ARAUJO, F. M. Ocorrência Familial e Associação de Polimorfismos dos Genes H19 e IGF2 com as Síndromes Hipertensivas Gestacionais. 2007. 118f. Disertação (Mestrado) Faculdade de Medicina, Universidade de São Paulo, Ribeirão Preto, 2007. As síndromes hipertensivas gestacionais [Pré-eclâmpsia/eclâmpsia (PE/E), hipertensão gestacional (HG) e hipertensão arterial crônica (HAC)] estão entre as maiores causas de morte materna e fetal. A PE é a mais prevalente dessas síndromes e o papel dos fatores genéticos na sua etiologia é bem aceito, embora o padrão de herança seja ainda assunto para debate. Os genes H19 e IGF2 sofrem imprinting (marcação) genômico e estão envolvidos na formação placentária e no desenvolvimento fetal. O objetivo do presente trabalho foi a pesquisa de ocorrência familial e da associação com os polimorfismos H19/RsaI e do IGF2/ApaI das síndromes hipertensivas gestacionais e do peso do recém-nascido. Todas as pacientes do estudo foram atendidas no Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo e o projeto foi aprovado pelo Comitê de Ética deste hospital e pela Comissão Nacional de Ética em Pesquisa. Para a condução do estudo familial foram selecionadas 226 mulheres (75 apresentavam PE, 49 com HG e 102 do grupo controle). Os dados foram analisados pelos Testes Exato de Fisher e do Qui-quadrado, resultando em uma maior freqüência estatisticamente significativa (p <0,05) de parentes de primeiro-grau com PE/E entre o grupo de PE/E comparado aos outros grupos. Não foi observada influência da cor da pele na distribuição entre os grupos de pacientes. Para a pesquisa de polimorfismos de comprimento de fragmento de restrição H19/RsaI (alelos A e B) e IGF2/ApaI (alelos A e G) através da reação em cadeia da polimerase , foi extraído DNA de sangue periférico de 236 pacientes (55 apresentavam PE, 40 com HG, 34 com HAC e 107 do grupo controle). Os resultados, analisados através dos Testes do Qui-quadrado e G, não mostraram associação estatisticamente significativa entre os polimorfismos e as síndromes hipertensivas gestacionais ou HAC. Houve uma maior freqüência do alelo G na população estudada. Foi observado que em torno de 80% das pacientes dos quatro grupos estudados apresentou pelo menos uma cópia do alelo B e uma do alelo G, concomitantemente. A associação do peso do recém-nascido com os polimorfismos foi analisada utilizando-se os Testes Kolmogorov-Smirnov (a P<0,05) e os Não-paramétricos de Kruskal-Wallis (a P<0,05), não tendo sido evidenciadas diferenças estatisticamente significativas. No grupo da PE houve uma diminuição estatisticamente significativa do peso dos recém-nascidos quando não havia correção para a idade gestacional. Embora não tenha sido evidenciada correlação entre os polimorfismos e os fenótipos estudados, trabalhos futuros com um número amostral maior serão importantes para auxiliar no entendimento do envolvimento de fatores epigenéticos nas síndromes hipertensivas gestacionais e fornecer indícios para a prevenção, o tratamento e o aconselhamento genético. / ARAUJO, F. M. Familial Occurrence and H19 and IGF2 Polymorphism Association with Gestational Hypertensive Disorders. 2007. 118p. Dissertation (Master\'s degree) - University of Medicine, University of São Paulo, Ribeirão Preto, 2007. Gestational hypertensive disorders [preeclampsia/eclampsia (PE/E), gestational hypertension (GH) and chronic hypertension (CH)] are among the largest causes of maternal and fetal death. PE is the more prevalent of those syndromes and the role of the genetic factors in its etiology is well accepted, although the pattern of inheritance is still subject for debate. The imprinted genes H19 and IGF2 are involved in the placental formation and in the fetal development. The objective of the present study was to verify the familial occurrence of these disorders and the H19/RsaI and IGF2/ApaI polymorphism association with gestational hypertensive disorders and the weight of the newborn. All patients of the study were referred to the Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto, University of São Paulo, and the project was approved by the Hospital Ethic Committee and the National Commission of Ethics in Research. For the familial study, 226 women were selected (75 presented PE/E, 49 with