WT1-mediated gene regulation in early urogenital ridge development

The Wilms tumor protein WT1 is involved in the development of several organs, including the gonads. WT1 mutations in humans lead to syndromes associated with impaired sexual development and Wt1 knockout mice show regression of gonad anlagen. As a transcription factor, WT1 fulfills its function by regulating a set of target genes. With respect to gonad development only few in vivo WT1 targets, e.g. steroidogenic factor 1 (SF1) have been identified so far. To get a comprehensive view of WT1 targets in the gonad, we compared gene expression in urogenital ridges of wild-type and Wt1(-/-) embryos. We found almost 150 genes differentially expressed higher than factor three, using microarray analysis. To confirm these results we performed quantitative real-time RT-PCR for many genes and observed a high degree of concordance between microarray and real-time RT-PCR results. Employing in situ hybridization we found 'WT1 activated genes' to be expressed in gonads, mesonephroi and coelomic epithelium--those parts of the urogenital ridge with Wt1 expression. Interestingly, many of the differentially expressed genes are known to show sex-specific expression at later time-points. These results provide a basis for investigation of developmental pathways in the urogenital ridge downstream of WT1 and for identification of new candidate genes involved in early urogenital ridge development. For example we provide a first potential target of WT1 in the coelomic epithelium--Muc16, and a gene regulated by the WT1 target SF1--Gata4.