Mago, a vertebrate homolog of Drosophila Mago nashi protein, is a component of the chromatoid body in the cytoplasm of the postmeiotic spermatid.

Post-transcriptional regulations play a crucial role during spermatogenesis of the vertebrates. Chromatoid body (CB) is a characteristic spermatid organelle that is supposed to exert its role in post-transcriptional processes, but its real functions remain largely unknown. Here we report identification of Mago from the rice field eel, and show its evolutionary conservation, differential expression and localization during gonadal transformation. The Mago interacts with Y14, which may facilitate nuclear export of both proteins in the Sertoli cells. Importantly, we have determined Mago as a novel component of the CB in the cytoplasm of the developing spermatid. Addition of Mago to the component list of the CB undoubtedly provides new clue as to the functions of the CB during spermatogenesis in the vertebrates.