Caractérisation moléculaire et fonctionnelle d’une usine inédite de méthylases de la lysine 9 de l’histone H3 (H3K9) – H3K9-methylome
Mechanisms of transcriptional repression are important during terminal differentiation of cells. In addition to tissue-specific transcription factors, chromatin modifications play a central role in cell fate regulation. Skeletal muscle terminal differentiation is orchestrated by the myogenic transcription factors of the MEF2 and MyoD families. These transcription factors, in collaboration with chromatin-modifying enzymes, act in specific combinations and within complex transcriptional regulatory networks to achieve skeletal myogenesis. Indeed, epigenetic mechanisms play also a central role during this process. Among these mechanisms, histone H3 lysine 9 (H3K9) methylation pathway, which is involved in gene silencing and in the formation and maintenance of heterochromatin, is of crucial interest during myogenesis. The main goal of our original project was to elucidate the epigenetic mechanims involved in the regulation of skeletal muscle genes during terminal (trans)-differentiation induced by MyoD. To get insight into this, we performed an exhaustive biochemical characterization of MyoD protein partners. In addtion to known partners, we have found that MyoD interacts physically and functionally with the Heterochromatin Protein HP1 family, which recognize methylated H3K9 to insure gene silencing and heterochromatin maintainance (Yahi et al. 2008). In addition, our results show for the first time that MyoD copurifies with 4 histone methyltransferases (HMTs) specific for H3K9, namely Suv39h1, G9A, GLP and SETDB1! We and others have already found that Suv39h1 and H3K9 methylation are involved in MyoD target genes regulation. Our recent results indicate, in another cell system (ES cells), the existence a functional factory of 4 H3K9 HMTases composed of Suv39h1, G9A, GLP and SETDB1 (Fritsch et al, submitted, manuscript provided in annex). Thus, H3K9 methylation and H3K9 HMTs seem to play crucial roles in facultative heterochromatin establishment during muscle differentiation. On another hand, Suv39h1, G9A, GLP, and SETBD1 were all linked to human diseases (Huntington disease, Parder-Willi syndrome, and tumorigenesis). It is thus extremely important to understand how these H3K9 HMTs achieve their roles, especially during myogenesis. The project proposed here aims at deciphering the role of this H3K9 HMT factory during skeletal muscle differentiation. Our goals are: 1- Study the individual roles of the H3K9 HMT Suv39h1, G9A, GLP and SETDB1 in the regulation of myogenesis (cell cycle exit and terminal differentiation); 2- Biochemical characterization of the protein complexes containing the H3K9 HMT Suv39h1, G9A, GLP and SETDB1 in myoblasts. We hope to confirm the existence of the H3K9 methylases factory in muscle cells and its collaboration with MyoD. 3- Global identification of the target genes of the H3K9 HMT Suv39h1, G9A, GLP and SETDB1 in myoblasts (ChIP-seq, SACO method). We will get a global picture of the physiological pathways (co)-regulated by this HMTs factory in myoblasts. The quaternary complex of H3K9 HMT plays a role during ES cells differentiation (Fritsch et al, submitted). We will get insight on its role during myogenesis. The results will at least help improving the efficiency of cellular reprogramming used in cellular therapy applied to myopathies. On another hand, in contrast to genetic aberrations, epigenetic mechanisms can be reversed by the use of chemical inhibitors. Thus, our results will contribute to develop fine therapies targeting components of H3K9 methylation multimeric complexes.
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
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