Differential patterns of expression of DAX-1 and steroidogenic factor-1 (SF-1) in the fetal rat testis

Gonadal differentiation is dependent upon a cascade of molecular and morphological events. Steroidogenic factor 1 (SF-1) and DAX-1 have been implicated in this process. A SF-1 binding site has been reported to be present on the DAX-1 gene. We therefore used immunocytochemistry to determine whether these two transcription factors are co-expressed in the fetal testis. DAX-1 was immunolocalised to the cytoplasm of interstitial cells from fetal testis of rat and human from day 15.5 and 16 weeks of gestation respectively. SF-1 was detected in nuclei of fetal Sertoli and interstitial cells. In the fetal rat expression of SF-1 in interstitial cells was not uniform; cells with abundant SF-1 all contained 3-beta HSD and were classified as Leydig cells. DAX-1 expression was not exclusive to cells which contained SF-1 and SF-1/DAX-1 co-expressing cells were not exclusively fetal Leydig cells. We conclude that in the fetal testis expression of the DAX-1 protein is not dependent upon the presence of SF-1 although SF-1 is present at an earlier stage of gestation in the gonad. DAX-1 may therefore play a separate or complementary role to that of SF-1 in the modulation of testicular gene expression and differentiation.