Thèses sur le sujet « Chromatin sequencing »

In embryonic stem cells (ESCs), the SWI/SNF, CHD, and INO80 families of ATP-dependent chromatin remodellers have been implicated in maintaining pluripotency-associated gene expression, however the involvement of ISWI family remodellers has yet to be defined. Here, we explore the importance of the mammalian ISWI homologue SNF2H (Smarca5) by deriving a conditional knockout mouse ESC line and observing the consequences of SNF2H depletion on the pluripotent state. Cre-mediated deletion of Snf2h disrupts hallmark characteristics of pluripotency, resulting in distinct morphological changes; reduced expression of the master transcription factors Oct4, Sox2, and Nanog; and reduced alkaline phosphatase activity. To understand the mechanisms of SNF2H-mediated regulation, we mapped SNF2H-bound nucleosomes genome-wide. SNF2H is broadly distributed across the genome, but is preferentially enriched at active regulatory regions and transcription factor binding sites. These findings demonstrate the importance of SNF2H in ESCs and shed light on genome-wide mechanisms of transcriptional regulation.

Nei nuclei delle cellule eucarioti, l'informazione genetica codificata nel DNA è concentrata nel microscopico volume nucleare in forma di cromatina, un complesso di DNA e proteine. I meccanismi molecolari che gestiscono la compattazione e il ripiegamento della cromatina e che consentono l'espressione mirata delle porzioni di genoma necessarie alle attività della cellula sono noti come ‘epigenoma’. L’azione dell’epigenoma determina un avvolgimento e un posizionamento nucleare della cromatina specifico per ogni tipo cellulare, con aree dense e trascrizionalmente inattive (eterocromatina) ed aree meno dense, ricche di geni e trascrizionalmente attive (eucromatina). In questo nostro lavoro descriviamo l'organizzazione della cromatina nel nucleo di diverse popolazioni cellulari e ne analizziamo alcuni aspetti fisiologici e patologici. Innanzitutto, studiando le cellule staminali muscolari di topi privi della proteina strutturale nucleare lamina-A/C, descriviamo un irregolare processo di differenziamento dovuto alla redistribuzione dei repressori trascrizionali del gruppo Polycomb (PcG proteins), che dai i loro geni target si diffondono verso regioni cromatiniche fiancheggianti. La conseguente alterazione nell’espressione genica causa l’esaurimento prematuro della riserva di cellule staminali quiescenti e l’accumulo di grasso intramuscolare, portando a una senescenza accelerata e alla distrofia muscolare. D’altro canto, anche il progressivo accumulo di una forma aberrante di lamina-A, la progerina, caratteristica della sindrome di Hutchinson-Gilford (HGPS), causa gravi alterazioni nella struttura della cromatina. In particolare, la progerina interferisce con le strutture eterocromatiniche periferiche associate alla lamina nucleare, i Lamina Associated Domains (LADs). Per il nostro secondo progetto abbiamo sviluppato un nuovo metodo, SAMMY-seq, basato sull’high-throughput sequencing di frazioni di cromatina con diversa solubilità. Tramite questa tecnologia, individuiamo alterazioni nella solubilità dell’eterocromatina in fibroblasti primari derivanti da pazienti progerici in uno stadio precoce di malattia. I cambiamenti strutturali osservati a questo stadio non alterano la deposizione del marcatore eterocromatinico H3K9me3, ma sono associati a variazioni sito-specifiche nella regolazione trascrizionale di geni target delle PcG proteins. Infine, ottimizzando ulteriormente il protocollo di SAMMY-seq, nel nostro terzo progetto mostriamo un’organizzazione non convenzionale della cromatina nei linfociti T CD4+ quiescenti derivanti da sangue periferico di donatori. In queste cellule, l’eterocromatina risulta sensibile alla digestione enzimatica operata dalla DNAsi, mentre l’eucromatina si rivela resistente a diversi processi di estrazione. Un’analisi preliminare del contenuto di questi compartimenti indica la presenza, nell’eucromatina, dei geni specifici per l’attivazione linfocitaria, oltre che dei geni attivi. Ulteriori studi chiariranno il ruolo di questa organizzazione non convenzionale della cromatina nella funzione cellulare linfocitaria.
In every eukaryotic cell, the genomic information coded in the DNA is packed into the small nuclear volume as chromatin, a complex of DNA and proteins. The ensemble of molecular mechanisms that organize chromatin compaction and allow the specific expression of the portions of genome useful for cell’s biological functions is known as the epigenome. As a result of epigenome activity, chromatin is folded and positioned in the nucleus in a cell-specific manner, generating areas of highly compacted, repressed, heterochromatin and areas of decondensed, gene-rich and transcriptionally active, euchromatin. In our work, we describe chromatin organization in different cell populations and analyse some of its implications in the physiological functions and pathological dysfunctions of the cell. In the first project, we focus on murine muscle stem cells lacking the nuclear structural protein Lamin A/C. We show their irregular differentiation program, due to a spreading of Polycomb group (PcG) of proteins repressors from their target genes over the flanking regions. The consequent alteration in gene expression cause premature exhaustion of quiescent stem cells and accumulation of intramuscular fat, resulting in accelerated senescence and muscular dystrophy progression. On the other hand, the progressive accumulation of a Lamin A aberrant form, Progerin, in Hutchinson-Gilford progeria syndrome (HGPS) also leads to chromatin structure disruption. In particular, it interferes with Lamina Associated Domains (LADs), the peripheral heterochromatin structures associated to the nuclear lamina. For our second project, we develop a new method, SAMMY-seq, based on high-throughput sequencing of chromatin fractions of different solubility. Thanks to this technology, we highlight early changes in heterochromatin accessibility in human HGPS primary fibroblasts. This early structural changes do not alter the deposition of the H3K9me3 heterochromatin mark but are associated with site-specific variations in the PcG-dependent transcriptional regulation. Finally, further improving SAMMY-seq technology, in our third project we describe an unconventional genome organization in resting human CD4+ T lymphocytes extracted from the peripheral blood of healthy donors. In these cells, heterochromatin is sensitive to DNAse digestion while euchromatin is resistant to serial processes of extraction. Preliminary analysis of the content of these compartments suggests that euchromatin contains, beside the actively transcribed genes, also inactive genes specific for lymphocyte activation. Further studies will elucidate the role of this unconventional chromatin organization in lymphocytes functions.

CCCTC-binding factor (CTCF) binds DNA, thereby helping to partition the mammalian genome into discrete structural and regulatory domains. In doing so, it insulates chromatin and fine-tunes gene activation, repression, and silencing. Complete removal of CTCF from mammalian cells causes catastrophic genomic dysregulation, most likely due to widespread collapse of 3D chromatin looping within the nucleus. In contrast, Ctcf hemizygous mice with lifelong reduction in CTCF expression are viable but have an increased incidence of spontaneous multi-lineage malignancies. In addition, CTCF is mutated in many human cancers and is thus implicated as a tumour suppressor gene. This study aimed to interrogate the genome-wide consequences of a reduced genomic concentration of Ctcf and its implications for carcinogenesis. In a genetically engineered mouse model, Ctcf hemizygous cells showed modest but robust changes in almost a thousand sites of genomic CTCF occupancy; these were enriched for lower affinity binding events with weaker evolutionary conservation across the mouse lineage. Furthermore, several hundred genes concentrated in cancer-related pathways were dysregulated due to changes in transcriptional regulation. Global chromatin structure was preserved but some loop interactions were destabilised, often around differentially expressed genes and their enhancers. Importantly, these transcriptional alterations were also seen in human cancers. These findings were then examined in a hepatocyte-specific mouse model of Ctcf hemizygosity with diethylnitrosamine-induced liver tumours. Ctcf hemizygous mice had a subtle liver-specific phenotype, although the overall tumour burden in Ctcf hemizygous and wild-type mice was the same. Using whole genome sequencing, the highly reproducible mutational signature caused by DEN exposure was characterised, revealing that Braf(V637E), orthologous to BRAF(V600E) in humans, was the predominant oncogenic driver in these liver tumours. Taken together, while Ctcf loss is partially physiologically compensated, chronic CTCF depletion dysregulates gene expression by subtly altering transcriptional regulation. This study also represents the first comprehensive genome-wide and histopathological characterisation of this commonly used liver cancer model.

