Characterization of chromatin accessibility in psoriasis / 医学前沿

The pathological hallmarks of psoriasis involve alterations in T cell genes associated with transcriptional levels, which are determined by chromatin accessibility. However, to what extent these alterations in T cell transcriptional levels recapitulate the epigenetic features of psoriasis remains unknown. Here, we systematically profiled chromatin accessibility on Th1, Th2, Th1-17, Th17, and Treg cells and found that chromatin remodeling contributes significantly to the pathogenesis of the disease. The chromatin remodeling tendency of different subtypes of Th cells were relatively consistent. Next, we profiled chromatin accessibility and transcriptional dynamics on memory Th/Treg cells. In the memory Th cells, 803 increased and 545 decreased chromatin-accessible regions were identified. In the memory Treg cells, 713 increased and 1206 decreased chromatin-accessible regions were identified. A total of 54 and 53 genes were differentially expressed in the peaks associated with the memory Th and Treg cells. FOSL1, SPI1, ATF3, NFKB1, RUNX, ETV4, ERG, FLI1, and ETC1 were identified as regulators in the development of psoriasis. The transcriptional regulatory network showed that NFKB1 and RELA were highly connected and central to the network. NFKB1 regulated the genes of CCL3, CXCL2, and IL1RN. Our results provided candidate transcription factors and a foundational framework of the regulomes of the disease.

Non-coding RNAs and chromatin: key epigenetic factors from spermatogenesis to transgenerational inheritance

Cellular fate and gene expression patterns are modulated by different epigenetic factors including non-coding RNAs (ncRNAs) and chromatin organization. Both factors are dynamic throughout male germ cell differentiation on the seminiferous tubule, despite the transcriptional inactivation in the last stages of spermatogenesis. Sperm maturation during the caput-to-cauda transit on the epididymis involves changes in chromatin organization and the soma-to-germ line transference of ncRNAs that are essential to obtain a functional sperm for fertilization and embryo development. Here, the male environment (diseases, drugs, mental stress) is crucial to modulate these epigenetic factors throughout sperm maturation, affecting the corresponding offspring. Paternal transgenerational inheritance has been directly related to sperm epigenetic changes, most of them associated with variations in the ncRNA content and chromatin marks. Our aim is to give an overview about how epigenetics, focused on ncRNAs and chromatin, is pivotal to understand spermatogenesis and sperm maturation, and how the male environment impacts the sperm epigenome modulating the offspring gene expression pattern.

Effect of interactions of chromatin regulatory elements with different promoters on the regulation of gene expression / 生物工程学报

The effect of altering the promoter region of ubiquitous chromatin-opening element (UCOE) and matrix attachment region (MAR) on stable and efficient expression of genes was investigated. Four different promoters were tested, namely, oct4 containing an enhancer region, sox2 having a CpG island, nanog having no regulatory elements, and CMV containing a CpG island and an enhancer region. Eight reporter plasmids were constructed: pOCT4-UCOE, pOCT4-MAR, pSOX2-UCOE, pSOX2-MAR, pNANOG-UCOE, pNANOG-MAR, pCMV-UCOE, and pCMV-MAR. Stable and efficient expression was observed when UCOE combined with the oct4 promoter, whereas the sox2 was the best promoter suited for MAR. Comparison of the stable clones of oct4-UCOE and sox2-MAR showed that UCOE-regulated expression is more stable and efficient than MAR-regulated expression. When CpG island-containing promoter is linked with UCOE, stable and efficient expression could be observed. These data suggest that an enhancer region in the promoter leads to high, yet unstable expression when combined with UCOE, whereas CpG islands stabilize expression. In conclusion, UCOE and MAR interact with regulatory elements on the promoter by altering the chromatin open state and chromatin loop to regulate gene expression.

