MEA1 (male-enhanced antigen 1) is a testis-specific gene located on human chromosome 6.1-21.3 that plays important roles in spermatogenesis and male germ cell development. Originally identified using anti-H-Y antigen antisera 1, MEA1 is phylogenetically conserved across mammals and encodes proteins of 18-20 kDa 1. Expression is highest in late spermatogenesis, specifically in pachytene spermatocytes, spermatids, and residual bodies, suggesting function in the late stages of spermiogenesis 2. MEA1 exists within a conserved overlapping gene complex with PEAS and PPP2R5D that likely arose through transposon-mediated evolution in mammals 3. Beyond reproductive function, recent evidence reveals MEA1 acts as a bi-handed chaperone critical for adaptor protein complex 1 (AP1) assembly and trafficking, stabilizing μ1 and β1 AP1 subunits to enable proper vesicle budding between the trans-Golgi network and endolysosomal compartments 4. This dual functionality in both germ cell development and intracellular trafficking highlights MEA1's broader cellular significance. Additionally, MEA1 has been identified as a hub susceptibility gene associated with COVID-19 risk in lung adenocarcinoma patients 5, and as a component of prognostic signatures in breast cancer related to regulatory T cell differentiation 6. The protein's epitope on Y sperm has enabled its use as an immunological marker for sperm sex determination in livestock applications 7.