Hira, also known as histone cell cycle regulator, is a crucial histone chaperone. It is mainly involved in the deposition of the histone variant H3.3 onto chromatin, which is independent of DNA synthesis. This process participates in regulating chromatin dynamics, gene expression, and various biological processes such as cell senescence, development, and cancer-related pathways [2,5,6].

In gene knockout studies, inactivation of Hira in senescent cells does not directly block NF-κB target gene expression but activates the senescence-associated secretory phenotype (SASP) through a CCF-cGAS-STING-TBK1-NF-κB pathway, indicating its role in inflammation regulation during cell senescence [1]. In Fh1-deficient cells, Hira depletion enhances cell proliferation and invasion, activating MYC and its target genes, which is relevant to understanding tumorigenesis in hereditary leiomyomatosis and renal cell carcinoma (HLRCC) [3]. In muscle stem cells of adult mice, conditional ablation of Hira compromises their regenerative and self-renewing capacity, leading to tissue repair failure, suggesting its importance in maintaining skeletal muscle cellular identity [4].

In conclusion, Hira is essential for multiple biological functions mainly through its role in H3.3 histone deposition. Gene knockout and conditional knockout mouse models have revealed its significance in disease areas such as cell senescence-related inflammation, HLRCC-associated tumorigenesis, and muscle tissue repair failure. These studies help to better understand the underlying mechanisms of these diseases and potentially provide new therapeutic targets.