Transcription factor that plays a key role in male sex determination and differentiation by controlling testis development and male germ cell proliferation. Plays a central role in spermatogonia by inhibiting meiosis in undifferentiated spermatogonia and promoting mitosis, leading to spermatogonial development and allowing abundant and continuous production of sperm. Acts both as a transcription repressor and activator: prevents meiosis by restricting retinoic acid (RA)-dependent transcription and repressing STRA8 expression and promotes spermatogonial development by activating spermatogonial differentiation genes, such as SOHLH1. Also plays a key role in postnatal sex maintenance by maintaining testis determination and preventing feminization: represses transcription of female promoting genes such as FOXL2 and activates male-specific genes. May act as a tumor suppressor. May also play a minor role in oogenesis. Testis-specific. In adult testis, expressed in Sertoli cells in all regions of the seminiferous tubules. Expressed dynamically in premeiotic germ cells (spermatogonia), with high expression only in regions of the seminiferous tubule that are early in the spermatogenic cycle (at protein level). Expressed in all mitotic spermatogonia. Expression decreases with the onset of spermatogonial differentiation and disappears at the initiation of meiosis. Detected already at 9.5 dpc. At 10.5 dpc, expressed in the genital ridges of both sexes. At 14.5 dpc, during gonadal sexual differentiation, expression declines in the ovary, but is maintained in the testis, where it becomes restricted to Sertoli and germ cells in the developing seminiferous tubules of the testis. Accumulates primarily in Sertoli cells. From P1, appears in germ cells and reach high levels by P7, just before meiosis begins. From P7 through adult stage, present in Sertoli cells and undifferentiated germ cells, but not in differentiating germ cells. Severe defects in the adult testis with hypoplastic testes and disorganization of seminiferous tubules and absence of germ cells, due to pre-meiotic germ cell death in testes. Sertoli cell fail to differentiate. Female mutant mice have normal ovaries and are fertile. Depending on the strain background mice also show testis teratomas: deletion in 129/Sv strain causes a high incidence of teratomas, whereas these tumors do not form in C57BL/6J mutant mice. Deletion of Dmrt1 during fetal development causes postnatal Sertoli cells to lose male-promoting Sox9 and instead activation of female-promoting genes such as Foxl2, leading to reprogrammation of Sertoli cells into granulosa cells. As a consequence, theca cells form, estrogen is produced and germ cells appear feminized. Belongs to the DMRT family.