The epigenome carries dynamic information that controls gene expression and maintains cell identity during both disease and normal development. The inherent plasticity of the epigenome paves new avenues for developing diagnostic and therapeutic tools for human diseases. Microfluidic technology has improved the sensitivity and resolution of epigenomic analysis due to its outstanding ability to manipulate nanoliter-scale liquid volumes. In this thesis, I report three projects focusing on low-input, cell-type-specific and spatially resolved histone modification profiling on microfluidic platforms. First, I applied Microfluidic Oscillatory Washing-based Chromatin Immunoprecipitation followed by sequencing (MOWChIP-seq) to study the effect of culture dimensionality, hypoxia stress and bacterium infection on histone modification landscapes of brain tumor cells. I identified differentially marked regions between different culture conditions. Second, I adapted indexed ChIPmentation and introduced mu-CM, a low-input microfluidic device capable of performing 8 assays in parallel on different histone marks using as few as 20 cells in less than 7 hours. Last, I investigated the spatially resolved epigenome and transcriptome of neuronal and glial cells from coronal sections of adult mouse neocortex. I applied unsupervised clustering to identify distinct spatial patterns in neocortex epigenome and transcriptome that were associated with central nervous system development. I demonstrated that our method is well suited for scarce samples, such as biopsy samples from patients in the context of precision medicine.
Doctor of Philosophy
Epigenetic is the study of alternations in organisms not caused by alternation of the genetic codes. Epigenetic information plays pivotal role during growth, aging and disease. Epigenetic information is dynamic and modifiable, and thus serves as an ideal target for various diagnostic and therapeutic strategies of human diseases. Microfluidics is a technology that manipulates liquids with extremely small volumes in miniaturized devices. Microfluidics has improved the sensitivity and resolution of epigenetic analysis. In this thesis, I report three projects focusing on low-input, cell-type-specific and spatially resolved histone modification profiling on microfluidic platforms. Histone modification is one type of epigenetic information and regulates gene expression. First, we studied the influence of culture condition and bacterium infection on histone modification profile of brain tumor cells. Second, we introduced mu-CM, combining a low-input microfluidic device with indexed ChIPmentation and is capable of performing 8 assays in parallel using as few as 20 cells. Last, we investigated spatial variations in the epigenome and transcriptome across adult mouse neocortex, the outer layer of brain involving in higher-order function, such as cognition. I identified distinct spatial patterns responsible for central nervous system development using machine learning algorithm. Our method is well suited for studying scarce samples, such as cells populations isolated from patients in the context of precision medicine.

Atriplex hortensis (2n = 2x = 18, 1C genome size ~1.1 gigabases), also known as garden orach, is a highly nutritious, broadleaf annual of the Amaranthaceae-Chenopodiaceae family that has spread from its native Eurasia to other temperate and subtropical environments worldwide. Atriplex is a highly complex and polyphyletic genus of generally halophytic and/or xerophytic plants, some of which have been used as food sources for humans and animals alike. Although there is some literature describing the taxonomy and ecology of orach, there is a lack of genetic and genomic data that would otherwise help elucidate the genetic variation, phylogenetic position, and future potential of this species. Here, we report the assembly of the first highquality, chromosome-scale reference genome for orach cv. ‘Golden’. Sequence data was produced using Oxford Nanopore’s MinION sequencing technology in conjunction with Illumina short-reads and chromatin-contact mapping. Genome assembly was accomplished using the high-noise, single-molecule sequencing assembler, Canu. The genome is enriched for highly repetitive DNA (68%). The Canu assembly combined with the Hi-C chromatin-proximity data yielded a final assembly containing 1,325 scaffolds with a contig N50 of 98.9 Mb and with 94.7% of the assembly represented in the nine largest, chromosome-scale scaffolds. Sixty-eight percent of the genome was classified as highly repetitive DNA, with the most common repetitive elements being Gypsy and Copia-like LTRs. The annotation was completed using MAKER which identified 31,010 gene models and 2,555 tRNA genes. Completeness of the genome was assessed using the Benchmarking Universal Single Copy Orthologs (BUSCO) platform, which quantifies functional gene content using a large core set of highly conserved orthologous genes (COGs). Of the 1,375 plant-specific COGs in the Embryophyta database, 1,330 (96.7%) were identified in the Atriplex assembly. We also report the results of a resequencing panel consisting of 21 accessions which illustrates a high degree of genetic similarity among cultivars and wild material from various locations in North America and Europe. These genome resources provide vital information to better understand orach and facilitate future study and comparison.

Proteins that bind to DNA or RNA are both known to influence alternative splicing. However, there has not been so far a systematic experimental exploration of the relationship between these factors in their effect on splicing. In this thesis, we make use of the large amounts of publicly available high throughput sequencing data that now make it possible to explore this question on a genome-wide scale. We made exhaustive use of a method known as profiling to address this question. As most profiling methods in common use are merely qualitative, the first task of the thesis was to generate a quantitative profiling method and bioinformatics tool, ProfileSeq, which we validated by reproducing previous results from the literature. ProfileSeq and other methods were combined to mine for relationships between DNA and RNA binding factors with potential relevance to splicing. We found significant associations between the transcription factor CTCF and the RNA binding protein LIN28A, and similarly between SPI1 and RNA-binding proteins that bind to AC-rich motifs, such as hnRNPL. These represent putative relationships relevant to splicing, as these results were reached by more than one independent method with independent datasets. We also show evidence that CTCF acts as a barrier between regions of H3K4me3 marking inside genes. A number of other results of potential interest to both the bioinformatics and molecular biology communities are also described
Las proteínas que se unen al DNA o al RNA pueden influir el splicing alternativo. Sin embargo, no ha habido aún una exploración sistemática de la relación entre estos dos tipos de factores en su acción sobre el splicing. En esta tesis hacemos uso de datos públicos de secuenciación de alto rendimiento para explorar esta cuestión a escala de todo el genoma. Hemos hecho un uso sistemático de la construcción de perfiles de información genómica para abordar esta cuestión. Debido a que los métodos i comúnmente utilizados para construir perfiles hace sólo comparaciones cualitativas, la primera tarea de esta tesis consistió en desarrollar un método para cuantificar perfiles e implementarlo en una herramienta bioinformática, ProfileSeq, la cual hemos validado mediante la reproducción de resultados previamente descritos en la literatura. Posteriormente, ProfileSeq se usó con datos de actividad de unión al DNA o al RNA de distintas proteínas para estudiar la relevancia en el splicing. Se encontraron varias asociaciones significativas. Entre ellas, la del factor de transcripción CTCF y la proteína de unión a RNA LIN28A. De manera similar, se encontró una relación entre SPI1 y proteínas de unión a RNA que se unen a motivos ricos en AC, como hnRNPL. Estos resultados representan relaciones putativas relevantes para el splicing, ya que se alcanzaron por más de un método diferente y usando datos independientes, También mostramos evidencia de que CTCF actúa como una barrera entre las regiones intragénicas de marcaje diferencial con H3K4me3. También se describen otros resultados de interés potencial tanto para la bioinformática como para la biología molecular.

A cell, the building block of all life, stores a plethora of information in its genome, epigenome, and transcriptome which needs to be analyzed via various Omic studies. The heterogeneity in a seemingly similar group of cells is an important factor to consider and it could lead us to better understand processes such as cancer development and resistance to treatment, fetal development, and immune response. There is an ever growing demand to be able to develop more sensitive, accurate and robust ways to study Omic information and to analyze subtle biological variation between samples even with limited starting material obtained from a single cell. Microfluidics has opened up new and exciting possibilities that have revolutionized how we study and manipulate the contents of the cell like the DNA, RNA, proteins, etc. Microfluidics in conjunction with Next Gen Sequencing has provided ground-breaking capabilities for handling small sample volumes and has also provided scope for automation and multiplexing. In this thesis, we discuss a number of platforms for developing low-input or single cell Omic technologies. The first part talks about the development of a novel microfluidic platform to carry out single-cell RNA-sequencing in a one-pot method with a diffusion-based reagent swapping scheme. This platform helps to overcome the limitations of conventional microfluidic RNA seq methods reported in literature that use complicated multiple-chambered devices. It also provides good quality data that is comparable to state-of-the-art scRNA-seq methods while implementing a simpler device design that permits multiplexing. The second part talks about studying the transcriptome of innate leukocytes treated with varying levels of LPS and using RNA-seq to observe how innate immune cells undergo epigenetic reprogramming to develop phenotypes of memory cells. The third part discusses a low-cost alternative to produce tn5 enzyme which low-cost NGS studies. And finally, we discuss a microfluidic approach to carrying out low-input epigenomic studies for studying transcription factors. Today, single-cell or low-input Omic studies are rapidly moving into the clinical setting to enable studies of patient samples for personalized medicine. Our approaches and platforms will no doubt be important for transcriptomic and epigenomic studies of scarce cell samples under such settings.
Doctor of Philosophy
This is the era of personalized medicine which means that we are no longer looking at one-size-fits-all therapies. We are rather focused on finding therapies that are tailormade to every individual’s personal needs. This has become more and more essential in the context of serious diseases like cancer where therapies have a lot of side-effects. To provide tailor-made therapy to patients, it is important to know how each patient is different from another. This difference can be found from studying how the individual is unique or different at the cellular level i.e. by looking into the contents of the cell like DNA, RNA, and chromatin. In this thesis, we discussed a number of projects which we can contribute to advancement in this field of personalized medicine. Our first project, MID-RNA-seq offers a new platform for studying the information contained in the RNA of a single cell. This platform has enough potential to be scaled up and automated into an excellent platform for studying the RNA of rare or limited patient samples. The second project discussed in this thesis involves studying the RNA of innate immune cells which defend our bodies against pathogens. The RNA data that we have unearthed in this project provides an immense scope for understanding innate immunity. This data provides our biologist collaborators the scope to test various pathways in innate immune cells and their roles in innate immune modulation. Our third project discusses a method to produce an enzyme called ‘Tn5’ which is necessary for studying the sequence of DNA. This enzyme which is commercially available has a very high cost associated with it but because we produced it in the lab, we were able to greatly reduce costs. The fourth project discussed involves the study of chromatin structure in cells and enables us to understand how our lifestyle choices change the expression or repression of genes in the cell, a study called epigenetics. The findings of this study would enable us to study epigenomic profiles from limited patient samples. Overall, our projects have enabled us to understand the information from cells especially when we have limited cell numbers. Once we have all this information we can compare how each patient is different from others. The future brings us closer to putting this into clinical practice and assigning different therapies to patients based on such data.

