Reprogramming of epigenetic marks during early development across vertebrates

XIII Congress of the Iberian Association of Comparative Endocrinology - XIII Congreso de la Asociación Ibérica de Endocrinología Comparada (AIEC), 16-17 September 2021
Epigenetics concerns mechanisms modifying gene expression that do not imply changes to the DNA sequences. Epigenetic marks, also to be maintained during mitotic division, can be transmitted from parental germ cells to offspring. DNA methylation, one of the most studied epigenetic modifications, is commonly associated with gene expression silencing. In vertebrates, it mostly occurs in CpG sites. Promoters and other regulatory regions are usually enriched with CpGs. DNA methylation has important roles in vertebrates, being associated with phenomena such as genome imprinting and reprogramming, the latter playing an important role in embryonic development. Reprogramming during early development is well studied in mammals. However, much is still to be done in fish. Here we review the situation concerning epigenetic reprogramming events that occur during embryo development across vertebrates. In mammals is well demonstrated that reprogramming occurs during primordial germ cell development and early embryogenesis. In the second process, paternal and maternal methylomes experience active demethylation during the early cleavage stages, reaching the lowest level upon specification to the inner cell mass. Nevertheless, in fish, information is available only for a couple of species. In zebrafish (Danio rerio) methylation changes were mostly detected in oocyte-specific CpGs, to resemble paternal methylome before zygotic genome activation. In contrast, in medaka (Oryzias latipes), strategies similar to mammals seem to be adopted, since in both parental genomes methylation levels were decreased up to 20%, earlier, by the 1st cell cycle. This scarce data seems to suggest that epigenome reprogramming could be species-specific in fish. Consequently, our objective is to determine what is the situation during European sea bass (Dicentrarchus labrax) embryo development, firstly because it is phylogenetically distant from medaka (Cyprinodontiforme) and zebrafish (Cyprinid), and second, to improve our knowledge about epigenetic inheritance to devise breeding strategies able to maintain certain favorable traits in cultured species
Research funded by the Ministry of Science and Innovation “EPIPURE” (PID2019-108888RB-I00) grant to FP