{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n MacroH2A1 is a versatile histone variant that plays multifaceted roles in chromatin regulation across diverse cellular contexts. Its alternatively spliced isoforms – macroH2A1.1 and macroH2A1.2 – function both as mediators of transcriptional repression and as dynamic regulators of chromatin architecture. In developing germ cells, macroH2A1 contributes to chromatin remodeling events that underlie meiotic sex chromosome inactivation, as its proper localization within the sex (XY) body depends on upstream chromatin signals (see."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " At sites of DNA damage, macroH2A1.1 directly senses PARP1 activation; its binding to poly(ADP‐ribose) leads to transient chromatin compaction, influencing the recruitment of repair factors and thus facilitating the DNA damage response."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": " In somatic cells, macroH2A1 is enriched on repressed chromatin, including the inactive X chromosome, and its regulated deposition by ubiquitin ligase complexes is critical for stable X inactivation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "6"}]}, {"type": "t", "text": " Moreover, the variant is implicated in tumor suppression; loss or reduced expression of macroH2A1 correlates with increased oncogenic potential in melanoma and other cancers, in part via deregulation of oncogenic targets such as CDK8."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": " Consistent with its role as an epigenetic “lock,” macroH2A1 also impedes induced pluripotency by reinforcing repressive chromatin states at key pluripotency gene loci."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": " In addition, emerging data indicate that macroH2A1 modulates the DNA double‐strand break repair pathway by influencing the balance between BRCA1- and 53BP1-mediated repair"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": ", and it acts as a key regulator of the senescence-associated secretory phenotype by undergoing genome-wide relocation during oncogene-induced senescence."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "13"}]}, {"type": "t", "text": " Finally, in specialized contexts such as alternative telomere lengthening, macroH2A1.1 partners with factors like tankyrase to modulate telomere cohesion and recombination."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "14"}]}, {"type": "t", "text": " Collectively, these studies underscore the central role of macroH2A1 in establishing and modulating chromatin states that integrate DNA repair, transcriptional regulation, cell fate determination, and tumor suppression."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "15", "end_ref": "19"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Oscar Fernandez-Capetillo, Shantha K Mahadevaiah, Arkady Celeste, et al. 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