In questo lavoro, metodi provenienti dalla Fisica, dalla Statistica e dalla Teoria dei Grafi sono stati impiegati per caratterizzare ed analizzare profili di apertura e accessibilità della cromatina ottenuti con la tecnica ATAC-seq in singole cellule, nella fattispecie linfociti B provenienti da tre pazienti affetti da Leucemia Linfocitica Cronica. Una pipeline bioinformatica è stata sviluppata per processare i dati di sequencing ed ottenere le posizioni accessibili del genoma per ciascuna cellula. La quantità di regioni aperte e la loro distribuzione spaziale lungo il DNA sono state caratterizzate. Infine, l’apertura simultanea nelle stesse singole cellule di regioni regolatrici è stata impiegata come metrica per valutare relazioni funzionali, e in questo modo grafi tra enhancer e promoter sono stati costruiti e le loro proprietà sono state analizzate. La distribuzione spaziale lungo il genoma di regioni aperte consecutive ricapitola proprietà strutturali come gli array di nucleosomi e le strutture a loop della cromatina. Inoltre, i profili di accessibilità delle regioni regolatrici sono significativamente conservati nelle singole cellule. I network tra enhancer e promoter forniscono un modo per caratterizzare la rilevanza di ciascuna regione regolatrice in termini di centralità. Le statistiche sulla connettività tra enhancer e promoter confermano il modello di relazione uno-a-uno come il più frequente, in cui un promoter è regolato dall'enhancer ad esso più vicino. Infine, anche il funzionamento dei superenhancer è stato indagato. In conclusione, ATAC-seq si rivela un'efficace tecnica per indagare l'apertura della cromatina in singole cellule, i cui profili di accessibilità ricapitolano caratteristiche strutturali e funzionali della cromatina. Al fine di indagare i meccanismi della malattia, il panorama di accessibilità dei lifociti tumorali può essere confrontato con quello di cellule sane e cellule trattate con farmaci epigenetici.

Microfluidics has revolutionized how molecular biology studies are conducted. It permits profiling of genomic and epigenomic features for a wide range of applications. Microfluidics has been proven to be highly complementary to NGS technology with its unique capabilities for handling small volumes of samples and providing platforms for automation, integration, and multiplexing. In this thesis, we focus on three projects (diffusion-based PCR, MID-RRBS, and SurfaceChIP-seq), which improved the sensitivities of conventional assays by coupling with microfluidic technology. MID-RRBS and SurfaceChIP-seq projects were designed to profiling genome-wide DNA methylation and histone modifications, respectively. These assays dramatically improved the sensitivities of conventional approaches over 1000 times without compromising genomic coverages. We applied these assays to examine the neuronal/glial nuclei isolated from mouse brain tissues. We successfully identified the distinctive epigenomic signatures from neurons and glia. Another focus of this thesis is applying electrical field to investigate the intracellular contents. We report two projects, drug delivery to encapsulated bacteria and mRNA extraction under ultra-high electrical field intensity. We envision rapid growth in these directions, driven by the needs for testing scarce primary cells samples from patients in the context of precision medicine.
Ph. D.

Cellular function and physiology are largely established through regulated gene expression. The first step in gene expression, transcription of the genomic DNA into RNA, is a process that is highly aligned at the levels of initiation, elongation and termination. In eukaryotes, protein-coding genes are exclusively transcribed by RNA polymerase II (Pol II). Upon transcription of the first 15-20 nucleotides (nt), the emerging nascent RNA 5’ end is modified with a 7-methylguanosyl cap. This is one of several RNA modifications and processing steps that take place during transcription, i.e. co-transcriptionally. For example, protein-coding sequences (exons) are often disrupted by non-coding sequences (introns) that are removed by RNA splicing. The two transesterification reactions required for RNA splicing are catalyzed through the action of a large macromolecular machine, the spliceosome. Several non-coding small nuclear RNAs (snRNAs) and proteins form functional spliceosomal subcomplexes, termed snRNPs. Sequentially with intron synthesis different snRNPs recognize sequence elements within introns, first the 5’ splice site (5‘ SS) at the intron start, then the branchpoint and at the end the 3’ splice site (3‘ SS). Multiple conformational changes and concerted assembly steps lead to formation of the active spliceosome, cleavage of the exon-intron junction, intron lariat formation and finally exon-exon ligation with cleavage of the 3’ intron-exon junction. Estimates on pre-mRNA splicing duration range from 15 sec to several minutes or, in terms of distance relative to the 3‘ SS, the earliest detected splicing events were 500 nt downstream of the 3‘ SS. However, the use of indirect assays, model genes and transcription induction/blocking leave the question of when pre-mRNA splicing of endogenous transcripts occurs unanswered. In recent years, global studies concluded that the majority of introns are removed during the course of transcription. In principal, co-transcriptional splicing reduces the need for post-transcriptional processing of the pre-mRNA. This could allow for quicker transcriptional responses to stimuli and optimal coordination between the different steps. In order to gain insight into how pre-mRNA splicing might be functionally linked to transcription, I wanted to determine when co-transcriptional splicing occurs, how transcripts with multiple introns are spliced and if and how the transcription termination process is influenced by pre-mRNA splicing. I chose two yeast species, S. cerevisiae and S. pombe, to study co-transcriptional splicing. Small genomes, short genes and introns, but very different number of intron-containing genes and multi-intron genes in S. pombe, made the combination of both model organisms a promising system to study by next-generation sequencing and to learn about co-transcriptional splicing in a broad context with applicability to other species. I used nascent RNA-Seq to characterize co-transcriptional splicing in S. pombe and developed two strategies to obtain single-molecule information on co-transcriptional splicing of endogenous genes: (1) with paired-end short read sequencing, I obtained the 3’ nascent transcript ends, which reflect the position of Pol II molecules during transcription, and the splicing status of the nascent RNAs. This is detected by sequencing the exon-intron or exon-exon junctions of the transcripts. Thus, this strategy links Pol II position with intron splicing of nascent RNA. The increase in the fraction of spliced transcripts with further distance from the intron end provides valuable information on when co-transcriptional splicing occurs. (2) with Pacific Biosciences sequencing (PacBio) of full-length nascent RNA, it is possible to determine the splicing pattern of transcripts with multiple introns, e.g. sequentially with transcription or also non-sequentially. Part of transcription termination is cleavage of the nascent transcript at the polyA site. The splicing status of cleaved and non-cleaved transcripts can provide insights into links between splicing and transcription termination and can be obtained from PacBio data. I found that co-transcriptional splicing in S. pombe is similarly prevalent to other species and that most introns are removed co-transcriptionally. Co-transcriptional splicing levels are dependent on intron position, adjacent exon length, and GC-content, but not splice site sequence. A high level of co-transcriptional splicing is correlated with high gene expression. In addition, I identified low abundance circular RNAs in intron-containing, as well as intronless genes, which could be side-products of RNA transcription and splicing. The analysis of co-transcriptional splicing patterns of 88 endogenous S. cerevisiae genes showed that the majority of intron splicing occurs within 100 nt downstream of the 3‘ SS. Saturation levels vary, and confirm results of a previous study. The onset of splicing is very close to the transcribing polymerase (within 27 nt) and implies that spliceosome assembly and conformational rearrangements must be completed immediately upon synthesis of the 3‘ SS. For S. pombe genes with multiple introns, most detected transcripts were completely spliced or completely unspliced. A smaller fraction showed partial splicing with the first intron being most often not spliced. Close to the polyA site, most transcripts were spliced, however uncleaved transcripts were often completely unspliced. This suggests a beneficial influence of pre-mRNA splicing for efficient transcript termination. Overall, sequencing of nascent RNA with the two strategies developed in this work offers significant potential for the analysis of co-transcriptional splicing, transcription termination and also RNA polymerase pausing by profiling nascent 3’ ends. I could define the position of pre-mRNA splicing during the process of transcription and provide evidence for fast and efficient co-transcriptional splicing in S. cerevisiae and S. pombe, which is associated with highly expressed genes in both organisms. Differences in S. pombe co-transcriptional splicing could be linked to gene architecture features, like intron position, GC-content and exon length.

