DNA methylation is essential for mammalian development and transcriptional repression of genes and retrotransposons during embryo development and in somatic cells. The patterns of DNA methylation are established by de novo DNA methyltransferases, which are regulated by developmental signalling and require access to chromatin. Besides DNA methyltransferases, other proteins have recently been implicated in DNA methylation, such as the ATP-dependent chromatin remodeler LSH. The absence of LSH in mouse embryos leads to defects in DNA methylation and development. In relation to this, mutations in LSH have been found to cause Immunodeficiency-Centromeric instability-Facial anomalies (ICF) syndrome. This syndrome is characterized by centromeric instability and CpG hypomethylation of centromeric satellite repeats, and is most often caused by mutations in the catalytic domain of the DNA methyltransferase DNMT3B. LSH is essential for developmentally programmed de novo DNA methylation of large chromosomal domains including promoters of protein coding genes and repetitive sequences. Importantly, fibroblasts derived from chromatin remodeling ATPase LSH-null mouse embryos, which lack DNA methylation at transposons and specific gene promoters, are capable of re-establishing normal patterns of DNA methylation and transcriptional silencing of misregulated genes upon re-expression of LSH. The ATP hydrolysis by LSH is essential for its function in gene silencing and de novo DNA methylation. However, the molecular mechanisms of LSH-dependent gene silencing and de novo DNA methylation are yet unclear. Here we use an inducible system that enables controlled expression of LSH in Lsh-null mouse embryonic fibroblasts (MEFs) to follow chromatin dynamics, transcriptional silencing and establishment of de novo DNA methylation. This conditionally reversible Lsh knockout cellular system allowed us to study the order of events occurring immediately after LSH restoration in MEF cell lines in order to elucidate the molecular mechanism of LSH-dependent gene silencing. We have demonstrated that LSH upon its restoration localises to the promoters of LSH-dependent loci leading to a mild decrease in the occupancy of H3, which reinforces the previously shown role of LSH as a chromatin remodeler. Simultaneously, there is removal of acetyl groups from H3 tails when LSH is bound to these target regions, which might be facilitated by the interaction of HDACs with LSH. The removal of H3Ac marks is followed by deposition of H3K9me2 by G9a/GLP histone methylases at the same time point when misregulated genes are silenced. This suggests that LSH creates a suitable substrate for G9a/GLP promoting gene silencing. Surprisingly, transcriptional repression occurs without acquisition of DNA methylation at the promoters of these loci. This order of events implies that LSH plays a role as a chromatin remodeler leading to changes in chromatin structure and modifications that facilitate epigenetic gene silencing without DNA methylation in the initial period when LSH is restored in MEF cell lines. Furthermore, deposition of H3K9me2 by the G9a/GLP complex is critical for silencing of specific genes, but not for repetitive elements such as IAPs. The histone modification H3K27me3 seems to play a transitory role in the silencing of IAP retrotransposons in the absence of G9a/GLP activity. In conclusion, this work has demonstrated that changes in chromatin modifications leading to a transcriptionally repressive chromatin state can be established in somatic cells by the chromatin remodeler LSH without acquisition of DNA methylation. This suggests that the primary role of LSH is to promote changes in chromatin structure and modifications that lead to gene silencing and not DNA methylation, which most likely occurs as a consequence of transcriptional silencing.

Epigenetic alterations including DNA methylation and microRNAs may provide important insights into gene-environment interaction in complex immune diseases such as inflammatory bowel disease (IBD). An integrative genome-wide approach was used to analyse whole blood genetic, DNA methylation and gene expression data in 240 newly diagnosed IBD patients and 190 controls. Using the Illumina 450k array, differences in whole blood DNA methylation were observed in IBD cases versus controls including 439 differentially methylated positions (DMPs) and 5 differentially methylated regions (DMRs). The top DMP (RPS6KA2, discovery Holm adjusted p=1.22×10-16, replication p=1×10-9) and DMRs (VMP1, ITGB2, TXK) were replicated in an independent cohort using pyrosequencing. Paired genetic and epigenetic data allowed the identification of methylation quantitative trait loci (meQTL); two of the five DMRs (VMP1, ITGB2) demonstrated significant association with genetic polymorphisms. Methylation in the VMP1/microRNA-21 region was significantly associated with two single nucleotide polymorphisms (cg18942579 -rs10853015 [meQTL FDR adjusted p=9.4 × 10-5], cg16936953 - rs8078424 [meQTL FDR adjusted p=8.8 × 10-5]), both of which are in linkage disequilibrium with a known IBD susceptibility variant (rs1292053). Separated leukocyte methylation data highlight the cell type of origin of epigenetic signals seen in whole blood. IBD-associated hypermethylation within the TXK gene transcription start-site negatively correlated with gene expression in whole blood and CD8+ T-cells, but not other cell types, highlighting that cell-specificity and gene location-specificity of DNA methylation change is critical when associating methylation and gene expression. These data offer significant translational potential as diagnostic biomarkers. Least absolute shrinkage and selection operator (lasso) modelling identified 30 methylation probes can be used to accurately discriminate IBD cases from controls (Area under receiver operating characteristic curve = 0.898, sensitivity = 90.6%, specificity = 84.7%). MicroRNAs (miRNA) are small non-coding nucleic acids that have the capacity to modulate gene expression. MiRNAs have been increasingly implicated in many of the important IBD pathogenic pathways including autophagy, intestinal epithelial barrier integrity and the Th17 pathway. In common with all epigenetic mechanisms, miRNA expression is dynamic and cell-specific. Small RNA sequencing (RNA-seq) was performed on RNA extracted from CD14+, CD4+ and CD8+ cells isolated from 8 newly diagnosed cases of ileal or ileocolonic CD and 8 age and sex matched controls. There was a median of 2.4 million reads per sample (range 132,800-12.8 million reads per sample). One microRNA was differentially expressed in CD compared with controls (hsa-miR-503-5p log fold change = 0.7, FDR adjusted p = 9.1 × 10-5) in CD4+ lymphocytes, however this finding did not remain significant when alternative normalisation methods were used. The small number of cases used in microRNA analyses raises the possibility of both type I and II error, and limits the ability to draw firm conclusion from this series of experiments. Site-specific differences in DNA methylation in IBD relate to underlying genotype and associate with cell-specific alteration in gene expression. This is the most detailed characterisation of the epigenome carried out in IBD to date. The findings strongly validate this approach in complex disease, are replicable, and provide clear translational opportunities.

