Thèse de doctorat en Biologie moléculaire et cellulaire
Sous la direction de Minoo Rassoulzadegan.
Soutenue en 2011
à Nice , dans le cadre de École doctorale des Sciences de la vie et de la santé (Sophia Antipolis, Alpes-Maritimes) , en partenariat avec Université de Nice-Sophia Antipolis. Faculté des sciences (autre partenaire) .
Epigenetics deals with heritable alterations in gene expression that is not based on changes n DNA sequence. It was thought that DNA methylation and chromatin-encoded epigenetic information were the only epigenetic marks transmitted to the following generations. Recently, our group described the role of RNA in hereditary epigenetic variation, paramutation in mice. The role of RNA was demonstrated by the establishment of a heritable phenotype following microinjection into one-cell embryos of Kit heterozygous sperm RNA. It was further confirmed by induction of hereditary phenotypes after microinjection of an oligoribonucleotide with a Kit RNA sequence or small noncoding RNAs (miR-222 and miR-124). We now report that, Dnmt2, a RNA methyltransferase, is required for induction by small non-coding RNAs of hereditaty epigenetic variation of expression of the Kit and Sox9 genes, inactivation of the Dnmt2 gene precluded their occurrence. Kit* paramutants, which maintain a mutant phenotype with a Kit+/+ genotype, were not observed in the progeny of crosses between Dnmt2-/- Kittm1al∫+ heterozygotes, no were they generated by microinjection in fertilized eggs of RNAs of the Dnmt2-negative Kit heterozygotes. The Sox9 “giant” phenotype was similary not generated by miR-124 RNA in Dnmt2-/- embryos. Interaction of the Dnmt2 protein with Kit RNA was evidenced by co-immunoprecipitation assays. Bisulfite sequencing assays detected Dnmt2-dependent cytosine methylation in Kit RNA, exclusively in embryos undergoing the modification. RNA methylation effected by Dnmt2 appears as a key feature of the induction of epigenetic variations by non-coding RNAs. In the other hand, growing evidence indicates thet ncRNAs play a key role in regulation of basal transcription machinery. Several studies have recently revealed that noncoding RNAs such as B2RNA, 7SK and U1 snRNA are involved in the regulation of CTD phosphorylation of RNA polymerase II by modulating kinase activity of Cyclin H/T1. Here we reported cardiac hypertrophy in Dnmt2 mutant mice which is accompanied by enhanced activity of RNA polymerase II. Our results showed significant changes in the expression profiles of B2 RNA abd ASK in wild type compare to Dnmt2 mutant mice. In this study, we are attempting to determine that methyl transferase activity of Dnmt2 has a potential role in epigenetic inheritance and pathology.