Gene activity is regulated at two separate layers. Through structural and chemical properties of DNA – the primary layer of encoding – local signatures may enable, or disable, the binding of proteins or complexes of them with regulatory potential to the DNA. At a higher level – the structural layer of encoding – gene activity is regulated through the properties of higher order DNA structure, chromatin, and chromosome organization. Cells with abnormal chromosome compaction or organization, e.g. cancer cells, may thus have perturbed regulatory activities resulting in abnormal gene activity. Hence, there is a great need to decode the transcriptional regulation encoded in both layers to further our understanding of the factors that control activity and life of a cell and, ultimately, an organism. Modern genome-wide studies with those aims rely on data-intense experiments requiring sophisticated computational and statistical methods for data handling and analyses. This thesis describes recent advances of analyzing experimental data from quantitative biological studies to decipher the structural layer of encoding in human cells. Adopting an integrative approach when possible, combining multiple sources of data, allowed us to study the influences of chromatin (Papers I and II) and chromosomal aberrations (Paper IV) on transcription. Combining chromatin data with chromosomal aberration data allowed us to identify putative driver oncogenes and tumor-suppressor genes in cancer (Paper IV). Bayesian approaches enabling the incorporation of background information in the models and the adaptability of such models to data have been very useful. Their usages yielded accurate and narrow detection of chromosomal breakpoints in cancer (Papers III and IV) and reliable positioning of nucleosomes and their dynamics during transcriptional regulation at functionally relevant regulatory elements (Paper II). Using massively parallel sequencing data, we explored the chromatin landscapes of human cells (Papers I and II) and concluded that there is a preferential and evolutionary conserved positioning at internal exons nearly unaffected by the transcriptional level. We also observed a strong association between certain histone modifications and the inclusion or exclusion of an exon in the mature gene transcript, suggesting a functional role in splicing.

The shift of medical technology from a doctor's application of individualized medicine toward precision medicine has been accelerated by the advent of Next Generation Sequencing. Individualized medicine is where a doctor tries to understand the intricacies of a patient's medical state, where precision medicine uses a wealth of data to understand the individuality of a patient on a biological level to determine treatment course. Next Generation Sequencing allows for the collection of genome wide analyses such as genomic, transcriptomic, and epigenomic sequencing, which provides the backbone of the data driven precision medicine. In order to obtain and use this data, it needs to be produced from minimal amounts of patient tissue, such as the amount from a needle biopsy. In order to perform so many different assays it is paramount that we develop high sensitivity methodologies, such that we can gain an understanding of the patient's physiology without causing much discomfort in gathering large amounts of sample. In pursuit of making more tests, data, and assays available for use in precision medicine, we have developed 3 different microfluidic technologies, which automate and simplify the assays needed for the data collection at a high sensitivity, as well as a versatile platform for therapeutic production. First, we developed a epigenomic assay for chromatin immunoprecipitation, which gives us information on histone modifications across the genome. These histone modifications heavily impact gene expression and how the chromatin is organized, as well promoting or inhibiting transcription of genes. Our technology allowed us to perform multiple parallel assays from as few as 50 cells quickly and reliably using our fluidized bed technology. Next, we developed a library preparation system, which reduces the cost of library preparation by 20x and reduces operator pipetting by 100x. Our system uses a droplet based reactor to quickly and reliably prepare sequencing libraries using the lowest amount of DNA to date, 10 pg. Finally, we designed a therapeutics-on-a-chip platform which is capable of producing clinically relevant proteins on demand from temperature stable components. Using our system, we are capable of producing a number of different therapeutics on demand quickly without rearrangement of the system.
Doctor of Philosophy
Technical advances in the healthcare industry have made a range of new data available to physicians and patients. Home use DNA testing kits have made it possible to examine one’s predisposition to certain genetic diseases. Using these advanced methods, we are able to gain insights into a patient’s disease state where we were previously unable. Unfortunately, some of these new analyses currently require large amounts of patient sample, which make the examinations largely impractical to perform. In order to overcome the sample requirements, which make these analyses impractical, we develop microscale reactor systems capable of reducing the amount of material required for these new analyses. Here I demonstrate our developed technologies to automate 3 different processes aimed at enabling the study of protein-DNA interactions and produce therapeutics at the point of care. First, we developed an analytical system to study protein-DNA interactions (which are important to understanding patient responses to treatment), that allow for parallel analyses which can be done with sample from less than one needle biopsy, where existing methods would require dozens or more (50 vs 10,000,000 cells.) Next, we developed automated system for preparing DNA sequencing libraries using as little as 10 pg DNA (~2 cells of DNA). The device run multiple reactions simultaneously while reducing batch to batch variation and operator hands-on time. Finally, we developed a v Therapeutics-On-a-Chip platform that produces clinically relevant therapeutic proteins in clinically relevant dosages using a cell-free approach, while saving the trouble and cost associated with protein storage and transportation.

The main focus of this research was the development of microfluidic technology for ultrasensitive and fast molecular analysis of cells. Chromatin immunoprecipitation (ChIP) assay followed by next generation sequencing serves as the primary technique to characterize the genomic locations associated with histone modifications. However, conventional ChIP-seq assay requires large numbers of cells. We demonstrate a novel microfluidics-based ChIP-seq assay which dramatically reduced the required cell number. Coupled with next generation sequencing, the assay permitted the analysis of histone modifications at the whole genome from as few as ~100 cells. Using the same device, we demonstrated that MeDIP-seq with tiny amount of DNA (<5ng) generated high quality genome-wide profiles of DNA methylation. Off-chip sonication often leads to sample loss due to multiple tube transferring. In addition, conventional sonicators are not able to manipulate samples with small volume. We developed a novel microfluidic sonicator, which is able to achieve on-chip DNA/chromatin shearing into ideal fragment size (100~600bp) for both chromatin immunoprecipitation (ChIP) and methylated DNA immunoprecipitation (MeDIP). The integrated on-chip sonication followed by immunoprecipitation (IP) reaction can significantly reduce sample loss and contamination. Simple and accessible detection methods that can rapidly screen a large cell population with single cell resolution have been seriously lacking. We demonstrate a simple protocol for detecting translocation of native proteins using a common flow cytometer which detects fluorescence intensity without imaging. Using our approach, we successfully detected the translocation of native NF-kappa B (an important transcription factor) at its native expression level and examine the temporal dynamics in the process. Droplets with encapsulated beads and cells have been increasingly used for studying molecular and cellular biology. However, a mixed population of droplets with an uneven number or type of encapsulated particles is resulted and used for screening. We developed a fluorescence-activated microfluidic droplet sorter that integrated a simple deflection mechanism. By passing droplets through a narrow interrogation channel, the encapsulated particles were detected individually. The microcontroller conducted the computation to determine the number and type of encapsulated particles in each droplet and made the sorting decision. Our results showed high efficiency and accuracy for sorting and enrichment.
Ph. D.

