SummaryEye colour differences among humans are the result of different amounts of melanin produced, as well as due to differences in the shape and distribution of the organelles in charge of producing melanin. Eye colour is a highly heritable trait, where several genes across the genome are involved in the process, but we currently do not fully understand which are the causal variants and how they modulate eye colour variation. By performing genome-wide association studies of eye colour across Canadian individuals of European ancestry, we identify several candidate causal signals in and near the gene OCA2, and one candidate signal in other genes, such as TYR, TYRP1, IRF4 and SLC24A4. Furthermore, we provide insights about how significant loci may modulate eye colour variation by testing for shared signals with polymorphisms associated with the expression of genes and DNA methylation. Overall, we provide a better picture of the genetic architecture of eye colour and the molecular mechanisms contributing to its variation.

genetics↗

Development of a machine learning model to estimate biotic ligand model-based predicted no-effect concentrations for copper in freshwater

The copper biotic ligand model (BLM) has been used for environmental risk assessment by taking into account the bioavailability of copper in freshwater. However, the BLM-based environmental risk of copper has been assessed only in Europe and North America, with monitoring datasets containing all of the BLM input variables. For other areas, it is necessary to apply surrogate tools with reduced data requirements to estimate the BLM-based predicted no-effect concentration (PNEC) from commonly available monitoring datasets. To develop an optimized PNEC estimation model based on an available monitoring dataset, an initial model that considers all BLM variables, a second model that requires variables excluding alkalinity, and a third model using electrical conductivity as a surrogate of the major cations and alkalinity have been proposed. Furthermore, deep neural network (DNN) models have been used to predict the nonlinear relationships between the PNEC (outcome variable) and the required input variables (explanatory variables). The predictive capacity of DNN models in this study was compared with the results of other existing PNEC estimation tools using a look-up table and multiple linear and multivariate polynomial regression methods. Three DNN models, using different input variables, provided better predictions of the copper PNECs compared with the existing tools for four test datasets, i.e., Korean, United States, Swedish, and Belgian freshwaters. The adjusted r2 values in all DNN models were higher than 0.95 in the test datasets, except for the Swedish dataset (adjusted r2 > 0.87). Consequently, the most applicable model among the three DNN models could be selected according to the data availability in the collected monitoring database. Because the most simplified DNN model required only three water quality variables (pH, dissolved organic carbon, and electrical conductivity) as input variables, it is expected that the copper BLM-based risk assessment can be applied to monitoring datasets worldwide.

pharmacology and toxicology↗

Mct11 deficiency alters hepatic glucose metabolism and energy homeostasis

Genetic variation at the SLC16A11 locus contributes to the disproportionate impact of type 2 diabetes (T2D) on Latino populations. We recently demonstrated that T2D risk variants reduce SLC16A11 liver expression and function of MCT11, the monocarboxylate transporter encoded by the SLC16A11 gene. Here, we show that SLC16A11 expression within the liver is primarily localized to the low oxygen pericentral region, and that T2D risk variants disrupt oxygen-regulated SLC16A11 expression in human hepatocytes. Under physiologic oxygen conditions, MCT11 deficiency alters hepatocyte glucose metabolism, resulting in elevated intracellular lactate and a metabolic shift toward triacylglycerol accumulation. We also demonstrate an impact of Mct11 deficiency on glucose and lipid metabolism in Slc16a11 knockout mice, which display physiological changes that are observed in individuals with T2D. Our findings provide mechanistic insight into how SLC16A11 disruption impacts hepatic energy metabolism and T2D risk, and highlight MCT11-mediated regulation of lactate levels as a potential therapeutic target.

genetics↗

Superantigens promote Staphylococcus aureus bloodstream infection by eliciting pathogenic interferon-gamma (IFNγ) production that subverts macrophage function

