Tumor suppressor p53-binding protein 1 (53BP1) is an integral part of a sophisticated network of cellular pathways termed as the DNA damage response (DDR). These pathways are specialized in the maintenance of genome integrity. Recently, it was reported that nuclear import of 53BP1 depends on importin ß. Here, I used fluorescence microscopy and co-immunoprecipitation experiments to identify its nuclear localization signal (NLS). Clusters of basic amino acids 1667-KRK-1669 and 1681-KRGRK- 1685 were required for 53BP1 interaction with importin ß and for its nuclear localization. Short peptide containing these two clusters was sufficient for interaction with importin ß and targeting EGFP to the nucleus. Additionally, the effect of 53BP1 phosphorylation at S1678 on its nuclear import was examined. Mimicking the phosphorylation in the 53BP1-S1678D mutant decreased the binding to importin ß and resulted in a mild defect in 53BP1 nuclear import. However, 53BP1 entered the nucleus continuously during the cell cycle, suggesting that CDK-dependent phosphorylation of S1678 probably does not significantly contribute to the regulation of 53BP1 nuclear transport. Taken together, 53BP1 NLS meets the attributes of a classical bipartite NLS. Although no cell cycle-dependent regulation of its import was observed, the...

A Leucemia Linfóide Aguda (LLA) é uma doença heterogênea em relação à biologia e ao prognóstico. Além de alterações genéticas, anormalidades epigenéticas, estão estreitamente relacionadas ao processo de carcinogênese e entre os mecanismos epigenéticos, a acetilação das histonas é um componente essencial para a regulação da estrutura da cromatina e atividade transcricional. Esse processo é mediado pelas histonas acetiltransferases (HATs). Por outro lado, a desacetilação, por meio das histonas desacetilases (HDACs), está relacionada à condensação da cromatina e repressão transcricional. A expressão anormal das HDACs tem sido associada ao processo de leucemogênese, revelando ser uma área promissora na caracterização de grupos de risco e tratamento do câncer. Os objetivos deste trabalho foram avaliar a expressão dos genes da classe I de HDACs (HDAC 1, 2, 3 e 8), correlacionar os resultados com as características clínicas e de prognóstico (idade, gênero, grupo de risco, contagem inicial de blastos, imunofenótipo, resposta ao tratamento, doença residual mínima nos dias 14 e 18 e a sobrevida livre de eventos) em 46 amostras consecutivas de medula óssea de crianças e adolescentes portadores de LLA; comparar e correlacionar a expressão dos genes estudados entre as amostras de pacientes portadores LLA e 10 amostras de medula óssea sem doença hematológica. A análise da expressão gênica foi realizada através da técnica de PCR em Tempo Real pelo método TaqMan®. Foi observado um aumento da expressão do gene HDAC1 nas amostras dos pacientes bons respondedores ao ix tratamento. O gene HDAC2 foi mais expresso no grupo de pacientes do gênero masculino (p=0,038). Esse gene também mostrou uma expressão aumentada nos pacientes de alto risco (p=0,060) e com sobrevida menor (p=0,065), entretanto os valores encontrados não foram estatisticamente significativos. Além disso, foi observada uma expressão aumentada dos genes HDAC2 (p=0,007), HDAC3 (p=0,014) e HDAC8 (p=0,002) em amostras de pacientes com LLA quando comparadas às amostras de medula óssea sem doença hematológica. Houve correlação entre a expressão de todos os genes de classe I das HDACs, exceto entre HDAC1 e HDAC8. Os resultados obtidos nesse trabalho sugerem que as HDACs de classe I, podem representar importantes alvos para futuros estudos em LLA, no entanto são necessários de testes funcionais para confirmar estes resultados. / Acute Lymphoblastic Leukemia (ALL) is a heterogeneous disease with distinct biologic and prognostic groups. In addition to genetic alterations, epigenetic processes play an important role in carcinogenesis, among which histone acetylation/deacetylation is crucial for chromatin modulation structure and transcriptional activity. Histone acetylation is regulated by the enzyme histone acetyl transferases (HATs). On the other hand, the deacetylation process is regulated by histone deacetylases (HDACs) enzymes, which is associated with the chromatin condensation and transcriptional repression. Abnormal expression of HDACs is a common feature of cancer and has revealed a promising field to stratify cancer treatment and risk classification. The investigation of these expression profiles may