Germline mutations in the Wilms' tumor suppressor gene are associated with abnormal urogenital development in Denys-Drash syndrome

WT1 mutations in Meacham syndrome suggest a coelomic mesothelial origin of the cardiac and diaphragmatic malformations

Meacham syndrome is a rare sporadically occurring multiple malformation syndrome characterized by male pseudohermaphroditism with abnormal internal female genitalia comprising a uterus and double or septate vagina, complex congenital heart defect and diaphragmatic abnormalities. We report on eight new cases of this condition, two of whom were shown to have heterozygous missense mutations in the C-terminal zinc finger domains of WT1: Arg366Cys and Arg394Trp. These data represent clinical and molecular evidence that the WT1 gene plays a central role in normal development of the diaphragm and the proepicardially derived tissues. Identification of WT1 expression in the region of coelomic mesothelium which will form the proepicardium and diaphragm provides a plausible unifying patterning defect in these cases. Interestingly, the Arg366Cys mutation has been previously reported in Denys-Drash syndrome and Arg394Trp mutation has been previously reported in both isolated Wilms tumor and Denys-Drash syndrome. This phenotypic diversity with a single mutation suggests there are other factors modulating all aspects of WT1 function during human development. If genetic modifiers of WT1 can be identified in animal models these become good candidate genes for the cases with Meacham syndrome we report on here where WT1 mutations cannot be identified.

Development of the renal glomerulus: good neighbors and good fences

The glomerulus of the mammalian kidney is an intricate structure that contains an unusual filtration barrier that retains higher molecular weight proteins and blood cells in the circulation. Recent studies have changed our conception of the glomerulus from a relatively static structure to a dynamic one, whose integrity depends on signaling between the three major cell lineages: podocytes, endothelial and mesangial cells. Research into the signaling pathways that control glomerular development and then maintain glomerular integrity and function has recently identified several genes, such as the nephrin and Wilms' tumor 1 genes, that are mutated in human kidney disease.

Disentangling genetic vs. environmental causes of sex determination in the common frog, Rana temporaria

BACKGROUND

Understanding of sex ratio dynamics in a given species requires understanding its sex determination system, as well as access for reliable tools for sex identification at different life stages. As in the case of many other amphibians, the common frogs (Rana temporaria) do not have well differentiated sex chromosomes, and an identification of individuals' genetic sex may be complicated by sex reversals. Here, we report results of studies shedding light on the sex determination system and sex ratio variation in this species.

RESULTS

A microsatellite locus RtSB03 was found to be sex-linked in four geographically disparate populations, suggesting male heterogamy in common frogs. However, in three other populations examined, no or little evidence for sex-linkage was detected suggesting either ongoing/recent recombination events, and/or frequent sex-reversals. Comparison of inheritance patterns of alleles in RtSB03 and phenotypic sex within sibships revealed a mixed evidence for sex-linkage: all individuals with male phenotype carried a male specific allele in one population, whereas results were more mixed in another population.

CONCLUSION

These results make sense only if we assume that the RtSB03 locus is linked to male sex determination factor in some, but not in all common frog populations, and if phenotypic sex-reversals - for which there is earlier evidence from this species - are frequently occurring.

How are podocytes affected in nail-patella syndrome?

Nail-patella syndrome is an autosomal-dominant hereditary disease named for dysplastic fingernails and toenails and hypoplastic or absent kneecaps evident in patients with the syndrome. Prognosis is determined by the nephropathy that develops in many such patients. Besides podocyte foot-process effacement, pathognomonic changes in the kidney comprise electron-lucent areas and fibrillar inclusions in the glomerular basement membrane. These characteristic symptoms are caused by mutations in the gene encoding the transcription factor LMX1B, a member of the LIM-homeodomain gene family. Comparable with the human syndrome, homozygous Lmx1b knockout mice lack patellae and suffer from severe podocyte damage. In contrast, however, podocin and the alpha3 and alpha4 chains of collagen IV are absent in the glomeruli of Lmx1b knockout mice. Further studies with podocyte-specific Lmx1b knockout mice have confirmed the importance of LMX1B in podocytes, as these mice apparently develop foot processes initially but lose them later on. We therefore conclude that LMX1B is essential for the development of metanephric precursor cells into podocytes and possibly also for maintaining the differentiation status of podocytes. LMX1B can serve as a model system to elucidate a genetic program in podocytes.