Epigenetics is subjected to a pressing attention from the scientific community, because of its potential to explain the mechanisms of gene activation or repression. In this thesis I present a discovery-driven project aimed to the investigation of the epigenetic role in human myogenesis (and in particular the differentiation of myoblasts in myotubes). Studying epigenetics still presents significant hurdles, both experimental and computational. Therefore my first task was the establishment of robust protocols for investigating the role of epigenetics players during skeletal muscle differentiation. In particular, I focused on setting up the tools for studying DNA methylation and protein-DNA interactions, through bisulfite sequencing and chromatin immunoprecipitation. In this thesis, together with the description of the protocols that I developed, I report the first results that were obtained on myogenic cells. DNA methylation was investigated with bisulfite treatment of the DNA coupled with next generation sequencing. A novel method for studying the whole methylome was conceived and applied on one myoblast sample using SOLiD 5500xl platform giving reliable results. However, since the cost of methylome sequencing is still very high, instead of producing data for the whole methylome, I decided to focus on selected regions that could be relevant in methylation studies. For this reason I used the SureSelect MethylSeq Target Enrichment kit (Agilent) that effectively captures more than 2,700,000 CpG sites in the human genome. We identified less than 600 differentially methylated sites (DMS) in myoblasts compared to myotubes, however we observed that the activation of muscle specific genes seem to be poorly correlated with DNA methylation changes. Therefore, we argue that DNA methylation does not show a major role in the control of muscle specific genes. Interestingly, further analysis revealed that a high percentage of differentially methylated regions (DMR) localizes near novel non-coding RNA genes. On the one hand, this observation suggests a role for novel regulatory RNAs in the epigenetics of muscle differentiation; on the other hand, DNA methylation might have a role in the regulation of these RNAs. Together with DNA methylation, chromatin compaction is a major epigenetics player. In order to describe the epigenetic landscape of muscle differentiation, I optimized the ChIP-seq approach to define the localization of specific histone modifications on DNA. After setting-up the protocol for ChIP-seq, H3K4me3, H3K27me3 and H3K9ac histone modifications were mapped on myoblast DNA. As I started integrating gene expression and ChIP-seq data, I verified that a great concordance exists between gene expression and ChIP-seq results. In particular, euchromatin-associated histone modifications are found in transcription start sites of active genes, and heterochromatic signature spans promoters and bodies of inactive genes. Further investigation show that genes for non-coding RNAs have an euchromatic signature. This observation, together with the findings of DMRs in novel non-coding RNA genes, endorses the hypothesis of a role for novel regulatory RNAs in myogenic differentiation. In conclusion, the integration of BS-seq, ChIP-seq and RNA-seq data are opening interesting scenarios concerning the involvement of regulatory RNAs, while recent reports are suggesting to extend our investigation even to DNA hydroxymethylation in the epigenetics of muscle differentiation.
Negli ultimi anni l’epigenetica ha raccolto un sempre crescente interesse da parte della comunità scientifica, grazie al suo potenziale di spiegare i meccanismi di attivazione e repressione dell’espressione genica. In questa tesi si presentano i risultati di un progetto di analisi del ruolo dell’epigenetica nella miogenesi umana, mediante approcci genomici. Gli studi di epigenetica presentano tuttora ostacoli significativi, sia dal punto di vista sperimentale che di analisi computazionale del dato prodotto. Il mio primo obiettivo è stato quindi la messa a punto di un protocolli robusti per l’analisi del ruolo dei meccanismi epigenetici durante il differenziamento del muscolo scheletrico, in particolare la metilazione del DNA e le interazioni DNA-proteine (mediante il sequenziamento di DNA trattato con bisulfito e immunoprecipitazione della cromatina). In questa tesi, oltre alla descrizione dei protocolli sviluppati, sono riportati i primi risultati ottenuti applicando i suddetti protocolli alle cellule miogeniche. La metilazione è stata analizzata mediante trattamento con bisulfito del DNA, sequenziato successivamente con tecniche di nuova generazione (NGS). A tal riguardo è stato messo a punto un nuovo metodo per lo studio del metiloma intero, che è stato applicato ad un campione di mioblasti e successivamente sequenziato con la piattaforma SOLiD 5500xl. Questo approccio richiede tuttavia una quantità massiva di sequenze, che ad oggi risultano ancora eccessivamente costose. È stato quindi affiancato allo studio del metiloma il sequenziamento delle regioni più comunemente analizzate in studi di metilazione (ovvero regioni promotoriali ed isole CpG) con un kit di arricchimento di regioni target che cattura selettivamente più di 2.700.000 siti CpG nel genoma umano. Con questo approccio sono stati identificati meno di 600 siti differenzialmente metilati (DMS) nei mioblasti confrontati con i miotubi. Questo studio ha permesso di osservare che l’attivazione di geni muscolari sembra poco correlata con cambiamenti nella metilazione del DNA, permettendo di ipotizzare che la metilazione del DNA non abbia un ruolo centrale nel controllo dell’attivazione dei geni muscolo-specifici. L’analisi di questi dati ha inoltre permesso di rilevare che una significativa frazione di regioni differenzialmente metilate (DMR) localizza in prossimità di geni codificanti non-coding RNA. Da un lato quest’osservazione suggerisce che gli RNA regolatori potrebber avere un ruolo nell’epigenetica nel differenziamento muscolare, e inoltre che la metilazione del DNA potrebbe avere un ruolo nella regolazione di questi RNA. Un altro aspetto importante della regolazione epigenetica, oltre alla metilazione del DNA, è lo stato di condensazione della cromatina. Per vagliarne il contributo nell’ambito del differenziamento muscolare, è stato ottimizzato un approccio di immunoprecipitazione della cromatina seguito dal sequenziamento (ChIP-Seq) per definire la localizzazione nel DNA di specifiche modificazioni istoniche: H3K4me3, H3K27me3 and H3K9ac. I risultati di questi esperimenti di ChIP-Seq sono stati confrontati con quelli di analisi del profilo di espressione (RNA-Seq), permettendo di verificare un ampio margine di sovrapposizione fra il livello di espressione ed i risultati di ChIP-Seq. In particolare le modificazioni istoniche associate all’eucromatina localizzano nei pressi del sito di inizio di trascrizione di geni espressi, mentre i marker di eterocromatina fiancheggiano i promotori dei geni non attivi. Questa osservazione, assieme all’osservazione di DMR in nuovi RNA non codificanti, supporta l’ipotesi di un ruolo per nuovi circuiti regolatori di RNA nel differenziamento miogenic.

Current sequencing technologies allows researchers unprecedented insight into our biology, and how these biological mechanisms can become distorted and lead to disease. These aberrant mechanisms can be brought about by many causes, but some occur as a result of genetic mutations or external factors through the epigenome. Here, we used our microfluidic technology to profile the epigenome and transcriptome to study such aberrant mechanisms in three different diseases and illnesses: breast cancer, chronic inflammation, and mental illness. We profiled the epigenome of breast tissue from healthy women with the BRCA1 mutation to understand how the mutation may facilitate eventual breast cancer. Epigenomic changes in breast cells suggest that cells in the basal compartment may differentiate into a different cell type, and perhaps become the source of breast cancer. Next, we compared the epigenome and genome of murine immune cells under low-grade inflammation and acute inflammation conditions. We found that low-grade inflammation preferentially utilizes different signaling pathways than in acute inflammation, and this may lead to a non-resolving state. Finally, we analyzed the effect of the maternal immune activation on unborn offspring, and how these changes could cause later mental illness. The insights we made into these diseases may lead to future therapies.
Doctor of Philosophy
Despite advances in medical and scientific research, there is still a dearth of information on how diseases affect the expression of our genes, such as breast cancer, chronic inflammation, and influenza. Mutation in the BRCA1 gene is probably the most well-known mutation that can lead to breast cancer. We know the overarching reason that mutation in BRCA1 can lead to cancer, as BRCA1 is responsible for repairing damage in the DNA, so mutations can compound and create cancerous cells. However, we do not know the exact mechanisms by which this actually happens. Another widespread problem is chronic inflammation, which can promote or lead to diseases such as diabetes, cancer, Alzheimer's, Rheumatoid arthritis, and heart disease. In addition, there are many causes of chronic inflammation that many people have experienced at some point in time, including stress, insomnia, being sedentary, poor eating habits, and obesity. Despite this, we still do not fully understand why chronic inflammation differs from normal inflammation, which is a healthy process, or why it does not resolve. There are also other connections that are surprising, and many are not aware of. If a pregnant woman gets the flu during her second trimester, her baby has much higher odds of developing schizophrenia later in its lifetime. Given the prevalence of the flu, there is a very real chance that an expecting mother will be infected during her pregnancy.

Epigenetic modifications, such as DNA methylation and histone modifications, play important roles in gene expression and regulation, and are highly involved in cellular processes such as stem cell pluripotency/differentiation and tumorigenesis. Chromatin immunoprecipitation (ChIP) is the technique of choice for examining in vivo DNA-protein interactions and has been a great tool for studying epigenetic mechanisms. However, conventional ChIP assays require millions of cells for tests and are not practical for examination of samples from lab animals and patients. Automated microfluidic chips offer the advantage to handle small sample sizes and facilitate rapid reaction. They also eliminate cumbersome manual handling. In this report, I will talk about three different projects that utilized microfluidic immunoprecipitation followed by next genereation sequencing technologies to enable low input and high through epigenomics profiling. First, I examined RNA polymerase II transcriptional regulation with microfluidic chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) assays. Second, I probed the temporal dynamics in the DNA methylome during cancer development using a transgenic mouse model with microfluidic methylated DNA immunoprecipitation followed by next generation sequencing (MeDIP-seq) assays. Third, I explored negative enrichment of circulating tumor cells (CTCs) followed by microfluidic ChIP-seq technology for studying temporal dynamic histone modification (H3K4me3) of patient-derived tumor xenograft on an immunodeficient mouse model during the course of cancer metastasis. In the first study, I adapted microfluidic ChIP-seq devices to achieve ultrahigh sensitivity to study Pol2 transcriptional regulation from scarce cell samples. I dramatically increased the assay sensitivity to an unprecedented level (~50 K cells for pol2 ChIP-seq). Importantly, this is three orders of magnitude more sensitive than the prevailing pol2 ChIP-seq assays. I showed that MNase digestion provided better ChIP-seq signal than sonication, and two-steps fixation with MNase digestion provided the best ChIP-seq quality followed by one-step fixation with MNase digestion, and lastly, no fixation with MNase digestion. In the second study, I probed dynamic epigenomic changes during tumorigenesis using mice often require profiling epigenomes using a tiny quantity of tissue samples. Conventional epigenomic tests do not support such analysis due to the large amount of materials required by these assays. In this study, I developed an ultrasensitive microfluidics-based methylated DNA immunoprecipitation followed by next-generation sequencing (MeDIP-seq) technology for profiling methylomes using as little as 0.5 ng DNA (or ~100 cells) with 1.5 h on-chip process for immunoprecipitation. This technology enabled me to examine genome-wide DNA methylation in a C3(1)/SV40 T-antigen transgenic mouse model during different stages of mammary cancer development. Using this data, I identified differentially methylated regions and their associated genes in different periods of cancer development. Interestingly, the results showed that methylomic features are dynamic and change with tumor developmental stage. In the last study, I developed a negative enrichment of CTCs followed by ultrasensitive microfluidic ChIP-seq technology for profiling histone modification (H3K4Me3) of CTCs to resolve the technical challenges associated with CTC isolation and difficulties related with tools for profiling whole genome histone modification on tiny cell samples.
Ph. D.

Background: Histone modifications play an important role in gene regulation. Their genomic locations are of great interest. Usually, the location is measured by ChIP-seq and analyzed with a peak-caller. Replicated ChIP-seq experiments become more and more available. However, their analysis is based on single-experiment peak-calling or on tools like PePr which allows peak-calling of replicates but whose underlying model might not be suitable for the conditions under which the experiments are performed. Results: We propose a new peak-caller called \"Sierra Platinum\" that allows peak-calling of replicated ChIP-seq experiments. Moreover, it provides a variety of quality measures together with integrated visualizations supporting the assessment of the replicates and the resulting peaks, as well as steering the peak-calling process. Conclusion: We show that Sierra Platinum outperforms currently available methods using a newly generated benchmark data set and using real data from the NIH Roadmap Epigenomics Project. It is robust against noisy replicates.