represent an important clinical factor for diagnosis and management of hematological malignances. The objectives of the present study were to analyze the expression profile of the class 1 HDACs (HDAC1, 2, 3 and 8) genes in bone marrow samples obtained from 46 childhood ALL samples, to correlate the results with prognostic and clinical features (age, gender, risk group, immunophenotype, treatment response, minimal residual disease and event free survival) of the patients; to evaluated differences in gene expression between ALL samples and 10 bone marrow samples without hematological disease and to verify the correlation of these genes. The gene expression analysis were made using xi TaqMan real-time polymerase chain reaction. A higher expression of HDAC1 in patients with better treatment response was observed. The HDAC2 showed a higher expression in male gender (p=0,038). HDAC2 also showed a higher expression for higher risk (p=0,060) and lower survival patients (p=0,065), however the statistical analysis did not show significant results. Furthermore, there was a higher expression of HDAC2 (p=0,007), HDAC3 (p=0,014) and HDAC8 (p=0,002) in ALL samples when compared to healthy donors. Class I HDACs showed correlation in gene expression, except for HDAC1 and HDAC8. These results suggest that class I HDACs can represent important targets for ALL research; however, it is necessary to perform functional investigation to confirm these results.

Made available in DSpace on 2017-07-21T20:43:51Z (GMT). No. of bitstreams: 1 Gisele Stasievski.pdf: 4714308 bytes, checksum: b2c52f5edeedbfaeb8a4ba4c4fc12ff1 (MD5) Previous issue date: 2016-08-30 / The composites with wood load have been gaining space among the materials of this class because their good mechanical properties, dimensional stability, low cost, and contribute for the environmental factor. For a good adhesion of wood particles in polymeric matrix, a compatibility process are required, because wood have polar characteristic meanwhile polymers have a-polar groups. The process used in this study is a chemical treatment by acetylation, where the purpose is to reduce the polarity of wood and ensure strong adhesion between components. A mixture of equal proportions of acetic acid and acetic anhydride catalyzed by sul-furic acid are the reagents of the pine wood acetylation. The treated wood was processed with polypropylene and infrared spectroscopy was used to analyze composite effective chemical modification. The thermal and mechanical proper-ties were compared to virgin polymer and adhesion between fiber-matrix was ver-ified by microscopic analysis. / Os compósitos com carga de madeira vêm ganhando espaço dentre os materiais dessa classe devido suas boas propriedades mecânicas, estabilidade dimensio-nal, baixo custo, e por contribuírem com o fator ambiental. Para que a adesão das partículas de madeira seja adequada em matriz polimérica se faz necessário um processo de compatibilização, isso porque a madeira possui característica polar e os polímeros grupos apolares. O processo usado no presente estudo tra-ta-se de um tratamento químico por acetilação, onde o objetivo é reduzir a pola-ridade da madeira e garantir adesão forte entre os componentes. Uma mistura de igual proporção entre acido acético e anidrido acético catalisada por acido sul-fúrico são os reagentes para a acetilação da madeira de pinus. A madeira tratada foi processada com polipropileno e espectroscopia por infravermelho foi utilizada para analisar a efetiva modificação química do compósito. As propriedades tér-micas e mecânicas foram comparadas ao polímero virgem e a adesão fibra-matriz foi verificada através de analise microscópica.

The important role of the central intermediary metabolite acetyl-coenzyme A (AcCoA)for several anabolic and catabolic pathways is well characterised. However, the role of AcCoA as the only known donor of acetyl groups for protein acetylation in regulation of enzyme activities, protein complex stability as well as epigenetic status off chromatin, is only recently emerging. Among multiple other pathways, the autophagy pathway has now been shown to be directly regulated by protein acetylation and deacetylation. Therefore, it was reasoned that the availability of AcCoA, via the modulation of AcCoA generating enzymes, may regulate autophagy. This study has focussed on the role of the acetate-mediated route to nuclear-cytosolic AcCoA synthesis, catalysed by AcCoA synthetase 2 (ACSS2), in the regulation of autophagy.