Wt1 and retinoic acid signaling are essential for stellate cell development and liver morphogenesis

Previous studies of knock-out mouse embryos have shown that the Wilms' tumor suppressor gene (Wt1) is indispensable for the development of kidneys, gonads, heart, adrenals and spleen. Using OPT (Optical Projection Tomography) we have found a new role for Wt1 in mouse liver development. In the absence of Wt1, the liver is reduced in size, and shows lobing abnormalities. In normal embryos, coelomic cells expressing Wt1, GATA-4, RALDH2 and RXRalpha delaminate from the surface of the liver, intermingle with the hepatoblasts and incorporate to the sinusoidal walls. Some of these cells express desmin, suggesting a contribution to the stellate cell population. Other cells, keeping high levels of RXRalpha immunoreactivity, are negative for stellate or smooth muscle cell markers. However, coelomic cells lining the liver of Wt1-null embryos show decreased or absent RALDH2 expression, the population of cells expressing high levels of RXRalpha is much reduced and the proliferation of hepatoblasts and RXRalpha-positive cells is significantly decreased. On the other hand, the expression of smooth muscle cell specific alpha-actin increases throughout the liver, suggesting an accelerated and probably anomalous differentiation of stellate cell progenitors. We describe a similar retardation of liver growth in RXRalpha-null mice as well as in chick embryos after inhibition of retinoic acid synthesis. We propose that Wt1 expression in cells delaminating from the coelomic epithelium is essential for the expansion of the progenitor population of liver stellate cells and for liver morphogenesis. Mechanistically, at least part of this effect is mediated via the retinoic acid signaling pathway.

Structure of the Wilms tumor suppressor protein zinc finger domain bound to DNA

The zinc finger domain of the Wilms tumor suppressor protein (WT1) contains four canonical Cys(2)His(2) zinc fingers. WT1 binds preferentially to DNA sequences that are closely related to the EGR-1 consensus site. We report the structure determination by both X-ray crystallography and NMR spectroscopy of the WT1 zinc finger domain in complex with DNA. The X-ray structure was determined for the complex with a cognate 14 base-pair oligonucleotide, and composite X-ray/NMR structures were determined for complexes with both the 14 base-pair and an extended 17 base-pair DNA. This combined approach allowed unambiguous determination of the position of the first zinc finger, which is influenced by lattice contacts in the crystal structure. The crystal structure shows the second, third and fourth zinc finger domains inserted deep into the major groove of the DNA where they make base-specific interactions. The DNA duplex is distorted in the vicinity of the first zinc finger, with a cytidine twisted and tilted out of the base stack to pack against finger 1 and the tip of finger 2. By contrast, the composite X-ray/NMR structures show that finger 1 continues to follow the major groove in the solution complexes. However, the orientation of the helix is non-canonical, and the fingertip and the N terminus of the helix project out of the major groove; as a consequence, the zinc finger side-chains that are commonly involved in base recognition make no contact with the DNA. We conclude that finger 1 helps to anchor WT1 to the DNA by amplifying the binding affinity although it does not contribute significantly to binding specificity. The structures provide molecular level insights into the potential consequences of mutations in zinc fingers 2 and 3 that are associated with Denys-Drash syndrome and nephritic syndrome. The mutations are of two types, and either destabilize the zinc finger structure or replace key base contact residues.

The Wilms tumor genes wt1a and wt1b control different steps during formation of the zebrafish pronephros

The Wilms tumor protein WT1 is an essential factor for kidney development. In humans, mutations in WT1 lead to Wilms tumor, a pediatric kidney cancer as well as to developmental anomalies concerning the urogenital tract. Inactivation of Wt1 in mice causes multiple organ defects most notably agenesis of the kidneys. In zebrafish, two paralogous wt1 genes exist, wt1a and wt1b. The wt1 genes are expressed in a similar and overlapping but not identical pattern. Here, we have examined the role of both wt1 genes in early kidney development employing a transgenic line with pronephros specific GFP expression and morpholino knockdown experiments. Inactivation of wt1a led to failure of glomerular differentiation and morphogenesis resulting in a rapidly expanding general body edema. In contrast, knockdown of wt1b was compatible with early glomerular development. After 48 h, however, wt1b morphant embryos developed cysts in the region of the glomeruli and tubules and subsequent pericardial edema at 4 days post-fertilization. Thus, our data suggest different functions for wt1a and wt1b in zebrafish nephrogenesis. While wt1a has a more fundamental and early role in pronephros development and is essential for the formation of glomerular structures, wt1b functions at later stages of nephrogenesis.

Role of transcription factors in podocytes

Despite a wealth of information on structural proteins, comparatively little is known on the transcriptional regulation of podocyte structure and function. In this review we will highlight those transcription factors which, by gene inactivation or classical transgenic experiments, have been shown to be essential for podocytes or probably will turn out to be so. The tumor suppressor protein WT1 is not only indispensable for the initial stages of kidney development, but also very likely maintains the integrity of the fully differentiated podocyte. In the kidney, the LIM homeodomain transcription factor LMX1B is specifically synthesized in podocytes, and mutations in LMX1B lead to nail-patella syndrome and the associated nephropathy. Other transcription factors such as hypoxia-inducible factors and PAX2 are likely to play a role in podocytes, whereas the significance of others, e.g. of POD1 and CITED2, is more speculative at this point.

