TISSUE-SPECIFIC REGULATION OF THE WTI LOCUS

The 11p13 Wilms' tumor locus consists of two coordinately regulated tr anscripts, WT1 and WIT-1. These genes are highly expressed in the deve loping urogenital system, beginning with the urogenital ridge at day 1 0.5, the metanephric blastema at day 11.5, and during glomerular forma tion at day 13.5, becoming ultimately restricted to the podocytes. Str omal cells of the gonad also show abundant expression. WT1 is expresse d at lower levels in spleen, uterus, mesothelial linings of organs in the abdominal and thoracic cavities, and the ependymal layer of the ve ntral aspect of the spinal cord. WIT-1 mRNA is about 10-fold less abun dant than WT1, but appears to be expressed in the same tissue-restrict ed manner. Expression of the WT1 protein is required for kidney develo pment, although its physiological function remains to be determined. T he function of WIT-1 is similarly unknown but one intriguing possibili ty is that it is an antisense regulator of WT1. An understanding of ev ents controlling spatial and temporal regulation of these genes will g reatly improve our ability to study the role of WT1 and WIT-1 in uroge nital development. We have found that while chimeric reporter construc ts containing 0.6-2.5 kb of the 5' region of the WT1 gene direct trans cription in many different cell lines, we were unable to detect expres sion in 13.5-day mouse embryos. However, a cosmid containing about 42 kb encompassing this region was able to direct the expression of abund ant levels of mRNA from the appropriate transcription initiation sites in both stable transfectants of mouse Leydig cells (TM3) or in transg enic embryos. We are currently localizing the DNA elements required fo r this expression. (C) 1996 Wiley-Liss, Inc.