| 1. |
- Bernenko, Dolores, et al.
(författare)
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Mapping the semi-nested community structure of 3D chromosome contact networks
- 2022
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Mammalian DNA folds into 3D structures that facilitate and regulate genetic processes such as transcription, DNA repair, and epigenetics. Several insights derive from chromosome capture methods, such as Hi-C, which allow researchers to construct contact maps depicting 3D interactions among all DNA segment pairs. These maps show a complex cross-scale organization spanning megabase-pair compartments to short-ranged DNA loops. To better understand the organizing principles, several groups analyzed Hi-C data assuming a Russian-doll-like nested hierarchy where DNA regions of similar sizes merge into larger and larger structures. Apart from being a simple and appealing description, this model explains, e.g., the omnipresent chequerboard pattern seen in Hi-C maps, known as A/B compartments, and foreshadows the co-localization of some functionally similar DNA regions. However, while successful, this model is incompatible with the two competing mechanisms that seem to shape a significant part of the chromosomes’ 3D organization: loop extrusion and phase separation. This paper aims to map out the chromosome’s actual folding hierarchy from empirical data. To this end, we take advantage of Hi-C experiments and treat the measured DNA-DNA interactions as a weighted network. From such a network, we extract 3D communities using the generalized Louvain algorithm. This algorithm has a resolution parameter that allows us to scan seamlessly through the community size spectrum, from A/B compartments to topologically associated domains (TADs). By constructing a hierarchical tree connecting these communities, we find that chromosomes are more complex than a perfect hierarchy. Analyzing how communities nest relative to a simple folding model, we found that chromosomes exhibit a significant portion of nested and non-nested community pairs alongside considerable randomness. In addition, by examining nesting and chromatin types, we discovered that nested parts are often associated with active chromatin. These results highlight that crossscale relationships will be essential components in models aiming to reach a deep understanding of the causal mechanisms of chromosome folding.
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| 2. |
- Bernenko, Dolores, et al.
(författare)
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Mapping the semi-nested community structure of 3D chromosome contact networks
- 2023
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Ingår i: PloS Computational Biology. - : Public Library of Science (PLoS). - 1553-734X .- 1553-7358. ; 19:7
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Tidskriftsartikel (refereegranskat)abstract
- Mammalian DNA folds into 3D structures that facilitate and regulate genetic processes such as transcription, DNA repair, and epigenetics. Several insights derive from chromosome capture methods, such as Hi-C, which allow researchers to construct contact maps depicting 3D interactions among all DNA segment pairs. These maps show a complex cross-scale organization spanning megabase-pair compartments to short-ranged DNA loops. To better understand the organizing principles, several groups analyzed Hi-C data assuming a Russian-doll-like nested hierarchy where DNA regions of similar sizes merge into larger and larger structures. Apart from being a simple and appealing description, this model explains, e.g., the omnipresent chequerboard pattern seen in Hi-C maps, known as A/B compartments, and foreshadows the co-localization of some functionally similar DNA regions. However, while successful, this model is incompatible with the two competing mechanisms that seem to shape a significant part of the chromosomes' 3D organization: loop extrusion and phase separation. This paper aims to map out the chromosome's actual folding hierarchy from empirical data. To this end, we take advantage of Hi-C experiments and treat the measured DNA-DNA interactions as a weighted network. From such a network, we extract 3D communities using the generalized Louvain algorithm. This algorithm has a resolution parameter that allows us to scan seamlessly through the community size spectrum, from A/B compartments to topologically associated domains (TADs). By constructing a hierarchical tree connecting these communities, we find that chromosomes are more complex than a perfect hierarchy. Analyzing how communities nest relative to a simple folding model, we found that chromosomes exhibit a significant portion of nested and non-nested community pairs alongside considerable randomness. In addition, by examining nesting and chromatin types, we discovered that nested parts are often associated with active chromatin. These results highlight that cross-scale relationships will be essential components in models aiming to reach a deep understanding of the causal mechanisms of chromosome folding.
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| 3. |
- Brindefalk, B., et al.
