Biology subjects

Feuk, L.

Publications and source records attributed to Feuk, L..

7 recordsLinked to original sources

bioRxiv2023

A complete digital karyotype of the B-cell leukemia REH cell line resolved by long-read sequencing

The B-cell acute lymphoblastic leukemia (ALL) cell line REH, with the t(12;21) ETV6-RUNX1 translocation, is known to have a complex karyotype defined by a series of large-scale chromosomal rearrangements. Taken from a 15-year-old at relapse, the cell line offers a practical model for the study of high-risk pediatric B-ALL patients. In recent years, short-read DNA and RNA sequencing have emerged as a complement to analog karyotyping techniques in the resolution of structural variants in an oncological context. However, it is challenging to create a comprehensive digital karyotype of a genome with these techniques alone. Here, we explore the integration of long-read PacBio and Oxford Nanopore whole genome sequencing (WGS), IsoSeq RNA-sequencing, and short-read sequencing to create a detailed digital karyotype of the REH cell line. WGS refined the breakpoints of known aberrations and clarified the molecular traits of disrupted ALL-associated genes BTG1 and TBL1XR1, as well as the glucocorticoid receptor NR3C1. Several previously underreported structural variants were also uncovered, including deletions affecting the ALL-associated genes VPREB1 and NFATC1. Meanwhile, transcriptome sequencing identified seven fusion genes within the genomic breakpoints. Together, our extensive whole-genome investigation makes high-quality open-source data available to the leukemia genomics community. KEY POINTSO_LIA complete digital karyotype of the REH cell line was produced with short- and long-read DNA and RNA sequencing technologies. C_LIO_LIThe study enabled precise identification of structural variants, and the fusion genes expressed as the result of these variants. C_LI

cancer biology↗

bioRxiv2021

CRISPR-Cas9 induces large structural variants at on-target and off-target sites in vivo that segregate across generations

To investigate the extent and distribution of unintended mutations induced by CRISPR-Cas9 in vivo, we edited the genome of fertilized zebrafish eggs and investigated DNA from >1100 larvae, juvenile and adult fish in the F0 and F1 generations. Four guide RNAs (gRNAs) were used, selected from 23 gRNAs with high on-target efficiency in vivo in previous functional experiments. CRISPR-Cas9 outcomes were analyzed by long-read sequencing of on-target sites and off-target sites detected in vitro. In founder larvae, on-target editing of the four gRNAs was 93-97% efficient, and three sites across two gRNAs were identified with in vivo off-target editing. Seven percent of the CRISPR-Cas9 editing outcomes correspond to structural variants (SVs), i.e., insertions and deletions [≥]50 bp. The adult founder fish displayed a mosaic pattern of editing events in somatic and germ cells. The F1 generation contained high levels of genome editing, with all alleles of 46 examined F1 juvenile fish affected by on-target mutations, including four cases of SVs. In addition, 26% of the juvenile F1 fish (n=12) carried off-target mutations. These CRISPR-induced off-target mutations in F1 fish were successfully validated in pooled larvae from the same founder parents. In conclusion, we demonstrate that large SVs and off-target mutations can be introduced in vivo and passed through the germline to the F1 generation. The results have important consequences for the use of CRISPR-Cas9 in clinical applications, where pre-testing for off-target activity and SVs on patient material is advisable to reduce the risk of unanticipated effects with potentially large implications.

genomics↗

bioRxiv2021

Long-read whole genome analysis of human single cells

With long-read sequencing, we have entered an era where individual genomes are routinely assembled to near completion and where complex genetic variation can efficiently be resolved. Here, we demonstrate that long reads can be applied to study the genomic architecture of individual human cells. Clonally expanded CD8+ T-cells from a human donor were used as starting material for a droplet-based multiple displacement amplification (dMDA) to generate long molecules with minimal amplification bias. PacBio HiFi sequencing generated up to 20 Gb data and 40% genome coverage per single cell. The data allowed for accurate detection and haplotype phasing of single nucleotide variants (SNVs), structural variants (SVs), and tandem repeats, including in genomic regions inaccessible by short reads. Somatic SNVs were detected in the nuclear genome and mitochondrial DNA. An average of 1278 high-confidence SVs per cell were discovered in the PacBio data, nearly four times as many compared to those found in Illumina dMDA data from clonally related cells. Single-cell de novo assembly resulted in a genome size of up to 598 Mb and 1762 (12.8%) complete gene models. In summary, the work presented here demonstrates the utility of whole genome amplification combined with long-read sequencing toward the characterization of the full spectrum of genetic variation at the single-cell level.

genomics↗

bioRxiv2020

Characterization of the nuclear and cytosolic transcriptomes in human brain tissue reveals new insights into the subcellular distribution of RNA transcripts

