H1T2/H1FNT is a germ cell-specific linker histone variant expressed during spermiogenesis specifically in round and elongating spermatids. Infertile phenotype of homozygous H1T2 mutant male mice revealed the essential function of H1T2 for the DNA condensation and histone-to-protamine replacement in spermiogenesis. However, the mechanism by which H1T2 imparts the inherent polarity within spermatid nucleus including the additional protein partners and the genomic domains occupied by this linker histone are unknown. Sequence analysis revealed the presence of Walker motif, SR domains and putative coiled-coil domains in the C-terminal domain of rat H1T2 protein. Genome-wide occupancy analysis using highly specific antibody against the CTD of H1T2 demonstrated the binding of H1T2 to the LINE L1 repeat elements and to a significant percentage of the genic regions (promoter-TSS, exons and introns) of the rat spermatid genome. Immunoprecipitation followed by mass spectrometry analysis revealed the open chromatin architecture of H1T2 occupied chromatin encompassing the H4 acetylation and other histone PTMs characteristic of transcriptionally active chromatin. In addition, the present study has identified the interacting protein partners of H1T2-associated chromatin mainly as nucleo-skeleton components, RNA-binding proteins and chaperones. Linker histone H1T2 possesses unique domain architecture which can account for the specific functions associated with chromatin remodeling events facilitating the initiation of histone to transition proteins/protamine transition in the polar apical spermatid genome. Our results directly establish the unique function of H1T2 in nuclear shaping associated with spermiogenesis by mediating the interaction between chromatin and nucleo-skeleton, positioning the epigenetically specialized chromatin domains involved in transcription coupled histone replacement initiation towards the apical pole of round/elongating spermatids.

中文翻译：

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全基因组占有率揭示了 H1T2 (H1fnt) 定位于大鼠精子细胞中的重复区域和转录活性染色质结构域的一个子集

H1T2/H1FNT 是一种生殖细胞特异性接头组蛋白变体，在精子发生过程中特别在圆形和伸长的精子细胞中表达。纯合 H1T2 突变雄性小鼠的不育表型揭示了 H1T2 在精子发生中对 DNA 浓缩和组蛋白到鱼精蛋白替代的基本功能。然而，H1T2 赋予精子细胞核内固有极性的机制包括额外的蛋白质伙伴和该接头组蛋白占据的基因组结构域是未知的。序列分析显示大鼠 H1T2 蛋白的 C 末端结构域中存在 Walker 基序、SR 结构域和推定的卷曲螺旋结构域。使用针对 H1T2 的 CTD 的高度特异性抗体进行的全基因组占有率分析表明，H1T2 与 LINE L1 重复元件和大鼠精子细胞基因组的显着百分比的基因区域（启动子-TSS、外显子和内含子）结合。免疫沉淀和质谱分析揭示了 H1T2 的开放染色质结构占据染色质，包括 H4 乙酰化和转录活性染色质的其他组蛋白 PTM 特征。此外，本研究已确定 H1T2 相关染色质的相互作用蛋白伙伴主要为核骨架成分、RNA 结合蛋白和伴侣蛋白。接头组蛋白 H1T2 具有独特的结构域结构，可以解释与染色质重塑事件相关的特定功能，促进极尖精子细胞基因组中组蛋白向过渡蛋白/鱼精蛋白转变的启动。我们的研究结果直接确立了 H1T2 在与精子发生相关的核成形中的独特功能，通过介导染色质和核骨架之间的相互作用，将参与转录耦合组蛋白置换起始的表观遗传特化染色质结构域定位到圆形/伸长精子细胞的顶端极。