Advances in three-dimensional genomics / 生物工程学报

Three-dimensional (3D) genomics is an emerging discipline that studies the 3D spatial structure and function of genomes, focusing on the 3D spatial conformation of genome sequences in the nucleus and its biological effects on biological processes such as DNA replication, DNA recombination and gene expression regulation. The invention of chromosome conformation capture (3C) technology speeds up the research on 3D genomics and its related fields. Furthermore, the development of 3C-based technologies, such as the genome-wide chromosome conformation capture (Hi-C) and chromatin interaction analysis using paired-end tag sequencing (ChIA-PET), help scientists get insight into the 3D genomes of various species. Aims of 3D genomics are to reveal the spatial genome organization, chromosomal interaction patterns, mechanisms underlying the transcriptional regulation and formation of biological traits of microorganism, plant, animal. Additionally, the identification of key genes and signaling pathways associated with biological processes and disease via chromosome 3C technology boosts the rapid development of agricultural science, life science and medical science. This paper reviews the research progress of 3D genomics, mainly in the concept of 3D genomics, the development of chromosome 3C technologies and their applications in agricultural science, life science and medical science, specifically in the field of tumor.

Three-dimensional chromosome conformation capture and its derived technologies / 生物工程学报

Linear chromatin is compacted into eukaryotic nucleus through a complex and multi-layered architecture. Consequently, chromatin conformation in a local or long-distance manner is strongly correlated with gene expression. Chromosome conformation capture (3C) technology, together with its variants like 4C/5C/Hi-C, has been well developed to study chromatin looping and whole genome structure. In this review, we introduce new technologies including chromosome capture combined with immunoprecipitation, nuclei acid-based hybridization, single cell and genome sequencing, as well as their application.

Alternativas al modelo de investigación y desarrollo de medicamentos / Alternatives to the drug research and development model

Un tercio de la población mundial carece de acceso a los medicamentos y la situación es peor en los países pobres, en los que hasta un 50% de la población carece de acceso. El fracaso de los sistemas actuales de incentivos, basados en la propiedad intelectual, para ofrecer los productos farmacéuticos necesarios, especialmente en los países del sur, llama a la acción. Los problemas relacionados con el acceso a medicamentos no pueden ser resueltos tan solo a través de mejoras o adaptaciones de los modelos de incentivos existentes. El modelo del sistema de propiedad intelectual no ofrece la innovación necesaria para los países en desarrollo, se necesitan nuevos mecanismos que de forma simultánea y eficaz promuevan la innovación y el acceso a los medicamentos. Un tratado internacional vinculante sobre investigación y desarrollo, que se negocie bajo los auspicios de la Organización Mundial de la Salud, puede proporcionar el marco adecuado para garantizar el establecimiento de prioridades, la coordinación y la financiación sostenible de los medicamentos a precios asequibles para los países en desarrollo.

One-third of the global population lacks access to medications; the situation is worse in poor countries, where up to 50% of the population lacks access. The failure of current incentive systems based in intellectual property to offer the necessary pharmaceutical products, especially in the global south, is a call to action. Problems related to drug access cannot be solved solely through improvements or modifications in the existing incentive models. The intellectual property system model does not offer sufficient innovation for developing countries; new mechanisms that effectively promote innovation and drug access simultaneously are needed. A binding international agreement on research and development, negotiated under the auspices of the World Health Organization, could provide an adequate framework for guaranteeing priority-setting, coordination, and sustainable financing of drugs at reasonable prices for developing countries.

Caracterização da proteína quinase C Beta I nuclear em células tronco embrionárias / Characterization of protein kinase C beta I in embryonic stem cell nucleus

