Deep-frying is now a popular cooking method all over the world due to its low cost and time-saving property. It also provides special and likeable flavor, helps prolong shelf lives of commercial products, and offering food products of stable quality. However, by- products formed during the frying process, such as malonaldehyde, were shown to be harmful to human health. Such compounds can be taken in when having fried foods, potentially inducing or promoting some diseases. However, there is limited research studying the direct effects of frying oil consumption on cancer. In order to have a better understanding of the effects on cancer by frying oil, we used a well-established AOM/DSS- induced colon cancer animal model to study the impact by frying oil. After 10-week treatment with diet containing deep-frying oil (3.8% in diet) or with un-oxidized oil (10% in diet), the mice showed enhanced tumorigenesis in colon, where the total tumor burden significantly increased (4.5 ± 1.9 mm2 for the treatment group, compared with 0.5 ± 0.5 mm2 for the control group, P < 0.05). Also, the expression of pro-inflammatory and pro- tumorigenic cytokines (Mcp-1, Inf-γ, Il-6, Il-1β, Myc, Axin2 and Vegf) were increased in the mice treated with frying oil diets. Together the results showed that consumption of deep-frying oil promoted the colorectal cancer in mice, providing more detailed information for health instruction.

Multiple studies have implicated the POZ-ZF and methyl-DNA-binding transcription factor, Kaiso, in the regulation of genes and pathways that are important for development and tumorigenesis. In Xenopus embryos and mammalian cultured cells, Kaiso has been implicated as a negative regulator of the canonical Wnt signaling pathway. Paradoxically however, Kaiso depletion extends lifespan and delays polyp onset in the ApcMin/+ mouse model of intestinal tumorigenesis, where aberrant activation of Wnt signaling results in the development of neoplasias. These findings call into question Kaiso’s role as a negative regulator of canonical Wnt signaling and led us to hypothesize that Kaiso promotes intestinal tumorigenesis by a mechanism independent of its role in canonical Wnt signaling. To further delineate Kaiso’s role in intestinal tumorigenesis and to determine Kaiso’s role in regulating canonical Wnt signaling in the murine intestine, we generated a Kaiso transgenic mouse model expressing an intestine-specific murine Kaiso transgene. We then crossed our Kaiso transgenic mice with ApcMin/+ mice and analyzed the resultant progeny. Unexpectedly, Kaiso transgenic mice exhibited intestinal inflammation, increased expression of Wnt target genes and deregulated progenitor cell differentiation, although ectopic expression of Kaiso was not sufficient to drive tumorigenesis in the intestine. In agreement with previous studies, ectopic Kaiso expression in ApcMin/+ mice resulted in a significantly shortened lifespan and increased tumour burden. While we were unable to determine the precise mechanism by which Kaiso promotes intestinal tumour development, we found that Kaiso-induced inflammation is enhanced in the ApcMin/+ background and ectopic Kaiso expression further intensifies Wnt target gene expression in this model. Collectively, these studies have identified novel roles for Kaiso in regulating inflammation and cell-fate determination in the intestine. Furthermore, our findings suggest that Kaiso may contribute to intestinal tumorigenesis by promoting inflammation, which has been shown to be a predisposing factor for colorectal cancer development. Lastly, we have demonstrated distinct tissue and organism-specific roles for Kaiso in regulating canonical Wnt signaling. While, the aforementioned studies were the primary focus of this thesis, we also examined Kaiso’s role in DNA methylation-dependent repression of two tumour-associated genes, cyclinD1 and HIF1A. Our studies revealed that Kaiso binds and regulates the cyclinD1 locus via both sequence-specific and methylation-dependent DNA binding, suggesting that these alternate modes by which Kaiso binds to DNA may not be mutually exclusive. Furthermore, we identified a previously unexplored role for Kaiso in regulating the expression of the master regulator of hypoxia, HIF1A, which implicates Kaiso in modulating hypoxia-driven tumorigenic processes. / Thesis / Doctor of Philosophy (PhD)