Ao longo dos últimos anos observou-se um aumento no número de idosos no mundo, com isso faz-se necessário buscar terapias que amenizem os danos relacionados e também elucidar os mecanismos envolvidos neste processo. O exercício físico tem sido sugerido como uma ferramenta importante, não farmacológica, para atenuar os déficits relacionados à idade. Ainda, estudos recentes sugerem uma relação entre o processo de envelhecimento cerebral e o desequilíbrio de mecanismos epigenéticos, contudo, estes dados ainda não são conclusivos. Sabe-se que o grau de neuroplasticidade varia com a idade e que as estruturas encefálicas podem responder diferentemente à exposição ao exercício. Estudos demonstram que o córtex pré-frontal está envolvido em funções de alta ordem como atenção, tomada de decisão e memória de trabalho. Portanto, o objetivo deste trabalho foi avaliar os efeitos de diferentes protocolos de exercício físico (sessão única e exercício diário moderado) sobre a modulação de marcadores epigenéticos em córtex pré-frontal de ratos Wistar de 3 e 21 meses de idade. Os animais foram submetidos ao protocolo de sessão única (20 minutos) ou o exercício diário moderado (20 minutos durante 14 dias), 1 hora após a última sessão foram eutanasiados. O córtex pré-frontal foi dissecado e a acetilação da H4, o conteúdo da DNA metiltransferase (DNMT1 e DNMT3b), assim como a atividade da histona metiltransferase H3K27 foram analisadas. Os resultados serão apresentados na versão completa desta dissertação. / Over the past few years the number of elderly people has increased in the world, therefore it is necessary to search therapies that ameliorate age-related deficits as well as elucidate the mechanisms involved in this process. Physical exercise has been suggested as an important non-pharmacological approach to alleviate the age-related decline. Furthermore, recent studies have suggested a relationship between the process of brain aging and imbalance of epigenetic mechanisms, however, these data are not conclusive. It is well described that prefrontal cortex is involved in higher functions like attention, decision making and working memory. Then, the aim of this study was to investigate the effects of two exercise protocols (single session and daily moderate exercise) on the modulation of epigenetic markers in the prefrontal cortex from Wistar rats of 3- and 21- months-old. Animals were submitted to single session protocol (20 minutes) or the daily moderate exercise (20 minutes for 14 days), and 1hour after the last exercise session animals were euthanized. Prefrontal cortex was dissected out and acetylation of H4, the content of DNA methyl transferase (DNMT1 and DNMT3B), as well as histone methyltransferase H3K27 activity were analyzed. Results will be presented in the full version.

A amilose, na presença de agentes complexantes adequados, tende a formar complexos de inclusão. Os mesmos são carregadores promissores, já que os ligantes aprisionados podem ser libertados posteriormente, o que conduz a muitas aplicações. Porém, a utilização da amilose nativa (AM) na formação dos complexos é limitada devido a sua baixa solubilidade em água. Sendo assim, estudos envolvendo a modificação desta molécula tornam-se promissores. O objetivo da presente tese foi preparar complexos de inclusão a partir da amilose nativa (AM) e modificada (AMA) usando como ligantes Rifampicina (RIF), Rodamina B (RB) e o Azul de Bromotimol (AB). Primeiramente, dentre os métodos existentes para modificação, escolheu-se a acetilação. O grau de acetilação foi investigado e a estrutura da amilose foi caracterizada por meio de FTIR, MEV, TGA e DSC. Quando comparada à AM, AMA apresentou maior solubilidade em água. A presença das bandas de absorção no FTIR à 1727, 1240 e 1122 cm-1, confirmaram a acetilação. Os resultados de MEV sugeriram que a superfície lisa da AM foi transformada em uma superfície mais áspera em AMA e as análises de TGA e DSC mostraram uma estrutura instável para a mesma. Após esta etapa os complexos foram produzidos e a influência da temperatura e dos ligantes foi avaliada através da caracterização físico-química. UV-vis, DLS, PZ e MEV foram as técnicas usadas neste processo. As análises de UV confirmaram a formação dos complexos e aqueles desenvolvidos na temperatura de 65°C foram mais eficientes. Dentre estes destacam-se aqueles complexos preparados com RIF. O diâmetro hidrodinâmico médio (dh) dos complexos medidos por DLS variou entre 70 e 100 nm, indicando que os mesmos podem ser utilizados em sistema de liberação controlada. Comparando o dh da AM e AMA, observou-se que os tamanhos são maiores após a complexação, o que pode indicar que para AMA ou a interação forma complexos mais compactos, ou os ligantes não