Identification of Novel Wilms' Tumor Suppressor Gene Target Genes Implicated in Kidney Development

The Wilms' tumor suppressor gene (WT1) encodes a zinc finger transcription factor that is vital during development of several organs including metanephric kidneys. Despite the critical regulatory role of WT1, the pathways and mechanisms by which WT1 orchestrates development remain elusive. To identify WT1 target genes, we performed a genome-wide expression profiling analysis in cells expressing inducible WT1. We identified a number of direct WT1 target genes, including the epidermal growth factor (EGF)-family ligands epiregulin and HB-EGF, the chemokine CX3CL1, and the transcription factors SLUG and JUNB. The target genes were validated using quantitative reverse transcriptase-polymerase chain reaction, small interfering RNA knockdowns, chromatin immunoprecipitation, and luciferase reporter analyses. Immunohistochemistry of fetal kidneys confirmed that a number of the WT1 target genes had overlapping expression patterns with the highly restricted spatiotemporal expression of WT1. Finally, using an in vitro embryonic kidney culture assay, we found that the addition of recombinant epiregulin, amphiregulin, CX3CL1, and interleukin-11 significantly enhanced ureteric bud branching morphogenesis. Our genome-wide screen implicates WT1 in the transcriptional regulation of the EGF-family of growth factors as well as the CX3CL1 chemokine during nephrogenesis.

Transcriptional regulation of podocyte disease

The podocyte is a highly specialized visceral epithelial cell that forms the outermost layer of the glomerular capillary loop and plays a critical role in the maintenance of the glomerular filtration barrier. Several transcriptional factors regulate the podocyte function under normal and disease conditions. In this review, the role of Wilms tumor 1 (WT1), LIM homeobox transcription factor 1, beta (Lmx1b), pod1, pax-2, kreisler, nuclear factor-kappa B (NF-kappaB), smad7, and zinc fingers and homeoboxes (ZHX) proteins in the development of podocyte disease is outlined. The regulation of several important podocyte genes, including transcriptional factors, by ZHX proteins, their predominant non-nuclear localization in the normal in vivo podocyte, and changes in ZHX expression related to the development of minimal change disease and focal and segmental glomerulosclerosis are discussed. Finally, some future therapeutic strategies for glomerular disease are proposed.

Wilms' tumor protein Wt1 is an activator of the anti-Müllerian hormone receptor gene Amhr2

The Wilms' tumor protein Wt1 plays an essential role in mammalian urogenital development. WT1 mutations in humans lead to a variety of disorders, including Wilms' tumor, a pediatric kidney cancer, as well as Frasier and Denys-Drash syndromes. Phenotypic anomalies in Denys-Drash syndrome include pseudohermaphroditism and sex reversal in extreme cases. We have used cDNA microarray analyses on Wt1 knockout mice to identify Wt1-dependent genes involved in sexual development. The gene most dramatically affected by Wt1 inactivation was Amhr2, encoding the anti-Müllerian hormone (Amh) receptor 2. Amhr2 is an essential factor for the regression of the Müllerian duct in males, and mutations in AMHR2 lead to the persistent Müllerian duct syndrome, a rare form of male pseudohermaphroditism. Here we show that Wt1 and Amhr2 are coexpressed during urogenital development and that the Wt1 protein binds to the promoter region of the Amhr2 gene. Inactivation and overexpression of Wt1 in cell lines was followed by immediate changes of Amhr2 expression. The identification of Amhr2 as a Wt1 target provides new insights into the role of Wt1 in sexual differentiation and indicates, in addition to its function in early gonad development and sex determination, a novel function for Wt1, namely, in Müllerian duct regression.

WT1 intron 9 splice acceptor site mutation in a 46,XY male with focal segmental glomerulosclerosis

The Wilms' tumor suppressor gene (WT1) plays crucial roles in urogenital and gonadal development. Germline mutations of WT1 have been reported in patients with Denys-Drash syndrome (DDS) and Frasier syndrome (FS). Based on clinical overlaps reported to date, it has been suggested that these two syndromes should be considered as part of a spectrum of diseases caused by WT1 gene mutations, rather than as separate diseases. We report a new mutation in an intron 9 splice acceptor site (IVS -1G-->) in a Japanese 46,XY male patient with focal segmental glomerulosclerosis (FSGS) and bilateral cryptorchism. The clinical phenotype of this patient resembled FS without male pseudohermaphroditism. Interestingly, although the patient's right kidney was diagnosed with FSGS, his left kidney showed severe hypoplasia. There are no previous case reports of FSGS and renal hypoplasia in the same individual with a WT1 mutation. The findings for this case further suggest that the renal phenotype has various manifestations and is not always decided by the type of WT1 mutation. The possibility that the position of the WT1 mutation may influence the course of the nephropathy should be evaluated in a larger patient cohort.

High WT1 expression is associated with very poor survival of patients with osteogenic sarcoma metastasis

PURPOSE

Although metastasis is the primary determinant of poor survival of patients with osteogenic sarcoma, some patients live much longer than others, indicating metastatic heterogeneity underlying survival outcome. The purpose of the investigation was to identify genes underlying survival outcome of patients with osteogenic sarcoma metastasis.

EXPERIMENTAL DESIGN

We have used microarray to first compare mRNA expression between normal bone and osteogenic sarcoma specimens, identified genes overexpressed in osteogenic sarcoma, and compared expression of the selected gene between a poorly metastatic (SAOS) and two highly metastatic cell lines (LM8 and 143B). Finally, expression of the selected gene was assessed by immunostaining of osteogenic sarcoma samples with known survival outcome.

