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Bourque, G.

Publications and source records attributed to Bourque, G..

At least 19 recordsLinked to original sources

TEExplorer: A Web Portal to Investigate TE-Epigenome Associations Across Human Cell Types

Approximately half of the human genome is derived from transposable elements (TEs) and several studies support the involvement of TEs in genome regulation in development, immunity and disease. We previously leveraged 4614 ChIP-seq samples from the International Human Epigenome Consortium (IHEC) EpiATLAS dataset and did a comprehensive analysis of the relationship between TEs and 6 histone marks across 57 human cell types. However, with over 6 million measurements of TE / histone mark / cell type enrichment, it was challenging to navigate the results and it was not possible to integrate them with user data. To address this, we developed a web tool, TEExplorer, which makes available TE overlaps and enrichments in an accessible and intuitive manner. The tool presents an interactive view of TE families and subfamilies, with their overlap and enrichments across histone marks and cell types. Finally, the tool allows users to upload their own ChIP-seq BED file to obtain the TE overlap and enrichment relative to random controls and compare their data with the EpiATLAS dataset. With TEExplorer, researchers with an interest in a particular TE family or subfamily, histone mark, or cell type, or those bringing their own ChIP-seq dataset, can dynamically explore and contrast hundreds of associations found within the large EpiATLAS dataset. AvailabilityOnline portal: https://teexplorer.c3g.sd4h.ca

genomics↗

Integrated Metabolic Complex Genetic Interaction 1 Network of Chromosome 4p Loss in Basal Breast Cancer

Basal breast cancer subtype is enriched for triple-negative breast cancer (TNBC) and exhibits a recurrent large chromosomal deletion in chromosome 4p (chr4p). Chr4p loss is associated with poor survival, evolves early in tumorigenesis and confers on cells a proliferative state. Here, we map the integrated metabolic complex genetic interaction network of chr4p in basal breast cancer to identify targetable vulnerabilities. Differential gene expression analysis of patient derived xenografts and cancer cell models revealed that chr4p loss is associated with changes in cellular energetics and reduction/oxidation balance. Analysis of DepMap pooled genome-wide CRISPR-Cas9 screens identified complex genetic interactions specific to chr4p deletion in basal breast cancer cell models. Functional assays revealed that chr4p loss is associated with disrupted mitochondrial respiratory function and reduced glycolytic capacity, suggesting metabolic rewiring. Increased reactive oxygen species and lipid peroxidation compromised antioxidant defense mechanisms. Ultimately, this study sheds light on targeted therapies for basal breast cancer harboring large chromosomal deletions.

genomics↗

Long-read sequencing reveals telomere inheritance patterns from human trios

Telomeres are essential for maintaining genomic integrity and are associated with cellular aging and disease, yet the factors influencing their inheritance across generations remain poorly understood. Leveraging PacBio HiFi long-read sequencing and 75 parent-offspring trios (n = 225) from the Genomic Answers for Kids program, we analyzed individual telomeres across chromosomes and their inheritance. Telomere length (TL) varied between chromosome arms in a way that was consistent in parents and offsprings, with average values ranging from 5000 to 8000 base pairs. Maternal and paternal TL together were a strong predictor of child TL (R2 = 0.59). Notably, using telomeric variant repeats, we developed a tool that enabled allelic tracing for 53.3% of maternally and 49.9% of paternally inherited telomeres. In the child, paternally transmitted alleles were significantly longer than age-matched maternal ones ({Delta}mean = 409 bp, p = 2.6e-05), particularly when from older parents ({Delta}mean = 698 bp, p = 8.9e-05) and at chromosome arms with shorter average TL ({Delta}mean = 752 bp, p = 1.6e-06). These findings reveal parent-of-origin effects and heritable influences on TL, providing novel insights into telomere dynamics and their potential implications in age-related disease susceptibility.

genetics↗

Simultaneous epigenomic profiling and regulatory activity measurement using e2MPRA