GH and 102 from the control group). The data were analyzed by Exact of Fisher and Qui-square tests, and the frequency of families with at least one female first-degree relative (mothers and/or sisters) with PE/E was higher among the PE/E group compared to the other groups, and it was statistically significant (P<0.05). There was no statistically significant influence of the \"skin color\". Blood samples of 236 pregnant women (55 with PE/E, 40 with GH, 34 with CH and 107 from the control group) were obtained for DNA extraction, and PCR. Genotyping was carried out by enzymatic digestion with ApaI (IGF2) and RsaI (H19). The statistical analyses were performed by Qui-square and G tests. The genotypes were not significantly associated with the different groups. A higher frequency of the G allele (IGF2) was observed. Around 80% of the patients presented at least one copy of the allele B (H19) and G (IGF2), concomitantly. The association of the weight of the newborn with the polymorphisms was analyzed using the Kolmogorov-Smirnov (P <0.05) and the No-parametric Test of Kruskal-Wallis (P <0.05) tests, and statistically significant differences were not evidenced. In the group of the PE/E there was a statistically significant decrease of the weight of the newborn when the correction for the gestational age was not carried out. Although correlation has not been evidenced between the polymorphisms and the phenotypes, future studies with a higher number of patients and other imprinted genes will be important to elucidate the involvement of epigenetic factors for the prevention, treatment and genetic counseling of the gestational hypertensive disorders

Le couple télomère/télomérase apparaît comme une cible prometteuse pour de potentiels agents anticancéreux qui seraient actifs sur un large éventail de tumeurs. Le laboratoire d’accueil a montré dans un modèle de leucémie aiguë promyélocytaire (LAP), qu'un agent utilisé en clinique, l'acide rétinoïque (ATRA), exerce une activité anti-tumorale en réprimant la transcription de la sous-unité catalytique hTERT indépendamment de la différenciation. Ce modèle (NB4) avec ses variants cellulaires résistant (NB4-LR1SFD) ou non à la répression de hTERT (NB4-LR1) par l’ATRA constitue un outil de choix pour l’identification de facteurs régulateurs de hTERT et la recherche des bases moléculaires de sa réactivation.Une approche transcriptomique a été utilisée afin d’identifier de nouveaux gènes et/ou réseaux de signalisation induits par l’ATRA et régulateurs de hTERT. L’analyse bioinformatique nous a permis de construire des profils d’expression différentielle entre les 2 lignées et des réseaux d’interaction. Parmi les candidats, H19, un ARN long de 2.5Kb, polyadénylé et non codant. H19 est classé parmi les gènes supresseurs de tumeurs : en son absence il y a développement de cancer (cas de la tumeur de Wilms, rhabdomyosarcome embryonnaire, Syndrome Beekwith-Wiedman) ; sa réintroduction par transfection conduit à une perte de tumoriginicité. Cependant H19 est reconnu de plus en plus comme un oncogène vu que son expression est élevée dans plusieurs types de cancers solides. Par contre peu d’études s’intéressent au rôle de H19 dans les leucémies, d’où notre intérêt pour l’étudier dans le modèle LAP que nous avons développé.Nous avons mis au point la mesure d’expression de H19 par RT-PCR quantitative, validé les données obtenues dans l’analyse transcriptomique et montré que le traitement ATRA induit l’expression de H19 dans les cellules NB4-LR1 alors que cette expression est plutôt diminuée dans les cellules NB4-LR1SFD. L’induction observée dans les cellules NB4-LR1 existe indépendamment de la différenciation. Par contre, cette induction peut être observée associée à la différenciation ou à l’apoptose dans la lignée cellulaire NB4-LR1SFD parallèlement à une diminution importante de l’expression de hTERT. Ce résultat important montre que la lignée NB4-LR1SFD ne présente pas de défaut général d’induction de H19. Ces données suggèrent l’existence d’une corrélation inverse entre le niveau d’expression de hTERT et celui de H19 dans ce modèle cellulaire. De façon importante, l’analyse des banques de données issues de patients LAP publiquement accessibles retrouve cette corrélation inverse.Une