As proteína quinases C (PKC) pertencem à família das serina/treonina quinases, que vem sendo apontadas como importantes enzimas para os processos de proliferação e diferenciação das células tronco embrionárias (CTE), todavia, a função exata de cada isoforma dessa família ainda não está clara. Dados anteriores do nosso laboratório indicam que dentre as PKCs expressas em CTE, formas cataliticamente ativas da PKCßI são altamente expressas no núcleo das CTE murinas. Estas ao se diferenciarem expressam essa quinase no seu citoplasma ou deixam de expressar a mesma, e que a maioria dos alvos da PKCßI em CTE indiferenciada estão envolvidos em processos de regulação da transcrição de proteínas envolvidas em processos de proliferação/ diferenciação. Dando continuidade aos resultados anteriores do laboratório, no presente trabalho, com técnicas de proteômica e fosfoproteômica identificamos outros alvos nucleares da PKCßI em CTE indiferenciadas. Vimos que de fato inibindo-se a PKCßI diminuiu-se a fostorilação de fatores envolvidos com a indiferenciação das CTE. Dentre os alvos da PKCßI encontramos a proteína adaptadora, TIF1 que recruta proteínas remodeladoras de cromatina. Essa proteína é essencial para a manutenção do estado indiferenciado das CTE. In vitro a PKCßI foi capaz de fosforilar a TIF1ß e inibindo-se a PKCßI por RNAi vimos uma diminuição na expressão da TIF1ß e no fator de indiferenciação Nanog cuja expressão já foi demonstrada ser regulada pela TIF1ß. Além disso vimos que inibindo-se a PKCßI com o peptídeo inibidor da PKCßI aumentou a expressão de proteínas reguladas pelo c-Myc. E que o RNAi para a PKCßI aumentou a expressão de proteínas que regulam a expressão do c-Myc. Não vimos nenhum efeito na fosforilação ou expressão do c-Myc após a inibição da PKCßI o que sugere que a PKCßI ative proteínas repressoras do c-Myc. Nossos estudos sugerem que a PKCßI regula a manutenção do estado indiferenciado das CTE regulando a expressão e atividade da Tif1ß um possível alvo direto da PKCßI. Levando a modificações da cromatina e regulação da expressão de genes que mantém as CTE indiferenciadas. Outro ponto de regulação da PKCßI parece ser a nibição da atividade de c-Myc o que seria importante para a manutenção do estado indiferenciado visto que o c-Myc é um amplificador das vias de sinalização que mantém as células proliferando. Desta forma a PKCßI parece ter um papel central na regulação da expressão gênica de CTE à nível de modificações epigenéticas e a nível transcricional mantendo as CTE indiferenciadas

The Protein kinase C (PKC) family of serine/treonine kinases, are being described as important enzymes for proliferation and diferentiation of embryonic stem cells (ESC), however, the exact function of the different isoenzymes of this family still is unclear. Previous data from our laboratory indicates that amongst the PKCs expressed in ESC, catalytically active forms of PKCßI are highly expressed in nucleus of murine ESC. When these cells differentiate this kinase can be found in the cytoplasm or not expressed at all, and that the majority of PKCßI targets in undifferentiated ESC are involved in the regulation of proteins involved in transcription of proteins involved in proliferation/ diferentiation. Continuing our previous work herewith using proteomics and phosphoproteomics techniques we identified other nuclear PKCßI targets in undifferentiated ESC. We indeed saw that inhibiting PKCßI decreased the phosphorylation of factors involved with maintainance of the undifferentiated state of ESC. Amongst the targets of PKCßI we found the adaptor protein, TIF1ßI, that recruits cromatin remodeling proteins. This protein is essential for the maintenance of the undifferentiated state of ESC. In vitro PKCßI phosphorylated TIF1ß and inhibiting PKCßI with RNAi decreased the expression of TIF1ß and of the undifferentiation factor Nanog whose expression has been shown to be regulated by TIF1ß. We also saw that inhibiting PKCßI with a peptide inhibitor increased the expression of proteins regulated by c-Myc, and that RNAi for PKCßI increased the expression of proteins that regulate the expression of c-Myc. We did not see any effect on the phosphorylation or expression of c-Myc after inhibition of PKCßI suggesting that PKCßI activates c-Myc repressor proteins. Our studies sugest that PKCßI regulates the maintenance of the undiferentiated state of ESC regulating the expression and activity of Tif1ß a possibly a direct target of PKCßI, leading to chromatin modifications and regulation of genes that maintain ESC undiferentiated. Another form of regulation of PKCßI seems to be by inhibiting the activity of c-Myc which is importante to maintain ESC undifferentiated since c-Myc is na an amplifyer of signaling patheways that maintain ESC proliferating. Together PKCßI has a central role in the regulation of the gene expression of ESC at the level of epigenetic modifications and transcriptional regulation

