Histone H4K16 acetylation modulates the dynamics of linker H1 and heterochromatin protein HP1 in male X chromosome dosage compensation

Drosophila dosage compensation is an epigenetic phenomenon in which the transcription of most genes on X-chromosome is enhanced by approximately two folds in males to equalize that in females. In this study, we provide evidence that transcriptional repressors, such as HP1 and linker histone H1, are globally reduced on male X chromosome. We further investigated the role of HP1 and linker H1 on X chromosome dosage compensation using flies with overexpression of HP1 and H1, we demonstrate that these repressors surpress H4K16 acetylation, presence of the elongating RNA Pol II and the transcription of the genes on male X chromosomes. To understand how H1 and HP1 are regulated on male X chromosome, we next explored the relationship between MOF and the two repressors of chromatin. We show that the hyperacetylation of H4K16 induced by MOF resulted in the loss of H1 and HP1 on chromatin and global chromatin decondensation. Our biochemical analysis further shows that the presence of acetylation on histone H4 at lysine 16 directly inhibits the interaction between histone H4 and linker H1. This study therefore provides novel clues on understanding the dynamic regulation of chromatin regulators on male X chromosome dosage compensation. In this study, we used ChIP-Seq to accurately map HP1 binding profiles on whole drosophila genome in drosophila S2 and Kc cells. Chromatin components do not work solely; they cooperate with each other to regulate the transcription activity. So besides HP1, we also generated ChIP maps of histone H1 and the histone marks H3K4me2, H3K9me2, H3K36me3 and H4K16Ac in drosophila S2 cells. Affinity-purified polyclonal antibody of HP1 was used in this experiment, 5ul for each ChIP. H4K16ac (07-329) and H3K4me2 (07-030) antibodies purchased from Upstate were also used in this experiment, 5ul for each ChIP. H3K36me3 (ab9050) and H3K9me2 (ab1220) antibodies were purchased from Abcam, 5ul for each ChIP. The polyclonal antibody for Sample H1_S2 was made by our lab (detailed information can be found in Ni et al.,2006 Genes Dev.).