Cis-regulatory elements (CREs) have a major effect on phenotypes including disease. They are identified in a genome-wide manner by analyzing the binding of transcription factors (TFs), various co-factors and histone modifications in DNA using assays such as ChIP-seq, Cut&Tag and ATAC-seq. However, these assays are descriptive and require high-throughput technologies, such as massively parallel reporter assays (MPRAs), to test the functional activity and variant effect on these sequences. Currently, technologies that can simultaneously analyze both the regulatory function of a specific sequence and the TFs, cofactors and epigenomic modifications that determine it do not exist. Here, we developed enrichment followed by epigenomic profiling MPRA (e2MPRA), a novel technology that utilizes lentivirus-based MPRA to enrich for the integration of specific CREs into the genome followed by Cut&Tag or ATAC-seq targeted specifically for these sequences. This method allows to simultaneously analyze in a high-throughput manner regulatory activity, protein binding and epigenetic modification of thousands of candidate CREs and their variants. We demonstrate that e2MPRA can be used to dissect the epigenetic functions of TF motifs arranged in synthetic enhancers, as well as to analyze the effect of enhancer sequence variants on epigenetic modifications. In summary, this technology will increase our understanding of the regulatory code, its effect on the epigenome and how its alteration can lead to a variety of phenotypes including human disease.

genomics↗

Finding an optimal sequencing strategy to detect short and long genetic variants in a human genome

Advances in DNA sequencing have transformed genomics, enabling comprehensive insights into human genetic variation. While short-read sequencing (SRS) remains dominant due to its high accuracy and affordability, its limitations in complex genomic regions have spurred the adoption of long-read sequencing (LRS) platforms, such as those from Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT). Despite these advances, there is still a lack of systematic, large-scale benchmarking of variant calling performance across diverse platforms, variant types, sequencing depths, and genomic contexts. Here, we present a comprehensive benchmark of sequencing technologies and variant calling algorithms, evaluating their performance in detecting single nucleotide polymorphisms (SNPs), insertions/deletions (indels), and structural variants (SVs). We show that while SRS combined with DeepVariant or DRAGEN offers excellent small variant detection in well-mapped regions, LRS technologies significantly outperform SRS in complex regions and SV detection. PacBio achieves high SNP and smaller SV accuracy even at moderate coverage, while ONT excels in detecting large SVs. The SV callers Dysgu and SVIM emerged as top performers across LRS datasets. Our results highlight that no single platform is optimal for all variant types or regions: SRS remains optimal for high-throughput small variant detection in accessible regions, whereas LRS is critical for capturing SVs and resolving difficult-to-map loci. These findings offer practical guidance for selecting sequencing technologies, coverage and variant calling strategies tailored to specific research or clinical goals, contributing to more accurate and cost-effective genomic analyses. Highlights[bullet] State-of-the-art short variant calling algorithms are highly comparable but focus on precision and sensitivity differently [bullet]Short-read technologies outperform long-read technologies for small SNP and InDels, with the exception of difficult-to-map variants. [bullet]To capture the majority of variants, a minimum coverage of 15x for PacBio, 20x for SRS, or 30x for ONT is required. However, optimal coverage depends on zygosity, variant type, and the region of interest. [bullet]Long-read technologies outperform short-read technologies for all validation sets tested for deletions and insertions in all size categories.

genomics↗

STRkit: precise, read-level genotyping of short tandem repeats using long reads and single-nucleotide variation

Variation in short tandem repeats (STRs) is implicated in Mendelian disease and complex traits, but can be difficult to resolve with short-read genome sequencing. We present STRkit, a software package for genotyping STRs using long read sequencing (LRS) that uses nearby single-nucleotide variants to improve genotyping accuracy without a priori haplotype information. We show that STRkit has unique strengths versus other methods: it can use data from both major LRS technologies (Pacific Biosciences HiFi [PB] and Oxford Nanopore [ONT]) to output both allele and read-level copy number and sequence, performs best in benchmarking with F1 scores of 0.9633 and 0.9056 with PB and ONT data respectively, achieves a Mendelian inheritance rate of 97.86% with PB data, and is open source software. STRkits features open up new possibilities for association testing, assessing patterns of STR inheritance, and better understanding the functional effects of these notable repeat elements.

bioinformatics↗

PARPAL: PARalog Protein Redistribution using Abundance and Localization in Yeast Database