Estudo da cromatina nos sítios de fixação à matriz nuclear no domínio do gene TP53 e das modificações epigenéticas e no modelo de progressão tumoral mamária 21T / MARs chromatin study on TP53 gene domain and epigenetic modifications in a breast cancer progression model

Dentre os diversos tipos de câncer agressivos, o câncer de mama é o mais comum em mulheres. Mutações hereditárias e adquiridas, assim como alterações epigenéticas atuam em sinergia na carcinogênese mamária e na progressão tumoral. A proteína P53 é uma supressora de tumor e possui uma atuação fundamental na integridade genômica. Apesar do vasto conhecimento sobre o controle da P53 a nível de proteína, ainda pouco se sabe sobre o controle transcricional do gene TP53. A série 21T, uma série de 4 linhagens celulares originadas da mama da mesma paciente, representando diferentes estágios de progressão tumoral mamária, é um eficiente modelo para investigação das alterações epigenéticas e suas influências na expressão gênica ao longo da progressão do câncer de mama. Nós analisamos a organização do domínio do gene TP53 através da técnica de arranjo de DNA, em diversas linhagens celulares de câncer de mama e linhagens controle, e realizamos uma tentativa de caracterizar estes elementos de DNA nas linhagens controle não-tumorais HB2 e MCF10A e nas tumorais MCF-7, MDA-MB-231, T47D, através dos marcadores epigenéticos de eucromatina, H4Ac, e heterocromatina, H3K9me3. Ainda analisamos a ligação de proteínas à região associada à matriz nuclear (MAR), denominada MAR 2, e a possível ligação da proteína ligante à matriz nuclear (MARBP), PARP-1, através de ensaios de gel shift (EMSA). Detectamos que na linhagem controle epitelial mamária, HB2, o gene TP53 está posicionado num domínio de DNA relativamente pequeno, aproximadamente 50 kb, delimitado por dois sítios de fixação à matriz nuclear. Interessantemente, esta estrutura de domínio se apresentou radicalmente diferente nas linhagens de câncer de mama estudadas, MCF7, T47D, MDA-MB-231 e BT474, nos quais o tamanho do domínio estudado estava aumentado e a transcrição do TP53 diminuída...

Breast cancer is the most common aggressive cancer type in women. Inherited and acquired mutations as well as epigenetic alterations act together in breast carcinogenesis and tumor progression. P53 is a tumor suppressor protein critical for genome integrity. Although its control at the protein level is well known, the transcriptional regulation of the TP53 gene is still unclear. The 21T series, a series of 4 breast cell lines originating from the same patient and representative of the breast tumor progression stages, is a suitable model to investigate epigenetic alterations and their influences upon gene expression during breast tumor progression. We have analyzed the organization of the TP53 gene domain using DNA arrays in several breast cancer and control cell lines and we made an attempt to characterize these DNA elements in breast non-cancerous cell lines HB2 and MCF-10, and cancerous MCF-7, MDA-MB-231 and T47D, through the determination of epigenetic markers of euchromatin, H4Ac, and heterochromatin, H3K9me3. We further analyzed the matrix attachment region (MAR), named MAR 2, protein binding, and possible MAR 2 binding of the important MAR binding protein (MARBP), PARP-1, by Electrophoretic mobility Shift Assay (EMSA). We have found that in the control breast epithelial cell line, HB2, the TP53 gene is positioned within a relatively small DNA domain, encompassing 50 kb, delimited by two nuclear matrix attachment sites. Interestingly, this domain structure was found to be radically different in the studied breast cancer cell lines, MCF7, T47D, MDA-MB-231 and BT474, in which the domain size was increased and TP53 transcription was decreased...

