{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Histone H3 proteins—including the canonical variants encoded by genes such as HIST1H3C (often referenced as H3.1) and the replacement variant H3.3 encoded by H3F3A—play central roles in chromatin structure and function. These proteins not only package DNA into nucleosomes but also act as dynamic platforms for the regulation of gene expression, DNA replication, repair, and genome stability. Several studies in pediatric brain tumors have shown that specific point mutations affecting key lysine residues (for example, the K27M substitution) in these variants induce a global reduction in repressive trimethylation (H3K27me3) and drive unique oncogenic transcriptional programs. In diffuse intrinsic pontine glioma (DIPG) and pediatric glioblastoma, mutations in H3.3 (H3F3A) and, less frequently, in the canonical H3.1 (encoded by HIST1H3B/C) demarcate molecularly and clinically distinct tumor subgroups that differ in cellular phenotypes and patient outcomes."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "4"}]}, {"type": "t", "text": " In normal cells, the distinct deposition pathways for histone H3 variants are mediated by specialized chaperones (such as DAXX for H3.3 and replication‐coupled factors for H3.1), which ensure timely nucleosome assembly and maintenance of epigenetic memory."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " Furthermore, post‐translational modifications on these histones—such as methylation or acetylation at lysine residues (e.g. K27, K36, or K56)—further modulate chromatin accessibility and function in processes ranging from transcription elongation to centromere assembly and DNA repair."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": " Notably, aberrant methylation of the HIST1H3C promoter has been identified as a prognostic biomarker in neuroblastoma, underscoring its role in tumor biology and potential as a diagnostic and therapeutic target."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": " Collectively, these findings emphasize that histone H3 variants—including those corresponding to H3C12/HIST1H3C—are not merely structural components of chromatin but also key regulators of epigenetic programs, whose alterations can profoundly influence developmental processes and tumorigenesis.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Dong-Anh Khuong-Quang, Pawel Buczkowicz, Patricia Rakopoulos, et al. 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