Basic helix-loop-helix transcription factor Tcf21 is downstream target of male sex-determining gene SRY

The cascade of molecular events involved in mammalian sex determination has been shown to involve the SRY gene, but specific downstream events have eluded researchers for decades. The current study identifies one of the first direct downstream targets of the male sex-determining factor SRY as the basic-helix-loop-helix (bHLH) transcription factor TCF21. SRY was found to directly associate with the Tcf21 promoter SRY/SOX9 response element both in vitro and in vivo during male sex determination. TCF21 was found to promote an in vitro sex reversal of embryonic ovarian cells to promote precursor Sertoli cell differentiation. Therefore, SRY acts directly on the Tcf21 promoter to, in part, initiate a cascade of events associated with Sertoli cell differentiation and embryonic testis development. We used microarrays to determine genes whose expression was stimulated in rat E13 ovarian cell sub-cultures in the presence of a pCMV-myc-expression plasmid over-expressing the Sry, Tsf21, and/or Tcf12 (Reb-alfa) genes. RNA samples from the control group (untreated E13 rat ovarian cells) are compared to RNA from 4 groups of treated E13 rat ovarian cells: 1) Sry overexpressing, 2) Tcf21 overexpressing, 3) Tcf12 (Reb alfa) overexpressing, and 4) Tcf21 + Tcf12 (Reb-alfa) overexpressing. Untreated E13 testis cell sub-cultures were also analyzed. 3 biological replicates each group.