interagiram com a AMA. Análise de PZ mostrou que os complexos AM-RB e AM-AB apresentam alta estabilidade (PZ < -30 mV) e que os demais complexos apresentam valores de PZ próximos da neutralidade, o que pode melhorar a adsorção dos mesmos em sistemas biológicos. Os complexos AMA-RB e AMA-AB não formaram complexos no estado sólido e os demais formaram uma estrutura amorfa após precipitação. Em conclusão, este estudo levou ao desenvolvimento de um método eficaz para a preparação de complexos de inclusão de amilose. / In the presence of suitable complexing agents, amylose tends to form inclusion complexes. This polymer is considered a promisor carrier since the ligands confined in its chains can be released later, leading to various applications. However, the use of native amylose (AM) in complexes formation is restricted due to its low water solubility. Therefore, studies regarding amylose modification become promising. The aim of this thesis was preparing inclusion complexes made of native (AM) and modified (AMA) amylose using rifampicin (RIF), rhodamine B (RB), and bromothymol blue (AB) as ligands. At first, acetylation was the chosen modification among the modified methods described in the literature. The acetylation degree was investigated and the modified macromolecule was characterized using FTIR, SEM, TGA, and DSC analysis. Compared with AM, AMA presented increased water solubility. The presence of absorption bands at 1727, 1240, and 1121 cm-1 confirmed the acetylation. SEM images suggested that the smooth surface of AM was turned into a rougher surface in AMA, while TGA and DSC results showed a less stable structure for AMA. After this step, the complexes were prepared and the influence of the temperature and ligand type was evaluated through physicochemical characterization. UV-Vis, DLS, PZ, and SEM were the techniques used in this process. UV-Vis analysis confirmed complexes formation, revealing that the ones prepared at 65°C were more efficient. Among those, complexes prepared with RIF stand out. The average hydrodynamic diameter (dh) of the complexes measured by DLS ranged from 70 to 100 nm, indicating that these complexes can be used in controlled release systems. Comparing the dh of AM and AMA, it was observed that the sizes were larger after complexation, which may indicate more compact complexes or no interaction between AMA and ligands. ZP results showed that AM-RB and AM-AB complexes presented high stability (PZ < -30 mV), while the others presented PZ values near neutrality, which can increase their adsorption in biological systems. AMA-RB and AMA-AB did not form complexes in solid state, while the others formed an amorphous structure after precipitation. In conclusion, this study leaded to an effective method development for the amylose inclusion complexes preparation.

Les ARNnc sont impliqués dans la régulation de l’expression de gènes chez les Procaryotes, les Archées et les Eucaryotes. Cette régulation peut être effectuée au niveau transcriptionnel ou post-transcriptionnel. Elle fait parfois intervenir des modifications des histones comme la méthylation ou l’acétylation. J’ai étudié le gène TIR1 dont l’expression est fortement réduite lorsqu’un ARNnc codant antisens nommé TIR1axut est stabilisé. J’ai montré que cette régulation est dépendante de l’histone déacétylase Hda1. De plus, j’ai montré que l’acétylation de H3K14 et H3K18 ne sont pas directement impliquées dans la régulation de TIR1 mais qu’un résidu polaire est nécessaire pour la répression de TIR1 en présence de l’ARNnc antisens. En outre, j’ai mis en évidence que la répression de TIR1 par son XUT est en parti post-transcriptionnel, mais ne fait pas varier la stabilité de l’ARNm. Finalement, j’ai tenté en vain de comprendre le ciblage de l’activité histone déacétylase de Hda1 le long de TIR1 en cherchant la présence d’hybride ARN/ADN grâce à un anticorps reconnaissant ce type de structure. / NcRNAs are involved in gene regulation in Prokaryotes, Eukaryotes and Archaea. This regulation could be transcriptional or post-transcriptional. Histone modifications could be involved such as methylation or acetylation. I studied TIR1 gene whose expression is highly reduced when an antisense ncRNA called TIR1axut is stabilized. I showed that this regulation is Hda1-dependant. In addition to that, I showed that H3K14ac and H3K18ac are not directly responsible for TIR1 repression but a polar residue is required for a proper silencing of TIR1 in a XUT depending manner. Moreover, I showed that TIR1 repression is due to a post-transcriptional effect but does not affect mRNA stability. Finally, I tried in vain to understand Hda1 targeting on TIR1 searching for RNA/DNA hybrids using an antibody that recognizes such structures.

