A mutant form of the Wilms' tumor suppressor gene WT1 observed in Denys-Drash syndrome interferes with glomerular capillary development.
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The Wilms' tumor suppressor gene WT1 encodes a zinc finger protein that is required for urogenital development. In the kidney, WT1 is most highly expressed in glomerular epithelial cells or podocytes, which are an essential component of the filtering system. Human subjects heterozygous for point mutations in the WT1 gene develop renal failure because of the formation of scar tissue within glomeruli. The relationship between WT1 expression in podocytes during development and glomerular scarring is not well understood. In this study, transgenic mice that expressed a mutant form of WT1 in podocytes were derived. The capillaries within transgenic glomeruli were dilated, indicating that WT1 might regulate the expression of growth factors that affect capillary development. Platelet endothelial cell adhesion molecule-1 expression was greatly reduced on glomerular endothelial cells of transgenic kidneys. These results suggest that WT1 controls the expression of growth factors that regulate glomerular capillary development and that abnormal capillary development might lead to glomerular disease. (+info)
Mice lacking the 68-amino-acid, mammal-specific N-terminal extension of WT1 develop normally and are fertile.
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Mutations in the Wilms' tumor 1 gene, WT1, cause pediatric nephroblastoma and the severe genitourinary disorders of Frasier and Denys-Drash syndromes. High levels of WT1 expression are found in the developing kidney, uterus, and testis--consistent with this finding, the WT1 knockout mouse demonstrates that WT1 is essential for normal genitourinary development. The WT1 gene encodes multiple isoforms of a zinc finger-containing protein by a combination of alternative splicing and alternative translation initiation. The use of an upstream, alternative CUG translation initiation codon specific to mammals results in the production of WT1 protein isoforms with a 68-amino-acid N-terminal extension. To determine the function in vivo of mammal-specific WT1 isoforms containing this extension, gene targeting was employed to introduce a subtle mutation into the WT1 gene. Homozygous mutant mice show a specific absence of the CUG-initiated WT1 isoforms yet develop normally to adulthood and are fertile. Detailed histological analysis revealed normal development of the genitourinary system. (+info)
Role of Wilms tumor 1 (WT1) in the transcriptional regulation of the Mullerian-inhibiting substance promoter.
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The Wilms tumor 1 (WT1) gene product may regulate the mullerian-inhibiting substance (MIS) gene, because mutations in WT1 can cause persistence of the mullerian duct in men. In the present study, we show by gel shift and chromatin immunoprecipitation assays that WT1 bound to a GC-rich sequence in the murine Mis promoter. Mutation in this site abolished WT1-mediated activation of the Mis promoter. The WT1, SRY box protein 9, and steroidogenic factor 1 could synergistically activate the Mis promoter, and at least two factors were necessary for minimal activation. The WT1 is an essential factor for activation of the Mis promoter; therefore, the persistence of the mullerian duct in patients with Denys-Drash syndrome may result from deregulation of the MIS gene. (+info)
Murine Denys-Drash syndrome: evidence of podocyte de-differentiation and systemic mediation of glomerulosclerosis.
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Denys-Drash syndrome (DDS) is caused by dominant mutations of the Wilms' tumour suppressor gene, WT1, and characterized by a nephropathy involving diffuse mesangial sclerosis, male pseudohermaphroditism and/or Wilms' tumourigenesis. Previously, we reported that heterozygosity for the Wt1tmT396 mutation induces DDS in heterozygous and chimeric (Wt1tmT396/+<-->+/+) mice. In the present study, the fate of Wt1 mutant cells in chimeric kidneys was assessed by in situ marker analysis, and immunocytochemistry was used to re-examine the claim that glomerulosclerosis (GS) is caused by loss of WT1 and persistent Pax-2 expression by podocytes. Wt1 mutant cells colonized glomeruli efficiently, including podocytes, but some sclerotic glomeruli contained no detectable Wt1 mutant cells. The development of GS was preceded by widespread loss of ZO-1 signal in podocytes (even in kidneys where <5% of glomeruli contained Wt1 mutant podocytes), increased intra-renal renin expression, and de novo podocyte TGF-beta1 expression, but not podocyte Pax-2 expression or loss of WT1, synaptopodin, alpha-actinin-4 or nephrin expression. However, podocytes in partially sclerotic glomeruli that still expressed WT1 at high levels showed reduced vimentin expression, cell cycle re-entry, and re-expressed desmin, cytokeratin and Pax-2. The results suggest that: (i) GS is not due to loss of WT1 expression by podocytes; (ii) podocyte Pax-2 expression reflects re-expression rather than persistent expression, and is the consequence of GS; (iii) GS is mediated systemically and the mechanism involves activation of the renin-angiotensin system; and (iv) podocytes undergo typical maturational changes but subsequently de-differentiate and revert to an immature phenotype during disease progression. (+info)
Prophylactic bilateral nephrectomies in two paediatric patients with missense mutations in the WT1 gene.
