The function of Ensembl gene identifier ENSG00000174529 (TMEM81, transmembrane protein 81) is as follows. Essential fertilization factor required for male fertility. Part of a conserved trimeric sperm complex with the essential fertilization factors IZUMO1 and SPACA6 which bridges sperm and oocyte membranes during fertilization by binding to IZUMO1R/JUNO on the oocyte. .