Molecular mechanism of sex determination and its disease

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In humans, as in other mammals, sex determination is controlled by a dominant switch termed TDF for Testis Determining Factor. The SRY gene is thought to be the TDF, which encodes a transcription factor with one HMG box as a DNA binding domain. Mutations in the SRY HMG box have been identified in 15% cases of XY sex reversal in humans. Introduction of mouse SRY gene (Sry) into XX female mice induced testis differentiation and subsequent male development. However, little is known about mechanism of transcriptional regulation by SRY. Mutations of another transcription factor, WT1, are frequently observed in Denys-Drash syndrome (DDS) patients with urogenital malformation.During analysis of WT1-associated proteins, we found that WT1 bound to Sox30, which encodes a novel transcription factor with one HMG box. Further analysis showed that WT1 bound to its HMG box. This observation prompted us to analyze interaction between WT1 and SRY, both of which are expressed in the somatic cells of.early gonads. We published a paper describing the following results in Oncogene. i) WT1 binds to SRY in vitro and in cultured cells and this interaction is mediated by the zinc finger domain of WT1 and the HMG box of SRY. ii) WT1 and SRY synergistically activate transcription from a promoter that contains SRY binding sequence and also from the SRY promoter. WT1 mutants found in DDS, however, did not show this activity. iii) WT1 is recruited on a SRY-binding sequence in a SRY dependent manner, while recruitment of DDS mutants is significantly inhibited.These observations suggest that WT1 and SRY interaction plays an important role in early gonadal development and its disease.