Expression of HMGB1 and HMGN2 in gingival tissues, GCF and PICF of periodontitis patients and peri-implantitis

High mobility group chromosomal protein B1 (HMGB1) and N2 (HMGN2), two members of High mobility group (HMG) family, play important role in inflammation. The purposes of this study were to investigate the expression of HMGB1 and HMGN2 in periodontistis. The expression of HMGB1 and HMGN2 mRNA in gingival tissues and gingival crevicular fluid (GCF) in chronic periodontitis (CP), generalized aggressive periodontitis (G-AgP) patients and healthy subjects was detected by real-time PCR. The protein level of HMGB1 and HMGN2 in peri-implant crevicular fluid (PICF), peri-implant crevicular fluid of peri-implantitis (PI-PICF) and normal patients was determined by Western blotting. Furthermore, IL-1â, IL-6, IL-8, TNF-á and HMGB1 levels in GCF, PI-PICF and healthy-PICF samples from different groups were determined by ELISA. HMGN2 expression was increased in inflamed gingival tissues and GCF from CP and G-ApG groups compared to control group. HMGB1 expression was the highest in the gingival tissues and GCF from CP patients and was accompanied by increased concentrations of IL-1â, IL-6, IL-8 proinflammaory cytokines. To our knowledge, this is the first study reporting that the expression of HMGB1 and HMGN2 was increased in the gingival tissues and GCF in CP and G-AgP and the PICF in PICF. Our data suggest that HMGB1 may be a potential target for the therapy of periodontitis and PI.

Avaliação computacional da compactação da cromatina e de características morfométricas da cabeça de espermatozoides de coelho (Oryctolagus cuniculus) / Computational evaluation of chromatin condensation and morphometric characteristics of rabbit (Oryctolagus cuniculus) sperm head

Investigou-se a correlação entre a morfometria da cabeça e a intensidade da condensação e heterogeneidade da cromatina em espermatozoides de coelho (Oryctolagus cuniculus). Para tal, utilizaram-se 35 esfregaços de sêmen de coelhos da raça Nova Zelândia, corados com azul de toluidina e avaliados por análise de imagem computacional. As imagens foram obtidas digitalmente em tons de cinza e avaliadas por algoritmos desenvolvidos em ambiente de programação Scilab. As mensurações obtidas da cabeça dos espermatozoides foram área, perímetro, comprimento, largura, relação comprimento largura, elipsidade, fator de forma, descritores Fourier e simetria lateral e anteroposterior. Também foram avaliadas a intensidade da compactação e a heterogeneidade da cromatina espermática. Os espermatozoides de coelho apresentaram compactação e heterogeneidade cromatínica mais intensas do que os de touro e observou-se correlação significativa entre características morfométricas da cabeça e compactação e heterogeneidade cromatínica. Conclui-se que a cromatina é importante para a constituição morfológica da cabeça de espermatozoides de coelho e que a cromatina espermática de coelho é naturalmente mais heterogênea e menos compactada que a de touro.

The correlation between the head morphometry and the intensity of condensation and heterogeneity of sperm chromatin were investigated in rabbit (Oryctolagus cuniculus). To this, 35 semen smears from New Zealand rabbits were stained with toluidine blue and evaluated by computer image analysis. The images were obtained in digital grayscale and analyzed by algorithms developed in the Scilab programming environment. The measurements obtained from the sperm heads were area, perimeter, length, width, length:width ratio, ellipticity, shape factor, lateral and anterior-posterior symmetries, and Fourier descriptors. The intensity and heterogeneity of the compaction of sperm chromatin was also evaluated. The rabbit spermatozoa showed chromatin heterogeneity and condensation more intense than the bull spermatozoa, and it was observed correlation between morphometric characteristics of the head and chromatin compaction and heterogeneity. The results suggest that chromatin is important for the morphological constitution of the head morphology spermatozoa head, as well as, rabbit sperm chromatin is inherently more heterogeneous and less condensed than the bull sperm chromatin.

Epigenetics and epigenetic mechanisms in disease with emphasis on autoimmune diseases.

