The Histone H3K79 Methyltransferase Dot1L Is Essential for Mammalian Development and Heterochromatin Structure

Abstract

Dot1 is an evolutionarily conserved histone methyltransferase specific for lysine 79 of histone H3 (H3K79). In Saccharomyces cerevisiae, Dot1-mediated H3K79 methylation is associated with telomere silencing, meiotic checkpoint control, and DNA damage response. The biological function of H3K79 methylation in mammals, however, remains poorly understood. Using gene targeting, we generated mice deficient for Dot1L, the murine Dot1 homologue. Dot1L-deficient embryos show multiple developmental abnormalities, including growth impairment, angiogenesis defects in the yolk sac, and cardiac dilation, and die between 9.5 and 10.5 days post coitum. To gain insights into the cellular function of Dot1L, we derived embryonic stem (ES) cells from Dot1L mutant blastocysts. Dot1L-deficient ES cells show global loss of H3K79 methylation as well as reduced levels of heterochromatic marks (H3K9 di-methylation and H4K20 tri-methylation) at centromeres and telomeres. These changes are accompanied by aneuploidy, telomere elongation, and proliferation defects. Taken together, these results indicate that Dot1L and H3K79 methylation play important roles in heterochromatin formation and in embryonic development. Histone methylation plays a critical role in the regulation of gene expression and chromatin structure. Among the sites of histone methylation, lysine 79 of histone H3 (H3K79) is unique in that it is not located within the H3 N-terminal tail but in the globular domain. Our knowledge about H3K79 methylation comes primarily from studies in yeast. This study focuses on the role of H3K79 methylation in mammalian development and cellular function. We show that genetic disruption of Dot1L, the only known H3K79 methyltransferase gene in mouse, results in embryonic lethality. At the cellular level, Dot1L deficiency leads to alterations in constitutive heterochromatin, accompanied by telomere elongation, aneuploidy, and proliferation defects. Our work represents a key step toward understanding the function of H3K79 methylation in mammals.