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BACKGROUND: Denys-Drash syndrome (DDS) is associated with mutations of the Wilms' tumour 1 (WT1) gene, and is characterized by pseudohermaphroditism, a progressive glomerulopathy, and the development of Wilms' tumour. More than 90% of patients with DDS who carry constitutional intragenic WT1 mutations are at high risk (90%) for the development of Wilms' tumour. WT1 is a signalling protein with 90% of WT1 mutations occurring in the WT1 zinc finger region as single nucleotide polymorphisms, the majority of which are missense mutations. METHODS: Constitutional DNA was extracted from peripheral blood. Direct sequencing and restriction enzymes were employed to analyse mutations. RESULTS: Two children, 46XY males who had evidence of pseudohermaphroditism, hypogonadism and renal failure with a glomerulopathy atypical for DDS, but no Wilms' tumour or nephroblastomatosis, on investigation, prior to transplant, were identified with missense mutations in the WT1 gene, in exons 8 and 9, respectively. The decision to do prophylactic nephrectomies was based on the genetic identification of WT1 mutations supporting a diagnosis of incomplete DDS, with the potential for increased risk of malignancy with the development of Wilms' tumour. The nephrectomy specimens demonstrated nephrogenic rests (nephroblastomatosis), which have a potential for malignant transformation. CONCLUSIONS: WT1 missense mutations in exons 8 and 9 can be regarded as having the potential for malignant change supporting prophylactic nephrectomy in apparent incomplete DDS patients with end-stage renal disease. (+info)
Twenty-eight-year-old female with primary amenorrhea and chronic renal failure: a case of Frasier syndrome?
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Frasier syndrome is a very rare developmental disorder of autosomal recessive inheritance. It is characterized by male hermaphroditism, primary amenorrhea, chronic renal failure (CRF), and a number of other abnormalities. A 28-year-old Nigerian female who was considered as a possible case of Frasier syndrome first presented to us in July 2002 with primary amenorrhea, congenital bilateral absence of middle toes, elevated blood pressure, and the uremic syndrome. The management of the case was mainly conservative, including blood pressure control with appropriate antihypertensives. The problems inherent in this index case are discussed while proffering appropriate management approach in a near-ideal situation, which unfortunately is nonexistent in our local environment. The presentation of this case is informed by the need to create awareness about this rare syndrome being a possible cause of CRF in some of our patients. (+info)
The Wt1+/R394W mouse displays glomerulosclerosis and early-onset renal failure characteristic of human Denys-Drash syndrome.
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Renal failure is a frequent and costly complication of many chronic diseases, including diabetes and hypertension. One common feature of renal failure is glomerulosclerosis, the pathobiology of which is unclear. To help elucidate this, we generated a mouse strain carrying the missense mutation Wt1 R394W, which predisposes humans to glomerulosclerosis and early-onset renal failure (Denys-Drash syndrome [DDS]). Kidney development was normal in Wt1(+/R394W) heterozygotes. However, by 4 months of age 100% of male heterozygotes displayed proteinuria and glomerulosclerosis characteristic of DDS patients. This phenotype was observed in an MF1 background but not in a mixed B6/129 background, suggestive of the action of a strain-specific modifying gene(s). WT1 encodes a nuclear transcription factor, and the R394W mutation is known to impair this function. Therefore, to investigate the mechanism of Wt1 R394W-induced renal failure, the expression of genes whose deletion leads to glomerulosclerosis (NPHS1, NPHS2, and CD2AP) was quantitated. In mutant kidneys, NPHS1 and NPHS2 were only moderately downregulated (25 to 30%) at birth but not at 2 or 4 months. Expression of CD2AP was not changed at birth but was significantly upregulated at 2 and 4 months. Podocalyxin was downregulated by 20% in newborn kidneys but not in kidneys at later ages. Two other genes implicated in glomerulosclerosis, TGFB1 and IGF1, were upregulated at 2 months and at 2 and 4 months, respectively. It is not clear whether the significant alterations in gene expression are a cause or a consequence of the disease process. However, the data do suggest that Wt1 R394W-induced glomerulosclerosis may be independent of downregulation of the genes for NPHS1, NPHS2, CD2AP, and podocalyxin and may involve other genes yet to be implicated in renal failure. The Wt1(R394W) mouse recapitulates the pathology and disease progression observed in patients carrying the same mutation, and the mutation is completely penetrant in male animals. Thus, it will be a powerful and biologically relevant model for investigating the pathobiology of the earliest events in glomerulosclerosis. (+info)
Variants in the Wilms' tumor gene are associated with focal segmental glomerulosclerosis in the African American population.
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Wilms' tumor gene (WT1) is important for nephrogenesis and gonadal growth. WT1 mutations cause Denys-Drash and Frasier syndromes, which are characterized by glomerular scarring. To test whether genetic variations in WT1 and WIT1 (gene immediately 5' to WT1) associate with focal segmental glomerulosclerosis (FSGS), patients with biopsy-proven idiopathic and HIV-1-associated FSGS were enrolled in a multicenter study. We genotyped SNP rs6508 located in WIT1 exon 1, three SNPs (rs2301250, rs2301252, rs2301254) in the promoter shared by WT1 and WIT1, rs2234590 in exon 6, rs2234591 in intron 6, rs16754 in exon 7, and rs1799937 in intron 9 of WT1. Cases (n = 218) and controls (n = 281) were compared in the African American population. Stratification by HIV-1 infection status showed that SNPs rs6508, rs2301254, and rs1799937 were significantly associated with FSGS [rs6508 odds ratio (OR) 1.82, P = 0.006; rs2301254 OR 1.65, P = 0.049; rs1799937 OR 1.91, P = 0.005] in the non-HIV-1 group and rs2234591 (OR 0.234, P = 0.011) in the HIV-1 group. Haplotype analyses in the population revealed that seven SNPs were associated with FSGS; five SNPs had the highest contingency score [-log10(P value) = 13.57] in the HIV-1 group. This association could not be explained by population substructure. We conclude that SNPs in WT1 and WIT1 genes are significantly associated with FSGS, suggesting that variants in these genes may mediate pathogenesis by altering WT1 function. Furthermore, HIV-1 infection status interacts with genetic variations in both genes to influence this phenotype. We speculate that nephropathy liability alleles in WT1 pathway genes cause podocyte dysfunction and glomerular scarring. (+info)