Within the past 70 years since the discovery of 5-methylcytosine, we have acquired considerable knowledge about genomic DNA methylation patterns, the dynamics of DNA methylation throughout development, and the enzymatic machinery that establishes and perpetuates genomic methylation patterns. Nonetheless, in the field of epigenetics major questions remain open about the mechanisms of spatiotemporal control that exist to ensure the fidelity of methylation patterns. This thesis aims to decipher the regulatory logic and upstream pathways influencing one of the DNA methyltransferases by leveraging the diverse resources of molecular genetics, biochemistry, and structural biology. The primary subject of my research, DNA methyltransferase 1 (DNMT1), is crucial for maintaining genomic methylation patterns upon DNA replication and cell division. In addition to its C-terminal catalytic domain, mammalian DNMT1 harbors several N-terminal domains of unknown function: a succession of seven glycine-lysine (GK) repeats, resembling histone tails, and two Bromo-Adjacent Homology (BAH) domains that are absent from bacterial DNA methyltransferases. The work I present in this thesis characterizes the role of these hitherto enigmatic domains in regulating DNMT1 activity. In my studies, I found that mutation of the (GK) repeats motif leads to de novo methylation by DNMT1 specifically at paternally imprinted genes. Conventionally, de novo methylation is thought to be undertaken by complete different enzymes, DNMT3A and DNMT3B, whereas DNMT1 is limited to perpetuating the patterns these other methyltransferases had set down. Recombinant DNMT1 had been previously shown to efficiently methylate unmethylated DNA substrate in vitro, but this is the first time its de novo methyltransferase capability has been observed in vivo. Based on these data, I propose a new model in which DNMT1 is the enzyme responsible for laying down de novo methylation patterns at paternally imprinted genes in the male germline, explaining the previously observed non-essential role of other DNA methyltransferases in the establishment of paternal imprints. Furthermore, I demonstrated that acetylation of the (GK) repeats motif inhibits this de novo methyltransferase activity of DNMT1, making this particular motif an essential regulatory platform for controlling the diverse in vivo functions of the enzyme. Though the (GK) repeats motif had previously been proposed to regulate the stability of DNMT1 protein through its interaction with the deubiquitinase USP7, I tested the biological relevance of this interaction and found that USP7 deletion does not alter DNMT1 protein levels. In fact, USP7 appears to play no part in regulating maintenance DNA methylation, as I present evidence that USP7 localization to replication foci is entirely independent of DNMT1. Finally, I demonstrated that the tandem BAH domains of DNMT1 are required for its maintenance methyltransferase activity as they are involved in targeting the enzyme to replication foci during S phase. Based on biochemical data supporting an interaction between DNMT1's BAH1 domain and histones, I propose that this targeting could occur through BAH1's recognition of specific histone modifications, thus providing a potential mechanistic link between maintenance DNA methylation and chromatin markings. This thesis identifies DNMT1 as a novel de novo methyltransferase in vivo and also characterizes the regulatory functions of the enzyme's BAH domains and the (GK) repeats. These results elucidate the multiple regulatory mechanisms within the DNMT1 molecule itself that control its functions in mammalian cells, thereby providing critical insights as to how the DNA methylation landscape takes shape and yielding surprising revelations about the parts that well-studied proteins have to play in this process.