diminution d’activité télomérasique est observée dans des extraits cellulaires incubés en présence de l’ARN H19 transcrit in vitro. Cette diminution d’activité est observée aussi après surexpression de H19 in cellulo. Les expériences de RIP (RNA immunoprecipitation) ont montré une diminution de la quantité de hTR lié à hTERT suite à une augmentation d’expression de H19 après traitement ATRA in vitro ou après surexpression de H19 in cellulo. Une hypothèse serait que H19 induirait un déplacement de hTR du complexe hTR-hTERT. Cependant, les expériences de « pull-down » n’ont pas réussi à confirmer l’hypothèse d’une interaction possible entre l’ARN H19 et la protéine TERT.Mon travail de thèse identifie pour la première fois H19, un ARN long non codant, comme facteur régulateur potentiel de hTERT pouvant modifier son activité. Ce travail proposerait non seulement un mécanisme nouveau de régulation de l’activité télomérase mais aussi une fonction nouvelle pour H19 dans ce type de cancer. / The telomere / telomerase pair appears to be a promising target for potential anticancer agents that would be active on a wide range of tumors. The host laboratory has shown in a model of acute promyelocytic leukemia (APL), that a clinically used agent, retinoic acid (ATRA), exerts anti-tumor activity by repressing the transcription of the catalytic subunit hTERT regardless of differentiation. This model (NB4) with its resistant cell variants (NB4-LR1SFD) or not to the repression of hTERT (NB4-LR1) by ATRA is a tool of choice for the identification of hTERT regulatory factors and the search for molecular bases of its reactivation.A "microarray" approach has been used to identify new ATRA-mediated genes and / or signaling networks and potential hTERT regulators. Bioinformatic analysis allowed us to build differential expression profiles between the 2 lineages and interaction networks. Among the candidates, H19, a 2.5Kb long, polyadenylated and non-coding RNA. H19 is classified as a tumor suppressor gene: in its absence there is cancer development (case of Wilms tumor, embryonic rhabdomyosarcoma, Beckwith-Wiedman syndrome); its reintroduction by transfection leads to a loss of tumorigenicity. However H19 is increasingly recognized as an oncogene as its expression is elevated in several types of solid cancers. However, few studies are interested in the role of H19 in leukemias, hence our interest in studying it in the APL model that we have developed.We developed the H19 expression measurement by quantitative RT-PCR, validated the data obtained in the "microarray" analysis and showed that the ATRA treatment induces the expression of H19 in NB4-LR1 cells whereas this expression is rather diminished in NB4-LR1SFD cells. The induction observed in NB4-LR1 cells exists independently of differentiation. On the other hand, this induction can be observed associated with the differentiation or apoptosis in the NB4-LR1SFD cell line in parallel with a significant decrease in the expression of hTERT. This important result shows that the NB4-LR1SFD line does not have a general H19 induction defect. These data suggest the existence of an inverse correlation between the expression level of hTERT and that of H19 in this cellular model. Importantly, the analysis of publicly accessible APL patients’ databases finds this inverse correlation as well.We observed a decrease in telomerase activity in cellular extracts incubated in the presence of in vitro transcribed H19 RNA. This decrease in activity was also observed after overexpression of H19 in cellulo. The RIP (RNA immunoprecipitation) experiments showed a decrease in hTR amount bound to hTERT following an increase in H19 expression after ATRA treatment in vitro or after overexpression of H19 in cellulo. We hypothesize that H19 induces a displacement of hTR from the hTR-hTERT complex. However, the "pull-down" experiments failed to confirm the hypothesis of a possible interaction between H19 RNA and TERT protein.My thesis work identifies, for the first time, the long non-coding RNA H19, as a potential regulator of hTERT that can modify its activity. This work would propose not only a new mechanism of regulation of telomerase activity but also a new function for H19 in this type of cancer.

