Probably participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions. Its tissue specificity suggests a regulatory role in the germline. Specifically associated with the Y chromosome loops. Testis specific. Not expressed in the embryo. Becomes progressively more strongly expressed during larval and pupal development. In testis, it is strongly expressed in young spermatocytes, and postmeiotic spermatid stages, then expression decreases at the nuclear elongation stage. Strongly expressed in the waste bag, in which material no longer needed for the mature sperm is eliminated. Not expressed in the stem cells and spermatogonial cells. Not expressed maternally. The TrxT gene, which encodes an testis specific thioredoxin, is adjacent to the dhd gene and shares some regulatory region with it. Belongs to the thioredoxin family.