Practice question

Histone variants mark chromosome-wide silencing programs. While macroH2A is best characterized for Barr body enrichment, ubiquitylated forms of H2A.Z have been detected on facultative heterochromatin of inactive X in female mammalian cells, colocalizing with H3K27me3, loss of H4 acetylation and DNA methylation. This variant participates in dynamic relocalization of HP1 and establishment of facultative heterochromatin post-meiosis, replacing macroH2A at certain developmental stages. Its presence reflects context-dependent roles beyond active promoters, contributing to stable propagation of X-chromosome inactivation through recruitment of PRC2 and transcriptional repressor complexes.