<p> PEA3 is a member of the ets family of transcription factors. It is expressed throughout embryonic development and in mouse mammary adenocarcinomas induced by expression of the receptor tyrosine kinase Neu. Mice lacking PEA3 due to a targeted disruption of the gene, develop normally, however, male mice fail to mate for yet undetermined reasons. To further understand the role of PEA3 in mammary gland development and tumorigenesis, the effects of loss of function of PEA3 were examined in tumor formation and in mammary gland development. </p> <p> Analysis of tumor formation in PEA3 +I+ and PEA3 -/-animals failed to show a statistically significant difference in tumor onset. Loss of PEA3 did not affect the tumor morphology, nor did it inhibit metastasis of these tumors to the lung. These data indicate that PEA3 is not required for tumor formation or metastasis. </p> <p> PEA3 deficient animals displayed defects in branching morphogenesis in the mammary gland. Decreased ductal branching was observed in virgin and pregnant females. Mice with decreased levels of PEA3 expression also exhibited defects in branching morphogenesis, indicating a dosage effect. PEA3 is expressed in the myoepithelial cells during puberty and pregnancy. It is also express in the highly proliferative cap cell layer of the terminal end bud. In the embryonic mammary gland, PEA3 is expressed as early as 10.5 days in the mammary epithelium and continues late in embryogenesis. Expression in the male mammary gland is lost at approximately embryonic day 16. </p> / Thesis / Candidate in Philosophy

Mathematical modeling of cancer is of significant interest due to its potential to aid in our understanding of the disease, including investigation into which factors are most important in the progression of cancer. With this knowledge and model different paths of treatment can be examined; (e.g. simulation of different treatment techniques followed by the more costly venture of testing on animal models). Significant work has been done in the field of cancer modeling with models ranging from the more broad systems, avascular tumor models, to smaller systems, models of angiogenic pathways. A preliminary model of a vascularized tumor has been developed; the model is based on fundamental principles of mechanics and will serve as the framework for a more detailed model in the future. The current model is a system of nonlinear partial differential equations (PDEs) separated into two basic sub-models, avascular and angiogenesis. The avascular sub-model is primarily based of Fickian diffusion of nutrients into the tumor. While the angiogenesis sub-model is based on the diffusion and chemotaxis of active sprout tips into the tumor. These two portions of the models allow the effects of microvessels on nutrient concentration within the tumor, as well as the effect of the tumor in driving angiogenesis, to be examined. The results of the model have been compared to experimental measurements of tumor growth over time in animal models, and have been found to be in good agreement with a correlation coefficient of (r2=0.98). / Master of Science

Activated protein tyrosine kinases, which have been implicated in the genesis of a number of human cancers, rely on a variety of protein-protein interactions to transmit their proliferative signals within the cell. These interactions are often mediated by Src homology 2 and 3 (SH2 and SH3) domains. A class of proteins which are mainly composed of such domains, termed adaptor proteins, has been identified. The Growth factor receptor bound proteins Grb2 and Grb7 are SH2 domain adaptor proteins which have been shown to associate directly or in complex with many tyrosine kinases, including the c-ErbB-2/Neu receptor tyrosine kinase. While overexpression of either protein alone in rat fibroblasts is not transforming, human breast cancer cell lines exhibit Grb2 and Grb7 gene amplification, and mRNA and protein overexpression. The role of Grb2 in polyomavirus middle T antigen-mediated mammary tumorigenesis has been examined utilizing gene targeting and transgenic approaches. Initial characterization of the progeny of matings involving Grb2+/mice and MMTV/middle T transgenic mice indicated that delayed tumor kinetics may