OAZ3 encodes a testis-specific ornithine decarboxylase antizyme expressed exclusively in haploid germ cells during spermatogenesis 1. Unlike other antizymes, OAZ3 produces a major 12 kDa protein (p12) that lacks the typical antizyme domain and does not regulate ornithine decarboxylase or polyamine metabolism 2. Instead, p12 localizes to sperm tail structures including outer dense fibers and fibrous sheath, where it interacts with myosin phosphatase targeting subunit 3 (MYPT3) to modulate protein phosphatase PP1β and PP1γ2 activity 2. OAZ3 functions as part of a testis-specific protein complex with GGN1, GGNBP1, GGNBP2, and FANCL involved in spermatogenesis 34. The gene shows evidence of balancing selection, suggesting functional importance, though mutations are not commonly associated with male infertility 5. OAZ3 has been identified as a potential biomarker for nonobstructive azoospermia, demonstrating significant diagnostic value 6. The protein's unique regulation of phosphatase activity rather than polyamine metabolism represents a novel function among antizyme family members, highlighting its specialized role in male fertility through sperm tail function regulation.