RESULTS

Microarray analysis revealed 5.3-fold more expression of WT1 mRNA in osteogenic sarcoma compared with normal bone and >2-fold overexpression in 143B and LM8 cells compared with SAOS. Furthermore, WT1 mRNA was absent in normal bone (10 of 10) by reverse transcription-PCR but present in osteogenic sarcoma-derived cell lines (5 of 8). One hundred percent (42 of 42) of low-grade osteogenic sarcoma specimens expressed no WT1 as determined by immunostaining; however, 24% (12 of 49) of the high-grade specimens showed intense staining. Mean survival of patients with high-grade metastatic osteogenic sarcoma but low WT1 staining (27 of 37) was 96.5 +/- 129.3 months, whereas mean survival of patients with high-grade metastatic osteogenic sarcoma having intense staining (10 of 37) was 18.3 +/- 12.3 months (P > 0.0143). All splice variants of WT1 mRNA, including a hitherto unknown variant (lacking exons 4 and 5), were found to be expressed in osteogenic sarcoma.

CONCLUSION

WT1 seems to be associated with very poor survival of patients with osteogenic sarcoma metastasis.

WT1 and glomerular diseases

The WT1 gene encodes a zinc finger transcription factor involved in kidney and gonadal development and, when mutated, in the occurrence of kidney tumor and glomerular diseases. Patients with Denys-Drash syndrome present with early nephrotic syndrome with diffuse mesangial sclerosis progressing rapidly to end-stage renal failure, male pseudohermaphroditism, and Wilms' tumor. Incomplete forms of the syndrome have been described. Germline WT1 missense mutations located in exons 8 or 9 coding for zinc fingers 2 or 3 have been detected in nearly all patients with Denys-Drash syndrome and in some patients with isolated diffuse mesangial sclerosis. Patients with Frasier syndrome present with normal female external genitalia, streak gonads, XY karyotype and progressive nephropathy with proteinuria and nephrotic syndrome with focal and segmental glomerular sclerosis progressing to end-stage renal disease in adolescence or young adulthood. They frequently develop gonadoblastoma. Germline intronic mutations leading to the loss of the +KTS isoforms have been observed in all patients with Frasier syndrome. The same mutations have been observed in genetically female patients with isolated FSGS. Transmission of the mutation is possible. Frasier mutations have also been reported in children with Denys-Drash syndrome.

ZHX proteins regulate podocyte gene expression during the development of nephrotic syndrome

Transcriptional regulation of podocyte gene expression in primary glomerular disease is poorly understood. In this study, we demonstrate a prominent role of members of the ZHX (zinc fingers and homeoboxes) family of proteins in regulating podocyte gene expression during the development of nephrotic syndrome. While studying mechanisms of glomerular disease, rat ZHX3 was cloned from a down-regulated gene fragment; its cellular localization, DNA binding, and transcriptional repressor properties were characterized; and its ability to influence podocyte gene expression directly or via ZHX1 and ZHX2 was studied. In eukaryotic promoters, ZHX3 bound to the CdxA binding motif. ZHX proteins were mostly sequestered in the non-nuclear compartment in the normal in vivo podocyte by virtue of heterodimer formation, and loss of heterodimerization was associated with entry into the nucleus. In experimental minimal change disease, ZHX3 was transiently down-regulated prior to the onset of proteinuria, and recovery of expression was associated with migration of ZHX3 protein into the nucleus and the development of proteinuria. This expression pattern mirrored the increased nuclear ZHX3 expression noted in vivo in the podocytes in human minimal change disease biopsies. In vitro, migration of ZHX3 protein into the nucleus during recovery from transient ZHX3 knockdown reproduced the gene expression profile of in vivo minimal change disease. Severe sustained knockdown of ZHX3 caused down-regulation of genes involved in focal sclerosis, including WT1, mediated mostly by increased nuclear entry of ZHX2 and ZHX1. In summary, ZHX proteins are major transcriptional mediators of podocyte disease.

WT1 interacts with the splicing protein RBM4 and regulates its ability to modulate alternative splicing in vivo

Wilm's tumor protein 1 (WT1), a protein implicated in various cancers and developmental disorders, consists of two major isoforms: WT1(-KTS), a transcription factor, and WT1(+KTS), a post-transcriptional regulator that binds to RNA and can interact with splicing components. Here we show that WT1 interacts with the novel splicing regulator RBM4. Each protein was found to colocalize in nuclear speckles and to cosediment with supraspliceosomes in glycerol gradients. RBM4 conferred dose-dependent and cell-specific regulation of alternative splicing of pre-mRNAs transcribed from several reporter genes. We found that overexpressed WT1(+KTS) abrogated this effect of RBM4 on splice-site selection, whereas WT1(-KTS) did not. We conclude that the (+KTS) form of WT1 is able to inhibit the effect of RBM4 on alternative splicing.