Biacetilo (2,3-butanediona) é um contaminante de comida e cigarro, também implicado na hepatoxicidade do álcool e em doenças pulmonares. O metilglioxal (MG), um &#945;-oxoaldeído reativo frequentemente associado ao diabetes e envelhecimento, é produto da fragmentação oxidativa de trioses fosfato, acetona e aminoacetona. Por sua vez, peroxinitrito - um potente oxidante, agente nitrante e nucleófilo formado in vivo pela reação controlada por difusão do ânion radical superóxido com o radical óxido nítrico (k ~1010 M-1s-1) é capaz de se adicionar a CO2 e compostos carbonílicos, gerando produtos potencialmente tóxicos ou sinalizadores celulares. Aminoácidos, peptídeos e nucleobases podem ser acetilados nos grupos amina e na porção desoxiribose. Relativamente ao tratamento com peroxinitrito isolado, níveis superiores de 3-nitrotirosina foram detectados quando tirosina foi tratada com peroxinitrito/biacetilo ou metilglioxal. Ambos os grupos amina de lisina (Lys) ou um deles de derivados de lisina bloqueados e um deles (Ac-Lys-OMe, Z-Lys-OMe) foram acetilados pelo sistema biacetilo ou metilglioxal/peroxinitrito. Em tetrapeptídeos sintéticos contendo lisina como aminoácido amino-terminal (H-KALA-OH, Ac-KALA-OH and H-K(Boc)ALA-OH), a lisina foi acetilada pelo sistemas dicarbonilico/peroxinitrito no grupo &#945;-amina (em maior extensão) e/ou no &#949;-amina (em menor extensão). No conjunto, estes resultados podem ser interpretados à luz do mecanismo proposto para a reação de compostos &#945;-dicarbonílicos com peroxinitrito, o qual envolve sequencialmente: (i) adição nucleofílica de peroxinitrito à carbonila; (ii) homólise do aduto peroxinitroso formado, liberando &#8226;NO2 e um radical oxila do reagente carbonílico; (iii) &#946;-clivagem do radical oxila a um ácido carboxílico (ácido acético no caso de biacetilo e ácido fórmico, a partir de metilglioxal) e radical acetila; (iv) captação do radical acetila pelo oxigênio molecular dissolvido dando acetato, ou por aminoácido ou nucleobase, se presentes, gerando o produto acetilado. Tais resultados são interessantes ao levantar a hipótese de acetilação radicalar como mecanismo de modificação pós-traducional de proteínas, até então considerado um processo realizado apenas por acetilases. / Diacetyl (2,3-butanedione) is a food and cigarette contaminant recently implicated in alcohol hepatotoxicity and lung disease. In turn, methylglyoxal (MG) is an &#945;-oxoaldehyde frequently associated with diabetes and aging that is putatively formed by the oxidative fragmentation of trioses phosphate, acetone and aminoacetone. Peroxynitrite - a potent oxidant, nitrating agent and nucleophile formed in vivo by the diffusion-controlled reaction of superoxide radical with nitric oxide (k ~1010 M-1s-1) - is able to form adducts with carbon dioxide and carbonyl compounds. When initially present in the reaction mixtures before addition of ONOO-, amino acids, peptides and nucleobases undergo acetylation at the amino group and purine moieties in the presence of biacetyl or methylglyoxal. Higher levels of 3-nitrotyrosine nitration were measured when peroxynitrite/biacetyl or metilglioxal was added to tyrosine, in comparison with peroxynitrite alone. Both amino groups of L-lysine or one of the amino groups of L-lysine derivatives (Z-Lys-OH and Ac-Lys-OH) were acetylated by biacetyl and methylglyoxal/peroxynitrite system. Using tetrapeptides containing lysine at the terminal amino acid (H-KALA-OH, Ac-KALA-OH and H-K(Boc)ALA-OH), the lysine residue was acetylated at both or either &#945;-amino (major adduct) and &#949;-amino group (minor adduct). Altogether these data can be interpreted by the mechanism proposed to describe the reaction of &#945;-dicarbonyls with peroxynitrite as follows: (i) nucleophilic addition of peroxynitrite to the carbonyl group of the reagent; (ii) homolysis of the formed peroxynitroso carbonyl adduct to &#8226;NO2 and a carbonyloxyl radical; (iii) &#946;-cleavage of the oxyl radical to acetyl radical plus acetic acid (from diacetyl) or formic acid (from methylglyoxal); (iv) competitive scavenging of the acetyl radical by dissolved molecular oxygen and by added amino acid, peptide or nucleobase, ultimately yielding acetate or acetylated biomolecule. If occurring in vivo, these radical reactions may contribute to the post-translational modification of proteins catalyzed by transacetylases.