This thesis is divided in three sections; the main project is described in the first part, while additional projects are developed in two appendixes. In the main project we studied YAP, the downstream effector of the Hippo pathway, a transcriptional co-factor that plays a fundamental role in de-differentiation, cell proliferation and transformation. While its upstream regulation has been extensively studied, its role as transcriptional co-factor is still poorly understood. We show that YAP co-adjuvates the transcriptional responses of Myc oncogene to promote cell proliferation and transformation; when both YAP and Myc are overexpressed, YAP is recruited on genomic sites pre-marked by Myc, TEAD and active chromatin and potentiate the expression of cell cycle genes regulated by Myc. In addition, we show that YAP promotes cell de-differentiation by antagonizing in cis the expression of liver-specific genes controlled by HNF4A master regulator, thus providing a mechanism on how YAP can revert the phenotype of a differentiated hepatocyte into a progenitor cell. In the first appendix we explain the mechanism of BRD4 inhibition, a promising strategy for the treatment of Myc-driven tumors. The efficacy of this strategy relies on the control of transcriptional elongation mediated by BRD4 on gene promoters, independently of the downregulation of Myc oncogene. Although the inhibition of BRD4 causes its genome-wide displacement on promoters, the effects on transcription are restricted to a subset of sensitive genes. This specificity relies on the fact that while most genes compensate the drop in elongation caused by BRD4 inhibition with further recruitment of RNA Pol2 on promoters and maintain a proficient mRNA transcription, vulnerable genes are not able to promote these compensatory effects, because RNA Pol2 recruitment on these promoters is already maximized. Our results show how the impairment of elongation genome-wide can affect specific transcriptional programs. In the second appendix we describe a new web application, Chrokit, aimed at analyzing genomic data in a fast and intuitive way. Chrokit handles a set of genomic regions of interest and performs several tasks on them, such as selecting particular subsets, computing overlaps and visualize reads enrichment of specific chromatin features interactively. The application is multiplatform and can be run on dedicated servers to maximize computational power and provide accessibility to multiple users simultaneously.

Rôle des hélicases DDX5 et DDX17 dans la régulation transcriptionnelle et la maturation des ARN du Virus de l'hépatite B. La chronicité du virus de l'hépatite B (VHB) repose sur la persistance de l'ADN circulaire et clos de manière covalente (ADNccc) dans le noyau des hépatocytes infectés. Le génome viral présente une structure chromatinisée sujette à des régulations épigénétiques impactant son activité biologique à différents niveaux. Une meilleure connaissance des facteurs cellulaires orchestrant la régulation transcriptionnelle et post-transcriptionnelle de l'ADNccc est fondamentale dans la compréhension des mécanismes à l'origine de la persistance du VHB. Afin d'identifier les acteurs cellulaires impliqués dans la biologie de l'ADNccc, un ambitieux projet de protéomique de l'ADNccc (ChROP) a été initié par le Dr. Barbara Testoni. Parmi les candidats identifiés, les hélicases à ARN DDX5 et DDX17 ont particulièrement attiré notre attention. DDX5 et DDX17 jouent un rôle crucial dans la régulation de la transcription et le métabolisme des ARN. Nous avons donc évalué leur rôle dans la régulation transcriptionnelle de l'ADNccc et le métabolisme des ARN viraux. Afin d'étudier de manière précise les différents transcrits du VHB, une technique de 5' RACE a été mise au point au laboratoire par le Dr. Bernd Stadelmayer, et a fait l'objet d'une publication. Cette technique a permis l'étude des ARN du VHB dans un contexte de déplétion des hélicases DDX5 et DDX17. Par ailleurs, DDX5/17 appartiennent au complexe insulateur de CCCTC-binding protein (CTCF). Nous avons donc en parallèle étudié le rôle de CTCF dans la biologie de l'ADNccc et le métabolisme des ARN viraux. Dans des cellules HepG2-NTCP et des hépatocytes primaires humains infectés par le VHB, la répression de DDX5/17 entraine un raccourcissement de tous les ARN viraux. Des séquençages de dernière et troisième génération ont permis l'identification de variants d’épissage alternatif ainsi qu’une utilisation différentielle du site de polyadénylation lors de la transcription des transcrits viraux. Des expériences d'immunoprécipitation de l'ARN ont montré que DDX5 et DDX17 s'associent directement aux ARN viraux et recrutent CPSF6 et NUDT21, deux facteurs impliqués dans le choix du site de polyadénylation. Par ailleurs, nous avons identifié des sites de liaison de CTCF sur le génome du VHB et par mutagénèse dirigé, nous avons mis en évidence que la mutation de ces sites impacte le recrutement de CTCF et de DDX5/17 sur l’ADNccc et affecte métabolisme des ARN viraux. L'ensemble de ces données met donc en lumière un rôle essentiel de DDX5 et DDX17 dans la maturation des ARN viraux, en complexe avec la protéine insulatrice CTCF et des facteurs de temrination, à l'interface entre l'ADNccc et les transcripts du VHB
Role of the DEAD-box helicases DDX5 and DDX17 in HBV transcriptional regulation and RNA processingChronicity of hepatitis B virus (HBV) infection hinges on the persistence of covalently-closed-circular DNA (cccDNA) in the nucleus of infected hepatocytes. The viral genome associates with histones and non-histone proteins to build a chromatin structure that is subjected to epigenetic regulation translating into different levels of biological activity. A better understanding of the host factors orchestrating HBV minichromosome transcriptional regulation and RNA processing is fundamental for deciphering the mechanisms at the basis of HBV persistence and reactivation. In order to identify the cellular factors regulating cccDNA biology, an ambitious project of cccDNA proteomics (ChroP) has been initiated by Dr. Barbara Testoni. Among the identified cccDNA-associated proteins, the DEAD-box RNA helicases DDX5 and DDX17 particularly interested us for their driving role in mammalian transcriptional regulation and RNA metabolism. Thus, we investigated their role in cccDNA transcriptional activity regulation and HBV RNA processing. Precise characterization of HBV transcripts was performed with a 5' RACE approach set up and published in our lab by Dr. Bernd Stadelmayer. This technique was applied to study viral transcript in a context of DDX5/17 depletion. Furthermore, DDX5/17 belong to the insulator complex CCCTC-binding protein (CTCF). We therefore investigated the role of CTCF in cccDNA biology and viral RNA metabolism. In HBV infected HepG2-NTCP and Primary Human Hepatocytes, siRNA knockdown of DDX5/17 led to a shortening of all the viral transcripts, together with an increase in viral transcript levels and viral particles accumulation in the cytoplasm, without affecting the global level of cccDNA. Next and third generation sequencing allowed the identification of alternative splicing of pgRNA-derived spliced variants and differential usage of polyadenylation site during HBV RNA transcription. Moreover, RNA immunoprecipitation of DDX5 and DDX17 revealed that both of these proteins are directly associated to the viral transcripts and recruit two factors, CPSF6 and NUDT21, involved in alternative polyadenylation site choice. Moreover, we identified CTCF binding sites on HBV genome and by site directed mutagenesis we showed that mutations in CTCF binding sites affect CTCF and DDX5/17 recruitment to cccDNA and subsequently impact HBV RNA processing. Altogether, our data highlight an essential role of DDX5 and DDX17 in the fine tuning of HBV RNA processing, in complex with the insulator protein CTCF and termination factors at the interface between cccDNA and HBV transcripts

Parmi plus de 20000 espèces de trématodes hermaphrodites, les Schistosomatidae ont un statut particulier car ils sont gonochoriques (i.e. deux sexes séparés). Le gonochorisme chez ces espèces, et leur dimorphisme sexuel, seraient en fait une stratégie d’adaptation à leur habitat : le système veineux des vertébrés à sang chaud, dont l’Homme. Malgré un mode chromosomique de déterminisme du sexe (i.e. hétérogamétie femelle ZW), les individus mâles et femelles demeurent phénotypiquement identiques durant tous les stades larvaires de leur cycle de vie hétéroxène. La différenciation sexuelle n’a lieu qu’après l’infestation de leur hôte définitif. Dans ce travail, nous nous sommes intéressés aux facteurs moléculaires déclenchant cette différenciation chez Schistosoma mansoni. Nous avons établi le profil d’expression sexe-dépendant de gènes conservés de la cascade de détermination/différenciation chez les animaux : les DMRT (Double-sex and Male-abnormal-3 Related Transcription Factors). Nous avons par ailleurs généré un transcriptome comparatif mâle/femelle (RNA-seq) sur 5 stades de développement in vivo, dont 3 stades « schistosomules » inédits. Cela nous a permis d’identifier de potentiels gènes « clés » de la différenciation sexuelle et de souligner l’importance de l’interaction hôte-parasite. Enfin, par la combinaison de cette approche transcriptomique et d’une analyse épigénomique (ChIP-seq), nous avons montré une dynamique de la compensation de dose génique au cours du cycle de vie chez les femelles ainsi que la mise en place d’une stratégie transcriptionnelle particulière chez les mâles, optimisant leur développement dans l’hôte et ainsi, leur succès reproducteur
Parasitic flatworms include more than 20.000 species that are mainly hermaphrodites. Among them, the hundred species of Schistosomatidae are intriguing because they are gonochoric. The acquisition of gonochorism in these species is supposed to provide genetic and functional advantages to adapt to their hosts: warm-blooded animals. Sex of schistosomes is genetically determined at the time of fertilization (i.e. ZW female heterogametic system). However, there is no phenotypic dimorphism through all the larval stages of its complex lifecycle: sexual dimorphism appears only in the definitive host. The molecular mechanisms triggering this late sexual differentiation remain unclear, and this is precisely the topic of our present work. We performed transcriptomic (RNA-Sequencing and quantitative-PCRs) and structural (ChIP-Sequencing) analyses at different stages of Schistosoma mansoni development. Here, we present data suggesting that the sexual differentiation relies on a combination of genetic and epigenetic factors. In a genetic point of view, we show a sex-associated expression of the DMRT genes (Double-sex and Mab-3 Related Transcription Factors) that are known to be involved in sex determination/differentiation through all the animal kingdom. In addition, we propose new potential sex-determining key genes and a pivotal role of host-pathogen interaction at the time of development. In a structural point of view, we highlight a dynamic status of dosage compensation in females and chromatin modifications in males. This intense remodeling reveals a specific transcriptomic strategy which optimizes male development and beyond that, schistosomes reproductive success