Les génomes des cellules cancéreuses subissent de profonds changements tant au niveau de leur structure, qu'au niveau épigénétique. Les tumeurs de sein présentent en particulier des profils d'anomalies génétiques et épigénétiques complexes et hétérogènes. Alors qu'une meilleure compréhension de la dynamique d'apparition des anomalies permettrait de mieux appréhender la complexité des tumeurs, peu d'informations sont disponibles à ce sujet. En effet la plupart des données, ont été, et sont produites à partir de tumeurs primitives ou de lignées cancéreuses établies et ne renseignent pas sur la séquence d'événements qui accompagnent le passage de l'état normal à cancéreux. De ce fait, nous nous sommes intéressés aux étapes précoces de la cancérogenèse. Nos travaux se basent sur l'utilisation d'un modèle de transformation progressive in vitro de cellules épithéliales mammaires primaires (HMEC). Les cellules, transduites de façon séquentielle à l'aide de constructions rétrovirales portant des shARN et différentes combinaisons d'oncogènes, ont été caractérisées à chaque étape au niveau cellulaire et moléculaire (CFH, MeDIP, Micro-array) afin de répondre aux questions suivantes : (1) Quelle est la séquence d'apparition des modifications épigénétiques et structurales au cours de la transformation tumorale ? (2) Les profils d'anomalies génétiques et épigénétiques sont-ils modulés en fonction de la voie oncogénique initialement activée dans la tumeur ? Contrairement aux données de la littérature, nous avons obtenu des cellules transformées grâce à l'expression de seulement deux éléments génétiques définis et non trois. Nos résultats indiquent que l'inactivation de p53 provoque la mise en place d'un terrain favorable à l'acquisition de nouvelles anomalies génomiques mais induit surtout d'importantes modifications du méthylome. De plus nous avons montré que les profils de remaniements génétiques et épigénétiques dépendent de l'oncogène initialement activé. Pour finir, nos résultats indiquent que la nature de l'oncogène initialement activé et responsable de la transformation, conditionne la dynamique de production et de sélection des anomalies et supportent l'hypothèse que l'hétérogénéité du cancer du sein peut être à l'origine de l'activation de voies oncogéniques distinctes. / The genome of cancer cells undergoes profound changes at genetic and epigenetic level. Breast tumors exhibit in particular complex and heterogeneous genetic and epigenetic profiles. While a better understanding of the dynamics of these changes could allow a better understanding of tumor complexity, little information is available on this subject. In fact, most data have been, and are produced from primary tumors or established cancer cell lines and do not provide information on the sequence of events that accompany the transition from normal to cancerous state. Therefore, we have been interested in the early stages of carcinogenesis. To this aim, we have developed a stepwise transformation model of HMECs (human mammary epithelial cell) by sequential transduction of oncogenes and/or shRNA. Each cellular variant have been characterized at the cellular and molecular level (CGH, MeDIP, and Micro-array) in order to answer the following questions (1) what is the sequence of structural and epigenetic changes during malignant transformation? (2) The patterns of genetic and epigenetic abnormalities are they modulated according to the oncogenic pathway initially activated in the tumor? Contrary to the literature data, we have obtained transformed cells with the expression of only two defined genetic elements. Our results indicate that p53 inactivation promotes the acquisition of genomic alteration but mainly induces significant changes at the DNA methylation level. In addition, we have shown that the remodeling of genetic and epigenetic profiles depends on the oncogene initially activated. Finally, our results suggest that the nature of the oncogene initially activated and responible for the transformation affects the dynamics of production and selection of anomalies, and supports the hypothesis that the heterogeneity of breast cancer may be due to activation of different oncogenic pathways.

A exposição ao estresse induz um aumento dos níveis de óxido nítrico (NO) e glutamato em estruturas do cérebro de ratos, as quais estão relacionadas com o transtorno de depressão maior (DM) em humanos. Ademais, o estresse está diretamente relacionado com o aumento da metilação do DNA, uma alteração epigenética repressiva, no hipocampo de animais. Estudos anteriores demonstraram o efeito tipo antidepressivo dos inibidores da enzima óxido nítrico sintase (NOS) em animais submetidos ao estresse. Porém não se sabe se há uma relação entre o aumento do NO e glutamato induzido pelo estresse e alteração na metilação do DNA em genes relacionado com a patofisiologia da DM. Assim, o objetivo deste estudo foi investigar os efeitos dos inibidores da NOS nas alterações comportamentais e nos mecanismos intracelulares relacionado com a metilação do DNA no cérebro de ratos submetidos ao teste do desamparo aprendido (learned helplessness - LH) e em cultura celular do hipocampo desafiadas com NMDA e dexametasona. Métodos: Estudo 1: Cultura primária de células do hipocampo ou cultura imortalizada HiB5 foram desafiadas/estressadas com NMDA (30µM,1h), L-arginina (500µM,1h) e/ou dexametasona (1µM, 1h ou 24h) e pré-tratadas com inibidor seletivo da