N-myc oncogene expression in porcine renal development and oncogenesis

A fish model of renal regeneration and development

The fish kidney provides a unique model for investigating renal injury, repair, and development. Like mammalian kidneys, fish kidneys have the remarkable ability to repair injured nephrons, designated renal regeneration. This response is marked by a recovery from acute renal failure by replacing the injured cells with new epithelial cells, restoring tubule integrity. In addition, fish have the ability to respond to renal injury by de novo nephron neogenesis. This response occurs in multiple fish species including goldfish, zebrafish, catfish, trout, tilapia, and the aglomerular toadfish. New nephrons develop in the weeks after the initial injury. This nephrogenic response can be induced in adult fish, providing a more abundant source of developing renal tissue compared with fetal mammalian kidneys. Investigating the roles played by different parts of the nephron during development and repair can be facilitated using fish models with differing renal anatomy, such as aglomerular fish. The fish nephron neogenesis model may also help to identify novel genes involved in nephrogenesis, information that could eventually be used to develop alternative renal replacement therapies.

Apoptosis and expression of the bcl-2 proto-oncogene in the fetal and adult human kidney: evidence for the contribution of bcl-2 expression to renal carcinogenesis

bcl-2 was identified as a transcript associated with the t(14;18) and imparts resistance to apoptotic cell death. bcl-2 is normally expressed in many tissues and exhibits remarkable structural and functional conservation. Using immunohistochemical and in situ DNA labeling techniques we examined the localization of bcl-2 in the developing human kidney. bcl-2 expression was rapidly upregulated in the induced metanephrogenic mesenchymal cells that differentiate into renal vesicles and nephrons. bcl-2 expression was undetectable in uninduced mesenchyme and in the renal ampullae and associated collecting system. The distribution of apoptotic cells within the developing kidney was inversely correlated with expression of bcl-2. The localization of bcl-2 protein in the adult human kidney also was examined. bcl-2 was expressed at high levels in all renal neoplasms examined providing a potential basis for the deregulation of apoptosis in the development and progression of these tumors.

Infrequency of ras, p53, WT1, or RB gene alterations in Wilms tumors

BACKGROUND

Alteration of the ras family of oncogenes and of the tumor suppressor genes p53 and RB are the most common genetic events in human tumors. Although there have been no reports of the prevalence of these alterations in Wilms tumors, overexpression of the N-myc and insulin-like growth factor-II (IGF-II) genes have been observed, and alteration of another tumor suppressor gene (WT1) has been demonstrated.

METHODS

Forty-four Wilms tumor specimens were tested for the presence of N-, K-, and H-ras mutations in codons 12, 13, and 61 by single-strand conformation polymorphism (SSCP) analysis and direct DNA sequence analysis. Sixteen tumors were tested for abnormalities of WT1 by Southern and northern blot analysis and reverse transcriptase polymerase chain reaction (RT-PCR). N-myc, c-myc, WT1, and IGF-II mRNA expression was measured in 16 tumors by Northern blot analysis. Thirty-eight tumors were screened for p53 mutations by SSCP analysis and direct DNA sequence analysis. Nine tumors were analyzed for loss of heterozygosity (LOH) of RB.

RESULTS

Although the authors confirmed that N-myc and IGF-II are overexpressed in Wilms tumors, no mutations of ras family, p53, or RB genes were identified, and no gross alterations of WT1 were detected by Southern or Northern blot analysis.

CONCLUSIONS

These findings suggest that H-ras, K-ras, N-ras, p53, and RB are not involved in the pathogenesis of Wilms tumor.

Expression of a Wilms tumor gene in porcine kidney during compensatory renal growth

Expression of the putative Wilms tumor gene (WT-1) was studied to investigate its role in renal growth. Compensatory renal growth was induced in 35-day-old Yorkshire-swine by unilateral nephrectomy. The contralateral kidney was removed 0.5 to 72 hours following the initial operation and analyzed for WT-1 gene expression by Northern analysis. Compensatory renal growth was detectable by wet weight measurements at 12 hours following contralateral nephrectomy. WT-1 gene expression was detectable in the contralateral kidney as early as 0.5 hours following unilateral nephrectomy. Expression of this gene was not detected in normal kidney from swine of this age group or from sham operated swine. In addition, we demonstrated the expression of this gene in newborn rat, pig and human kidneys, as well as human fetal kidney, indicating its role in nephrogenesis. These data suggest that expression of the WT-1 gene is involved in the regulatory mechanisms that control different types of renal growth.