HSF5 (heat shock transcription factor 5) is a DNA-binding transcription factor that plays a critical role in male fertility and spermatogenesis 1. The protein is essential for meiotic prophase progression in spermatocytes under non-stress conditions, specifically regulating the transition beyond the pachytene stage 1. HSF5 functions by binding to promoters of key genes involved in crossover formation (HFM1, MSH5, MLH3), synapsis (SYCP1, SYCP2, SYCE3), recombination (TEX15), and meiotic sex chromosome 17 (MDC1), thereby regulating their transcription during meiotic progression 1. HSF5 deficiency causes complete male infertility in both humans and mice, with spermatogenic arrest at meiotic prophase I due to defects in meiotic recombination, crossover formation, and sex chromosome 17 1. Beyond reproductive function, HSF5 expression is associated with immune infiltration and serves as a prognostic biomarker in lung adenocarcinoma, where decreased expression correlates with poorer overall survival 2. The protein also shows differential expression patterns in various pathological conditions, including age-related changes in oocyte quality 3 and glycosylation pathway regulation in Alzheimer's disease 4. Gene therapy approaches using adeno-associated virus delivery have shown promise in rescuing spermatogenic defects in HSF5 knockout mice 1.