nNOS (NPA, 100nM, 30min antes do desafio) ou com inibidor da DNMT (5-Aza, 10 µM, 30 min antes do desafio). A expressão dos genes para as enzimas DNMTs, BDNF, NT4, TrkB e nNOS foram avaliadas por RT-qPCR, a expressão proteica das enzimas DNMT3b e nNOS foram avaliadas por western blotting. Estudo 2: Ratos foram submetidos à choques inescapáveis (0,4 mA; 40 choques) na sessão de pré-teste do LH, após sete dias os animais foram submetidos a sessão de teste (choques escapáveis de 0,4 mA). Os animais foram tratados com inibidores da NOS 7-nitroindazole (7-NI;60mg/kg,i.p), aminoguanidina (AMG; 30mg/kg,i.p) ou veículo por 7 dias e submetidos a sessão de teste 1h, após a última injeção. A metilação global foi analisada por imunoensaio (ELISA) e a expressão dos genes DNMT3b, BDNF, nNOS e iNOS foram avaliadas por RT-qPCR, nas estruturas: cortex, hipocampo ventral e hipocampo dorsal. Resultados: Estudo 1: O pré- tratamento com NPA, atenuou o aumento da expressão do mRNA para a enzima DNMT3b, em cultura primária do hipocampo desafiada com NMDA, dexametasona e Larginina, e também em cultura HiB5 desafiada com dexametasona. Porém, o NPA não inibiu a diminuição da expressão do BDNF (exon 1, exon 4 e exon 9), em cultura primária de células do hipocampo desafiadas com NMDA. O pré tratamento com 5-Aza, não inibiu as alterações induzidas pelo NMDA em cultura primária de hipocampo. Estudo 2: Ratos submetidos ao estresse dos choques inescapáveis na sessão de pré-teste apresentaram aumento no número de falhas em escapar dos choques na sessão de teste (desamparo aprendido), um efeito que foi atenuado pelo tratamento com AMG ou 7-NI. Interessantemente, o efeito comportamental do estresse foi acompanhado por aumento nos níveis da metilação global do DNA e DNMT3b no hipocampo ventral (vHPC), que foi atenuado pelos pré-tratamentos com AMG e 7-NI, porém não houve diferença estatisticamente significante no córtex e no hipocampo dorsal dos ratos. Conclusão: Os dados apresentados demonstraram que tanto o estresse (in vivo) quanto o desafio com glicocorticóides, NMDA e L-arginina (in vitro) são capazes de modular a expressão daenzima DNMT3b e a metilação de DNA no hipocampo. O tratamento com inibidores da NOS reduzem os efeitos do estresse in vivo (comportamental e molecular) e in vitro. Em conjunto, os dados sugerem que a liberação de glutamato e NO durante o estresse pode modular a expressão da enzima DNMT3b, levando ao aumento da metilação do DNA em genes relacionados com a resposta de adaptação ao estresse. Essa é a primeira evidência de que o NO pode modular metilação do DNA induzida por estresse. / Stress exposure increases glutamate and nitric oxide (NO) levels, as well as DNA methylation in the hippocampus. However, it is not yet known if there is a causal relationship between these events. Moreover, both nitric oxide synthase (NOS) inhibitors and DNA methylation inhibitors counteract the behavioral effects of stress. Therefore, our aim was to investigate the effects of NOS inhibitors on stress-induced changes on behaviour, DNA methylation and genes expression in the hippocampus of rats submitted to learned helplessness - LH. Moreover, the effects of direct administration of dexamethasone (glucocorticoid), NMDA and L-arginine was investigated in hippocampal cell cultures. Methods: Study 1: Primary hippocampal cell culture was challenged with NMDA (30µM,1h), L-arginine (500µM,1h) or dexamethasone (1µM,24h) and pretreated with nNOS inhibitor (NPA, 100nM, 30min before the challenge) or with DNMT inhibitor (5-Aza, 10 µM, 30 min before the challenge). DNMTs, BDNF, NT4, TrkB and nNOS gene expression was assessed by RT-qPCR. DNMT3b and nNOS levels were assessed by western blotting. Study 2: Rats were submitted to inescapable footshocks and treated with the NOS inhibitors 7-nitroindazole (7-NI; 60 mg/kg, i.p) or aminoguanidine (AMG; 30 mg/kg, i.p], or vehicle for 7 days and tested 1h after the last injection with escapable footshocks. The number of escape failures during the test, global DNA methylation (ELISA) and DNMT3b, BDNF, nNOS and iNOS mRNA expression (RT-qPCR) was evaluated. Results: NPA pretreatment attenuated DNMT3b mRNA expression in hippocampus primary cell culture challenged with NMDA, dexamethasone or L-arginine. Similarly effects were observed in HiB5 cell challenged with dexamethasone. However, NPA pretreatment did not inhibit the decrease of BDNF (exon 1, exon 4 and exon 9) induced by NMDA. Moreover, pretreatment with 5-Aza did not inhibit the decreased of BDNF induced by NMDA in primary cell culture. Study 2: Stress exposure increased the number of escape failures in the test, which was attenuated by treatment with AMG or 7-NI, an antidepressant-like effect. Interestingly, the increased DNA methylation DNMT3b mRNA expression in the ventral hippocampus (vHPC) of stressed rats were also attenuated by treatment with both AMG and 7-NI. Conclusions: NOS inhibitors attenuated stress-induced depressive-like behavior, DNA methylation and DNMT3b mRNA expression in the vHPC. In vitro, selective nNOS inhibition also blocks corticosterone-, NMDA- and L-arginine-induced DNMT3b mRNA expression in hippocampal cell culture. Altogether, our results suggest that glutamate release, leading to NO production during stress may mediate intracellular mechanisms that regulate DNMT3b expression and DNA methylation. This is the first evidence indicating that NO modulates DNA methylation induced by stress.