Whole-genome duplication (WGD) events are common across various organisms however the retention and evolution of WGD paralogs is not fully understood. Quantitative measure of protein redistribution in response to the deletion of their WGD paralog provides insight into sources of gene retention. Here, we describe PARPAL (PARalog Protein Retribution using Abundance and Localization in Yeast), a web database that houses results of high-content screening and deep learning neural network analysis of the redistribution of 164 proteins reflecting how their subcellular localization and protein abundance change in response to their paralog deletion. We interrogated a total of 82 paralog pairs in two genetic backgrounds for a total of [~]3,500 micrographs of [~]460,000 cells. PARPAL also links to other studies on trigenic interactions, protein-protein interactions and protein abundance. PARPAL is available at https://parpal.c3g-app.sd4h.ca and is a valuable resource for the yeast community interested in understanding the retention and evolution of paralogs and can help researchers to investigate protein dynamics of paralogs in other organisms.

systems biology↗

Survey of gene, lncRNA and transposon transcription patterns in four mouse organs highlights shared and organ-specific sex-biased regulation

BackgroundSex-biased gene regulation is the basis of sexual dimorphism in phenotypes and has been studied across different cell types and different developmental stages. However, sex-biased expression of transposable elements (TEs) that represent nearly half of the mammalian genome and have the potential of influencing genome integrity and regulation, remains underexplored. ResultsHere, we report a survey of gene, lncRNA and TE expression in four organs from mice with different combinations of gonadal and genetic sex. Data show remarkable variability among organs with respect to the impact of gonadal sex on transcription with the strongest effects observed in liver. In contrast, the X-chromosome dosage alone had modest influence on sex-biased transcription across different organs, albeit interaction between X-dosage and gonadal sex cannot be ruled out. The presence of the Y chromosome influenced TE, but not gene or lncRNA expression in liver. Notably, 90% of sex-biased TEs (sDETEs) reside in clusters. Moreover, 54% of these clusters overlap or reside close (<100 kb) to sex-biased genes or lncRNAs, share the same sex bias, and also have higher expression levels than sDETE clusters that do not co-localize with other types of sex-biased transcripts. We also tested the heterochromatic sink hypothesis that predicts higher expression of TEs in XX individuals and found no evidence to support it. ConclusionsOur data show that sex-biased expression of TEs varies among organs with highest numbers of sDETEs found in liver following the trends observed for genes and lncRNAs. It is enhanced by proximity to other types of sex-biased transcripts.

genomics↗

Transposable elements impact the regulatory landscape through cell type specific epigenomic associations

Transposable elements (TEs) are DNA sequences able to create copies of themselves within the genome. Despite their limited expression due to silencing, TEs still manage to impact the host genome. For instance, some TEs have been shown to act as cis-regulatory elements and be co-opted in the human genome. This highlights that the contributions of TEs to the host might come from their relationship with the epigenome rather than their expression. However, a systematic analysis that relates TEs in the human genome directly with chromatin histone marks across distinct cell types remains lacking. Here we leverage a new dataset from the International Human Epigenome Consortium with 4867 uniformly processed ChIP-seq experiments for 6 histone marks across 175 annotated cell labels and show that TEs have drastically different enrichments levels across marks. Overall, we find that TEs are generally depleted in H3K9me3 histone modification, except for L1s, while MIRs were highly enriched in H3K4me1, H3K27ac and H3K27me3 and Alus were enriched in H3K36me3. Furthermore, we present a generalised profile of the relationship between TEs enrichment and TE age which reveals a few TE families (Alu, MIR, L2) as diverging from expected dynamics. We also find significant differences in TE enrichment between cell types and that in 20% of the cases, these enrichments were cell-type specific. Moreover, we report that at least 4% of cell types-histone-TE combinations featured significant differences in enrichment between healthy and cancer samples. Notably, we identify 456 cell type-histone-TE triplets with strong cell-type specific enrichments. We show that many of these triplets are associated with relevant biological processes and genes expressed in the relevant cell type. These results further support a role for TE in genome regulation and highlight novel associations between TEs and histone marks across cell types.

genomics↗

Mouse embryonic stem cells require sustained DNMT1-mediated DNA methylation maintenance for epigenomic, genomic and functional integrity