(författare)
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Bacterial composition in Swedish raw drinking water reveals three major interacting ubiquitous metacommunities
- 2022
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Ingår i: Microbiologyopen. - : Wiley. - 2045-8827. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Background Surface raw water used as a source for drinking water production is a critical resource, sensitive to contamination. We conducted a study on Swedish raw water sources, aiming to identify mutually co-occurring metacommunities of bacteria, and environmental factors driving such patterns. Methods The water sources were different regarding nutrient composition, water quality, and climate characteristics, and displayed various degrees of anthropogenic impact. Water inlet samples were collected at six drinking water treatment plants over 3 years, totaling 230 samples. The bacterial communities of DNA sequenced samples (n = 175), obtained by 16S metabarcoding, were analyzed using a joint model for taxa abundance. Results Two major groups of well-defined metacommunities of microorganisms were identified, in addition to a third, less distinct, and taxonomically more diverse group. These three metacommunities showed various associations to the measured environmental data. Predictions for the well-defined metacommunities revealed differing sets of favored metabolic pathways and life strategies. In one community, taxa with methanogenic metabolism were common, while a second community was dominated by taxa with carbohydrate and lipid-focused metabolism. Conclusion The identification of ubiquitous persistent co-occurring bacterial metacommunities in freshwater habitats could potentially facilitate microbial source tracking analysis of contamination issues in freshwater sources.
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| 4. |
- Dwibedi, Chinmay Kumar, et al.
(författare)
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Biological amplification of low frequency mutations unravels laboratory culture history of the bio-threat agent Francisella tularensis
- 2020
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Ingår i: Forensic Science International. - : Elsevier. - 1872-4973 .- 1878-0326. ; 45
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Tidskriftsartikel (refereegranskat)abstract
- Challenges of investigating a suspected bio attack include establishing if microorganisms have been cultured to produce attack material and to identify their source. Addressing both issues, we have investigated genetic variations that emerge during laboratory culturing of the bacterial pathogen Francisella tularensis. Key aims were to identify genetic variations that are characteristic of laboratory culturing and explore the possibility of using biological amplification to identify genetic variation present at exceedingly low frequencies in a source sample. We used parallel serial passage experiments and high-throughput sequencing of F. tularensis to explore the genetic variation. We found that during early laboratory culture passages of F. tularensis, gene duplications emerged in the pathogen genome followed by single-nucleotide polymorphisms in genes for bacterial capsule synthesis. Based on a biological enrichment scheme and the use of high-throughput sequencing, we identified genetic variation that likely pre-existed in a source sample. The results support that capsule synthesis gene mutations are common during laboratory culture, and that a biological amplification strategy is useful for linking a F. tularensis sample to a specific laboratory variant among many highly similar variants.
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| 5. |
- Karlsson, Edvin, et al.
(författare)
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Airborne microbial biodiversity and seasonality in Northern and Southern Sweden
- 2020
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Ingår i: PeerJ. - : PeerJ. - 2167-8359. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms are essential constituents of ecosystems. To improve our understanding of how various factors shape microbial diversity and composition in nature it is important to study how microorganisms vary in space and time. Factors shaping microbial communities in ground level air have been surveyed in a limited number of studies, indicating that geographic location, season and local climate influence the microbial communities. However, few have surveyed more than one location, at high latitude or continuously over more than a year. We surveyed the airborne microbial communities over two full consecutive years in Kiruna, in the Arctic boreal zone, and Ljungbyhed, in the Southern nemoral zone of Sweden, by using a unique collection of archived air filters. We mapped both geographic and seasonal differences in bacterial and fungal communities and evaluated environmental factors that may contribute to these differences and found that location, season and weather influence the airborne communities. Location had stronger influence on the bacterial community composition compared to season, while location and season had equal influence on the fungal community composition. However, the airborne bacterial and fungal diversity showed overall the same trend over the seasons, regardless of location, with a peak during the warmer parts of the year, except for the fungal seasonal trend in Ljungbyhed, which fluctuated more within season. Interestingly, the diversity and evenness of the airborne communities were generally lower in Ljungbyhed. In addition, both bacterial and fungal communities varied significantly within and between locations, where orders like Rhizobiales, Rhodospirillales and Agaricales dominated in Kiruna, whereas Bacillales, Clostridiales and Sordariales dominated in Ljungbyhed. These differences are a likely reflection of the landscape surrounding the sampling sites where the landscape in Ljungbyhed is more homogenous and predominantly characterized by artificial and agricultural surroundings. Our results further indicate that local landscape, as well as seasonal variation, shapes microbial communities in air.