be the result of Grb2 dosage differences between mT+;Grb2+/-and mT+;Grb2+/+ animals. Transgenic animals expressing a dominant negative version of Grb2 in the mammary epithelium have been generated to explore an alternate method for disrupting signaling from middle T antigen. The role of Grb2 and Grb7 in Neu-mediated mammary tumorigenesis is also being examined. Both MMTV/Grb2 and MMTV/Grb7 transgenic mice that express the transgene in the mammary epithelium have been identified by ribonuclease protection analysis. Matings involving these strains and MMTV/neu mice should aid in determining the effects of overexpressing Grb2 or Grb7 on Neu-mediated mammary tumorigenesis. / Thesis / Master of Science (MS)

Dans les neuroblastomes, le gène N-MYC est amplifié dans 20-25 % des cas,associé à un mauvais pronostic. Au laboratoire, nous avions préalablement montré que la dérégulation de l’expression du gène TWIST1 était corrélée à celle de N-MYC dans les neuroblastomes agressifs de stade IV avec une amplification de N-MYC (Valsesia-Wittmann et al., 2004). Au cours de ma thèse, j’ai pu mettre en évidence que les gènes TWIST1 et TWIST2 étaient régulés positivement ou négativement de façon dose dépendante par les oncoprotéines Myc. De façon intéressante, le maintien de l’expression de TWIST1 est dépendant de l’expression des protéines Myc. Ces résultats suggèrent que la dérégulation et l’amplification des oncoprotéines Myc dans les neuroblastomes N-MYC Amplifiés pourraient permettre l’induction sélective et le maintien de l’expression de l’oncogène TWIST, agissant comme facteur de survie. / The N-MYC gene is amplified in 20-25 % of human neuroblastoma, and this amplification is associated with poor clinical outcome. We previously reported aconstant deregulation of TWIST1 in synergy with N-MYC in aggressive stage IVneuroblastoma harboring N-MYC amplification (Valsesia-Wittmann et al., 2004). We demonstrated here that specifically in neuroblastoma cells, TWIST1 and TWIST2 are negatively or positively regulated depending on Myc oncoproteins dosage, thus being a putative Myc transcriptional target. We confirmed by EMSA that Myc proteins could bind TWIST1 promoter. We further highlighted TWIST1 maintenance of expression strictly Myc dependant. Therefore, we propose that deregulation and amplification of Myc oncoproteins in aggressive neuroblastoma tumors induce selective expression and maintenance of TWIST1 oncogene, responsible forapoptosis resistance

<p>The Ras family of small GTPases, comprised of the KRAS, NRAS, and HRAS genes, are mutated to encode constitutively-active, GTP-bound, oncogenic proteins in upwards of one quarter or more of all human cancers, which is well established to promote tumorigenesis. Despite the prominent role these genes play in human cancer, the encoded proteins have proven difficult to pharmacologically inhibit. Therefore, it is important to understand how Ras proteins are activated. </p><p>RAS proteins cycle between a GDP-bound inactive state and a GTP-bound active state through guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). GEFs facilitate the GDP-to-GTP exchange of RAS and promote RAS activation. Similar to GEFs, reactive oxygen/nitrogen species can also promote RAS activation through reactions with the thiol residue of cysteine 118 (C118). This residue may therefore play a role in RAS activation in cancer. To test this possibility, I investigated the effect of mutating C118 to serine (C118S) in Kras on (1) carcinogen-induced lung tumorigenesis, and (2) xenograft tumor growth of HRAS12V-transformed cells.</p><p>To explore the impact of the C118S mutation in Kras on carcinogen-induced lung tumorigenesis, I introduced a C118S mutation into the endogenous murine Kras allele and exposed the resultant mice to the carcinogen urethane, which induces Kras mutation-positive lung tumors. Kras+/C118S and KrasC118S/C118S mice developed fewer and smaller lung tumors than Kras+/+ mice. Although the KrasC118S allele did not appear to affect tumorigenesis when the remaining Kras allele was conditionally oncogenic (KrasG12D), there was a moderate imbalance of oncogenic mutations favoring the native Kras allele in tumors from Kras+/C118S mice treated with urethane. Therefore, mutating C118 of Kras impedes urethane-induced lung tumorigenesis.