{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Histone H3.5 is a recently identified variant of histone H3 that exhibits a highly specialized and restricted function in the human testis. Unlike the canonical H3 variants, H3.5 is encoded via a retrotransposition event and is expressed specifically in the seminiferous tubules, where it is incorporated preferentially into euchromatic regions and associates with actively transcribed genes. Studies have shown that when ectopically expressed in cultured cells, H3.5 is assembled into chromatin, is post‐translationally modified, and can even compensate for deficiencies in H3.3 function, thus sustaining cell growth."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In the context of spermatogenesis, H3.5 is predominantly expressed in immature germ cells such as spermatogonia and early primary spermatocytes – a pattern distinct from other testis‐specific histones that are typically involved in the histone–protamine exchange during meiosis. Its expression correlates with markers of DNA replication (for example, PCNA), suggesting a role in facilitating DNA synthesis rather than regulating cell death. Moreover, the reduced levels of H3.5 observed in cases of non‐obstructive azoospermia (NOA), alongside its responsiveness to gonadotropin stimulation, underscore its potential importance in maintaining normal spermatogenic processes."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these findings indicate that H3.5 serves as a critical epigenetic regulator within the testes, contributing to the maintenance of an open chromatin state necessary for active transcription and proper germ cell proliferation. Its unique structural attributes and regulated expression suggest that perturbations in H3.5 may underlie defects in early germ cell development and spermatogenesis.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Raphael Schenk, Andreas Jenke, Matthias Zilbauer, et al. "}, {"type": "b", "children": [{"type": "t", "text": "H3.5 is a novel hominid-specific histone H3 variant that is specifically expressed in the seminiferous tubules of human testes."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Chromosoma (2011)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/s00412-011-0310-4"}], "href": "https://doi.org/10.1007/s00412-011-0310-4"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "21274551"}], "href": "https://pubmed.ncbi.nlm.nih.gov/21274551"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "K Shiraishi, A Shindo, A Harada, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Roles of histone H3.5 in human spermatogenesis and spermatogenic disorders."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Andrology (2018)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1111/andr.12438"}], "href": "https://doi.org/10.1111/andr.12438"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "29179259"}], "href": "https://pubmed.ncbi.nlm.nih.gov/29179259"}]}]}]}