Germ cell tumors in the intersex gonad: old paths, new directions, moving frontiers

The risk for the development of germ cell tumors is an important factor to deal with in the management of patients with disorders of sex development (DSD). However, this risk is often hard to predict. Recently, major progress has been made in identifying gene-products related to germ cell tumor development (testis-specific protein-Y encoded and octamer binding transcription factor 3/4) and in recognizing early changes of germ cells (maturation delay, preneoplastic lesions, and in situ neoplasia). The newly recognized "undifferentiated gonadal tissue" has been identified as a gonadal differentiation pattern bearing a high risk for the development of gonadoblastoma. It is expected that the combination of these findings will allow for estimation of the risk for tumor development in the individual patient (high risk/intermediate risk/low risk). This article reviews the recent literature regarding the prevalence of germ cell tumors in patients with DSD. Some major limitations regarding this topic, including a confusing terminology referring to the different forms of intersex disorders and unclear criteria for the diagnosis of malignant germ cells at an early age (maturation delay vs. early steps in malignant transformation) are discussed. Thereafter, an overview of the recent advances that have been made in our knowledge of germ cell tumor development and the correct diagnosis of early neoplastic lesions in this patient population is provided. A new classification system for patients with DSD is proposed as a tool to refine our insight in the prevalence of germ cell tumors in specific diagnostic groups.

Pierson syndrome: a novel cause of congenital nephrotic syndrome

In this report, we describe a newborn infant who presented with congenital nephrotic syndrome and renal insufficiency, as well as bilateral microcoria. This constellation of findings is a hallmark of Pierson syndrome, a newly recognized genetic disorder that is caused by a deficiency of beta2 laminin in the basement membrane. Our patient demonstrated classic histopathologic findings of Pierson syndrome on renal biopsy, including absence of beta2 laminin on immunofluorescent staining, and genetic testing confirmed the diagnosis. We conclude that Pierson syndrome should be included in the differential diagnosis for congenital nephrotic syndrome, especially in patients with ocular abnormalities.

The Wilms tumor gene, Wt1, is required for Sox9 expression and maintenance of tubular architecture in the developing testis

Mutation of the transcription factor and tumor suppressor gene WT1 results in a range of genitourinary anomalies in humans, including 46,XY gonadal dysgenesis, indicating that WT1 plays a critical role in sex determination. However, because knockout of Wt1 in mice results in apoptosis of the genital ridge, it is unknown whether WT1 is required for testis development after the initial steps of sex determination. To address this question, we generated a mouse strain carrying a Wt1 conditional knockout allele and ablated Wt1 function specifically in Sertoli cells by embryonic day 14.5, several days after testis determination. Wt1 knockout resulted in disruption of developing seminiferous tubules and subsequent progressive loss of Sertoli cells and germ cells such that postnatal mutant testes were almost completely devoid of these cell types and were severely hypoplastic. Thus, Wt1 is essential for the maintenance of Sertoli cells and seminiferous tubules in the developing testes. Of particular note, expression of the testis-determining gene Sox9 in mutant Sertoli cells was turned off at embryonic day 14.5 after Wt1 ablation, suggesting that WT1 regulates Sox9, either directly or indirectly, after Sry expression ceases. Our data, along with previous work demonstrating the role of Wt1 at early stages of gonadal development, thus indicate that Wt1 is essential at multiple steps in testicular development.

Chronic nephropathies of cocaine and heroin abuse: a critical review

Renal disease in cocaine and heroin users is associated with the nephrotic syndrome, acute glomerulonephritis, amyloidosis, interstitial nephritis, and rhabdomyolysis. The pathophysiologic basis of cocaine-related renal injury involves renal hemodynamic changes, glomerular matrix synthesis and degradation, and oxidative stress and induction of renal atherogenesis. Heroin is the most commonly abused opiate in the United States. Previous studies identified a spectrum of renal diseases in heroin users. The predominant renal lesion in black heroin users is focal segmental glomerulosclerosis and in white heroin users is membranoproliferative glomerulonephritis. Although the prevalence of heroin use in the United States has increased, the incidence of "heroin nephropathy" has declined. Because reports of heroin nephropathy predated the surveillance of hepatitis C virus and HIV, the varied findings might be related to the spectrum of viral illnesses that are encountered in injection drug users. Socioeconomic conditions, cultural and behavioral practices, or differences in genetic susceptibilities may be more associated with the development of nephropathy in heroin users than the drug's pharmacologic properties. Administration of cocaine in animal models results in nonspecific glomerular, interstitial, and tubular cell lesions, but there is no animal model of heroin-associated renal disease. The heterogeneity of responses that are associated with heroin is not consistent with a single or simple notion of nephropathogenesis. There are no well-designed, prospective, epidemiologic studies to assess the incidence and the prevalence of renal disease in populations of opiate users and to establish the validity of a syndrome such as heroin nephropathy. It is concluded although there is a paucity of evidence to support a heroin-associated nephropathy, the evidence from in vitro cellular and animal studies to support the existence of cocaine-induced renal changes is more convincing.