Renal cell carcinoma (RCC) is the most deadly of urological malignancies. While metastatic disease affects one third of patients at diagnosis, a further third of patients who undergo extirpative surgery with curative intent subsequently develop metastatic disease. Inconsistency in the clinical course ensures predicting subsequent metastasis is notoriously difficult, despite the routine use of prognostic clinico-pathological parameters in risk stratification. With greater understanding of pathways involved in disease pathogenesis, a number of biomarkers have been proposed to be of prognostic significance; however there are currently no molecular prognostic markers in clinical use. Genetic intra-tumoural heterogeneity (genetic ITH) has been described in clear cell RCC (ccRCC) and may limit the clinical translation of biomarkers. There has been no assessment of ITH at other molecular levels. The aim of this work was to define and compare proteomic, transcriptomic and DNA methylation ITH in ccRCC, and identify potential prognostic biomarkers. Using reverse phase protein arrays to study protein expression in multiple spatially separate regions of primary and metastatic ccRCC, proteomic ITH was demonstrated for the first time. Interestingly there was no significant difference in proteomic ITH in metastatic ccRCC tumour deposits compared to primary tumours. However, on analysis of differential protein expression between primary and metastatic ccRCC tissue using a tissue microarray and automated analysis of immunofluorescence, there was significantly greater expression of Ki67, p53, VEGFR1, SLUG and SNAIL in the metastases compared to the primary tumours. Subsequent profiling of gene expression and DNA methylation in multiple areas of the same primary tumours confirmed transcriptomic and methylomic ITH. On comparison of this multimolecular ITH, significantly greater proteomic ITH was seen compared to gene expression and DNA promoter methylation heterogeneity. Recent evidence suggests DNA methylation may be prognostically important in RCC and given the lower methylomic ITH in ccRCC, the identification of prognostic DNA methylation changes in ccRCC were pursued using the Infinium HumanMethylation450K Beadchip. Following development of an analysis pipeline, identification and validation of prognostic differentially methylated regions (DMR) was performed on an experimental cohort and published dataset respectively. Five DMRs, which were associated with disease recurrence in ccRCC, were identified. NEFM gene promoter methylation was the only DMR associated with cancer specific survival, independent of TNM stage and nuclear grade on multivariate analysis, which was confirmed on a third independent published dataset. This thesis therefore demonstrates multi-molecular ITH in ccRCC for the first time. Despite this, NEFM promoter methylation may be a useful independent prognostic marker of cancer specific survival.

Maternal age is a significant risk factor for adverse pregnancy outcomes, and is strongly associated with an increased risk of aneuploidy of the conceptus, as well as a significantly higher frequency of serious pregnancy complications known as the "Great Obstetrical Syndromes", including miscarriage, pre-eclampsia and fetal growth restriction. In the last 40 years average maternal age has increased considerably in many wealthy countries, and in the UK the number of babies born to women aged 35 and over is set to surpass those born to women under 25. The high incidence of aneuploidy in older mothers can be attributed to abnormalities in the oocyte and embryo, however the "Great Obstetrical Syndromes" do not appear to be related to the oocyte and may instead be linked to abnormal development of the placenta. In this thesis, I show that advanced maternal age in the mouse is associated with a drastically increased variability of developmental progression in utero, including developmental delays and growth restriction, severe embryonic abnormalities and higher resorption rates. I find that these embryonic defects are always accompanied by gross morphological and transcriptomic abnormalities in the placenta. Notably, I show that the increased risk of these complications can be rescued by transfer of embryos from aged females to a young surrogate mother, thus implicating the aged maternal uterus as the basis for embryonic and placental defects. Transcriptomic analysis of the decidua compartment in placentas from aged pregnancies revealed abnormal expression of genes involved in the decidualization process, which occurs during early pregnancy and facilitates implantation and development of the conceptus. I show that these defects are already obvious in the peri-implantation window, with endometrial stromal cells from aged females being unable to mount an adequate decidualization response due to a decline in their ability to respond to pregnancy hormones. This blunted decidualization reaction in turn may lead to abnormal development of the placenta. These age-associated decidualization defects are cell-intrinsic and can be recapitulated in vitro. The detected insufficient activation levels and abnormal intracellular distribution of phospho-STAT3, combined with highly variable progesterone receptor expression, may be possible causes of these defects. In addition, I examined the possible effects of ageing on the epigenome as a potential contributor to the decline in endometrial function. My results indicate that ageing of the uterus displays some of the common epigenetic hallmarks of tissue ageing. However, more importantly, decidual cells of aged females exhibit abnormal distributions of the histone modification H3K4me3, and are refractory to the profound DNA methylation remodeling that I find takes place during pregnancy. These age-related changes in the epigenome may underpin, or contribute to, the observed decline in uterine function during pregnancy. Understanding the mechanism underlying these epigenomic and functional changes in the ageing reproductive tract may pave the way for new therapeutic strategies to improve maternal and fetal outcomes of pregnancy in older mothers.

