BackgroundPolyamines are known to play important roles in the proliferation and differentiation of many types of cells. However, in the testis, where polyamines such as spermidine and spermine exist in high concentrations, their roles still remains to be elucidated.ResultsWe have cloned a testis‐specific gene encoding an ornithine decarboxylase antizyme known to control intracellular concentrations of polyamines in a feedback manner. The mRNA encoding the protein named ornithine decarboxylase antizyme in testis (OAZ‐t) was specifically expressed in haploid germ cells. In contrast, the mRNA level of somatic ornithine decarboxylase antizyme 1 (OAZ1) decreased markedly at the late stages of haploid germ cell differentiation. OAZ‐t mRNA was first observed in 23‐day‐old mice, whereas the OAZ‐t protein was detected much later, at 35 days after birth. Further experiments on OAZ‐t revealed that polyamines were capable of inducing a frameshifting at the frameshift sequence of OAZ‐t mRNA, resulting in the translation of OAZ‐t, as was the case with the somatic OAZ1. Transfection of OAZ‐t cDNA inactivated the ornithine decarboxylase activity in the HEK293 cells.ConclusionsResults indicate that the expression of OAZ‐t is controlled at both transcriptional and translational levels, and that OAZ‐t likely plays a key role in spermatogenesis by regulating the intracellular concentration of polyamines in haploid germ cells.