The epigenetic regulation is crucial during development and gametogenesis in vertebrates, but remains poorly understood in lophotrochozoans. This work aims to characterize in the oyster Crassostrea gigas orthologues of the Jumonji histone demethylases (JHDMs) and histone methylation. Nine Cg_Jumonji genes encoding putative JHDM orthologues have been characterized at the molecular and phylogenetic levels, for the first time in molluscs. Their expression and localization during gametogenesis and development suggest a conserved role for the Cg_Jumonji, despite the expression of recombinant Cg_Jumonji did lot lead, to date, to the characterization of their catalytic activity. In parallel, this study showed that histones, noticeably H3K4 and H3K9 residues, display specific methylation patterns which were regulated during early embryogenesis. In addition, the use of a specific inhibitor of JHDMs in vivo led to hypermethylation of histones and abnormal phenotypes of larvae. Microarray analyzes revealed that histone methylation is associated to differential transcriptomes during development, involving genes related to development and cell proliferation. Finally, an experiment showed the influence of temperature on both the Cg_ Jumonji expression and the methylation of histones during development. Taken together, these results indicate a critical importance of histone methylation during development of Crassostrea gigas and the putative implication of the Cg_jumonji in this context. This study illustrates for the first time the importance of histone methylation in Lophotrochozoa. Ultimately, these results will help to better understand the life cycle of the oyster, a molluk of major fundamental and applied interests, in interaction with its environment within a context of global changes and important mortalities.
Key words: Epigenetics, histone, methylation, Jumonji, environment, Mollusks, development, gametogenesis, Crassostrea gigas