SPAG8 is a human sperm membrane protein expressed during development and is a testis-specific component produced during male germ cell differentiation. This protein is localized in germ cells of the testis at all stages of spermatogenesis and is localized to the acrosomal region of mature spermatozoa. Alternatively spliced variants that encode different protein isoforms have been described but the full-length sequences of only two have been determined.