Lack of puberty despite elevated estradiol in a 46,XY phenotypic female with Frasier syndrome

Frasier syndrome is characterized by slowly progressive nephropathy, male pseudohermaphroditism, streak gonad, and high risk of gonadoblastoma development. Here we report a case of a 46,XY phenotypic female with Frasier syndrome, who was under hemodialysis. While her serum estradiol level was gradually increasing annually, gonadotropin level was constantly extremely high, and her appearance was still prepubertal. She was heterozygous for a novel guanine>adenine point mutation at position +1 of the splice donor site within intron 9 (IVS 9 + 1G>A) of the Wilms' tumor 1 gene. The possibility of this disease should be taken into consideration whenever we encounter a patient with steroid-resistant nephrotic syndrome and delayed puberty.

Immunohistochemical detection of WT1 protein in a variety of cancer cells

WT1 was first identified as a tumor suppressor involved in the development of Wilms' tumor. Recently, oncogenic properties of WT1 have been demonstrated in various hematological malignancies and solid tumors. Because WT1 has been identified as a molecular target for cancer immunotherapy, immunohistochemical detection of WT1 in tumor cells has become an essential part of routine practice. In the present study, the expression of WT1 was examined in 494 cases of human cancers, including tumors of the gastrointestinal and pancreatobiliary system, urinary tract, male and female genital organs, breast, lung, brain, skin, soft tissues and bone by immunohistochemistry using polyclonal (C-19) and monoclonal (6F-H2) antibodies against WT1 protein. Staining for C-19 and 6F-H2 was found in 35-100 and 5-88% of the cases of each kind of tumor, respectively. WT1-positive tumors included tumor of the stomach, prostate, and biliary and urinary systems, and malignant melanomas. A majority of the positive cases showed diffuse or granular staining in the cytoplasm, whereas ovarian tumors and desmoplastic small round cell tumors frequently showed nuclear staining. Glioblastomas, some of soft tissue sarcomas, osteosarcomas, and malignant melanomas of the skin showed extremely strong cytoplasmic staining as compared with other tumors. Western blot analysis showed that WT1 protein was predominantly expressed in the cytoplasm of the tumor cells in two cases of lung adenocarcinoma, supporting the intracytoplasmic staining for WT1 using immunohistochemistry. Immunohistochemical detection with routinely processed histologic sections could provide meaningful information on the expression of WT1 in cancer cells.

Recurrence of focal-segmental glomerulosclerosis in children after renal transplantation: clinical and genetic aspects

Focal segmental glomerulosclerosis (FSGS) is the primary renal disease in approximately one-tenth of pediatric patients receiving a renal allograft. Recurrence of proteinuria after renal transplantation is observed in approximately 30% of patients and negatively impacts graft survival. Risk factors for recurrence are a chronological age <15 years at onset of the nephrotic syndrome and a rapid progression of the disease in the native kidneys leading to end-stage renal disease in less than 3 years. Mesangial proliferation in the native kidneys is also an important negative predictive factor for disease recurrence. With rapid recurrence of FSGS and loss of the allograft, further renal transplants also carry a high likelihood of FSGS recurrence. Different pathogenic factors have been discussed for the recurrence of proteinuria/FSGS in the transplanted kidney, especially the involvement of a proteinuric circulating factor, whose production seems to follow T-cell dysfunction. In the last decade, mutations in genes encoding podocyte proteins have been identified in different forms of hereditary FSGS. Mutations of NPHS2 were detected in 26-38% of familial autosomal recessive steroid-resistant NS (SRNS), 6-19% of sporadic cases of SRNS, and in few adult patients with FSGS. Large multicenter studies demonstrated that patients with two pathogenic NPHS2 mutations have a very low risk of recurring FSGS after renal transplantation, whereas patients with only one mutation presumably have a risk comparable to non-NPHS2 FSGS patients. The management of FSGS following renal transplantation remains controversial. Following the assumption of a putative permeability factor, several studies have suggested the efficacy of plasmapheresis in inducing remission, preferably in conjunction with high-dose cyclosporine A or cyclophosphamide. Prospective studies will be necessary to better evaluate different therapeutic approaches.

[Genes involved in sex determination and differentiation]

Chromosomal sex is established at fertilization by the presence of an X or Y chromosome. The first step of male and female development is gonadal specialization in testes or ovaries; all other processes that follow result from secondary effects produced by testis and ovary hormones. Gonadal determination and differentiation and the development of external genitalia involve time- and tissue-specific expression of genes forming a gene cascade. Those genes, their expression profile and their role in the pathological manifestations related to gonadal and external genitalia development will be discussed in this review.

[Gonadal dysgenesis and tumors: genetic and clinical features]

Gonadal dysgenesis comprises a clinical spectrum of anomalies in patients with female, ambiguous or male phenotype, absent or impaired puberty and karyotype with or without Y chromosome and/or chromosome markers. Although Y-specific sequences are seldom cytogenetically evident, dysgenetic gonads are potentially prone to developing tumors. Gonadoblastoma, a mixed germ cell and sex-cord cells tumor with variable degree of focal calcification, is the most harmful due to its frequency. Other gonadal tumor, malign or not, also occur in gonadal dysgenesis. As they are not metastatic tumors and may be eradicated by selective excisions, the importance of detecting Y-sequences by molecular sensitized techniques is stressed in order to indicate prophylactic gonadectomy.