Les marqueurs épigénétiques, en particulier la méthylation de l’ADN des gènes soumis à empreinte parentale, sont sensibles aux changements environnementaux. Les techniques de l’aide médicalisée à la procréation (AMP) nécessitant la manipulation des gamètes et des embryons in vitro et dans la plupart des cas la stimulation hormonale de l’ovulation des patientes, peuvent interférer avec la reprogrammation et/ou le maintien de la méthylation des gènes soumis à empreinte. Afin d’évaluer ce risque nous avons analysé le profil de méthylation de KvDMR1, qui régule l’expression de KCNQ1OT1, dans des ovocytes humains mûris in vivo ou in vitro, provenant de patientes stimulées ou non. Nos résultats montrent que la mise en place de la méthylation au niveau de KvDMR1 se poursuit au cours de la maturation de l’ovocyte après reprise de la méiose, in vivo et in vitro et que la superovulation des patientes en AMP génère des ovocytes épigénétiquement immatures. Par ailleurs, l’étude de la méthylation de KvDMR1 et de H19 DMR (qui régule l’expression d’Igf2 et H19) dans des embryons issus d’ICSI, évolutifs ou présentant un défaut de développement, n’établit pas de lien entre les dérégulations de l’empreinte et l’arrêt du développement embryonnaire au stade blastocyste. / Epigenetic modifications, particularly DNA methylation of imprinted genes are sensible to environment. Techniques of assisted reproduction require in vitro manipulation of gamete and embryos and currently superovulation of patients. These technologies may interfere with eprogramming and maintenance of methylation at imprinted genes. To evaluate such a risk, we have determined the methylation profile of KvDMR1, the region that regulates KCNQ1OT1 imprinted gene, in human oocytes retrieved from stimulated or unstimulated cycles, at different phases of their maturation in vivo or in vitro. Our results show that the timing of establishment of the methylation profile of KvDMR1 covers the maturation phase of 199 oocyte growth, in vivo and in vitro, and that hyperstimulation likely recruits young follicles epigenetically immature. Analysis of the methylation profile of KvDMR1 and H19DMR (DMR of IGF2/H19) in ICSI embryos suggests that imprinting disorders are not responsible of embryo developmental failure prior the blastocyst stage

L'expression du gène Igf2, qui est soumis à l'empreinte génomique parentale chez les mammifères, est hautement régulée au cours du développement embryonnaire et de la période périnatale grâce à divers mécanismes transcriptionnels et post-transcriptionnels. Ces mécanismes mettent à contribution de longs ARN non codants produits au sein même du locus, dont le plus connu est l'ARN H19. En utilisant une approche de complémentation génétique par un transgène H19 dans myoblastes H19 KO de souris, nous démontrons l'existence de plusieurs nouveaux promoteurs d'Igf2. L'un de ces promoteurs, qui est conservé chez l'homme, peut être activé par un ARN ectopique antisens d'H19 (lncARN 91H) en dépit d'une méthylation complète de la région de contrôle empreinte située en cis sur le même allèle. Nous montrons également que les lncARN 91H présentent une certaine spécificité tissulaire et que leur transcription peut être initiée à partir des séquences conservées CS4, CS5 et CS9 situées en aval du gène H19. Quant à l'ARN H19, qui est l'ARN non codant majeur du locus, il semble pouvoir réguler ses transcrits antisens dans les myoblastes H19 KO complémentés par le transgène H19, mais surtout il participe activement à la régulation post-transcriptionnelle du gène Igf2 chez la souris. Nous observons en effet qu'il favorise la coupure endoribonucléolytique de l'ARN Igf2 par un mécanisme qui reste à découvrir. Enfin, nous mettons en évidence l'existence d'un l'arrêt de l'élongation de la transcription du gène d'Igf2, pour lequel nous proposons un modèle de régulation faisant intervenir un autre long ARN non codant du locus: le lncARN PIHit. Au-delà des mécanismes qui restent à explorer, nos résultats renforcent l'idée que la structure tridimensionnelle de la chromatine participe à la régulation de l'expression des gènes chez les mammifères. / In mammals, the expression of the Igf2 gene, which is subject to parental genomic imprinting, is tightly regulated during embryonic development and the perinatal period through several transcriptional