Monomethylation of Histone H4-Lysine 20 Is Involved in Chromosome Structure and Stability and Is Essential for Mouse Development

Abstract

PR-Set7/Set8/KMT5A is the sole enzyme known to catalyze monomethylation of histone H4 lysine 20 (H4K20) and is present only in multicellular organisms that compact a large fraction of their DNA. We found that mouse embryos that are homozygous null mutants for the gene PR-Set7 display early embryonic lethality prior to the eight-cell stage. Death was due to the absence of PR-Set7 catalytic activity, since microinjection of the wild type, but not a catalytically inactive version, into two-cell embryos rescued the phenotype. A lack of PR-Set7 activity resulted not only in depletion of H4K20me1 but also in reduced levels of the H4K20me2/3 marks catalyzed by the Suv4-20h1/h2 enzymes, implying that H4K20me1 may be essential for the function of these enzymes to ensure the dimethylated and trimethylated states. Embryonic stem cells that were inducibly deleted for PR-Set7 passed through an initial G 2 /M phase, but the progeny were defective at the subsequent S and G 2 /M phases, exhibiting a delay in their cell cycle, accumulation at G 2 /M, massive DNA damage, and improper mitotic chromosome condensation. Cell cycle analysis after synchronization indicated that the defects were a consequence of decreased H4K20me1 due to the absence of PR-Set7. Most importantly, the lack of H4K20me1 also resulted in defects in chromosome condensation in interphase nuclei. These results demonstrate the critical role of H4K20 monomethylation in mammals in a developmental context.Posttranslational modifications (PTMs) on histones influence intra-and internucleosomal interactions and thereby contribute to the diversity in nucleosome and chromatin structure that impacts distinct genomic processes. Among these modifications, histone methylation had been considered to be relatively stable, but recent studies demonstrated that, similar to the other PTMs, it too is subject to regulation. Many methylating and demethylating enzymes that target different lysine and arginine residues have been identified. These enzymes have distinct specificities with respect to the methylation status (monomethyl, dimethyl, and trimethyl) of each residue. Furthermore, increasing numbers of proteins harboring the motifs that specifically recognize various methylated residues have been identified. These proteins, or effectors, mediate/regulate elaborate chromatin-based processes, such as gene expression, which are dictated by the presence of the PTMs. Thus, the catalysis/removal of PTMs and their recognition by effectors constitute an intricately designed system that is key to genomic integrity and function.One of the residues of histone H4 that can be monomethylated, dimethylated, or trimethylated is lysine 20. Recent comprehensive analysis of H4 modifications with top-down mass spectrometry in human and in Drosophila melanogaster cells revealed that the dimethyl group is deposited on the majority of total H4K20, indicative of the wide distribution of H4K20me2 on chromatin (18, 34). On the other hand, H4K20me1 and H4K20me3 are relatively few in abundance. The study a...

Epigenetic inheritance: Uncontested?

“…This was confirmed by an independent study [52]. These results are consistent with the findings that H4K20me2-3, established by the Suv4-20 enzymes, requires H4K20me1 [53], which is catalyzed by PR-Set7, whose expression is cell cycle-regulated and present from G2 to early G1 [54][55][56][57][58].…”

Regulation of chromatin by histone modifications

“…For example, homozygous null mutant embryos for the gene PR-Set7 (an H4K20me1 HMT) display early lethality due to cell-cycle defects, massive DNA damage and improper mitotic chromosome condensation [115]. Moreover, mice deficient for the SUV39 H3K9 methyltransferase demonstrate reduced levels of heterochromatic H3K9me2/3 and they have impaired genomic stability and show an increased risk of developing cancer [116].…”

Characterization of non-canonical Polycomb Repressive Complex 1 subunits during early mouse embryogenesis

“…1,2,4 Secondly, PRC1.6 contains a recognition module, through L3MBTL2, for H4K20me1, which is essential for pre-implantation development, as deletion of PR-Set7 results in lethality by the 8-cell stage, in a manner dependent of its methyltransferase activity. 13,21 Since L3MBTL2 is a defining, unique feature of PRC1.6, we therefore assessed its localization through preimplantation development. L3MBTL2 was readily detected in the mature GV oocyte, where it exhibited a rather uniform nuclear localization, but was excluded from the DAPI-rich regions (Fig.…”