Epigenetics and phenotypic plasticity: histone modification in the European sea bass

Trabajo final presentado por Paula Gómez Álvarez para obtener el grado en Biología por la Universitat de Barcelona (UB), realizado bajo la dirección del Dr. Francesc Piferrer y la Dra. Dafni Anastasiadi del Institut de Ciències del Mar (ICM-CSIC).-- 35 pagesRecent evidence shows that epigenetic modifications are involved in the long-lasting effects of elevated temperature during early development in fish. However, the evidence concerns DNA methylation, but other epigenetic modifications such as histone modifications have not been properly addressed. The objective of this study was to determine whether histone modifications could contribute to explain observed changes in gene expression in fish exposed to elevated temperature during initial stages of life. We used farmed European sea bass as the target species. We used chromatin immunoprecipitation (ChIP) to analyse two histone modifications: H3K4me3, associated with gene transcription activation, and H3K9me3, associated with gene transcription repression. Each modification was studied independently in three genomic features: the gene promoter, the region around the Transcription Start Site (TSS) and the immediate region downstream. The two genes considered were aq1(aquaporin 1), which was not affected by temperature and was used as a control, and wisp1 (wnt< inducible signaling pathway protein 1), the expression of which was significantly downregulated by elevated temperature. The work carried out included all aspects of the technique including its optimization, to which a lot of efforts were devoted. Despite these efforts, results showed that, in accordance with was expected based on gene expression data, no statistical differences were found in the two histone modifications in any of the three genomic regions studied in the aq1 gene. However, and in contrast to expectations, no differences were found either in the in the two histone modifications in any of the three genomic regions studied in the wisp gene. Further, H3K4me3 was enriched although in a non-statistically significant manner. We consider several factors to explain the lack of differences, including the limited sample size that resulted in large standard deviations or the genomic regions selected. Lack of direct relationship between histone modifications (for that matter, any type of epigenetic modification, including also DNA methylation) and gene expression patterns are not rare. In any case, our results show the complexity and intrinsic multifactorial nature of gene expression regulation in vertebratesPeer Reviewe