Induction of mesothelioma in the rat is an important animal model for assessing the carcinogenic potential of fibers and for understanding the molecular basis underlying the development of these tumors. Mesotheliomas and nephroblastoma (Wilms' tumor) have many developmental, biochemical, and histological similarities; however, the expression of the Wilms' tumor suppressor gene, WT-1, has not been well characterized in the rat, and its expression pattern in rat or human mesothelioma has not been described. We report that WT-1 transcripts (3.2 kilobases) could be detected by Northern analysis in adult rat testis, spleen, kidney, lung, heart, and glomerular mesangial cells. Normal adult mesothelial cells also expressed this gene. Rat mesothelioma cell lines expressed WT-1 transcripts of 3.2 kilobases and an additional 2.8-kilobase transcript, previously only reported to be expressed in the testis. Normal and transformed rat mesothelial cells expressed all four of the WT-1 splice variants, except testis, which only expressed WT-1 splice variants containing exon 5. Seven of seven human mesothelioma cell lines examined also expressed WT-1 transcripts, suggesting that expression of this gene may be useful in the diagnosis of these tumors.

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This work was supported in part by the Department of Health and Human Services, NIEHS Grant ES 06658-01 (to C. W.) and by a grant from the North American Insulation Manufacturers Association (to J. E.).

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