Staphylococcus aureus is a foremost bacterial pathogen responsible for a vast array of human diseases. Staphylococcal superantigens (SAgs) constitute a family of potent exotoxins secreted by S. aureus, and SAg genes are found ubiquitously in human isolates. SAgs bind directly to MHC class II molecules and T cell receptors, driving extensive T cell activation and cytokine release. Although these toxins have been implicated in serious disease including toxic shock syndrome, we aimed to further elucidate the mechanisms by which SAgs contribute to staphylococcal pathogenesis during septic bloodstream infections. As most conventional mouse strains respond poorly to staphylococcal SAgs, we utilized transgenic mice encoding humanized MHC class II molecules (HLA-DR4) as these animals are much more susceptible to SAg activity. Herein, we demonstrate that SAgs contribute to the severity of S. aureus bacteremia by increasing bacterial burden, most notably in the liver. We established that S. aureus bloodstream infection severity is mediated by CD4+ T cells and interferon-gamma (IFN{gamma}) is produced to very high levels during infection in a SAg-dependent manner. Bacterial burden and disease severity were reduced by antibody blocking of IFN{gamma}, phenocopying isogenic SAg deletion mutant strains. Additionally, cytokine analysis demonstrated that the immune system was skewed towards a proinflammatory response that was reduced by IFN{gamma} blocking. Infection kinetics and flow cytometry analyses suggested this was a macrophage driven mechanism, which was confirmed through macrophage depletion experiments. Further validation with human leukocytes indicated that excessive IFN{gamma} allowed S. aureus to replicate at a higher rate within macrophages. Together, this suggests that SAgs promote S. aureus survival by manipulating immune responses that would otherwise be effective at clearing S. aureus. This work implicates SAg toxins as critical targets for preventing persistent or severe S. aureus disease.

microbiology↗

A novel method for robust estimation of ants' walking speed and curvature on convoluted trajectories derived from their gait pattern

Accurate measurements of travel distance and speed are crucial for the analysis of animal movements. Measuring the movements of ants entails measuring the change in locations registered at time intervals. This process involves dilemma of setting the proper time window: a short time window is vulnerable to spatial errors in observation, while a long time window leads to underestimation of the travel distance. To overcome these difficulties, we propose a novel algorithm that successively interpolates two consecutive points of ants trajectory for a given time window by embracing the alternating tripod gait of ants. We demonstrate that this algorithm is more reliable compared to the conventional method of travel distance estimation based on the sum of the consecutive straight-line displacements (SLD). After obtaining speed estimates for a range of sampling time windows, we applied a fitting method that can estimate the actual speed without prior knowledge of spatial error distribution. We compared results from several methods of speed and curvature extracted from the empirical data of ant trajectories. We encourage empirical scientists to utilize the proposed methods rather than the conventional SLD method of speed estimation as this process is a more reliable and subjective selection of the sampling time window can be avoided.

animal behavior and cognition↗

Diversity of Antibiotic Resistance genes and Transfer Elements-Quantitative Monitoring (DARTE-QM): a method for detection of antimicrobial resistance in environmental samples

Effective monitoring of antibiotic resistance genes and their dissemination in environmental ecosystems has been hindered by the cost and efficiency of methods available for the task. We developed a method entitled the Diversity of Antibiotic Resistance genes and Transfer Elements-Quantitative Monitoring (DARTE-QM), a system implementing high-throughput sequencing to simultaneously sequence thousands of antibiotic resistant genes representing a full-spectrum of antibiotic resistance classes commonly seen in environmental systems. In this study, we demonstrated DARTE-QM by screening 662 antibiotic resistance genes within environmental samples originated from manure, soil, and animal feces, in addition to a mock-community used as a control to test performance. DARTE-QM offers a new approach to studying antibiotic resistance in environmental microbiomes, showing advantages in efficiency and the ability to scale for many samples. This method provides a means of data acquisition that will alleviate the obstacles that many researchers in this area currently face.

