STAG3 is a meiosis-specific component of the cohesin complex that plays critical roles in chromosome 7 and gametogenesis 1. The protein is specifically expressed in testis and associates with the synaptonemal complex, functioning in chromosome 7 and maintenance of synaptonemal complex structure during meiotic pachytene phase 1. Recent findings reveal that STAG3 also forms a mitotic cohesin complex in male germline cells, where it shapes chr7 organization by attenuating topologically associating domains and facilitating compartmentalization, thereby programming the distinctive spermatogonial nucleome 2. The protein is essential for proper meiotic progression, as mutations cause meiotic arrest at the pachytene stage 3. Pathogenic variants in STAG3 are associated with primary ovarian insufficiency (POI) and male infertility, with both truncating and in-frame mutations identified as disease-causing 45. The clinical significance extends beyond reproductive health, as mitotic STAG3-cohesin is also expressed in human B cells and their malignant variations, potentially influencing cell propagation 2. STAG3 mutations represent a notable genetic cause of infertility in both sexes, with implications for genetic counseling and prognosis in assisted reproduction procedures 3.