Yuen, Ka Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 160-185). / Abstracts in English and Chinese. / ABSTRACT --- p.I / 摘要 --- p.IV / ACKNOWLEDGEMENTS --- p.VI / LIST OF ABBREVIATIONS --- p.VII / TABLE OF CONTENTS --- p.VIII / LIST OF TABLES --- p.XII / LIST OF FIGURES --- p.XIII / Chapter SECTION I: --- BACKGROUND --- p.1 / Chapter CHAPTER 1: --- Pseudomalignant nature of the placenta --- p.2 / Chapter 1.1 --- Overview --- p.2 / Chapter 1.2 --- "Proliferation, migration and invasion behaviour" --- p.3 / Chapter 1.3 --- Gene expression --- p.4 / Chapter 1.3.1 --- Angiogenic factors --- p.5 / Chapter 1.3.2 --- Growth factors --- p.5 / Chapter 1.3.3 --- Proto-oncogenes --- p.6 / Chapter 1.3.4 --- Tumour suppressor genes --- p.8 / Chapter CHAPTER 2: --- Epigenetics --- p.10 / Chapter 2.1 --- Overview --- p.10 / Chapter 2.2 --- DNA methylation in mammals --- p.11 / Chapter 2.3 --- Regulation of DNA methylation machinery --- p.12 / Chapter 2.4 --- Role of DNA methylation --- p.13 / Chapter 2.5 --- Aberrant DNA methylation --- p.16 / Chapter 2.6 --- DNA methylation in normal cells --- p.17 / Chapter 2.6.1 --- X-chromosome inactivation --- p.17 / Chapter 2.6.2 --- Genomic imprinting --- p.18 / Chapter 2.6.3 --- Cell-type-specific methylation --- p.19 / Chapter 2.6.4 --- Placental-specific methylation --- p.20 / Chapter 2.7 --- Aim of Thesis --- p.21 / Chapter SECTION II: --- MATERIALS AND METHODOLOGY --- p.23 / Chapter CHAPTER 3: --- Materials and methods --- p.24 / Chapter 3.1 --- Preparation of samples --- p.24 / Chapter 3.1.1 --- Collection of placental tissues --- p.24 / Chapter 3.1.2 --- Preparation of blood cells --- p.25 / Chapter 3.1.3 --- Preparation of cell lines --- p.25 / Chapter 3.1.4 --- Treatment of JAR and JEG3 with 5-aza-2'-deoxycytidine (5-aza-CdR) and Trichostatin A (TSA) --- p.26 / Chapter 3.2 --- Nucleic acid extraction --- p.26 / Chapter 3.2.1 --- DNA extraction from tissue samples --- p.26 / Chapter 3.2.2 --- DNA extraction from blood cells --- p.29 / Chapter 3.2.3 --- RNA extraction from cell lines --- p.30 / Chapter 3.3 --- Methylation analysis --- p.31 / Chapter 3.3.1 --- Principles of bisulfite modification --- p.31 / Chapter 3.3.2 --- Bisulfite Conversion --- p.32 / Chapter 3.3.3 --- Primer design for methylation-specific polymerase chain reaction / Chapter 3.3.4 --- Methylation-specific polymerase chain reaction (MSP) --- p.33 / Chapter 3.3.5 --- Primer design for bisulfite sequencing --- p.34 / Chapter 3.3.6 --- Cloning and bisulfite genomic sequencing --- p.35 / Chapter 3.4 --- Quantitative measurements of nucleic acids --- p.39 / Chapter 3.4.1 --- Principles of real-time quantitative PCR --- p.39 / Chapter 3.4.2 --- Real-time quantitative MSP --- p.42 / Chapter 3.4.3 --- Real-time reverse transcriptase (RT)-PCR --- p.42 / Chapter 3.5 --- MALDI-TOF mass spectrometry (MS) --- p.43 / Chapter 3.5.1 --- Principle of homogeneous MassEXTEND assay and MALDI-TOF MS --- p.43 / Chapter 3.5.2 --- Methylation-sensitive restriction enzyme digestion and homogeneous MassEXTEND assay for APC and H19 --- p.46 / Chapter SECTION III: --- A SEARCH FOR HYPERMETHYLATED TUMOUR SUPPRESSOR GENES IN THE HUMAN PLACENTA --- p.48 / Chapter CHAPTER 4: --- Screening on TSGs and non TSGs --- p.49 / Chapter 4.1 --- Introduction --- p.49 / Chapter 4.2 --- Materials and methods --- p.50 / Chapter 4.2.1 --- Sample collection --- p.50 / Chapter 4.2.2 --- Sample processing and DNA extraction --- p.50 / Chapter 4.2.3 --- Experimental Design --- p.51 / Chapter 4.3 --- Results --- p.63 / Chapter 4.3.1 --- Identification of hypermethylated TSGs by methylation-specific PCR screening --- p.63 / Chapter 4.3.2 --- Validation of hypermethylated TSGs by bisulfite sequencing --- p.69 / Chapter 4.4 --- Discussion --- p.77 / Chapter CHAPTER 5: --- Methylation status of TSGs in different tissues --- p.80 / Chapter 5.1 --- Introduction --- p.80 / Chapter 5.2 --- Materials and methods --- p.81 / Chapter 5.2.1 --- Sample collection --- p.81 / Chapter 5.2.2 --- Sample processing and DNA extraction --- p.81 / Chapter 5.2.3 --- Experimental design --- p.81 / Chapter 5.3 --- Results --- p.86 / Chapter 5.3.1 --- Methylation patterns of TSGs in non-placental fetal tissues --- p.86 / Chapter 5.4 --- Discussion --- p.90 / Chapter SECTION IV: --- FUNCTIONAL IMPLICATION OF HYPERMETHYLATED TUMOUR SUPPRESSOR GENES IN THE PLACENTA --- p.94 / Chapter CHAPTER 6: --- Imprinting checking --- p.95 / Chapter 6.1 --- Introduction --- p.95 / Chapter 6.2 --- Materials and methods --- p.96 / Chapter 6.2.1 --- Sample collection --- p.96 / Chapter 6.2.2 --- Sample processing and DNA extraction --- p.97 / Chapter 6.2.3 --- Experimental design --- p.97 / Chapter 6.3 --- Results --- p.100 / Chapter 6.3.1 --- Imprinting checking of H19 by enzyme digestion on placental tissues --- p.100 / Chapter 6.3.2 --- Imprinting checking of　APC by enzyme digestion on placental tissues --- p.101 / Chapter CHAPTER 7: --- CORRELATION OF HYPERMETHYLATION AND GENE EXPRESSION --- p.107 / Chapter 7.1 --- Introduction --- p.107 / Chapter 7.2 --- Materials and methods --- p.108 / Chapter 7.2.1 --- Sample preparation and