O grau de acetilação (GA) da quitosana é um parâmetro que influi nas interações inter e intramoleculares deste polímero e, portanto, em suas propriedades. É comum a incorporação de compostos a filmes de quitosana para melhora de suas propriedades, contudo, não há relatos da incorporação da resina de jatobá, composto natural com potencial atividade biológica, a estes filmes. Portanto, esta pesquisa buscou estudar a influência do grau de acetilação da quitosana e da inclusão da resina de jatobá sobre as propriedades de filmes de quitosana/gelatina, visando uma possível aplicação em cicatrização de feridas cutâneas. Foram produzidas amostras de quitosana a partir de gládios de lula com três diferentes valores de GA, variáveis de 7 a 35%. As soluções formadoras de filme apresentaram redução no valor de concentração inibitória mínima contra Staphylococcus aureus tanto com a redução no GA quanto com a incorporação da resina de jatobá, apesar da resina isoladamente não ter apresentado atividade antimicrobiana nas concentrações estudadas. Os ensaios reológicos demonstraram que a inclusão da resina de jatobá e maiores valores de GA reduziram os valores de viscosidade das soluções, enquanto a temperatura de gelificação também diminuiu com a inclusão da resina de jatobá. Os filmes apresentaram uma superfície lisa e compacta para as blendas quitosana/gelatina e uma morfologia rugosa e irregular após adição da resina de jatobá, quando analisados por MEV. A adição de resina de jatobá levou também a redução na estabilidade térmica dos filmes. Nos testes de absorção em PBS ficou evidente o efeito do GA da quitosana sobre a propriedade, exibindo valores de intumescimento consideravelmente maiores para os filmes conforme o aumento no GA, fator relacionado ao aumento do número de grupos acetila. Por outro lado, a adição de resina de jatobá e o processo de neutralização reduziram consideravelmente o grau de intumescimento dos filmes. Foi observado também que a redução no GA e a inclusão da resina de jatobá tanto aumentaram a permeação ao vapor de água dos filmes, quanto levaram a uma redução da solubilidade destes materiais. / The degree of acetylation (DA) of chitosan is a parameter that influences the inter and intramolecular interactions of this polymer and, therefore, its properties. In addition, it is common the incorporation of other compounds to chitosan films to improve their properties. However, there are no reports of the incorporation of jatoba resin, a natural compound with potential biological activity. Therefore, this research aimed to study the influence of the degree of chitosan acetylation and the inclusion of the jatoba resin on the properties of chitosan/gelatin films, with potential applications in wound healing. Samples of chitosan were produced from squid pens with three different DA values, ranging from 7 to 35%. The reduction in DA of chitosan and incorporation of the jatoba resin into the film-forming solutions resulted in reductions in the minimum inhibitory concentration against Staphylococcus aureus, although the isolated resin did not exhibit antimicrobial activity at the concentrations studied. The rheological tests showed that the inclusion of the jatoba resin and higher DA values reduced the viscosity of the solutions, while gelation temperature values decreased with the jatoba resin addition. The films presented a smooth and compact surface for the chitosan/gelatin blends and a rough and irregular morphology after addition of the jatoba resin. The addition of jatoba resin also led to the reduction in thermal stability of the films. The effect of the DA of chitosan on the absorption of PBS was evident, exhibiting considerably higher swelling values for the films as a function of the DA increase, a factor related to the increase in the number of acetyl groups. Moreover, the addition of jatoba resin and neutralization process considerably reduced the degree of swelling of the films. The water vapor permeability of the films increased due to both the reduction in DA and the inclusion of the jatoba resin, whereas these changes led to the reduction of the solubility of these materials.