</p><p>To explore the the impact of the C118S mutation in Kras on xenograft tumor growth of HRAS12V-transformed cells, I tested and found that redox-dependent reactions with cysteine 118 (C118) and activation of wild type KRAS are critical for oncogenic HRAS-driven tumorigenesis. Such redox-dependent activation of KRAS affected both PI3K-AKT and RAF-MEK-ERK pathways. These findings were confirmed in the endogenous mouse Kras gene. Speicfically, oncogenic HRAS-transformed KrasC118S/C118S MEFs grew in soft agar and as xenograft tumors more slowly than similarly transformed Kras+/+ MEFs, suggesting that redox-dependent reactions with C118 of Kras promotes transformation and tumorigenesis. </p><p>Taken together, I have demonstrated a critical role of redox-dependent reactions with Kras C118 in tumorigenesis.</p> / Dissertation

A família de genes HOX compreende um conjunto de fatores de transcrição altamente conservados evolutivamente. Em mamíferos, os genes HOX se subdividem em 4 clusters: HOXA, HOXB, HOXC e HOXD, atuando no desenvolvimento embrionário com a regulação de processos biológicos como proliferação, diferenciação, migração, angiogênese e apoptose que são reativados durante a carcinogênese. Estudos recentes apontam que os genes HOX podem exercer papel relevante na formação de diversos tumores sólidos, todavia ainda não foi possível caracterizar sistematicamente a expressão dos genes HOX em tumores bem como determinar seus alvos em tumores. Desta forma, o objetivo geral deste trabalho consistiu na caracterização in silico do modelo de atuação genes HOX na carcinogênese. Para cumprir este objetivo foi identificado o perfil diferencial dos genes HOX entre amostras normais e tumorais. Alvos de genes HOX foram identificados e, quando diferencialmente expressos, foram associados com os genes HOX, independentemente dos índices de metilação e CNA. Por fim, as associações finais entre os genes HOX e seus alvos foram enriquecidas com os bancos de dados KEGG e GO. Identificou-se diferentes assinaturas de expressão de genes HOX em diferentes tumores, associadas com o eixo ântero-posterior do corpo humano, bem como os folhetos embrionários originários aos tecidos tumorais, compatível com o padrão de expressão no desenvolvimento embrionário. Um número considerável de genes HOX atuam preferencialmente via enhancers na regulação de seus alvos. Como exemplo, os genes HOXB7 e HOXC11, que funcionam como moduladores anti tumorais. Finalmente, o estudo mostra que diante do número crescente de dados genômicos públicos, é possível viabilizar projetos de grande valor científico. / The HOX gene family comprises a set of evolutionarily highly conserved transcription factors. In mammals, HOX genes are subdivided into four clusters: HOXA, HOXB, HOXC and HOXD, acting on the embryonic development with regulation of biological processes such as proliferation, differentiation, migration, angiogenesis and apoptosis that are reactivated during carcinogenesis. Recent studies indicate that HOX genes may play a relevant role in the formation of several solid tumors, but it has not been possible to systematically characterize the expression of HOX genes in tumors as well as to determine their targets in tumors. Thus, the general aim of this project was to characterize the in vivo model of HOX genes in carcinogenesis. To accomplish this goal the differential profile of HOX genes was identified between normal and tumor samples. HOX gene targets were identified and, when differentially expressed, were associated with HOX genes regardless of methylation and CNA indices. Finally, the final associations between the HOX genes and their targets were enriched with the KEGG and GO databases. Different signatures of HOX gene expression were identified in different tumors, associated with the anteroposterior axis of the human body, as well as the embryonic leaflets originating from the tumor tissues, compatible with the expression pattern in the embryonic development. A considerable number of HOX genes preferentially act via enhancers in the regulation of their targets. As an example, the HOXB7 and HOXC11 genes, which function as pro-tumor modulators. Finally, the study shows that in view of the growing number of public genomic data, it is possible to make feasible projects of great scientific value.

