The Histone H4 Lysine 20 Monomethyl Mark, Set by PR-Set7 and Stabilized by L(3)mbt, Is Necessary for Proper Interphase Chromatin Organization

Article (PDF Available)inPLoS ONE 7(9):e45321 · September 2012with14 Reads
DOI: 10.1371/journal.pone.0045321 · Source: PubMed
Drosophila PR-Set7 or SET8 is a histone methyltransferase that specifically monomethylates histone H4 lysine 20 (H4K20). L(3)MBT has been identified as a reader of methylated H4K20. It contains several conserved domains including three MBT repeats binding mono- and dimethylated H4K20 peptides. We find that the depletion of PR-Set7 blocks de novo H4K20me1 resulting in the immediate activation of the DNA damage checkpoint, an increase in the size of interphase nuclei, and drastic reduction of cell viability. L(3)mbt on the other hand stabilizes the monomethyl mark, as L(3)mbt-depleted S2 cells show a reduction of more than 60% of bulk monomethylated H4K20 (H4K20me1) while viability is barely affected. Ploidy and basic chromatin structure show only small changes in PR-Set7-depleted cells, but higher order interphase chromatin organization is significantly affected presumably resulting in the activation of the DNA damage checkpoint. In the absence of any other known functions of PR-Set7, the setting of the de novo monomethyl mark appears essential for cell viability in the presence or absence of the DNA damage checkpoint, but once newly assembled chromatin is established the monomethyl mark, protected by L(3)mbt, is dispensable.
    • "Perhaps in the absence of new modification, feedback stabilisation of H4K20 monomethylation occurs. This could happen through the l(3)mbt protein, which has been shown to play a role in the stabilisation of H4K20 monomethylation (Sakaguchi et al., 2012). It could also be mediated by prevention of the removal of H4K20 monomethylation [e.g. by the demethylase PHF8 (Liu et al., 2010) or by conversion to di and tri forms]. "
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