Imaging glomeruli in renal biopsy specimens

Glomerular capillary loops are complex vascular filters composed of interdigitating podocytes and fenestrated endothelial cells with an intervening proteoglycan-rich extracellular matrix. This arrangement is crucial to maintaining the filtration barrier but renders the glomerulus difficult to analyze by conventional two-dimensional histochemical techniques. When pathologic lesions distort glomerular architecture, its complex morphology is even more challenging to interpret. Fortunately, recent advances in microscopes and computer software now enable glomerular enthusiasts to dissect this complex structure with finer detail. In this review we explore the application of new methodologies such as two-photon microscopy that optimize three-dimensional, multicolor imaging and single-cell segmentation of glomerular components.

Podocyte cell-specific expression of doxycycline inducible Cre recombinase in mice

Conventional silencing of many podocyte-specific genes in mice is associated with embryonic or perinatal lethality. Therefore, it would be of great importance to generate mouse models that allow the modification of genes that are expressed in podocytes at later stages of age. Herein is described a transgenic mouse with doxycycline-inducible podocyte-specific expression of Cre recombinase. For the generation of this binary system, a single transgenic construct that contained two separate genes was used: One encoding the optimized M2 version of the doxycycline-dependent transcription transactivator reverse tetracycline-controlled transcriptional activator (rtTA) under control of the human podocin (NPHS2) promoter and the other encoding the recombinase Cre under control of the rtTA/doxycycline-responsive minimal cytomegalovirus (CMV) Tet operator sequence 7 promotor. Microinjection of the JRC-CRE construct in fertilized oocytes from FVB/N mice resulted in 16 transgenic founders. Double-transgenic offspring from breeding of a selected founder with the Z/AP reporter mouse showed alkaline phosphatase staining only upon doxycycline administration and exclusively in podocytes. These data indicate that this new inducible Cre recombinase mouse line is an excellent tool in conditional, kidney glomerular podocyte-specific gene deletion in adult mice.

Mutations in the Wilms' tumor 1 gene cause isolated steroid resistant nephrotic syndrome and occur in exons 8 and 9

Primary steroid-resistant nephrotic syndrome (SRNS) is characterized by childhood onset of proteinuria and progression to end-stage renal disease. Approximately 10-25% of familial and sporadic cases are caused by mutations in NPHS2 (podocin). Mutations in exons 8 and 9 of the WT1 gene have been found in patients with isolated SRNS and in SRNS associated with Wilms' tumor (WT) or urogenital malformations. However, no large studies have been performed to date to examine whether WT1 mutations in isolated SRNS are restricted to exons 8 and 9. To address this question, we screened a worldwide cohort of 164 cases of sporadic SRNS for mutations in all 10 exons of the WT1 gene by multiplex capillary heteroduplex analysis and direct sequencing. NPHS2 mutations had been excluded by direct sequencing. Fifteen patients exhibited seven different mutations exclusively in exons 8 and 9 of WT1. Although it is possible that pathogenic mutations of WT1 may also reside in the introns, regions of the gene that were not able to be screened in this study, these data together with our previous results (Ruf et al.: Kidney Int 66: 564-570, 2004) indicate that screening of WT1 exons 8 and 9 in patients with sporadic SRNS is sufficient to detect pathogenic WT1 mutations and may open inroads into differential therapy of SRNS.

Two cases of isolated diffuse mesangial sclerosis with WT1 mutations

Here we report two cases of isolated diffuse mesangial sclerosis (IDMS) with early onset end-stage renal failure. These female patients did not show abnormalities of the gonads or external genitalia. Direct sequencing of WT1 PCR products from genomic DNA identified WT1 mutations in exons 8 (366 Arg>His) and 9 (396 Asp>Tyr). These mutations have been reported previously in association with Denys-Drash syndrome (DDS) with early onset renal failure. Therefore we suggest that, at least in part, IDMS is a variant of DDS and that investigations for the WT1 mutations should be performed in IDMS patients. In cases with identified WT1 mutations, the same attention to tumor development should be required as in DDS patients, and karyotyping and serial abdominal ultrasonograms to evaluate the gonads and kidney are warranted.