and post-transcriptional mechanisms. These mechanisms are involving long non-coding RNAs (lncRNAs) produced within the locus; among them the best known is probably the H19 RNA. Using a genetic complementation assay consisting in transfections of an H19 transgene into H19 KO myoblasts, we discovered several novel Igf2 promoters in the mouse. One of these promoters, that is conserved in the human, can be activated by ectopic H19 antisens RNAs (91H lncRNAs) despite a complete methylation of the Imprinting-Control Region located in cis on the same allele. We also show that the 91H lncRNAs possess some tissue-specific features and that their transcription can be initiated from the CS4, CS5 and CS9 conserved sequences located downstream of the H19 gene. On the other hand, the H19 RNA, that is the major lncRNA of the locus, appears to regulate its antisense transcripts in H19 KO myoblasts complemented with the H19 transgene, but its major function seems to be in regulating post-transcriptionally the Igf2 gene expression. Indeed, we have observed that it favours the endoribonucleolytic cleavage of the Igf2 messenger RNAs through a mechanism that remains to be elucidated. Finally, we reveal the existence of a premature transcriptional elongation stop of the Igf2 gene, for which we propose a regulation model involving another lncRNA of the locus: the PIHit lncRNA. Beyond the mechanisms that remain to be explored, our results strengthen the idea that, in mammals, the three-dimensional organization of the chromatin is involved in regulating gene expression.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Malgré le succès de l’Aide Médicale à la Procréation (AMP), des données récentes suggèrent un lien entre le recours à l’AMP et des pathologies liées à des erreurs épigénétiques. Afin d’évaluer l’impact des procédés in vitro de l’AMP sur la méthylation de l’ADN, nous avons analysé : 1) le profil de méthylation de 2 locus soumis à empreinte, H19DMR et KvDMR1, dans des ovocytes recueillis immatures, vitrifiés, puis mûris in vitro après réchauffement. Nous avons montré pour la première fois que le procédé vitrification/MIV pouvait constituer une alternative prometteuse pour préserver le potentiel procréatif des femmes avant un traitement anticancéreux, puisqu’il n’altérait pas l’empreinte parentale. 2) le profil de méthylation de H19DMR dans des embryons humains en retard de développement ainsi que dans les gamètes des géniteurs. Nous avons mis en évidence des anomalies de l’empreinte dans ces embryons, sans lien apparent avec les indications d’ICSI mais liées à des altérations survenues soit au cours de l’ovogenèse, soit au cours du développement précoce. 3) le profil de méthylation des promoteurs d’OCT4 et NANOG, gènes essentiels à l’expression de la pluripotence, dans des embryons bloqués après culture prolongée. Nous avons montré que le promoteur d’OCT4 était significativement hyperméthylé dans les embryons bloqués, en particulier dans la population de couples présentant uniquement une infertilité masculine, alors que le promoteur de NANOG était hypométhylé / Despite the success of Assisted Reproductive Technologies (ART), recent data suggest a link between the use of ART and diseases related to epigenetic errors. To evaluate the impact of ART on DNA methylation, we analyzed: 1) the methylation profile of 2 imprinted loci, H19DMR and KvDMR1, in immature oocytes which were vitrified and matured in vitro after warming. We have shown for the first time that vitrification/IVM process did not alter the imprinting. Then, this new technology could be a promising alternative to preserve the procreative potential of women before cancer treatment. 2) the methylation profile of H19DMR in human embryos with developmental anomalies and in the gametes of the parents. We have shown that imprinting errors in these embryos have no apparent link with ICSI indications, but were related to alterations in H19DMR occurring either during oogenesis or early development. 3) the methylation profile of the promoters of OCT4 and NANOG, essential genes for the expression of pluripotency in arrested embryos after prolonged culture. We have shown that the promoter of OCT4 was highly methylated in arrested embryos particularly in the population of couples with male infertility only, whereas the NANOG promoter was hypomethylated

