Histone H3K4 methylation keeps centromeres open for business

Abstract

Nucleosomes at eukaryotic centromeres combine the histone H3 variant CENP-A and canonical H3 di-methylated at lysine 4 (H3K4me2), whose functional importance within the centromere region remains elusive. In this issue, Bergmann et al reveal a role for H3K4me2 in CENP-A maintenance, and extend the profile of centromeric histone modifications to include H3K36 methylation, typically found in transcribed regions of the genome.

Figure 1

Endogenous human centromeres are assembled on α satellite (alphoid) DNA composed of tandem repeat arrays of 171 bp monomers, some of which include a CENP-B-binding motif. CENP-A-containing nucleosomes are interspersed with H3K4me2 and H3K36me2 euchromatin and assembled across a portion of the alphoid array. The new human artificial chromosome, comprised of alternating monomers of synthetic alphoid DNA containing CENP-B boxes or tetO sequences, exhibits chromatin features similar to endogenous centromeres. Initial tetO sequence-mediated recruitment of LSD1-EYFP-TetR fusion protein decreased H3K4me2 and H3K36me2 levels on the alphoid^tetO HAC, and diminished alphoid transcription and HJURP recruitment. New CENP-A assembly did not occur, although the HAC retained kinetochore function. Long-term LSD1-EYFP-TetR tethering to alphoid^tetO HAC resulted in CENP-A depletion, undetectable transcription of α satellite DNA, as well as reduction in euchromatin and mitotic instability.