microbiology↗

Histone H1 prevents non-CG methylation-mediated small RNA biogenesis in Arabidopsis heterochromatin

Flowering plants utilize small RNA molecules to guide DNA methyltransferases to genomic sequences. This RNA-directed DNA methylation (RdDM) pathway preferentially targets euchromatic transposable elements. However, RdDM is thought to be recruited by methylation of histone H3 at lysine 9 (H3K9me), a hallmark of heterochromatin. How RdDM is targeted to euchromatin despite an affinity for H3K9me is unclear. Here we show that loss of histone H1 enhances heterochromatic RdDM, preferentially at nucleosome linker DNA. Surprisingly, this does not require SHH1, the RdDM component that binds H3K9me. Furthermore, H3K9me is dispensable for RdDM, as is CG DNA methylation. Instead, we find that non-CG methylation is specifically required for small RNA biogenesis, and without H1 small RNA production quantitatively expands to non-CG methylated loci. Our results demonstrate that H1 enforces the separation of euchromatic and heterochromatic DNA methylation pathways by excluding the small RNA-generating branch of RdDM from non-CG methylated heterochromatin.

genomics↗

Redox regulation by TXNRD3 during epididymal maturation underlies capacitation-associated mitochondrial activation and sperm motility in mice

During epididymal transit, redox remodeling protects mammalian spermatozoa, preparing them for survival in the subsequent journey to fertilization. However, molecular mechanisms of redox regulation in sperm development and maturation remain largely elusive. In this study, we report that TXNRD3, a thioredoxin reductase family member particularly abundant in elongating spermatids at the site of mitochondrial sheath formation, regulates redox homeostasis to support male reproduction. Using Txnrd3-/- mice, our biochemical, ultrastructural, and live cell imaging analyses revealed impairments in sperm morphology and motility under conditions of TXNRD3 deficiency. We reveal that mitochondria develop more defined cristae during capacitation in wild type sperm. Absence of TXNRD3 alters redox status in both the head and tail during sperm maturation and capacitation, resulting in defective mitochondrial ultrastructure and activity under capacitating conditions. These findings provide insights into molecular mechanisms of redox homeostasis and bioenergetics during sperm maturation, capacitation, and fertilization.

physiology↗

Oct4 primarily controls enhancer activity rather than accessibility

The transcription factor Oct4 is essential for maintaining stem cell pluripotency and for efficient cell reprogramming, but its functional roles are far from being understood. Here, we investigate the functions of Oct4 by rapidly depleting Oct4 from mouse embryonic stem cells and conducting a time-resolved multiomics analysis. Oct4 depletion leads to an immediate loss of its binding to putative enhancers that are accessible in chromatin. Loss of Oct4 is accompanied by a concomitant decrease in mRNA synthesis from putative target genes that are part of the transcriptional network that maintains pluripotency. Oct4 binding to enhancers does not correlate with chromatin accessibility, whereas Sox2 can apparently retain accessibility after Oct4 depletion even in the absence of eRNA synthesis. These results are consistent with the model that Sox2 primarily acts as a pioneer factor that renders enhancers accessible, whereas Oct4 acts primarily as a transcriptional activator that stimulates transcription of pluripotency enhancers and their target genes.

genomics↗

Multiplexed single-molecule analysis of human telomerase synthesizing DNA

Genomic stability in proliferating cells critically depends on telomere maintenance by telomerase reverse transcriptase. Here we developed a real-time single-molecule RNA sequencing approach that visualizes telomerase catalysis and structural dynamics at single-nucleotide resolution using FRET and zero-mode waveguides. The method permits direct detection of dynamic steps and structural states throughout the telomerase catalytic cycle and can be generalized to other nucleic acid polymerase systems.

biophysics↗

Release of Notch activity coordinated by IL-1β signalling confers differentiation plasticity of airway progenitors via Fosl2 during alveolar regeneration