Epigenetics deals with molecular heritable patterns relating to chromatin, which exists in two alterable and inter-convertible states. The two conformations of chromatin i.e., compact and relaxed are due to epigenetic regulation. The alterations in chromatin normalize gene expression patterns. Thus, the epigenetic marks on chromatin are the deciding factors for either gene silencing or activation. The epigenetics introduced a new term viz., epiallele which deviates from the classical Mendelian allele. The remodeling of chromatin during embryonic phase, post-translational aberrations of chromatin proteins causing cellular dysfunction and possible epigenetic therapies are discussed in the present article. The role of epigenetic mechanisms in triggering / progression of several autoimmune diseases is being emphasized off late. The study of such complex epigenetic processes becomes very important in understanding the etiopathology of the disease as well as in designing target therapies.

Aumento del daño en el ADN y estrés oxidativo en espermatozoides de pacientes con oligozoospermia idiopática y antecedentes de criptorquidismo / Extent of sperm DNA damage in spermatozoa from men examined for infertility. Relationship with oxidative stress

Background: Cryptorchidism and oligozoospermia are clinical conditions closely associated with impaired fertility. Oxidative stress and related sperm DNA damage have been identified as significant causes of male infertility. Aim: To determine the extent of sperm nuclear DNA damage in patients affected with idiopathic oligozoospermia or undescended testes and to examine its relationship with oxidative stress. Patients and methods: We studied 20 patients with idiopathic oligozoospermia and 18 with undescended testes (who previously underwent orchiopexy) and 25 normozoospermic healthy controls. All subjects underwent semen analysis. Sperm DNA damage was evaluated by the sperm chromatin structure assay/flow cytometry (SCSA-FCM) and by the dUTP-biotin nick end labeling (TUNEL) assay. Levels of reactive oxygen species (ROS) and total antioxidant capacity (TAC) were assessed by a chemiluminescence assay. Results: DFI (percentage of sperm with denatured DNA) values and percentage of TUNEL positive cells were significantly greater in patients with oligozoospermia (DFI: 28.8±5.6; TUNEL+: 26.9±3.0) or cryptorchidism (DFI: 26.4±10.1; TUNEL+: 29.1±3.9), compared with controls (DFI: 7.1±0.9; TUNEL+: 14.2±1.2). Similarly, both groups of patients had significantly higher (p <0.01) levels of ROS. TAC levels did not differ between control and patient groups, suggesting that the DNA damage occurs before spermiation. Conclusions: Sperm DNA damage is significantly increased in men with idiopathic oligozoospermia and in cryptorchid subjects. The finding of increased ROS levels may indicate that seminal oxidative stress may be involved in the pathogenesis of sperm DNA damage in these patients.

The chromatin structure of the lysozyme GAS41 origin of DNA replication changes during the cell cycle

We used a rapid and simple protocol using lysolecithin for mapping HS sites in vivo. The protocol is based on partial digestion with DNase I of exponentially growing cells following permeabilization by short treatment with lysolecithin. Using this protocol, we analyzed the chromatin structure of the region surrounding two overlapping elements, an origin of bidirectional DNA replication and the GAS41 promoter, in chicken myelomonocytic HD11 cells arrested in G0, G0 and S phases as well as at the G0/S border. The results show that the chromatin of this region became more nuclease sensitive when cells were arrested in G0 phase and that this change in chromatin structure was reversible after the cells began to enter S phase.

Extendend chromatin fibers in spermatozoa of apis mellifera (HYMENOPTERA, APOIDEA)

The flow of chromatin from the nuclei of mouse liver cells and spermatozoa after treatment with concentratedsaline and detergent solutions under the simultaneous action of gravity results in the formation of extendedchromatin fibers (ECF). In mouse somatic nuclei, the increase in chromatin condensation is accompaniedby a decrease in the frequency of ECF formation. Since tightly packed chromatin with a very lysine-richhistone variant that resembles somatic H1 histones occurs in honey bee spermatozoa, we examined theformation of ECF in sperm cells of Apis mellifera, and compared the findings with data for mouse cells.Freshly prepared smears of fixed and unfixed semen from A. mellifera were lysed under the action of gravity,stained with toluidine blue at pH 4.0, and examined with polarized and unpolarized light. A protocol usingunfixed preparations and a short lysis period that resulted in abundant ECF production in mouse hepatocytes(which contain loosely-packed chromatin) and sperm cells produced ECF in only a few spermatozoa of A.mellifera. In contrast, a protocol using fixed preparations and a long lysis period produced fewer ECFs inthe former two cell types and no ECF formation in honey bee spermatozoa. The limited chromatin fluidityin A. mellifera spermatozoa may reflect their special DNA-protein composition and organization in the cellnuclei, the participation of nuclear matrix elements, a less effective disruption of the nuclear envelope andplasmalemmal components during lysis, and/or cytoplasmic spatial constraints resulting from particularitiesin the acrosomal complex.

