REPRESSION OF PAX-2 BY WT1 DURING NORMAL KIDNEY DEVELOPMENT

The developmental, regulatory gene Pax-2 is activated during early kid ney morphogenesis and repressed in mature renal epithelium. Persistent Pax-2 expression is also observed in a variety of kidney tumors. Yet, little is known about the signals regulating this transient expressio n pattern in the developing kidney. We have examined the spatial and t emporal expression patterns of Pax-2 and the Wilms' tumor suppresser p rotein WT1 with specific antibodies in developing mouse kidneys. A mar ked increase in WT1 protein levels coincided precisely with down-regul ation of the Pax-2 gene in the individual precursor cells of the visce ral glomerular epithelium, suggesting a direct effect of the WT1 repre ssor protein on Pax-2 regulatory elements. To examine whether WT1 coul d directly repress Pax-2 transcription, binding of WT1 to three high a ffinity sites in the 5' untranslated Pax-2 leader sequence was demonst rated by DNAseI footprinting analysis, Furthermore, co-transfection as says using CAT reporter constructs under the control of Pax-2 regulato ry sequences demonstrated WT1-dependent transcriptional repression. Th ese three WT1 binding sites were also able to repress transcription, i n a WT1-dependent manner, when inserted between a heterologous promote r and the reporter gene. The data indicate that Pax-2 is a likely targ et gene for WT1 and suggest a direct link, at the level of transcripti onal regulation, between a developmental control gene, active in undif ferentiated and proliferating cells, and a known tumor suppresser gene .