While the acquisition of cellular plasticity in adult stem cells is essential for rapid regeneration after tissue injury, little is known about the underlying molecular mechanisms governing this process. Our data reveal the coordination of airway progenitor differentiation plasticity by inflammatory signals during alveolar regeneration. Upon damage, IL-1{beta} signalling-dependent modulation of Jag1/2 expression in ciliated cells results in the inhibition of Notch signalling in secretory cells, which drives reprogramming and acquisition of differentiation plasticity. We identify a core role for the transcription factor Fosl2/Fra2 in secretory cell fate conversion to alveolar type 2 (AT2) cells retaining the distinct genetic and epigenetic signatures of secretory lineages. We furthermore reveal that KDR/FLK-1+ human secretory cells display a conserved capacity to generate AT2 cells via Notch inhibition. Our results demonstrate the functional role of a IL-1{beta}-Notch-Fosl2 axis for the fate decision of secretory cells during injury repair, proposing a new potential therapeutic target for human lung alveolar regeneration.

cell biology↗

The asymmetric Pitx2 regulates intestinal muscular-lacteal development and protects against fatty liver disease

Intestinal lacteals are the essential lymphatic channels for absorption and transport of dietary lipids and drive pathogenesis of debilitating metabolic diseases. Yet, organ-specific mechanisms linking lymphatic dysfunction to disease etiology remain largely unknown. In this study, we uncover a novel intestinal lymphatic program that is linked to the left-right (LR) asymmetric transcription factor Pitx2. We show that deletion of the asymmetric Pitx2 enhancer, ASE, alters normal lacteal development through the lacteal-associated contractile smooth muscle lineage. ASE deletion leads to abnormal muscle morphogenesis induced by oxidative stress, resulting in impaired lacteal extension and defective lymphatic-dependent lipid transport. Surprisingly, activation of lymphatic-independent trafficking directs dietary lipids from the gut directly to the liver, causing diet-induced fatty liver disease. In summary, our studies reveal the molecular mechanism linking gut lymphatic development to the earliest symmetry-breaking Pitx2 and highlight the important relationship between intestinal lymphangiogenesis and gut-liver axis. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/447753v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@1a7e81corg.highwire.dtl.DTLVardef@77915forg.highwire.dtl.DTLVardef@1e91610org.highwire.dtl.DTLVardef@1a7911d_HPS_FORMAT_FIGEXP M_FIG GRAPHICAL ABSTRACT C_FIG HIGHLIGHTS[~] Gut lymphangiogenesis is linked to Pitx2-driven LR asymmetry [~]Lacteal-associated smooth muscle requires ASE [~]ASE deletion leads to redox imbalance in intestinal smooth muscle lineage [~]ASE is required for the normal route of dietary lipid transport [~]Pitx2ASE/ASE neonates develop diet-induced fatty liver disease

developmental biology↗

Label-free three-dimensional analyses of live cells with deep-learning-based segmentation exploiting refractive index distributions

Visualisations and analyses of cellular and subcellular organelles in biological cells is crucial for the study of cell biology. However, existing imaging methods require the use of exogenous labelling agents, which prevents the long-time assessments of live cells in their native states. Here we propose and experimentally demonstrate three-dimensional segmentation of subcellular organelles in unlabelled live cells, exploiting a 3D U-Net-based architecture. We present the high-precision three-dimensional segmentation of cell membrane, nucleus membrane, nucleoli, and lipid droplets of various cell types. Time-lapse analyses of dynamics of activated immune cells are also analysed using label-free segmentation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/445351v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@b92093org.highwire.dtl.DTLVardef@9caa8org.highwire.dtl.DTLVardef@d81408org.highwire.dtl.DTLVardef@b3c87_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

Spatial analysis of tumor infiltrating lymphocytes based on deep learning using histopathology image to predict progression-free survival in colorectal cancer