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

ABSTRACT Ethanol is a classic teratogen capable of inducing a wide range of developmental abnormalities that vary in severity, from the barely perceptible to spontaneous abortion. These defects are collectively referred to as foetal alcohol spectrum disorders (FASD). Foetal alcohol syndrome (FAS) lies at the extreme end of this spectrum and is associated with three broad domains: prenatal and/or postnatal growth retardation, distinctive facial features and brain damage. Epidemiological and animal studies clearly indicate that the clinical variability of FASD is related to four distinct window periods: preconception, preimplantation, gastrulation and postorganogenesis. These developmental windows are correlated with peak periods of epigenetic reprogramming, suggesting a common mechanism of ethanol teratogenesis. Together with experimental evidence that ethanol inhibits DNA-methyltransferase, as well as folate metabolism, this suggests an ‘epigenetic model of FASD’. The aim of the present study was to explore the validity of this model by investigating the relationship between ethanol-induced growth retardation and imprinting, following ethanol exposure during the preimplantation period. Employing an experimental study design, together with a hybrid mouse model, embryos and placentae were harvested at 10.5 days post coitus (dpc). The weights of embryos and placentae, as well as methylation profiles at the H19 imprinting control region (ICR) – an important regulator of growth - were measured. It was found that ethanol-treated embryos and placentae were severely growth retarded in comparison to controls: r=-0.760 (p<0.01, one-tailed) and r=-0.816 (p<0.05, two-tailed), respectively. Bisulphite genomic sequencing revealed that the methylation profile at the H19 ICR was unaffected in ethanol-treated embryos, in comparison to saline-treated controls. Conversely, methylation at the paternal and maternal alleles in placentae was found to be reduced and increased, respectively, in comparison to embryos. These results imply that mechanisms for the maintenance of imprinting in the embryo are more robust than in the placenta. This is consistent with the relatively longlived nature of the embryo, which must maintain imprinting for a considerably longer period of time than the placenta. Bisulphite sequencing also revealed that the paternal allele of the H19 ICR had significantly decreased levels of methylation, while the maternal allele had increased levels of methylation, in ethanol treated-placentae, in comparison to saline controls. The changes observed at the paternal allele were localized to the CTCF1 DNA-binding site, while a trend for increased methylation at the maternal allele was observed at the CTCF2 site. A partial correlation further revealed that demethylation at the paternal allele in placentae partly mediated the effect of ethanol on placental weight. An ‘epigenetic switch model’, whereby paternal Igf2 is downregulated by the epigenetic switching of the paternal allele to the maternal epigenotype, is proposed to explain this relationship. However, partial correlations also indicated that demethylation at the paternal allele of the H19 ICR, as well as placental growth retardation, did not mediate the effect of ethanol on embryo growth. Collectively, these data suggest that imprinting at the H19 ICR is not a mechanism of embryo growth retardation prior to 10.5 dpc. In explaining these results, it is proposed that the growth retarded placenta was able to meet the nutritional demands of the similarly growth retarded embryo up until 10.5 dpc. However, an important question for future research would be to examine the relationship between ethanol-induced growth retardation and imprinting during late gestation. During the final growth spurt (>14.5 dpc) the growth retarded placenta may become unable to meet the increased demands for nutrition, which would exacerbate foetal growth restriction. In sum, the present study revealed a novel mechanism of ethanol-induced growth retardation in the placenta but indicated that imprinting at the H19 ICR does not mediate the effect of ethanol on the early embryo. Further research is required to resolve the relationship between imprinting and ethanol-induced growth retardation.

