{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n The H1 linker histone family, comprising multiple non‐redundant variants, plays diverse roles in the regulation of chromatin structure and function. Detailed studies demonstrate that individual H1 variants are differentially distributed along the genome, thereby influencing chromatin compaction, transcriptional regulation, and cell fate. In cancer cells, for example, low levels of the replacement subtype H1.0 have been associated with maintenance of self‐renewal and enhanced tumor cell growth, whereas re‐expression of H1.0 restricts long‐term proliferative potential by promoting differentiation (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " Genome‐wide mapping in embryonic stem cells shows that variants such as H1c and H1d are depleted from GC‐rich, actively transcribed regions yet enriched at major satellite repeats, indicating their role in organizing pericentric heterochromatin (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Comparative analyses in human somatic cells have further underlined that different H1 variants are associated with distinct genomic domains; for instance, H1.2 is preferentially localized at low guanine–cytosine (GC) content regions and at promoters of repressed genes, highlighting a function in gene silencing (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " Moreover, functional investigations in ovarian cancer cells reveal that overexpression of H1.3 leads to repression of the oncogenic noncoding RNA H19 via enhanced occupancy at its regulatory regions, implicating this variant in tumor suppression (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " In addition, high expression of H1x in neuroendocrine tumors appears to reflect its abundant presence in normal neuroendocrine cells, suggesting potential as a diagnostic marker (​"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": ", while studies of its intranuclear dynamics have correlated cell cycle–dependent localization with regulatory shuttling mechanisms (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Beyond transcriptional control, H1 variants directly associate with key cell cycle regulators; for example, H1.2 has been shown to stabilize the binding of the retinoblastoma protein (pRb) to chromatin at E2F target genes, thereby enhancing transcriptional repression and facilitating cell cycle exit (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": " In parallel, H1.5 has emerged as a novel modulator of pre‐mRNA splicing, where its localized binding at splice sites is linked to RNA polymerase II pausing and alternative exon inclusion (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n The expression of replication‐dependent H1 subtypes is tightly regulated during the cell cycle, with coordinated mRNA and protein level fluctuations that underscore their distinct functions in proliferating versus differentiated cells (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": " Moreover, loss or combined depletion of certain variants (such as H1.2 and H1.4) disrupts the repression of heterochromatin domains, leading to increased chromatin accessibility and the ectopic activation of interferon responses (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": " Complementary to the classical H1 histones, H1‐like proteins such as HP1BP3 extend the functional repertoire by fostering co‐transcriptional processing of primary microRNAs and contributing to global gene expression regulation (​"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": ", and additional H1‐like factors have been implicated in coordinating chromatin architecture necessary for cellular homeostasis (​."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these findings underscore that the H1 histone family is not merely structural but also serves as a dynamic regulator of chromatin states, gene transcription, RNA processing, and cell cycle progression. Their variant‐specific roles in maintaining genome integrity and controlling oncogenic processes highlight their potential as biomarkers and therapeutic targets in cancer and other diseases.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Cristina Morales Torres, Alva Biran, Matthew J Burney, et al. "}, {"type": "b", "children": [{"type": "t", "text": "The linker histone H1.0 generates epigenetic and functional intratumor heterogeneity."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Science (2016)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1126/science.aaf1644"}], "href": "https://doi.org/10.1126/science.aaf1644"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "27708074"}], "href": "https://pubmed.ncbi.nlm.nih.gov/27708074"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Kaixiang Cao, Nathalie Lailler, Yunzhe Zhang, et al. "}, {"type": "b", "children": [{"type": "t", "text": "High-resolution mapping of h1 linker histone variants in embryonic stem cells."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "PLoS Genet (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1371/journal.pgen.1003417"}], "href": "https://doi.org/10.1371/journal.pgen.1003417"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23633960"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23633960"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Lluís Millán-Ariño, Abul B M M K Islam, Andrea Izquierdo-Bouldstridge, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Mapping of six somatic linker histone H1 variants in human breast cancer cells uncovers specific features of H1.2."