Transcriptome analysis has mainly relied on analyzing RNA sequencing data from whole cells, overlooking the impact of subcellular RNA localization and its influence on our understanding of gene function, and interpretation of gene expression signatures in cells. Here, we performed a comprehensive analysis of cytosolic and nuclear transcriptomes in human fetal and adult brain samples. We show significant differences in RNA expression for protein-coding and lncRNA genes between cytosol and nucleus. Transcripts displaying differential subcellular localization belong to particular functional categories and display tissue-specific localization patterns. We also show that transcripts encoding the nuclear-encoded mitochondrial proteins are significantly enriched in the cytosol compared to the rest of protein-coding genes. Further investigation of the use of the cytosolic or the nuclear transcriptome for differential gene expression analysis indicates important differences in results depending on the cellular compartment. These differences were manifested at the level of transcript types and the number of differentially expressed genes. Our data provide a resource of RNA subcellular localization in the human brain and highlight differences in using the cytosolic or the nuclear transcriptomes for differential expression analysis.

molecular biology↗

bioRxiv2020

Amplification-free long read sequencing reveals unforeseen CRISPR-Cas9 off-target activity

A much-debated concern about CRISPR-Cas9 genome editing is that unspecific guide RNA (gRNA) binding may induce off-target mutations. However, accurate prediction of CRISPR-Cas9 off-target sites and activity is challenging. Here we present SMRT-OTS and Nano-OTS, two amplification-free long-read sequencing protocols for detection of gRNA driven digestion of genomic DNA by Cas9. The methods were assessed using the human cell line HEK293, which was first re-sequenced at 18x coverage using highly accurate (HiFi) SMRT reads to get a detailed view of all on- and off-target binding regions. We then applied SMRT-OTS and Nano-OTS to investigate the specificity of three different gRNAs, resulting in a set of 55 high-confidence gRNA binding sites identified by both methods. Twenty-five (45%) of these sites were not reported by off-target prediction software, either because they contained four or more single nucleotide mismatches or insertion/deletion mismatches, as compared with the human reference. We further discovered that a heterozygous SNP can cause allele-specific gRNA binding. Finally, by performing a de novo genome assembly of the HiFi reads, we were able to re-discover 98.7% of the gRNA binding sites without any prior information about the human reference genome. This suggests that CRISPR-Cas9 off-target sites can be efficiently mapped also in organisms where the genome sequence is unknown. In conclusion, the amplification-free sequencing protocols revealed many gRNA binding sites in vitro that would be difficult to predict based on gRNA sequence alignment to a reference. Nevertheless, it is still unknown whether in vivo off-target editing would occur at these sites.

genomics↗

bioRxiv2018

De novo assembly of two Swedish genomes reveals missing segments from the human GRCh38 reference and improves variant calling of population-scale sequencing data

We have performed de novo assembly of two Swedish genomes using long-read sequencing and optical mapping, resulting in total assembly sizes of nearly 3 Gb and hybrid scaffold N50 values of over 45 Mb. A further analysis revealed over 10 Mb of sequences absent from the human GRCh38 reference in each individual. Around 6 Mb of these novel sequences (NS) are shared with a Chinese personal genome. The NS are highly repetitive, have elevated GC-content and are primarily located in centromeric or telomeric regions. A BLAST search showed that 31% of the NS are different from any sequences deposited in nucleotide databases. The remaining NS correspond to human (62%) or primate (6%) nucleotide entries, while 1% of hits show the highest similarity to other species, including mouse and a few different classes of parasitic worms. Up to 1 Mb of NS can be assigned to chromosome Y, and large segments are missing from GRCh38 also at chromosomes 14, 17 and 21. Inclusion of these novel sequences into the GRCh38 reference radically improves the alignment and variant calling of whole-genome sequencing data at several genomic loci. Through a re-analysis of 200 samples from a Swedish population-scale sequencing project, we obtained over 75,000 putative novel SNVs per individual when using a custom version of GRCh38 extended with 17.3 Mb of NS. In addition, about 10,000 false positive SNV calls per individual were removed from the GRCh38 autosomes and sex chromosomes in the re-analysis, with some of them located in protein coding regions.

genomics↗

bioRxiv2017

High throughput expression profiling and in situ screening of circular RNAs in tissues

Circular RNAs (circRNAs) were recently discovered as a class of widely expressed noncoding RNA and have been implicated in regulation of gene expression. However, the function of the majority of circRNAs remains unknown. Studies of circRNAs have been hampered by a lack of essential approaches for detection, quantification and visualization. We therefore developed a target-enrichment sequencing method suitable for high-throughput screening of circRNAs and their linear counterparts. We also applied padlock probes and in situ sequencing to visualize and determine circRNAs localization in human brain tissue at subcellular levels. We measured circRNA abundance across different human samples and tissues. Our results demonstrate the potential of this RNA class to act as a specific diagnostic marker in blood and serum, by detection of circRNAs from genes exclusively expressed in the brain. The powerful and scalable tools we present will enable studies of circRNA function and facilitate screening of circRNA as diagnostic biomarkers.

genomics↗