<p>Genomic imprinting marks a subset of autosomal loci expressed in parent of origin-dependent monoallelic expression in a non-Mendelian fashion. To restore totipotency and to reset the imprint according to the sex of the individual, the mark must be erased during germline development. The imprinted <i>Igf2-H19</i> loci located distally on chromosome 7 in mouse and 11p15.5 in human, share common regulatory elements that regulate differential expression. Where the <i>H19 </i>is silenced when paternally inherited, the <i>Igf2</i> is silenced when maternally inherited. </p><p>The differentially methylated 5'-flank of <i>H19</i> gene, termed imprinting control region (ICR), shown to display a unique chromatin organisation harbours hypersensitive sites in linker regions flanked by positioned nucleosomes on the maternal allele. This unique chromatin conformation functions as a methylation-sensitive and unidirectional chromatin insulator, which later was found to depend on the chromatin insulator protein CTCF. </p><p>The <i>H19</i> ICR exhibits default-silencing functions in promoter-proximal positions. The maximal distance between the <i>H19</i> ICR and the promoter of the reporter gene required for this effect was 1.2 ± 0.3kb which can be compared to the 1.9 kb distance between the endogenous <i>H19 </i>ICR and <i>H19</i> promoter. Results suggest that the <i>H19</i> ICR adopts a chromatin conformation that must be separated by a minimal distance from pivotal <i>cis</i>-regulatory elements to avoid adverse effects on neighbouring promoters. </p><p>Poly(ADP-ribosy)lation represents a novel post-translational epigenetic mark that segregates with exclusively the maternal derived <i>H19</i> ICR and associated with factors that interact with the CTCF target sites. CTCF is itself poly(ADP-ribosy)lated and the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide relieves the insulator function of the <i>H19</i> ICR. </p><p>Designed zinc finger proteins were applied to examine if epigenetic marks provided an obstacle for targeted activation and silencing. The zinc finger protein ZFP809 with activator/repressor domain able to efficiently activate/silence the <i>IGF2</i> target. Murine hybrid cell lines of human chromosome 11, demonstrated that the ZFP809 overcame the epigenetic marks that repressed maternal <i>IGF2</i> and paternal <i>H19</i> allele, respectively. Results suggested that imprinted genes are not normally exposed to strong <i>cis</i>-regulatory elements and that the designed ZFPs can be exploited to develop a therapeutic method for rectifying epigenetic lesions.</p>

<p>An overall coordination between the expressions of genes is required for the proper development of an individual. Although most genes are expressed from both the constituent alleles of the genome, a small subset of autosomal genes are preferentially expressed from only one of the parental alleles, a phenomenon known as genomic imprinting. </p><p>The imprinted <i>H19</i> and <i>Igf2</i> genes are considered paradigms of genomic imprinting as their monoallelic expression pattern is coordinated by a short stretch of sequence located upstream of <i>H19</i>, known as the imprinting control region (ICR). This region shows differential methylation, with hypermethylation specifically on the paternal allele. On the maternal allele this region acts as an insulator and harbours maternal specific hypersensitive sites. </p><p>The hypersensitive sites were identified as the result of association of the vertebrate insulator protein CTCF with the region. This association was investigated in both an <i>in vitro</i> episomal system and in an <i>in vivo</i> mouse model system by mutating the CTCF target sites at the <i>H19</i> ICR. The importance of CTCF for the insulator property of the region was confirmed in both instances. In the mouse model, the disruption of the binding was also observed to affect the methylation profile of the ICR, which ultimately resulted in the de-repression of the maternal <i>Igf2</i> allele.</p><p>The relevance of multiple CTCF target sites in higher vertebrates for the proper insulator function was investigated using another knock-in mouse model with mutation at a single CTCF target site in the <i>H19</i> ICR. The investigation confirmed the cooperation between the target sites for the establishment of a functional insulator on the maternal allele. Target sites in the ICR were also analysed for their differential binding affinity for the CTCF protein.</p><p>The utilisation of the CTCF target sites was examined in different human tumours and cell lines. Methylation analysis conveyed a lack of correlation between the loss of insulator function and methylation status of the ICR with the loss of imprinting (LOI) of <i>IGF2</i>. Investigations also identified a novel mechanism, which neutralised the chromatin insulator function of the <i>H19</i> ICR without affecting its chromatin conformation. This principle might also help in explaining the loss of <i>IGF2</i> imprinting observed in some instances.</p><p>In conclusion, this thesis confirms the importance of CTCF in the formation of an epigenetically regulated chromatin insulator at the ICR, which in turn controls the expression pattern of <i>H19</i> and <i>Igf2</i>. The studies also confirm the role of CTCF in the maintenance of the methylation profile of the region. Investigations into the loss of <i>IGF2 </i>imprinting in human cancer indicate the involvement of other novel mechanisms besides CTCF in the regulation of insulator function.</p>