Female-specific hyperacetylation of histone H4 in the chicken Z chromosome.

Birds undergo genetic sex determination using a ZW sex chromosome system. Although the avian mechanisms of neither sex determination nor dosage compensation are understood, a female-specific non-coding RNA (MHM) is expressed soon after fertilisation from the single Z chicken chromosome and is likely to have a role in one or both processes. We have now discovered a prominent female-specific modification to the Z chromatin in the region of the MHM locus. We find that chicken chromatin at Zp21, including the MHM locus, is strongly enriched for acetylation of histone H4 at lysine residue 16 in female but not male chromosomes. Interestingly, this specific histone modification is also enriched along the length of the up-regulated Drosophila melanogaster male X chromosome where it plays a vital role in the dosage compensation process.