Epigenetic modifications are alterations in the cell nucleus that affect gene expression and can occur in chromatin at the level of DNA methylation or histone modifications. Such ‘epigenetic marks’ can be heritable through cell division but leave the DNA sequence unchanged. Post-­translational modifications can be found on the histone proteins associated with DNA; the majority of histone modifications are found on the lysine-­rich N-‐terminal amino acid “tails”. Histone acetylation and methylation influence the chromatin structure by loosening or tightening the packaging of DNA, respectively, in association with other chromatin modifiers. Condensed chromatin is linked to transcriptional silencing and genetic imprinting and also occurs at chromosomal centromeres, where it is linked to kinetochore binding. Heart development is well studied, but the epigenetic processes involved are not yet completely understood. While active chromatin mechanisms such as histone acetylation and chromatin remodelling have been described in the heart, the role of gene repressive epigenetic mechanisms has been poorly investigated. Cardiomyocytes are post-­mitotic cells that do not divide to regenerate a damaged heart. The regeneration of cardiomyocytes after myocardial infarction is an important topic of interest in cardiovascular science. There are various approaches to heart repair after infarction, including activating cardiomyocytes so they become mitotic once again, or growing cardiomyocytes in vitro to attach to a lesion site. An important factor in these approaches is understanding the epigenetic mechanisms controlling cell division. In this thesis, we aim to advance the current knowledge of the epigenetic repressive mechanisms involved in cardiomyocyte formation and heart development to explain their lack of regenerative capacities. We studied the epigenetic changes that occur during cardiac development leading to a non-­‐regenerative state to pinpoint the moment at which these changes arise. We found that the epigenetic process is independent of whether cardiac lineage differentiation occurs during embryogenesis or during differentiation in vitro. We discovered that cardiac heterochromatin displays a singular epigenetic signature during development as compared to brain, another post-­mitotic tissue, or liver, an actively regenerative tissue. We observed an epigenetic change in the repressive histone modification histone H3 lysine 9 trimethylation that was specific to heart development. This change involved a nuclear reorganisation of heterochromatin and a reduction of the levels of this mark in E13.5 and E14.5 embryos, as compared to E10.5 embryos. This was consistent with our observations of the histone lysine methyltransferase SUV39H1, the levels of which were lower after stage E10.5 of development. However, contradictorily, in differentiated cardiomyocytes in vitro, SUV39H1 was increased but showed low levels of H3K9me3, compared to ES cells, which had low levels of SUV39H1 and high levels of H3K9me3. We detected extremely low levels of the H3K9me3 in adult heart tissue. We observed that in adult hearts, the myocardium had maintained these major changes in H3K9me3, while this effect was not observed in the epicardium. Genomic studies were carried out to determine changes at a genomic level between the two key epigenetic stages in heart development we identified at E10.5 and E13.5. Methylated DNA immunoprecipitation sequencing and chromatin immunoprecipitation sequencing for H3K9me3 analyses were carried out to find overall changes in methylation patterns. No global changes in DNA methylation were detected between these developmental stages. These results imply that the differences observed in H3K9me3 are due to remodelling of the heterochromatin during heart development and cardiomyocyte formation, rather than quantitative changes.