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nucleic Acids Res (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/nar/gku079"}], "href": "https://doi.org/10.1093/nar/gku079"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24476918"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24476918"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "Magdalena Medrzycki, Yunzhe Zhang, Weijia Zhang, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Histone h1.3 suppresses h19 noncoding RNA expression and cell growth of ovarian cancer cells."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Cancer Res (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1158/0008-5472.CAN-13-2922"}], "href": "https://doi.org/10.1158/0008-5472.CAN-13-2922"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "25205099"}], "href": "https://pubmed.ncbi.nlm.nih.gov/25205099"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Julia Warneboldt, Florian Haller, Olaf Horstmann, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Histone H1x is highly expressed in human neuroendocrine cells and tumours."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "BMC Cancer (2008)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1186/1471-2407-8-388"}], "href": "https://doi.org/10.1186/1471-2407-8-388"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "19108733"}], "href": "https://pubmed.ncbi.nlm.nih.gov/19108733"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Stefan Stoldt, Dirk Wenzel, Ekkehard Schulze, et al. "}, {"type": "b", "children": [{"type": "t", "text": "G1 phase-dependent nucleolar accumulation of human histone H1x."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biol Cell (2007)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1042/bc20060117"}], "href": "https://doi.org/10.1042/bc20060117"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "17868027"}], "href": "https://pubmed.ncbi.nlm.nih.gov/17868027"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Shonagh Munro, Edward S Hookway, Melanie Floderer, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Linker Histone H1.2 Directs Genome-wide Chromatin Association of the Retinoblastoma Tumor Suppressor Protein and Facilitates Its Function."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Cell Rep (2017)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.celrep.2017.05.053"}], "href": "https://doi.org/10.1016/j.celrep.2017.05.053"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "28614707"}], "href": "https://pubmed.ncbi.nlm.nih.gov/28614707"}]}, {"type": "r", "ref": 8, "children": [{"type": "t", "text": "Ohad Glaich, Yodfat Leader, Galit Lev Maor, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Histone H1.5 binds over splice sites in chromatin and regulates alternative splicing."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nucleic Acids Res (2019)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/nar/gkz338"}], "href": "https://doi.org/10.1093/nar/gkz338"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "31076740"}], "href": "https://pubmed.ncbi.nlm.nih.gov/31076740"}]}, {"type": "r", "ref": 9, "children": [{"type": "t", "text": "Nicole Happel, Julia Warneboldt, Kristina Hänecke, et al. "}, {"type": "b", "children": [{"type": "t", "text": "H1 subtype expression during cell proliferation and growth arrest."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Cell Cycle (2009)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.4161/cc.8.14.8982"}], "href": "https://doi.org/10.4161/cc.8.14.8982"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "19587527"}], "href": "https://pubmed.ncbi.nlm.nih.gov/19587527"}]}, {"type": "r", "ref": 10, "children": [{"type": "t", "text": "Andrea Izquierdo-Bouldstridge, Alberto Bustillos, Carles Bonet-Costa, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Histone H1 depletion triggers an interferon response in cancer cells via activation of heterochromatic repeats."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nucleic Acids Res (2017)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/nar/gkx746"}], "href": "https://doi.org/10.1093/nar/gkx746"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "28977426"}], "href": "https://pubmed.ncbi.nlm.nih.gov/28977426"}]}, {"type": "r", "ref": 11, "children": [{"type": "t", "text": "Haoming Liu, Chunyang Liang, Rahul K Kollipara, et al. "}, {"type": "b", "children": [{"type": "t", "text": "HP1BP3, a Chromatin Retention Factor for Co-transcriptional MicroRNA Processing."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Mol Cell (2016)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.molcel.2016.06.014"}], "href": "https://doi.org/10.1016/j.molcel.2016.06.014"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "27425409"}], "href": "https://pubmed.ncbi.nlm.nih.gov/27425409"}]}, {"type": "r", "ref": 12, "children": [{"type": "t", "text": "Benjamin P Garfinkel, Naomi Melamed-Book, Eli Anuka, et al. "}, {"type": "b", "children": [{"type": "t", "text": "HP1BP3 is a novel histone H1 related protein with essential roles in viability and growth."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nucleic Acids Res (2015)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/nar/gkv089"}], "href": "https://doi.org/10.1093/nar/gkv089"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "25662603"}], "href": "https://pubmed.ncbi.nlm.nih.gov/25662603"}]}]}]}