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G9a histone methyltransferase plays a dominant role in euchromatic histone H3 lysine 9 methylation and is essential for early embryogenesis.

ABSTRACT: Covalent modification of histone tails is crucial for transcriptional regulation, mitotic chromosomal condensation, and heterochromatin formation. Histone H3 lysine 9 (H3-K9) methylation catalyzed by the Suv39h family proteins is essential for establishing the architecture of pericentric heterochromatin. We recently identified a mammalian histone methyltransferase (HMTase), G9a, which has strong HMTase activity towards H3-K9 in vitro. To investigate the in vivo functions of G9a, we generated G9a-deficient mice and embryonic stem (ES) cells. We found that H3-K9 methylation was drastically decreased in G9a-deficient embryos, which displayed severe growth retardation and early lethality. G9a-deficient ES cells also exhibited reduced H3-K9 methylation compared to wild-type cells, indicating that G9a is a dominant H3-K9 HMTase in vivo. Importantly, the loss of G9a abolished methylated H3-K9 mostly in euchromatic regions. Finally, G9a exerted a transcriptionally suppressive function that depended on its HMTase activity. Our results indicate that euchromatic H3-K9 methylation regulated by G9a is essential for early embryogenesis and is involved in the transcriptional repression of developmental genes.

SUBMITTER: Tachibana M

PROVIDER: S-EPMC186403 | biostudies-literature | 2002 Jul

REPOSITORIES: biostudies-literature

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G9a histone methyltransferase plays a dominant role in euchromatic histone H3 lysine 9 methylation and is essential for early embryogenesis.

Tachibana Makoto M Sugimoto Kenji K Nozaki Masami M Ueda Jun J Ohta Tsutomu T Ohki Misao M Fukuda Mikiko M Takeda Naoki N Niida Hiroyuki H Kato Hiroyuki H Shinkai Yoichi Y

Genes & development 20020701 14

Covalent modification of histone tails is crucial for transcriptional regulation, mitotic chromosomal condensation, and heterochromatin formation. Histone H3 lysine 9 (H3-K9) methylation catalyzed by the Suv39h family proteins is essential for establishing the architecture of pericentric heterochromatin. We recently identified a mammalian histone methyltransferase (HMTase), G9a, which has strong HMTase activity towards H3-K9 in vitro. To investigate the in vivo functions of G9a, we generated G9a ...[more]

PMID: 12130538

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Project description:Methylation of lysine 9 (K9) in the N-terminus tail of histone H3 (H3) in chromatin is associated with transcriptionally silenced genes and is mediated by histone methyltransferases. Murine G9a is a 1263 amino acid H3-K9 methyltransferase that possesses characteristic SET domain and ANK repeats. In this paper, we have used a series of green fluorescent protein-tagged deletion constructs to identify two nuclear localization signals (NLS), the first NLS embedded between amino acids 24 and 109 and the second between amino acids 394 and 401 of murine G9a. Our data show that both long and short G9a isoforms were capable of entering the nucleus to methylate chromatin. Full-length or N-terminus-deleted G9a isoforms were also catalytically active enzymes that methylated recombinant H3 or synthetic peptides representing the N-terminus tail of H3. In vitro methylation reactions using N-terminus tail peptides resulted in tri-methylation of K9 that remained processive, even in G9a enzymes that lacked an N-terminus region by deletion. Co-expression of G9a and H3 resulted in di- and tri-methylation of H3-K9, while siRNA-mediated knockdown of G9a in HeLa cells resulted in reduction of global H3-K9 di- and tri-methylation. A recombinant deletion mutant enzyme fused with maltose-binding protein (MBP-G9aDelta634) was used for steady-state kinetic analysis with various substrates and was compared with full-length G9a (G9aFL). Turnover numbers of MBP-G9aDelta634 for various substrates was approximately 3-fold less compared with G9aFL, while their Michaelis constants (K(m)) for recombinant H3 were similar. The K(AdoMet)m for MBP-G9aDelta634 was approximately 2.3-2.65 microM with various substrates. Catalytic efficiencies (kcat/K(m)) for both MBP-G9aDelta634 and G9aFL were similar, suggesting that the N-terminus is not essential for catalysis. Furthermore, mutation of conserved amino acids R1097A, W1103A, Y1120A, Y1138A and R1162A, or the metal binding C1168A in the catalytic region, resulted in catalytically impaired enzymes, thereby confirming the involvement of the C-terminus of G9a in catalysis. Thus, distinct domains modulate nuclear targeting and catalytic functions of G9a.

Dataset Information

G9a histone methyltransferase plays a dominant role in euchromatic histone H3 lysine 9 methylation and is essential for early embryogenesis.

Publications

G9a histone methyltransferase plays a dominant role in euchromatic histone H3 lysine 9 methylation and is essential for early embryogenesis.

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