processing --- p.108 / Chapter 7.2.2 --- DNA and RNA extraction from cell lines --- p.108 / Chapter 7.2.3 --- Experimental design --- p.108 / Chapter 7.3 --- Results --- p.111 / Chapter 7.3.1 --- Methylation status of APC in choriocarcinoma cell lines --- p.111 / Chapter 7.3.2 --- Demethylation of APC in choriocarcinoma cell lines --- p.114 / Chapter 7.4 --- Discussion --- p.115 / Chapter SECTION V: --- CONSERVATION OF METHYLATION IN PLACENTA ACROSS DIFFERENT SPECIES --- p.118 / Chapter CHAPTER 8: --- Methylation analysis of hypermethylated TSG homologues in the placentas of the mouse and rhesus monkey --- p.119 / Chapter 8.1 --- Introduction --- p.119 / Chapter 8.2 --- Materials and methods --- p.120 / Chapter 8.2.1 --- Sample collection --- p.120 / Chapter 8.2.2 --- Sample processing and DNA extraction --- p.120 / Chapter 8.2.3 --- Experimental design --- p.120 / Chapter 8.3 --- Results --- p.124 / Chapter 8.3.1 --- Methylation status of TSGs in rhesus monkey and murine placental tissues --- p.124 / Chapter 8.4 --- Discussion --- p.136 / Chapter SECTION VI: --- CONCLUDING REMARKS --- p.138 / Chapter CHAPTER 9: --- Conclusion and future perspectives --- p.139 / Chapter 9.1 --- Pseudomalignant nature of placenta at the epigenetic level --- p.139 / Chapter 9.2 --- Functional implication of TSG hypermethylation --- p.140 / Chapter 9.3 --- Significance of hypermethylated TSGs in the placental evolution --- p.142 / Chapter 9.4 --- Clinical implication of TSG hypermethylation --- p.143 / Chapter 9.5 --- Future perspectives --- p.145 / APPENDIX I COMPLETE BISULFITE SEQUENCING DATA FOR HYPERMETHYLATED TSGS --- p.147 / APPENDIX II BISULFITE SEQUENCING DATA FOR PTEN --- p.156 / APPENDIX III BISULFITE SEQUENCING DATA OF LOCI NOT SHOWING HYPERMETHYLATION --- p.158 / REFERENCES --- p.160

高通量大規模並行測序技術，又称為二代測序（NGS），極大的加速了生物和醫學研究的進程。隨著測序通量和複雜度的不斷提高，在分析大量的資料以挖掘其中的資訊的過程中，生物訊息學變得越發重要。在我的博士研究生期間（及本論文中），我主要從事於以下兩個領域的生物訊息學演算法的開發：DNA甲基化資料分析和基因間區長鏈非編碼蛋白RNA（lincRNA）的鑒定。目前二代測序技術在這兩個領域的研究中有著廣泛的應用，同時急需有效的資料處理方法來分析對應的資料。 / DNA甲基化是一種重要的表觀遺傳修飾，主要用來調控基因的表達。目前，全基因組重亞硫酸鹽測序（BS-seq）是最準確的研究DNA甲基化的實驗方法之一，該技術的一大特點就是可以精確到單個堿基的解析度。為了分析BS-seq產生的大量測序數據，我參與開發並深度優化了Methy-Pipe軟體。Methy-Pipe集成了測序序列比對和甲基化程度分析，是一個一體化的DNA甲基化資料分析工具。另外，在Methy-Pipe的基礎上，我又開發了一個新的用於檢測DNA甲基化差異區域（DMR）的演算法，可以用於大範圍的尋找DNA甲基化標記。Methy-Pipe在我們實驗室的DNA甲基化研究項目中得到廣泛的應用，其中包括基於血漿的無創產前診斷（NIPD）和癌症的檢測。 / 基因間區長鏈非編碼蛋白RNA（lincRNA）是一種重要的調節子，其在很多生物學過程中發揮作用，例如轉錄後調控，RNA的剪接，細胞老化等。lincRNA的表達具有很強的組織特異性，因此很大一部分lincRNA還沒有被發現。最近，全轉錄組測序技術（RNA-seq）結合基因從頭組裝，為新的lincRNA鑒定以及構建完整的轉錄組列表提供了最有力的方法。然而，有效並準確的從大量的RNA-seq測序數據中鑒定出真實的新的lincRNA仍然具有很大的挑戰性。為此，我開發了兩個生物訊息學工具：1）iSeeRNA，用於區分lincRNA和編碼蛋白RNA（mRNA）；2）sebnif，用於深層次資料篩選以得到高品質的lincRNA列表。這兩個工具已經在多個生物學系統中使用並表現出很好的效果。 / 總的來說，我開發了一些生物訊息學方法，這些方法可以幫助研究人員更好的利用二代測序技術來挖掘大量的測序數據背後的生物學本質，尤其是DNA甲基化和轉錄組的研究。 / High-throughput massive parallel sequencing technologies, or Next-Generation Sequencing (NGS) technologies, have greatly accelerated biological and medical research. With the ever-growing throughput and complexity of the NGS technologies, bioinformatics methods and tools are urgently needed for analyzing the large amount of data and discovering the meaningful information behind. In this thesis, I mainly worked on developing bioinformatics algorithms for two research fields: DNA methylation data analysis and large intergenic noncoding RNA discovery, where the NGS technologies are in-depth employed and novel bioinformatics algorithms are highly needed. / DNA methylation is one of the important epigenetic modifications to control the transcriptional regulations of the genes. Whole genome bisulfite sequencing (BS-seq) is one of the most precise methodologies for DNA methylation study which allows us to perform whole methylome research at single-base resolution. To analyze the large amount of data generated by BS-seq experiments, I have co-developed and optimized Methy-Pipe, an integrated bioinformatics pipeline which can perform both sequencing read alignment and methylation state decoding. Furthermore, I’ve developed a novel algorithm for Differentially Methylated Regions (DMR) mining, which can be used for large scale methylation marker discovery. Methy-Pipehas been routinely used in our laboratory for methylomic studies, including non-invasive prenatal diagnosis and early cancer detections in human plasma. / Large intergenic noncoding RNAs, or lincRNAs, is avery important novel family of gene regulators in many biological processes, such as post-transcriptional regulation, splicing and aging. Due to high tissue-specific expression pattern of the lincRNAs, a large proportion is still undiscovered. The development of Whole Transcriptome Shotgun Sequencing, also known as RNA-seq, combined with de novo or ab initio assembly, promises quantity discovery of novel lincRNAs hence building the complete transcriptome catalog. However, to efficiently and accurately identify the novel lincRNAs from the large transcriptome data stillremains a bioinformatics challenge.To fill this gap, I have developed two bioinformatics tools: I) iSeeRNAfor distinguishing lincRNAs from mRNAs and II) sebnif for comprehensive filtering towards high quality lincRNA screening which has been used in various biological systems and showed satisfactory performance. / In summary, I have developed several bioinformatics algorithms which help the researchers to take advantage of the strength of the NGS technologies(methylome and transcriptome studies) and explore the biological nature behind the large amount of data. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Sun, Kun. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 118-126). / Abstracts also in Chinese.