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| 6. |
- Karlsson, Edvin, 1985-
(författare)
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Using airborne eDNA to study ecosystem dynamics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this era of global biodiversity crisis, the need to monitor ecological communities over space and time is more pressing than ever to effectively direct biodiversity conservation and management efforts. To understand the natural dynamics of an ecosystem, and the impact of anthropogenic activities related to environmental and climate change, long time series are needed to accurately link such processes to ecosystem change. This thesis uses a unique resource of archived air filters collected in Sweden originally intended for radioactive particle measurements to reconstruct historical eDNA abundance in the most extensive time-series of airborne eDNA abundance to date - spanning across four decades. By using metabarcoding and metagenomic analysis, it is evident that airborne eDNA from a very large diversity of species is present in air, representing all major branches of the tree of life, including bacteria, fungi, plants, metazoans, and viruses, from a wide range of terrestrial and aquatic sources. These have seasonal as well as long term trends that in part can be explained by temporal variation in climate and regional differences. The data generated in this thesis comprise an extensive resource for analysis of trends related to climate and environmental change and will also allow deeper studies on phenology, phenological change, functional genomics, and potentially antibiotic resistance. The results presented here show the potential of using airborne eDNA to monitor species in the local ecosystem over time and the methods provides an efficient tool for assessment of broad scale biodiversity, in a non-invasive and cost-effective way.
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| 7. |
- Lewerentz, Jacob, 1992-
(författare)
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Genomic adaptation and gene-dosage regulation of Drosophila melanogaster cells, and long-read software developments
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cells are the vehicles that allows genetic code to proliferate in the world, taking on various forms – as illustrated by the tree of life. The cell features are determined by the manufacturing of proteins, a process that has its blueprints encoded as genes in the genome. It is crucial for all cells to have the right amount of protein, regardless of context (part of a multicellular organism or self-sustained). The protein landscape (amount and type) vary depending on the environment. Cells of the multicellular organism should maintain the protein balance to provide its’ intended function in the organism tissue. The cells of multicellular organisms are faced with an imbalance due to sex-related chromosomal imbalances and other genome effects that change the number of gene copies. Restoration from the imbalance is done by dosage compensation systems. Cells that are isolated from the organism and grown inside the lab are common in research, known as cell lines. Cancer cells are similar to cell lines and have lost their original function in the organism in favor of a self-sustained lifestyle. The new environment (context) for these isolated cells impose a challenge; the cells must reorganize their genomes (holding the blueprints for proteins) to obtain autonomy.In this thesis, the genome evolution of isolated cells, cell lines, has been studied using Drosophila melanogaster (the fruit fly). Compared to normal cells of the host organism, cell line genomes are highly mutated and rearranged. With the emergence of novel sequencing technologies that can read long fragments of the genome, this complexity of cell line genomes can be captured. On the topic of novel sequencing technologies, new software implementations are presented and the future of software for long reads and complex genomes is discussed. The main focus of this thesis is to describe how an established and commonly used cell line has reorganized its’ genome to sustain a culture environment. Important information about the genome structure is provided to the research community. The thesis also describes the genome reorganization in new cell lines, covering the early adaptations to cell autonomy. Together, these investigations are of high relevance to human cancer research. This thesis has also studied the fundamentals for regulation of protein balance in organismal cells. Specifically, a recognition sequence to the X chromosome of the protein Painting of Fourth. This protein is related to dosage compensation and primarily enhance transcription from the 4 thchromosome in Drosophila melanogaster, but has been observed tooccasionally bind to the X chromosome.
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| 8. |
- Lewerentz, Jacob, 1992-, et al.