Tumors are composed of fast-growing cells that become malignant under selection of biological functions needed for cancer development. In this thesis, I intend to uncover the basic evolutionary principles underlying cancer etiology. The first part constitutes a longitudinal analysis of a single CLL case, which tumor heterogeneity and clonal evolution were revealed by sequencing. The second explores the signatures of positive selection of somatic mutations allowing the identification of driver genes. The last part is an attempt to uncover the essential functions of the cancer cell using signals of purifying selection. Altogether, we have identified a landscape of cancer-related genes that can be used for improving current cancer treatments.
El tumor esta compuesto de células que crecen indiscriminadamente, bajo la lupa de selección natural. En esta tesis hemos intentado reconstruir los principios básicos de la evolución del cáncer, como estos describen la adquisición de mutaciones que inician la malignidad tumoral. El primer trabajo es un anaálisis genómico de un paciente con leucemia. El Segundo explora la heterogeneidad intratumoral para identificar genes drivers del cáncer. Y el último trabajo se enfoca en desenmascarar las señales de selección negativa. Nuestros resultados de estos tres trabajos constituyen una fuente de nuevos genes que pueden ser explorados como dianas terapéuticas del cáncer.

L’altération de l’environnement périnatal peut impacter à long terme l’expression des gènes notamment par le biais de modifications épigénétiques. Une stratégie pour accroitre la thermotolérance des poulets de chair, sensibles à la chaleur en fin d’élevage (J35) est la thermo-manipulation embryonnaire (TM). Lors d’un coup de chaleur à J35, les modifications d’expression de gènes observées chez les poulets TM pourraient être liées à une altération de l’épigénome induite lors de l’embryogenèse et persistante au cours du développement. Cette thèse s’intéresse à deux modifications post-traductionnelles des histones (MPTH) décrites pour être modulées par des variations thermiques : H3K27Me3 et H3K4Me3. Afin d’étudier ces MPTH sans a priori à J35, nous avons mis au point les techniques d’immunoprécipitation de la chromatine suivie de séquençage à haut débit dans deux tissus : l’hypothalamus et le muscle. Nos travaux montrent que le traitement semble impacter principalement l’épigénome de l’hypothalamus, en particulier au niveau de la marque H3K4me3, en modulant des voies liées à la morphogenèse et la réponse hormonale
Perinatal environment changes may alter gene expression throughout life via epigenetic modifications. A strategy to improve thermal tolerance of heat-sensitive chickens is a thermalmanipulation during embryogenesis (TM). During a heat challenge at the end of the rearing period (D35), modifications of gene expression have been reported in thermally-manipulated chickens. These alterations could be linked to epigenetic modifications induced during the TM that persist throughout life. This work focused on two histone post-translational modifications (HPTM): H3K27me3 and H3K4me3. We adjusted two methods of chromatin immunoprecipitation to conduct a whole genome study of these HPTM at D35, in the hypothalamus and skeletal muscle. We demonstrated that the TM has a major impact in the hypothalamus, especially on H3K4me3. These alterations seem to modulate the hypothalamic morphogenesis and its response to hormones, therefore possibly contributing to better adaptive capacities of TM chickens

Cis-elements govern the key step of transcription to regulate gene expression within a cell. Identification of utilized elements within a particular cell line will help further our understanding of individual and cumulative effects of trans-acting factors. These elements can be identified through an assay leveraging the ability of DNaseI to cut DNA that is in an open and accessible state making it hypersensitive to cleavage. Here we develop and explore computational techniques to measure open chromatin from sequencing and microarray data. We are able to identify 94,925 DNaseI hypersensitive sites genome-wide in CD4+ T cells. Interestingly, only 16%-20% of these sites were found in promoters. We also show that these regions are associated with different chromatin modifications. We found that DNaseI data can also be used to identify precise 'footprints' indicating protein-DNA interaction sites. Footprints for specific transcription factors correlate well with ChIP-seq enrichment, reveal distinct conservation patters, and reveal a cell-type specific arrangement of transcriptional regulation. These footprints can be used in addition to or in lieu of ChIP-seq data to better understand genomic regulatory systems.

Dissertation

Characterization of the 5' flanking region of rainbow trout ki-ras gene was begun with the cloning and sequencing of this region by the inverse PCR technique and dideoxynucleotide chain termination method. In total, a nucleotide sequence of 1080 bp upstream from the first coding ATG was sequenced. Although this region showed certain promoter elements, it does not share common features with other mammalian ras promoters, which lack the TATA and contain multiple GC boxes with Spl binding activities. In contrast, this region in trout ras contains typical TATA and CCAAT boxes. This structural difference of the trout ki-ras promoter from that of other mammalian ras genes may suggest that different transcriptional regulation mechanisms of the ras ger.e are used at various levels in evolution. The chromatin structure of the trout ki-ras gene was studied by probing invivo for DNase I hypersensitive sites. To overcome the difficulties of using the traditional indirect end labeling method for a single-copy gene, the technique of ligation-mediated PCR was applied. No hypersensitive sites were observed at or near the codon 12 region of the gene, either in normal (protooncogene) or tumor (oncogene) tissue from the liver. This result suggests that the local chromatin structure of trout ki-ras gene may not be an important factor for codon 12 mutations induced by genotoxins, and that changes of chromatin structure are unlikely to be promoted after tumor formation. Studies by micrococcal nuclease demonstrate that this ras gene, in the region around 12, lacks ordered nucleosome positioning or may be even free of nucleosomes. Such an irregular organization of ras oncogenic chromatin would resemble that of many other "normal", highly active eukaryotic genes. The intrinsic affinity of trout ki-ras gene for aflatoxin B₁ was determined by in vitro alkylation experiments. Exon 1 of the gene was synthesized and labeled at the 5'end of the coding strand by the PCR technique. Taking advantage of the selective cleavage of AFB1-DNA adducts by piperidine under alkali conditions, the frequency of AFB 1 attack to each guanyl site was determined by densitometric scans after the cleaved fragments were electrophoresed on sequencing gels. The results demonstrated that two guanyl sites of codon 12 had differential affinity to AFBl, the more 5' G was relatively inaccessible but the more 3' G was accessible, indicating that the sequence selectivity of AFB I may contribute to the preference of the initial adduction in vivo.
Graduation date: 1993

Eukaryotic genomes have extensive flexibility and plasticity to modify transcription and replication programs, yielding a myriad of differentiated cell types and survival mechanisms to adverse environmental conditions. As these genomic processes require precise localization of DNA-binding factors, their dynamic temporal and spatial distributions provide dramatically different interpretations of a static genome sequence. DNA-binding factors must compete with nucleosomes, the basic subunit of chromatin, for access to the underlying DNA sequence. Even though the spatial preferences of these proteins are partially explained by DNA sequence alone, the complete genome occupancy profile has remained elusive, and we currently have a limited understanding of how DNA-binding protein configurations directly impact transcription and replication function.

Profiling the entire chromatin environment has typically required multiple experiments to capture both DNA-binding factors and nucleosomes. Here, we have extended the traditional micrococcal nuclease (MNase) digestion assay to simultaneously resolve both nucleosomes and smaller DNA-binding footprints in Saccharomyces cerevisiae. Visualization of protected DNA fragments revealed a nucleotide-resolution view of the chromatin architecture at individual genomic loci. We show that different MNase digestion times can capture nucleosomes partially unwrapped or complexed with chromatin remodelers. Stereotypical DNA-binding footprints are evident across all promoters, even at low-transcribed and silent genes. By aggregating the chromatin profiles across transcription-factor--binding sites, we precisely resolve protein footprints, yielding in vivo insights into protein-DNA interactions. Together, our MNase method, in one experiment, provides an unprecedented assessment of the entire chromatin structure genome-wide.

