表观遗传学

Centromeres are sites of spindle attachment for chromosome segregation. During meiosis, recombination is absent at
centromeres and surrounding regions. To understand the molecular basis for recombination suppression, we have
comprehensively annotated the 3.5-Mb region that spans a fully sequenced rice centromere. Although transcriptional
analysis showed that the 750-kb CENH3-containing core is relatively deficient in genes, the recombination-free region
differs little in gene density from flanking regions that recombine. Likewise, the density of transposable elements is similar
between the recombination-free region and flanking regions. We also measured levels of histone H4 acetylation and histone
H3 methylation at 176 genes within the 3.5-Mb span. Active genes showed enrichment of H4 acetylation and H3K4
dimethylation as expected, including genes within the core. Our inability to detect sequence or histone modification
features that distinguish recombination-free regions from flanking regions that recombine suggest that recombination
suppression is an epigenetic feature of centromeres maintained by the assembly of CENH3-containing nucleosomes within
the core. CENH3-containing centrochromatin does not appear to be distinguished by a unique combination of H3 and H4
modifications. Rather, the varied distribution of histone modifications might reflect the composition and abundance of
sequence elements that inhabit centromeric DNA.