(författare)
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The path to immortalization of cells starts by managing stress through gene duplications
- 2023
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Ingår i: Experimental Cell Research. - : Elsevier. - 0014-4827 .- 1090-2422. ; 422:1
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Tidskriftsartikel (refereegranskat)abstract
- The genomes of immortalized cell lines (and cancer cells) are characterized by multiple types of aberrations, ranging from single nucleotide polymorphisms (SNPs) to structural rearrangements that have accumulated over time. Consequently, it is difficult to estimate the relative impact of different aberrations, the order of events, and which gene functions were under selective pressure at the early stage towards cellular immortalization. Here, we have established novel cell cultures derived from Drosophila melanogaster embryos that were sampled at multiple time points over a one-year period. Using short-read DNA sequencing, we show that copy-number gain in preferentially stress-related genes were acquired in a dominant fraction of cells in 300-days old cultures. Furthermore, transposable elements were active in cells of all cultures. Only a few (<1%) SNPs could be followed over time, and these showed no trend to increase or decrease. We conclude that the early cellular responses of a novel culture comprise sequence duplication and transposable element activity. During immortalization, positive selection first occurs on genes that are related to stress response before shifting to genes that are related to growth.
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| 9. |
- Lewerentz, Jacob, et al.
(författare)
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Transposon activity, local duplications and propagation of structural variants across haplotypes drive the evolution of the Drosophila S2 cell line
- 2022
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Ingår i: BMC Genomics. - : BioMed Central. - 1471-2164. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Immortalized cell lines are widely used model systems whose genomes are often highly rearranged and polyploid. However, their genome structure is seldom deciphered and is thus not accounted for during analyses. We therefore used linked short- and long-read sequencing to perform haplotype-level reconstruction of the genome of a Drosophila melanogaster cell line (S2-DRSC) with a complex genome structure.Results: Using a custom implementation (that is designed to use ultra-long reads in complex genomes with nested rearrangements) to call structural variants (SVs), we found that the most common SV was repetitive sequence insertion or deletion (> 80% of SVs), with Gypsy retrotransposon insertions dominating. The second most common SV was local sequence duplication. SNPs and other SVs were rarer, but several large chromosomal translocations and mitochondrial genome insertions were observed. Haplotypes were highly similar at the nucleotide level but structurally very different. Insertion SVs existed at various haplotype frequencies and were unlinked on chromosomes, demonstrating that haplotypes have different structures and suggesting the existence of a mechanism that allows SVs to propagate across haplotypes. Finally, using public short-read data, we found that transposable element insertions and local duplications are common in other D. melanogaster cell lines.Conclusions: The S2-DRSC cell line evolved through retrotransposon activity and vast local sequence duplications, that we hypothesize were the products of DNA re-replication events. Additionally, mutations can propagate across haplotypes (possibly explained by mitotic recombination), which enables fine-tuning of mutational impact and prevents accumulation of deleterious events, an inherent problem of clonal reproduction. We conclude that traditional linear homozygous genome representation conceals the complexity when dealing with rearranged and heterozygous clonal cells.
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| 10. |
- Mahmud, A. K. M. Firoj, et al.
(författare)
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Exploring a Drosophila Transcription Factor Interaction Network to Identify Cis-Regulatory Modules
- 2020
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Ingår i: Journal of Computational Biology. - : Mary Ann Liebert. - 1066-5277 .- 1557-8666. ; 27:8, s. 1313-1328
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Tidskriftsartikel (refereegranskat)abstract
- Multiple transcription factors (TFs) bind to specific sites in the genome and interact among themselves to form the cis-regulatory modules (CRMs). They are essential in modulating the expression of genes, and it is important to study this interplay to understand gene regulation. In the present study, we integrated experimentally identified TF binding sites collected from published studies with computationally predicted TF binding sites to identifyDrosophilaCRMs. Along with the detection of the previously known CRMs, this approach identified novel protein combinations. We determined high-occupancy target sites, where a large number of TFs bind. Investigating these sites revealed that Giant, Dichaete, and Knirp are highly enriched in these locations. A common TAG team motif was observed at these sites, which might play a role in recruiting other TFs. While comparing the binding sites at distal and proximal promoters, we found that certain regulatory TFs, such as Zelda, were highly enriched in enhancers. Our study has shown that, from the information available concerning the TF binding sites, the real CRMs could be predicted accurately and efficiently. Although we only may claim co-occurrence of these proteins in this study, it may actually point to their interaction (as known interaction proteins typically co-occur together). Such an integrative approach can, therefore, help us to provide a better understanding of the interplay among the factors, even though further experimental verification is required.
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