We utilized this approach to interrogate how the replication program is regulated by the chromatin environment surrounding DNA replication initiation sites. Pre-replicative complex (pre-RC) formation commences with recruitment of the origin recognition complex (ORC) to specific locations in the genome, termed replication origins. Although successful pre-RC assembly primes each site for S-phase initiation by loading the Mcm2-7 helicase, replication origins have substantially different activation times and efficiencies. We posited that replication origin function is substantially impacted by the local chromatin environment. Here, we resolved a high-resolution ORC-dependent footprint at 269 replication origins genome-wide. Even though ORC in S. cerevisiae remains bound at replication origins throughout the cell cycle, we detected a subset of inefficient origins that did not yield a footprint until G1, suggesting a more transient ORC interaction prior to pre-RC assembly. Nucleosome movement accommodated the pre-RC-induced expansion of the ORC-dependent footprint in G1, leading to increased activation efficiency. Mcm2-7 loading is preferentially directed to one side of each replication origin, in close proximity to the origin-flanking nucleosome. Our data demonstrates that pre-RC components are assembled into multiple configurations in vivo.

We anticipate that extending chromatin occupancy profiling to many different cell types will reveal further insights into genome regulation.

Dissertation

Ubiquitin C-terminal hydrolase L1 (UCHL1) is a multifunctional protein primarily expressed in neuronal cells and involved in numerous cellular processes. UCHL1 has been linked with neurodegenerative diseases and a wide range of cancers but its specific role remains unknown. Previous UCHL1 knockdown studies have shown that UCHL1 controls the expression of pro- and anti-apoptotic genes as well as genes involved in cell cycle regulation but it is unknown how UCHL1 regulates these genes. We have shown that UCHL1 is cross-linked to DNA in DU145 but not in LNCaP or PC3 prostate cancer cells. Therefore, we hypothesized that UCHL1 regulates the expression of pro- or anti-apoptotic genes as well as the genes involved in the cell cycle through its interaction with DNA. By utilizing ChIP and ChIP-seq analyses it is possible to determine the UCHL1 target sequences on the genomic DNA. It was shown that UCHL1 is only expressed in DU145 but not in LNCaP, PC3 or C4-2 prostate cancer cell lines. Additionally, UCHL1 is expressed and cross-linked to DNA in HEK293T cells. It is believed that UCHL1 is silenced by upstream promoter methylation when it is not expressed. However, treatment with the epigenetic drugs 5-aza-2′-deoxycytidine and trichostatin A (TSA) did not result in induction of UCHL1 expression in LNCaP, PC3 or C4-2 prostate cancer cell lines. UCHL1 is also associated with p53. However, ChIP assay results have shown that UCHL1 and p53 do not bind to genomic DNA of upstream promoter regions CDKN1A and BAX genes. Additionally, through UCHL1 ChIP-seq analyses in DU145 and HEK293T cells, we discovered that UCHL1 co-localizes to the DNA with the shelterin complex shedding light on a new role of UCHL1 that has never been described before.
October 2014

The regulation of gene expression at the right time, place, and degree is crucial for many cellular processes such as proliferation and development. In addition, in order to maintain cellular life, cells must rapidly and appropriately respond to various environmental stimuli. Sequence-specific transcription factors (TFs) can recognize functional regulatory DNA elements in a sequence-specific manner so that they can regulate only a specific group of genes, a process which enables cells to cope with diverse internal and external stimuli. Human has approximately 1,400 sequence-specific TFs whose aberrant expression causes a wide range of detrimental consequences including developmental disorders, diseases, and cancers; therefore, it is pivotal to identify the binding sites of each sequence-specific TF in order to unravel its roles in and mechanisms of gene regulation. Even though some TFs have been intensively studied, the majority of TFs still remain to be studied, particularly the tasks of identifying their genome-wide target genes and deciphering their biological roles in specific cellular contexts. Many questions remain unanswered: how many sites on the human genome a sequence-specific TF can bind; whether all TF-bound sites are functional; how a TF achieves binding specificity onto its targets; how and to what extent a TF is involved in gene regulation. Comprehensive identification of the binding sites of sequence-specific TFs and follow-up molecular studies including gene expression microarrays will provide close answers to these questions. Chromatin Immunoprecipitation coupled with recently developed high-throughput sequencing (ChIP-seq) allows us to perform genome-scale unbiased identification of the binding sites of sequence-specific TFs. Here, to gain insight into gene regulatory functions of TFs as well as their influences on gene expression, we conducted, in diverse cell lines, genome-wide identification of the binding sites of several sequence-specific TFs (CTCF, E2F4, MYC, Pol II) that are involved in a wide range of biological functions, including cell proliferation, development, apoptosis, genome stability, and DNA repair. Analysis of ChIP-seq data provided not only comprehensive binding profiles of those TF across the genome in diverse cell lines, but also revealed tissue-specific binding of CTCF, MYC, and Pol II as well as combinatorial usage among these three factors. Analyses also showed that some CTCF binding sites were inherited from parents to children and regulated in an individual-specific as well as allele-specific manner. Finally, genome-wide target identification of several TFs will broaden our understanding of the gene regulatory roles of these sequence-specific TFs.
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Dissertation presented as the partial requirement for obtaining a Master's degree in Data Science and Advanced Analytics, specialization in Data Science.
This work was supported by: GenomePT project (POCI-01-0145-FEDER-022184), supported by COMPETE 2020 - Operational Programme for Competitiveness and Internationalisation (POCI), Lisboa Por tugal Regional Operational Programme (Lisboa2020), Algarve Portugal Regional Opera tional Programme (CRESC Algarve2020), under the PORTUGAL 2020 Partnership Agree ment, through the European Regional Development Fund (ERDF), and by Fundação para a Ciência e a Tecnologia (FCT).
Thymic-derived Regulatory T cells (tTregs) play a central role in maintaining im mune homeostasis by suppressing pro-inflammatory activity of conventional T cells (tTconvs). Disruption of tTreg development and/or function is at the origin of many pathologies, from allergies and autoimmunity to chronic inflammation and cancer. To understand tTreg development it is necessary to characterise tTreg genes and uncover the regulation of their expression. This dissertation aims to contribute to the characterisation of regulatory CD4 T cells in the human thymus and the regulation of their development by exploring the relationship between differences in transcription factor binding to chormatin and changes in gene ex pression (differential gene expression). To do this, I analysed vast amounts of epigenomic and transcriptomic data produced by Next-Generation Sequencing, respectively, ATAC-seq and RNA-seq, generated from human tTregs and tTconvs using computational biology and data science methodologies. In this dissertation I will discuss 3 steps of this project where Data Science played an important role: The discovery of a linear relationship between transcription factor ac cessibility to chromatin and associated gene expression in tTregs; the systematization and standardization of a gene set enrichment analysis protocol (GSEA) to detect signatures of activated biological pathways in ranked datasets of differential gene expression; and the de velopment of systematised k-means clustering of Transcription Factor Binding Sites (TFBS), with heatmap visualisation, to discover relationships between the TFBS landscape and gene expression profile of tTregs.
GenomePT project (POCI-01-0145-FEDER-022184), supported by COMPETE 2020 - Operational Programme for Competitiveness and Internationalisation (POCI), Lisboa Por tugal Regional Operational Programme (Lisboa2020), Algarve Portugal Regional Opera tional Programme (CRESC Algarve2020), under the PORTUGAL 2020 Partnership Agree ment, through the European Regional Development Fund (ERDF), and by Fundação para a Ciência e a Tecnologia (FCT).

abstract: Photosynthesis is the primary source of energy for most living organisms. Light harvesting complexes (LHC) play a vital role in harvesting sunlight and passing it on to the protein complexes of the electron transfer chain which create the electrochemical potential across the membrane which drives ATP synthesis. phycobilisomes (PBS) are the most important LHCs in cyanobacteria. PBS is a complex of three light harvesting proteins: phycoerythrin (PE), phycocyanin (PC) and allophycocyanin (APC). This work has been done on a newly discovered cyanobacterium called Leptolyngbya Heron Island (L.HI). This study has three important goals: 1) Sequencing, assembly and annotation of the L.HI genome - Since this is a newly discovered cyanobacterium, its genome was not previously elucidated. Illumina sequencing, a type of next generation sequencing (NGS) technology was employed to sequence the genome. Unfortunately, the natural isolate contained other contaminating and potentially symbiotic bacterial populations. A novel bioinformatics strategy for separating DNA from contaminating bacterial populations from that of L.HI was devised which involves a combination of tetranucleotide frequency, %(G+C), BLAST analysis and gene annotation. 2) Structural elucidation of phycoerythrin - Phycoerythrin is the most important protein in the PBS assembly because it is one of the few light harvesting proteins which absorbs green light. The protein was crystallized and its structure solved to a resolution of 2Å. This protein contains two chemically distinct types of chromophores: phycourobilin and phycoerythrobilin. Energy transfer calculations indicate that there is unidirectional flow of energy from phycourobilin to phycoerythrobilin. Energy transfer time constants using Forster energy transfer theory have been found to be consistent with experimental data available in literature. 3) Effect of chromatic acclimation on photosystems - Chromatic acclimation is a phenomenon in which an organism modulates the ratio of PE/PC with change in light conditions. Our investigation in case of L.HI has revealed that the PE is expressed more in green light than PC in red light. This leads to unequal harvesting of light in these two states. Therefore, photosystem II expression is increased in red-light acclimatized cells coupled with an increase in number of PBS.
Dissertation/Thesis
Ph.D. Chemistry 2014