Epigenetic mechanisms are crucial for developmental programming and can be disrupted by environmental stressors, increasing susceptibility to disease. This has sparked interest in therapies for restoring epigenetic balance, but it remains uncertain whether disordered epigenetic mechanisms can be fully corrected. Disruption of DNA methyltransferase 1 (DNMT1), responsible for DNA methylation maintenance, has particularly devastating biological consequences. Therefore, here we explored if rescuing DNMT1 activity is sufficient to reverse the effects of its loss utilizing mouse embryonic stem cells. However, only partial reversal could be achieved. Extensive changes in DNA methylation, histone modifications and gene expression were detected, along with transposable element de-repression and genomic instability. Reduction of cellular size, complexity and proliferation rate were observed, as well as lasting effects in germ layer lineages and embryoid bodies. Interestingly, by analyzing the impact on imprinted regions, we uncovered 20 regions exhibiting imprinted-like signatures. Notably, while many permanent effects persisted throughout Dnmt1 inactivation and rescue, others arose from the rescue intervention. Lastly, rescuing DNMT1 after differentiation initiation worsened outcomes, reinforcing the need for early intervention. Our findings highlight the far-reaching functions of DNMT1 and provide valuable perspectives on the repercussions of epigenetic perturbations during early development and the challenges of rescue interventions. HIGHLIGHTS- Extensive changes to epigenomic landscapes and gene expression following transient loss of DNMT1 activity - Dysregulation of known imprinted regions and identification of 20 regions with imprinted-like signatures - De-repression of MERVL and MT2 LTRs with evidence of chimeric gene transcript generation - Shorter telomeres, DNA damage accumulation and reduction of cell size, internal complexity and proliferation rate - Lasting effects upon differentiation toward germ layer lineages and embryoid bodies - Worsened molecular and cellular outcomes when delaying Dnmt1 rescue until after differentiation initiation O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/592204v3_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@d88ea7org.highwire.dtl.DTLVardef@17d7c87org.highwire.dtl.DTLVardef@17ab304org.highwire.dtl.DTLVardef@7ef981_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGRAPHICAL ABSTRACTC_FLOATNO C_FIG

cell biology↗

Expanded methylome and quantitative trait loci detection by long-read profiling of personal DNA

Structural variants (SVs) are omnipresent in human DNA, yet their genotype and methylation status is rarely characterized due to previous limitations in genome assembly and detection of modified nucleotides. Because of this, the extent to which these regions act as quantitative-trait loci is also largely unknown. Here, we generated a pangenome graph summarizing the SVs in 782 de novo assembled genomes obtained from the Genomic Answers for Kids rare disease cohort, that captures 14.6 million CpGs in DNA segments that are absent from the CHM13v2 assembly (SV-CpGs), expanding their number by 43.6%. Next, using 435 methylomes from the same samples, we genotyped a total of 7.99 million SV-CpGs, of which 5.18 million (64.8%) were found to be methylated (SV-5mCpGs) in at least one sample. To understand the provenance and impact of these novel SV-CpGs, we noted that non-repeat sequences were the leading contributor of SV-CpGs (3.3 x 106), followed by centromeric satellites (1.58 x 106), simple repeats (1.19 x 106), Alus (0.67 x 106), satellites (0.39 x 106), L1s (0.27 x 106), and SVAs (0.19 x 106). Meanwhile, the methylation rate of SV-CpGs was the highest in repeat sequences. Moreover, in contrast to Alus and L1s, centromeric satellites, simple repeats and SVA sequences were overrepresented in SV-5mCpGs compared to reference CpGs. Similarly, we established that non-reference CpGs were more than twice (37% vs. 15%) as likely to be variable, showing intermediate methylation levels in the population. Lastly, to explore if SVs detected in this pangenome are potentially causal for functional variation in population we measured methylation quantitative trait loci (SV-mQTLs) using CHM13v2 as a backbone. This revealed over 230,464 methylation bins within 100 kbp of a common SV (>5% MAF) showing significant association (at 5% FDR) with methylation variation. Finally, we assessed how many of these SVs-mQTLs were the leading QTL variant compared to SNVs and identified 65,659 methylation bins (28.5%) where the leading variant was an SV. In conclusion, our results demonstrate that graph genome references providing full SV structures in combination with the associated methylation variation reveal tens-of-thousands of QTLs that are more accurately mapped in personal genomes, underscoring the importance of assembly-based analyses of human traits.