Metilación del ADN: un fenómeno epigenético de importancia médica / DNA methylation: an epigenetic process of medical importance

Methylation of CpG dinucleotides is an epigenetic mechanism involved in the regulation of gene expression in mammals. The patterns of CpG methylation are specie and tissue specific. The biological machinery of this system comprises a variety of regulatory proteins including DNA methyltransferases, putative demethylases, methyl-CpG binding proteins, histones modifying enzymes and chromatin remodeling complexes. DNA methylation maintains gene silencing and participates in normal development, genomic imprinting and X chromosome inactivation. In contrast, alterations in DNA methylation participate in the induction of some human diseases, especially those involving developmental defects and tumorigenesis. This review summarizes the molecular aspects of DNA methylation and its implications in cancer and other human diseases in which this epigenetic mechanism has been involved. Our understanding of the epigenetic changes that occur in human diseases will be very important for future management. Changes in the patterns of methylation can be used as markers in cancer and their potentially reversible state creates a target for therapeutic strategies involving specific gene re-activation or re-silencing.

La metilación del ADN en dinucleótidos CpG es uno de los mecanismos epigenéticos implicados en la regulación de la expresión génica en mamíferos. Los patrones de metilación son específicos para cada especie y tipo de tejido. La maquinaria implicada comprende diferentes proteínas reguladoras incluyendo a las ADN metiltransferasas, desmetilasas putativas, proteínas de unión a CpG metilados, enzimas modificadoras de histonas y complejos remodeladores de la cromatina. La metilación del ADN es de vital importancia para mantener el silenciamiento génico en el desarrollo normal, la impronta genómica y la inactivación del cromosoma X. En contraste, alteraciones en ella están implicadas en algunas enfermedades humanas, especialmente aquéllas relacionadas con defectos en el desarrollo y el proceso neoplásico. Esta revisión resume los aspectos moleculares de la metilación del ADN y su participación en el desarrollo normal, el cáncer y en algunas patologías humanas en las que los mecanismos epigenéticos han sido implicados. El conocimiento de las modificaciones epigenéticas que ocurren en las enfermedades humanas será importante para su manejo futuro. Los cambios en los patrones de metilación podrán ser empleados como marcadores en cáncer y el estado potencialmente reversible de este proceso constituye un blanco ideal para crear estrategias terapéuticas que impliquen la reactivación o el re-silenciamiento de genes específicos.

Molecular biology of ageing.

The process of deterioration or ageing of functions that occurs in all organisms after the attainment of reproductive ability is the sum total of the decline in activity of various organs. The functions of different organs begin to deteriorate at different times of the life span and at different rates. It is believed that different genes are involved in the ageing of different organs. Studies on isoenzyme patterns of enzymes show that the genes responsible for coding of different subunits of the enzymes are sequentially expressed during the life span. Also, the decrease in the levels of enzymes seen after adulthood is reversible and can be raised to adult level by inducing their genes by steroid hormones. Another factor that contributes to the decrease in the levels of enzymes is increasing compaction of the chromatin that houses the genes as seen from digestion of chromatin by DNase I and MNase. This decreases the rate of transcription of genes. The expression of many genes declines after adulthood which is due to the decrease in trans-acting nuclear proteins that bind to specific cis-acting sequences in the promoter regions of genes. These proteins are inducible by steroid hormones. Hence the deterioration of functions that occurs after adulthood can be delayed, and the adulthood period can by prolonged by manipulation of the expression of genes.