As proteínas S100A8/A9 são expressas em diferentes tipos celulares e quando sozinhas ou complexadas e em baixas concentrações, promoveram proliferação, migração celular e formação de estruturas capilares. Por outro lado, quando em altas concentrações, esse complexo inibe o crescimento de diversos tipos de células tumorais murinas e humanas. Ainda, tanto a proteína S100A9 humana, quanto um peptídeo sintético idêntico a porção C-terminal da proteína S100A9 murina (pS100A9m) possuem efeitos antinociceptivo e imunorregulatório. Apesar dessas evidencias, até o momento não foi investigado o efeito do pS100A9m sobre a angiogênese e a tumorigênese. Portanto, o objetivo do presente estudo foi investigar, in vitro, o efeito do pS100A9m sobre os eventos fundamentais envolvidos com a angiogênese e o desenvolvimento tumoral. Para tanto, a fim de avaliar o efeito do pS100A9m sobre a angiogênese foi utilizada a linhagem de células endoteliais tímicas murinas (tEnd.1) nos ensaios de proliferação, migração da célula endotelial em meio de cultura, avaliada nos modelos de wound healing e transwell ou migração em meio condicionado, obtido de células tumorais LLC WRC256, avaliada no modelo de transwell, ensaio de adesão (aos componentes de matriz, tais como o colágeno tipo I, fibronectina e laminina) e formação de tubos em matrigel tridimensional (3D). Para os estudos sobre o efeito do pS100A9m sobre as células tumorais, foi utilizada a linhagem de células LLC WRC256 para realização dos ensaios funcionais de proliferação, migração (wound healing) e adesão (sobre os componentes da matriz extracelular). Os resultados obtidos demonstraram que o pS100A9m inibe a proliferação, migração, adesão sobre os componentes de matriz e, consequentemente, a formação de estruturas capilares em matriz 3D. Em relação às células tumorais LLC WRC256, foi observada, novamente, a ação inibitória do pS100A9m sobre os eventos de proliferação e migração. Em relação à adesão, o peptídeo aumentou a capacidade de adesão das células tumorais sobre o colágeno tipo I e fibronectina, porém inibiu a adesão dessas células sobre laminina. Em conclusão, os dados aqui obtidos demonstram que o pS100A9m inibe in vitro os eventos fundamentais envolvidos com a angiogênese e com a progressão tumoral. Desta forma, o peptídeo da porção C-terminal da proteína S100A9 pode ser considerado uma nova ferramenta para o estudo da angiogênese e tumorigênese, além apresentar potencial para uma possível aplicação terapêutica nesses processos / The S100A8/A9 proteins are expressed in different cell types and alone or when complexed, and at low concentrations promoted proliferation, cell migration and formation of capillary structures. On the other hand, at higher concentrations, this compound inhibits the growth of many types of murine and human tumor cells. Moreover, both human S100A9 protein and a synthetic peptide identical to the C-terminal portion of murine S100A9 (mS100A9p) present antinociceptive and immunomodulatory effects. Despite these evidences, the effect of mS100A9p on angiogenesis and tumorigenesis has not been investigated. Therefore, the aim of this study was to investigate the in vitro effect of mS100A9p on crucial events involved in angiogenesis and tumor development. For this, in order to evaluate the effect of mS100A9p on angiogenesis was used the murine endothelial cell line derived from thymus hemangioma (tEnd.1) for proliferation assays, endothelial cell migration in the presence of culture medium (scratch wound healing and chemotaxis assays) or in conditioned medium prevenient from LLC WRC256 tumor cells (chemotaxis assays), adhesion assay (on extracellular matrix components, such as type I collagen, fibronectin and laminin) and tube like-structure formation in 3D matrix. For the analyzes of the effect of mS100A9p on tumor cells, the cell line LLC WRC256 was used to perform functional assays such as proliferation, migration (scratch wound healing model) and adhesion (on components of the extracellular matrix). The results showed that the mS100A9p inhibits the proliferation, migration and adhesion of endothelial cells to the matrix components and consequently the formation of capillary structures in 3D matrix. Regarding LLC WRC256 tumor cells, it was observed again the inhibitory action of the mS100A9p on proliferation and migration events. In relation to cellular adhesion, this peptide increased this parameter of tumor cells on type I collagen and fibronectin. However mS100A9p inhibited the adhesion of these cells on laminin. In conclusion, the data obtained show that the mS100A9p inhibits in vitro crucial events involved in angiogenesis and tumor progression. Thus, the C-terminal portion of murine S100A9 protein may be considered as a new tool for the study of tumorigenesis and angiogenesis besides presenting potential to a possible therapeutic application in these processes