bioinformatics↗

Cryptic endogenous retrovirus subfamilies in the primate lineage

Many endogenous retroviruses (ERVs) in the human genome are primate-specific and have contributed novel cis-regulatory elements and transcripts. However, current approaches for classifying and annotating ERVs and their long terminal repeats (LTRs) have limited resolution and are inaccurate. Here, we developed a new annotation based on phylogenetic analysis and cross-species conservation. Focusing on the evolutionary young MER11A/B/C subfamilies, we revealed the presence of 4 new subfamilies, that better explained the epigenetic heterogeneity observed within the MER11 instances, suggesting a new annotation for 412 (19.8%) of these repeat elements. Furthermore, we functionally validated the regulatory potential of these four new subfamilies using a massively parallel reporter assay (MPRA), which also identified motifs associated with their differential activities. Combining MPRA with new annotations across primates revealed an apes-specific gain of SOX related motifs through a single-nucleotide deletion. Lastly, by applying our approach across 53 simian-enriched LTR subfamilies, we defined a total of 75 new subfamilies and found that 3,807 (30.0%) instances from 26 LTR subfamilies could be categorized into a novel annotation, many of which with a distinct epigenetic profile. Thus, with our refined annotation of simian-enriched LTRs, it will be possible to better understand the evolution in primate genomes and potentially identify new roles for ERVs and their LTRs in the hosts.

genomics↗

GraffiTE: a Unified Framework to Analyze Transposable Element Insertion Polymorphisms using Genome-graphs

Transposable Elements are ubiquitous mobile DNA sequences evolving among their hosts genomes, generating insertion polymorphisms that contribute to genomic diversity. We present GraffiTE, a flexible pipeline to analyze polymorphic mobile elements. By integrating state-of-the-art structural variant detection algorithms and graph genomes, GraffiTE identifies polymorphic mobile elements from genomic assemblies and/or long-read sequencing data, and genotypes these variants using short or long read sets. Benchmarking on simulated and real datasets reports high precision and recall rates. GraffiTE is designed to allow non-expert users to perform comprehensive analyses, including in models with limited transposable element knowledge and is compatible with various sequencing technologies. GraffiTE is freely available at https://github.com/cgroza/GraffiTE. Here, we demonstrate the versatility of GraffiTE by analyzing human, Drosophila melanogaster, maize, and Cannabis sativa pangenome data. These analyses reveal the landscapes of polymorphic mobile elements and their frequency variations across individuals, strains, and cultivars.

bioinformatics↗

EpiVar Browser: advanced exploration of epigenomics data under controlled access

MotivationHuman epigenomic data has been generated by large consortia for thousands of cell types to be used as a reference map of normal and disease chromatin states. Since epigenetic data contains potentially identifiable information, similarly to genetic data, most raw files generated by these consortia are stored in controlled-access databases. It is important to protect identifiable information, but this should not hinder secure sharing of these valuable datasets. ResultsGuided by the Framework for responsible sharing of genomic and health-related data from the Global Alliance for Genomics and Health (GA4GH), we have developed a tool to facilitate the exploration of epigenomics datasets aggregate results, while filtering out identifiable information. Specifically, the EpiVar Browser allows a user to navigate an epigenetic dataset from a cohort of individuals and enables direct exploration of genotype-chromatin phenotype relationships. Because the information about individual genotypes is not accessible and aggregated in the output that is made available, no identifiable data is released, yet the interface allows for dynamic genotype - epigenome interrogation. This approach has the potential to accelerate analyses that would otherwise require a lengthy multi-step approval process and provides a generalisable strategy to facilitate responsible access to sensitive epigenomics data. Availability and implementationOnline portal instance: https://computationalgenomics.ca/tools/epivar Source code: https://github.com/c3g/epivar-browser

genomics↗

Evolution of chromosome arm aberrations in breast cancer through genetic network rewiring

