[EN] Epigenetics studies the heritable changes in gene function that cannot be explained by changes in the DNA sequence. There are three common epigenetic mechanisms known as the DNA methylation, histone modifications and non-coding RNAs. These mechanisms can modify the way genes are expressed in the organism and thus can regulate DNA expression. DNA methylation is the best studied epigenetic mechanism, and the only one that can covalently modify DNA. These reactions are catalyzed by a group of enzymes known as DNA methyl-transferases (dnmts). This methylation is usually associated to gene silencing and hence is very important to gene expression regulation.This epigenetic mechanism has been found to be important in the sex differenciation process in some species like the European Sea bass. The zebrafish, also known as Danio rerio, is used in this study as a model organism due to its many advantages over other organisms. Zebrafish embryonic development is roughly the same as other higher vertebrates. Also, zebrafish and the human genome are very similar, so studies in this model organism can be extrapolated easily. This study will show how to maintain a transgenic zebrafish line (vasa:EGFP) through selective breeding and its use to study piscine dnmts.Thus, to have a better understanding on how DNA-methylation works on gonadal development we studied the expression levels of two zebrafish dnmts: dnmt1and dnmt 3. The gene expression has been studied on individuals at different ages and from different gender to determine if there were differences between them. The data shows that the differences between male and female fishes most of the time are not significant. However, gene expression levels vary significantly throughout the development. Therefore DNA-methylation must be an important mechanism in zebrafish gonadal development

[ES] La epigenética se puede definir como el estudio de cambios heredables en la función genética que no pueden ser explicados por cambios producidos en la secuencia de ADN (Russo et al., 1996). Existen tres mecanismos epigenéticos que afenctan la expresión de los genes: la metilación del ADN, las modificaciones de histonas y los ARN no codificantes. El conjunto de modificaciones químicas del ADN junto con los cambios producidos por las histonas forman un complejo regulatorio que modula la estructura de la cromatina y la función génica. Los mecanismos epigenéticos otorgan a los organismos la habilidad de integrar información genómica y ambiental para modificar sus genes y generar un fenotipo determinado. Durante el desarrollo, las células se diferencian, adquieren y mantienen una identidad a partir de cambios en la expresión génica. Todo esto es crucial para los procesos de determinación y diferenciación sexual, siendo ambos procesos indispensables para el funcionamiento y la perpetuación de las especies (Piferrer, 2013). [...]

Trabajo final presentado por Antoni Costa Ribas para el grado de Biología de la Universitat de Barcelona (UB), realizado bajo la dirección del Dr. Francesc Piferrer del Institut de Ciències del Mar (ICM-CSIC) y de la Dra. Creu Palacín de la Universitat de Barcelona (UB).-- 71 pages, 9 figures, 4 tables, supplements