L'épigénétique est un composant essentiel du fonctionnement des génomes eucaryotes. Les divers phénomènes épigénétiques modifient l’état chromatinien et participent à la plasticité du génome, mais aussi au maintien de son identité fonctionnelle à travers les générations cellulaires. Parmi ces processus, la méthylation de l’ADN joue un rôle fondamental dans la régulation de l’expression des gènes.Chez les mammifères, la méthylation de l'ADN est associée à la répression transcriptionnelle, et elle remplit au moins trois fonctions essentielles. Premièrement, elle permet de réprimer les séquences répétées afin de préserver l’intégrité du génome. Deuxièmement, la méthylation contrôle l’expression des gènes soumis à l’empreinte parentale, qui sont des régulateurs cruciaux du développement et de la vie adulte. Enfin, la méthylation permet de réprimer certains gènes tissu-spécifiques dans les organes où ils doivent être silencieux. En plus de ces rôles physiologiques, la méthylation est liée au cancer. En effet, des patrons de méthylation anormaux sont fréquemment observés dans les cellules tumorales, et ces anomalies participent à la transformation cellulaire par plusieurs mécanismes.La méthylation exerce ces effets par l'intermédiaire de protéines dédiées, qui reconnaissent spécifiquement l'ADN méthylé et contrôlent la transcription en modulant la chromatine. Trois familles de protéines liant l'ADN méthylé sont connues chez les mammifères, et elles totalisent entre elles neuf membres. De nombreux arguments suggèrent que cette liste est encore incomplète, et que des protéines humaines liant l'ADN méthylé restent à découvrir. Dans cette optique, nous avons opté pour deux types d’approches distinctes, une approche basée sur la littérature et une approche génétique. L’étude des protéines candidates ne nous a pas permis d’identifier de nouvelles protéines liant l’ADN méthylé et l’approche génétique par phage display a révélé deux protéines intéressantes, CHD3 et HMGB1 qui doivent désormais être validées par des approches in vivo et in vitro.Par ailleurs, nous avons entrepris l’étude de la régulation des éléments répétés par la protéine Zbtb4 chez la souris. Les expériences préliminaires indiquent une possible régulation des satellites mineurs par Zbtb4. Le rôle de cette régulation sera, par la suite, approfondi. / Epigenetic phenomena are key contributors to the function of eukaryotic genomes. These processes act on chromatin, and they are used to render the genome dynamic, but also stable throughout successive rounds of cell division. Among epigenetic processes, DNA methylation is especially well known for its role in the regulation of gene expression.In mammals, DNA methylation is strongly correlated with transcriptional repression, and fulfills at least three essential roles. First, it maintains repeated sequences transcriptionally silenced, thus ensuring the stability of the genome. Second, it is responsible for the proper regulation of parentally imprinted genes, which are crucial regulators of embryonic development and adult life. Finally, DNA methylation ensures that some tissue-specific genes are kept inactive in the organs in which they should be repressed. Besides these roles in the physiology of normal cells, DNA methylation has strong links to cancer. Indeed the pattern of DNA methylation on the genome is frequently altered in cancer cells, and these anomalies contribute to transformation by several mechanisms.DNA methylation does not control transcription directly, but instead acts via a set of dedicated proteins that specifically recognize methylated DNA and repress transcription by acting at the chromatin level. At present, three families of such proteins, totalling 9 members altogether, are known in humans. However, several lines of evidence suggest that the list is not exhaustive, and that other human proteins that bind methylated DNA remain to be found. This was the goal of the current project.To this end, we opted for two distinct types approaches, an approach based on literature and a genetic approach. The study of candidate proteins does not allow us to identify new methylated DNA binding proteins and the genetic approach by phage display revealed two proteins of interest, HMGB1 and CHD3 that must now be validated by in vivo and in vitro approaches.Furthermore, we studied the regulation of DNA repeats by Zbtb4 in mice. Preliminary results show a regulation of minor satellites by Zbtb4. The role of this regulation will be analyse further in the future.