Les protéines du groupe Polybomb (PcG) sont conservées de la drosophile jusqu’à l’homme et assurent la « mémoire cellulaire » d’un état transcriptionnel réprimé au cours du développement. Un modèle a été proposé pour expliquer leur fonctionnement, qui propose que les deux principaux complexes, PRC1 et PRC2 (Polycomb Repressive Complexes 1 & 2), sont recrutés ensemble au niveau de séquences spécifiques appelés PREs (Polycomb Responsive Elements) où ils collaborent pour maintenir la chromatine dans un été réprimé.Au cours de ma thèse, j’ai voulu tester ce modèle en utilisant les disques imaginaux d’œil-antenne de drosophile, qui sont des structures larvaires préfigurant l’œil adulte. Étonnamment, alors que les mutants PRC1 et PRC2 présentent des phénotypes similaires dans l’embryon, seuls les clones mutants PRC1 présentent une transformation néoplasique et une surcroissance dans l’œil. Pour comprendre les mécanismes moléculaires qui sous-tendent ce découplage fonctionnel, nous avons réalisé des ChIP-Seq contre plusieurs marques d’histones actives et répressives, ainsi que contre des protéines du PcG. La comparaison de ces ChIP-Seq avec les profils embryonnaires a d’abord révélé un redéploiement majeur du PRC1 au stade larvaire, sur environ 1000 promoteurs actifs. Cette nouvelle classe de cibles, que nous avons appelée « Neo-PRC1 », se trouve au niveau de gènes actifs où la marque H3K27me3 normalement déposée par le PRC2 est remplacée par la marque active H3K27Ac. Ces gènes sont impliqués dans la régulation de la polarité, la prolifération ou encore la signalisation cellulaires, et un nombre substantiel d’entre eux est surexprimé dans les mutants PRC1, mais pas PRC2. Ces résultats suggèrent que l’activité suppresseur de tumeurs du PRC1 au stade larvaire découle de la régulation précise de gènes classiquement dérégulés dans les cancers, et ce en l’absence du PRC2En plus des sites situés sur des promoteurs actifs, nous avons détecté des sites PRC1 sans PRC2 au niveau de régions enrichies pour des marques de séquences amplificatrices (« Enhancers » en anglais) actives. Ces sites correspondent à des séquences amplificatrices spécifiquement actives au stade larvaire, et sont localisés à proximité de gènes codant pour des facteurs de transcription cruciaux pour le développement de l’œil, tels que les gènes du réseau de détermination de la rétine (RDGN). Pour mieux comprendre l’action du PRC1 sur ces cibles, j’ai réalisé des expériences de Hi-C (High-throughput Chromosome Conformation Capture) dans l’œil et l’embryon, révélant ainsi que ces séquences amplificatrices contactent les promoteurs proches spécifiquement au stade larvaire. De plus, la fréquence des contacts est positivement corrélée au niveau de PRC1 fixé. Étonnamment, ces gènes cibles sont sous-exprimés dans les mutants PRC1 mais pas dans les mutants PRC2, ce qui suggère que les contacts PRC1-dépendants entre ces séquences amplificatrices et leurs promoteurs cibles promeuvent la transcription. Pour vérifier cette hypothèse, j’ai étudié l’impact de la délétion via CRISPR de deux sites PRC1 impliqués dans une boucle régulatrice ; l’un situé au promoteur d’un gène du RDGN appelé dac et l’autre sur une séquence amplificatrice putative située en aval du gène. Des expériences de 3D-FISH révèlent que leur délétion entraîne la diminution des contacts entre la séquence amplificatrice et le promoteur, avec pour effet la sous-expression de dac. Ces résultats suggèrent que le PRC1 est impliqué dans la formation de boucles entre les séquences amplificatrices et leurs promoteurs cibles, et que cette topologie est nécessaire pour l’activation