Control mechanisms of testicular differentiation

In this paper the importance of unknown factors responsible for the initial differentiation of a gonadal primordium is stressed. The hypothesis that in the absence of testis determining genes (TDG) the indifferent gonad is programmed to become an ovary is considered further. The TDG(s) are expressed only among cells already marked as gonadal cells, and they seem mainly to change the chronological sequence and intensity of expression of processes common to both sexes. The chronology of the normal events necessary for testicular differentiation and the fact that some of these events can be dissociated from one another under experimental conditions in vitro, suggest that many genes are involved in testicular differentiation and that the so-called testis-determining genes are probably regulatory genes.