The basal breast cancer subtype is enriched for triple-negative breast cancer (TNBC) and displays consistent large chromosomal deletions. Here, we characterize the evolution and maintenance of chromosome 4p (chr4p) loss in basal breast cancer. TCGA data analysis showed recurrent deletion of chr4p in basal breast cancer. Phylogenetic analysis of a unique panel of 23 primary tumor/patient-derived xenograft basal breast cancers revealed early evolution of chr4p deletion. Mechanistically we show that Chr4p loss is associated with enhanced proliferation. Gene function studies identified an unknown gene, C4orf19, within chr4p, which suppressed proliferation when overexpressed and is a novel member of a PDCD10-GCKIII kinase module, we name as PGCA1. Genome-wide pooled overexpression screens using a barcoded library of human open reading frames, identified chromosomal regions, including chr4p, that suppress proliferation when overexpressed in a context-dependent manner implicating network interactions. Together this sheds light on the early emergence of complex aneuploid karyotypes involving chr4p and adaptive landscapes shaping breast cancer genomes.

genomics↗

WEGS: a cost-effective sequencing method for genetic studies combining high-depth whole exome and low-depth whole genome

0Whole genome sequencing (WGS) at high-depth (30X) allows the accurate discovery of variants in the coding and non-coding DNA regions and helps elucidate the genetic underpinnings of human health and diseases. Yet, due to the prohibitive cost of high-depth WGS, most large-scale genetic association studies use genotyping arrays or high-depth whole exome sequencing (WES). Here we propose a novel, cost-effective method, which we call "Whole Exome Genome Sequencing" (WEGS), that combines low-depth WGS and high-depth WES with up to 8 samples pooled and sequenced simultaneously (multiplexed). We experimentally assess the performance of WEGS with four different depth of coverage and sample multiplexing configurations. We show that the optimal WEGS configurations are 1.7-2.0 times cheaper than standard WES (no-plexing), 1.8-2.1 times cheaper than high-depth WGS, reach similar recall and precision rates in detecting coding variants as WES, and capture more population-specific variants in the rest of the genome that are difficult to recover when using genotype imputation methods. We apply WEGS to 862 patients with peripheral artery disease and show that it directly assesses more known disease-associated variants than a typical genotyping array and thousands of non-imputable variants per disease-associated locus.

genomics↗

ZMYM2 is essential for methylation of germline genes and active transposons in embryogenesis

ZMYM2 is a transcriptional repressor whose role in development is largely unexplored. We found that Zmym2-/- mice show embryonic lethality by E10.5. Molecular characterization of Zmym2-/- embryos revealed two distinct defects. First, they fail to undergo DNA methylation and silencing of germline gene promoters, resulting in widespread upregulation of germline genes. Second, they fail to methylate and silence the evolutionarily youngest and most active LINE element subclasses in mice. Zmym2-/- embryos show ubiquitous overexpression of LINE-1 protein as well as aberrant expression of transposon-gene fusion transcripts. Interaction and colocalization data indicate that ZMYM2 homes to germline genes via binding to the non-canonical polycomb complex PRC1.6 and to transposons via the TRIM28 complex. In the absence of ZMYM2, hypermethylation of histone 3 lysine 4 occurs at target sites, creating a chromatin landscape unfavourable for establishment of DNA methylation. ZMYM2-/- human embryonic stem cells also show aberrant upregulation and demethylation of young LINE elements, indicating a conserved role in repression of active transposons. ZMYM2 is thus an important new factor in DNA methylation patterning in early embryonic development.

molecular biology↗

A Draft Human Pangenome Reference

The Human Pangenome Reference Consortium (HPRC) presents a first draft human pangenome reference. The pangenome contains 47 phased, diploid assemblies from a cohort of genetically diverse individuals. These assemblies cover more than 99% of the expected sequence and are more than 99% accurate at the structural and base-pair levels. Based on alignments of the assemblies, we generated a draft pangenome that captures known variants and haplotypes, reveals novel alleles at structurally complex loci, and adds 119 million base pairs of euchromatic polymorphic sequence and 1,529 gene duplications relative to the existing reference, GRCh38. Roughly 90 million of the additional base pairs derive from structural variation. Using our draft pangenome to analyze short-read data reduces errors when discovering small variants by 34% and boosts the detected structural variants per haplotype by 104% compared to GRCh38-based workflows, and by 34% compared to using previous diversity sets of genome assemblies.

genomics↗