PurposeThis study aimed to explore the prognostic impact of spatial distribution of tumor infiltrating lymphocytes (TILs) quantified by deep learning (DL) approaches based on digitalized whole slide images stained with hematoxylin and eosin in patients with colorectal cancer (CRC). MethodsThe prognostic impact of spatial distributions of TILs in patients with CRC was explored in the Yonsei cohort (n=180) and validated in the TCGA cohort (n=268). Concurrently, two experienced pathologists manually measured TILs at the most invasive margin as 0-3 by the Klintrup-Makinen (KM) grading method and compared to DL approaches. Interobserver agreement for TILs was measured using Cohens kappa coefficient. ResultsOn multivariate analysis of spatial TILs features derived by DL approaches and clinicopathological variables including tumor stage, Microsatellite instability, and KRAS mutations, TILs densities within 200 m of the invasive margin (f_im200) was remained as the most significant prognostic factor for progression-free survival (PFS) (HR 0.004 [95% CI, 0.0001-0.1502], p=.002) in the Yonsei cohort. On multivariate analysis using the TCGA dataset, f_im200 retained prognostic significance for PFS (HR 0.031, [95% CI 0.001-0.645], p=.024). Interobserver agreement of manual KM grading based on Cohens kappa coefficient was insignificant in the Yonsei ({kappa}=.109) and the TCGA ({kappa}=.121), respectively. The survival analysis based on KM grading showed statistically significant different PFS from the TCGA cohort, but not the Yonsei cohort. ConclusionsAutomatic quantification of TILs at the invasive margin based on DL approaches showed a prognostic utility to predict PFS, and could provide robust and reproducible TILs density measurement in patients with CRC. Data and Code AvailabilitySource code and data used for this study is available at the following link: https://github.com/hwanglab/TILs_Analysis

bioinformatics↗

Expression Based Species Deconvolution and Realignment Removes Misalignent Error in Multi-species Single Cell Data

Although single-cell RNA sequencing of xenograft samples has been widely used, no comprehensive bioinformatics pipeline is available for human and mouse mixed single-cell analyses. Considering the numerous homologous genes across the human and mouse genomes, misalignment errors should be evaluated, and a new algorithm is required. We assessed the extents and effects of misalignment errors when using human and mouse combined reference data and developed a new bioinformatics pipeline with expression-based species deconvolution to minimize errors. We also evaluated false-positive signals for a species presumed to originate from ambient RNA of the other species and applied a computational method to remove them. Misaligned reads account for an average of 0.5% of total reads, but such reads were concentrated to few genes that were greatly affected. Human and mouse mixed single-cell data, analyzed using our pipeline, clustered well with unmixed data and showed higher k-nearest-neighbor batch effect test and Local Inverse Simpsons Index scores than those derived from Cell Ranger. We also applied our pipeline to multispecies multisample single-cell library containing breast cancer xenograft tissue and successfully identified all samples using genomic array and expression. Moreover, diverse cell types in the tumor microenvironment were well captured. We present our bioinformatics pipeline for mixed human and mouse single-cell data, which can also be applied to pooled libraries to obtain cost-effective single-cell data. We also address major consideration points when analyzing multispecies single-cell data for other applications.

bioinformatics↗

Phylomedicine of mutational processes in somatic cancer cell populations

Mutational processes in somatic cancer cell populations are constantly changing, leaving their signatures in the accumulated genomic variation in tumors. The inference of mutational signatures from the observed genetic variation enables spatiotemporal tracking of tumor mutational processes that evolve due to cellular environmental changes, mutations, and treatment regimes. Ultimately, mutational patterns illuminate the mechanistic understanding of their evolution in cancer progression. We show that the integration of cancer cell phylogeny with mutational signature deconvolution enables higher-resolution detection of gain and loss of mutational processes within the phylogeny. This approach to analyzing somatic genomic variations in 61 lung cancer patients revealed a high turn-over of mutational processes over time and closely related clonal lineages. Some mutational signatures (e.g., smoking-related) showed a higher propensity to be lost, whereas others (e.g., AID/APOBEC) were gained during lung tumors evolution. These observations shed light on the evolution of mutational processes in somatic cell evolution.

