Mcm9, also known as Minichromosome Maintenance 9 Homologous Recombination Repair Factor, is a crucial protein in multiple DNA-related processes. It is involved in DNA replication (specifically in the assembly of prereplication complexes where it binds Cdt1 and is required for loading the MCM2-7 helicase onto DNA replication origins) [5], meiosis, homologous recombination, and DNA mismatch repair [1,3]. These functions are vital for maintaining genomic integrity, which is essential for normal cellular function and development.

In knockout mouse models, mutations in related genes like Hrob, which recruits the MCM8-MCM9 helicase to sites of DNA damage, lead to infertility due to germ cell depletion and meiotic arrest, suggesting Mcm9's role in meiosis and germ cell development [6]. In humans, MCM9 mutations are associated with primary ovarian insufficiency, Sertoli cell-only syndrome, and early-onset cancer [2,4]. For example, homozygous pathogenic MCM9 variants in humans can cause ovarian dysgenesis in females and non-obstructive azoospermia in males [4].

In conclusion, Mcm9 is essential for DNA-related processes such as replication, meiosis, and DNA repair. Model-based research, including gene knockout studies in mice and human genetic studies, has revealed its significance in diseases like infertility and early-onset cancer. Understanding Mcm9's functions provides insights into the mechanisms underlying these diseases, potentially leading to better diagnostic and treatment strategies.