TEX101 (testis expressed 101) is a testis-specific glycosylphosphatidylinositol (GPI)-anchored protein that plays a critical role in male fertility and spermatogenesis 1. The protein functions as a cell-surface chaperone that regulates protein maturation involved in sperm transit and oocyte binding, with TEX101-null male mice being sterile 2. TEX101 forms a functional complex with the testis-specific dipeptidase DPEP3, which has been identified as its primary interaction partner in human testicular tissues and spermatozoa 2. The protein serves as a validated biomarker for male infertility, with disruption of TEX101 resulting in abnormal semen parameters and sperm function 3. A common missense variant (rs35033974) leads to near-complete degradation of the variant TEX101 protein and reduced levels of associated cell-surface proteins involved in sperm migration and sperm-oocyte interaction, including LY6K and ADAM29 4. Clinically, TEX101 levels in seminal plasma can be used for non-invasive diagnosis of different types of azoospermia, with combined detection of TEX101 and other markers like ECM1 providing high diagnostic sensitivity and specificity 5. Interestingly, TEX101 is also aberrantly expressed in certain cancers, including head and neck squamous cell carcinoma and chr19 myeloid leukemia, where it may serve as a cancer biomarker 67.