de ces gènes au cours du développement.Ma thèse a donc contribué à la découverte de nouvelles fonctions pour le PRC1, qui acquiert de nouvelles cibles au cours du développement et régule la transcription de gènes impliqués dans le cancer ou le développement indépendamment du PRC2, via des mécanismes dédiés. / Polycomb Group (PcG) are a set of highly conserved proteins implicated in cellular memory of transcriptional gene silencing throughout development. A classical model of PcG mode of action proposes that the two main Polycomb Repressive Complexes (PRC), PRC1 and PRC2, are co-recruited at specific DNA sequences called PREs (Polycomb Responsive Elements) where they collaborate to stably maintain a repressed chromatin state.My PhD work has challenged this collaborative model, by using as an experimental system the Drosophila larval Eye-Antennal imaginal Disc (EAD) that prefigures the adult eye. Surprisingly, while PRC1 and PRC2 mutants exhibit similar phenotypes in embryos, only PRC1 mutant clones show neoplastic transformation and massive overgrowth in EAD, while PRC2 mutant clones do not. To understand the molecular basis of this functional uncoupling, we generated ChIP-Seq directed against a large set of repressive and active Histone Marks (HTMs) as well as against core PcG proteins in EAD. A comparative analysis with Chip-Seq embryonic profiles firstly identified a massive de novo redeployment of PRC1 proteins at mostly 1000 active promoters that occurs only at larval stage. This new class of transcriptionally active PcG target genes, that we named “Neo-PRC1”, is devoid of the H3K27me3 epigenetic mark normally deposited by PRC2 and carry instead the active H3K27Ac mark. Moreover, this Neo-PRC1 category of PcG targets is enriched in ontologies linked to cell polarity, proliferation or signalling. A substantial subset of neo-PRC1 targets is up-regulated in PRC1 but not in PRC2 mutants, suggesting that the tumour-suppressor activity of PRC1 during Drosophila development might be exerted by fine-tuning the expression of cancer-related genes independently of PRC2.In addition to neo-PRC1 sites located at promoters, we next detected an enrichment of PRC1, but not PRC2, at regions enriched for active enhancer marks. These neo-sites which correspond to larval stage-specific enhancers are found in the vicinity of genes encoding for transcription factors playing a key role in EAD development, like genes implicated in the Retinal Determination Gene Network (RDGN). To understand the function of PRC1 at these enhancers, we performed comparative Hi-C (High-throughput Chromosome Conformation Capture) experiments between embryos and EADs, and discovered differential chromatin contacts occurring between the stage-specific neo-PRC1 enhancers and their closest promoters. The intensity of these 3D contacts is positively correlated with the PRC1-binding levels. Unexpectedly, in PRC1, but not in PRC2 mutants, these genes are down-regulated, suggesting that PRC1-dependent enhancer-promoter loops promote transcription. To study if larval 3D chromatin loops are PcG-dependent and functionally relevant, we analyzed the topological and transcriptional impact of two CRISPR-generated deletions affecting two PRC1 binding sites known to form a regulatory loop. These two PREs are respectively located close to the promoter and a putative 3’ enhancer of the dac locus encoding for a crucial member of the RDGN. 3D FISH experiments demonstrate that the removal of the dac endogenous PRC1 binding sites is sufficient to significantly decrease dac enhancer-promoter contacts as well as to trigger down-regulation of dac expression. Altogether, these results suggest that PRC1 might contribute to enhancer-promoter contacts at crucial developmental genes in EAD and that these PRC1-dependent long-range interactions could be necessary to allow a proper transcriptional induction during development.To summarize, my PhD project contributed in opening a new perspective, namely that in addition to conveying cellular memory, a main function of PcG correlates with a second wave of PRC1 recruitment during larval stage to subtly regulate and coordinate the expression of cancer-related and developmental genes through non-canonical molecular mechanisms.