{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Histone H2A family member C21 (H2AC21) is a replication‐dependent core histone that plays a pivotal role in the assembly and stability of nucleosomes, thereby influencing chromatin architecture and gene expression. Studies on histone acetylation have shown that modifications on H2A variants can modulate nucleosome conformation and stability, which in turn affect the regulation of transcriptional programs."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In particular, efficient deposition of H2A–H2B dimers is critical during replication‐coupled nucleosome assembly, emphasizing how proper expression of histone genes—such as those clustered within the HIST1 region, to which H2AC21 belongs—is essential for normal chromatin packaging. Defects in epigenetic reprogramming that lead to the coordinated downregulation of HIST1 cluster histone genes have been associated with impaired chromatin organization during early embryogenesis, as exemplified in somatic cell nuclear transfer blastocysts."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " Moreover, alterations in the expression of H2A family members have been linked to pathological conditions; for instance, aberrant upregulation of specific H2A variants correlates with the activation of NF‑κB and STAT3 pathways that contribute to chemoresistance in glioblastoma."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " In addition, interactions between nuclear factors (such as HMGB proteins) and H2A variants underscore a broader role in regulating global gene expression during processes like cellular differentiation and even in the transmission of epigenetic information in reproductive cells."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " Collectively, these findings highlight that H2AC21 is integral to establishing and maintaining chromatin dynamics that underlie both normal cellular homeostasis and disease‐associated epigenetic dysregulation.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Toyotaka Ishibashi, Deanna Dryhurst, Kristie L Rose, et al. 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