evolutionary biology↗

A UVB-responsive common variant at chr7p21.1 confers tanning response and melanoma risk via regulation of the aryl hydrocarbon receptor gene (AHR)

Genome-wide association studies have identified a melanoma-associated locus on chromosome band 7p21.1 with rs117132860 as the lead SNP, and a secondary independent signal marked by rs73069846. rs117132860 is also associated with tanning ability and cutaneous squamous cell carcinoma (cSCC). As ultraviolet radiation (UVR) is a key environmental exposure for all three traits, we investigated the mechanisms by which this locus contributes to melanoma risk, focusing on cellular response to UVR. Fine-mapping of melanoma GWAS identified four independent sets of candidate causal variants. A GWAS region-focused Capture-C study of primary melanocytes identified physical interactions between two causal sets and the promoter of the aryl hydrocarbon receptor gene (AHR). Subsequent chromatin state annotation, eQTL, and luciferase assays identified rs117132860 as a functional variant and reinforced AHR as a likely causal gene. As AHR plays critical roles in cellular response to dioxin and UVR, we explored links between this SNP and AHR expression after both 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and ultraviolet B (UVB) exposure. Allele-specific AHR binding to rs117132860-G was enhanced following both, consistent with predicted weakened AHR binding to the risk/poor-tanning rs117132860-A allele, and allele-preferential AHR expression driven from the protective rs117132860-G allele was observed following UVB exposure. Small deletions surrounding rs117132860 via CRISPR abrogates AHR binding, reduces melanocyte cell growth, and prolongs growth arrest following UVB exposure. These data suggest AHR is a melanoma susceptibility gene at the 7p21.1 risk locus, and rs117132860 is a functional variant within a UVB-responsive element, leading to allelic AHR expression, and altering melanocyte growth phenotypes upon exposure.

genetics↗

Cell type-specific meQTL extends melanoma GWAS annotation beyond eQTL and informs melanocyte gene regulatory mechanisms

While expression quantitative trait loci (eQTL) have been powerful in identifying susceptibility genes from genome-wide association studies (GWAS) findings, most trait-associated loci are not explained by eQTL alone. Alternative QTLs including DNA methylation QTL (meQTL) are emerging, but cell-type-specific meQTL using cells of disease origin has been lacking. Here we established an meQTL dataset using primary melanocytes from 106 individuals and identified 1,497,502 significant cis-meQTLs. Multi-QTL colocalization using meQTL, eQTL, and mRNA splice-junction QTL from the same individuals together with imputed methylome-wide and transcriptome-wide association studies identified susceptibility genes at 63% of melanoma GWAS loci. Among three molecular QTLs, meQTLs were the single largest contributor. To compare melanocyte meQTLs with those from malignant melanomas, we performed meQTL analysis on skin cutaneous melanomas from The Cancer Genome Atlas (n = 444). A substantial proportion of meQTL probes (45.9%) in primary melanocytes are preserved in melanomas, while a smaller fraction of eQTL genes is preserved (12.7%). Integration of melanocyte multi-QTL and melanoma meQTL identified candidate susceptibility genes at 72% of melanoma GWAS loci. Beyond GWAS annotation, meQTL-eQTL colocalization in melanocytes suggested that 841 unique genes potentially share a causal variant with a nearby methylation probe in melanocytes. Finally, melanocyte trans-meQTL identified a hotspot for rs12203592, a cis-eQTL of a transcription factor, IRF4, with 131 candidate target CpGs. Motif enrichment and IRF4 ChIPseq analysis demonstrated that these target CpGs are enriched in IRF4 binding sites, suggesting an IRF4-mediated regulatory network. Our study highlights the utility of cell-type-specific meQTL.

genetics↗