Molecular genetic analysis of a de novo balanced translocation t(6;17)(p21.31;q11.2) associated with hypospadias and anorectal malformation

We report a young boy with penoscrotal hypospadias, anal atresia (AA) with a recto-urethral fistula, a hypoplastic kidney and a balanced translocation t(6;17)(p21.31;q11.2). Physical mapping of the breakpoints localized the chromosome 6 breakpoint within an intron of the gene lipoma HMGIC fusion partner-like 5 (LHFPL5) whereas the chromosome 17 breakpoint was mapped to the first intron of the 182-FIP gene encoding the Fragile X Mental Retardation Protein Interacting Protein. Sequence analysis across the breakpoints revealed an almost perfectly balanced translocation with a 2 bp deletion on the derivative chromosome 6 and a 7 bp duplication on the derivative chromosome 17. We identified a fusion transcript consisting of the first exon of 182-FIP and the last exon of LHFPL5 in patient-derived cells. Quantitative expression analysis of the genes flanking the breakpoints, revealed increased transcript levels for SFRS protein kinase 1 (SRPK1) and TAO kinase 1 (TAOK1) which suggests a positional effect due to the translocation. We hypothesize that the urogenital and anorectal malformations in the patient result from one or several mechanisms including disruption of the genes 182-FIP and LHFPL5, altered expression of the genes flanking the translocation breakpoints and, a gain of function mechanism mediated by the 182-FIP-LHFPL5 fusion transcript.

Vascular endothelial growth factor (VEGF) is suppressed in WT1-transfected LNCaP cells

The Wilms' tumor suppressor gene product (WT1) regulates expression of growth control genes. Microarray analysis of gene expression profiles of hormone-treated LNCaP prostate cancer cell lines transfected with either wild-type WT1 or a zinc finger mutant form, DDS (R394W), revealed significantly altered patterns of expression. Validation studies using quantitative real-time PCR confirmed the differential expression of the tumor progression gene, vascular endothelial growth factor (VEGF). WT1-LNCaP cells had significantly reduced levels of VEGF mRNA when compared to vector control cells; in contrast, DDS-LNCaP cells showed elevated levels of VEGF transcripts. To address a functional role for WT1 overexpression, we investigated whether induction of VEGF expression, by the synthetic androgen R1881, would be disrupted in wild-type or mutant WT1-transfected LNCaP cells. Hormone treatment failed to elevate VEGF transcript levels above uninduced baseline levels in WT1-LNCaP cells, despite 48 h of treatment with 5 nM R1881. Consistent with our quantitative real-time PCR analysis, immunofluorescent staining of VEGF protein was reduced in WT1-LNCaP cells in both the presence and absence of R1881 treatment. Conversely, VEGF levels increased in vector control and DDS-LNCaP cells treated with 5 nM R1881. Not only do these studies point out the regulatory potential of WT1 for VEGF, but they also indicate an altered function for the mutant DDS isoform. Because VEGF is associated with neovascularization and promotion of metastasis in a variety of solid tumors including prostate cancer, a better understanding of the regulation of VEGF expression by transcription factors, such as WT1, is important for halting disease progression.

Clinical course of congenital nephrotic syndrome and Denys-Drash syndrome in Japan

BACKGROUND

The prognosis of Japanese patients with congenital nephrotic syndrome (CNS) and Denys-Drash syndrome (DDS) is not clear.

METHODS

Five patients with CNS and four patients with DDS, which causes secondary CNS, were studied retrospectively.

RESULTS

Seven patients were sporadic and two DDS patients were identical twins. Five CNS patients presented with edema within 3 months of birth. In four DDS patients, edema was not noted and end-stage renal disease developed between 7 months and 6 years of age. Of these five CNS patients, one patient had cerebral thrombosis and cytomegalovirus pneumonia at the onset and another patient died during dialysis. Frequent intravenous albumin administration required, growth and development during infancy were varied. Of the nine patients with CNS and DDS, seven received renal transplantation and were alive with functioning grafts at the last follow up. Catch-up growth was observed in five patients after transplantation. Five school-aged patients attended school and received adequate grades and two adults worked full-time. Of the DDS patients, dysuria due to hypospadias persisted in one patient and treatment for hypogonadism was needed in one patient.

CONCLUSIONS

CNS and DDS were diagnosed early after onset and adequate treatment was started. Growth and development after renal transplantation were relatively good. Thrombotic episodes or severe infection in CNS patients was difficult to manage and complications resulting from DDS affected the quality of life.

Expression, purification, and characterization of the 4 zinc finger region of human tumor suppressor WT1

Wilm's Tumor gene 1 (WT1) encodes a zinc finger protein with four distinct splice isoforms. WT1 has a critical role in genesis of various cancer types both at the DNA/RNA and the protein level. The zinc-finger DNA-binding capacity of the protein is located in the C-terminal domain. Two recombinant proteins, 6HIS-ZN-wt1 and 6HIS-ZN+wt1, corresponding to two alternative splice variants of the C-terminal regions of human WT1 (-KTS) and WT1 (+KTS), respectively, were over-expressed with hexa-histidine fusion tags in inclusion bodies in Escherichia coli for crystallization studies. A combination of Ni2+-NTA affinity and size-exclusion chromatography was applied for purification of the proteins in denaturing conditions. The effects of various buffers, salts and other additives were scrutinized in a systematic screening to establish the optimal conditions for solubility and refolding of the recombinant WT1 proteins. Circular dichroism analysis revealed the expected betabetaalpha content for the refolded proteins, with a notable degradation of the alpha-helical segment in the DNA-free state. Electrophoretic mobility shift assay with double-stranded DNA containing the double Egr1 consensus site 5'-GCG-TGG-GCG-3' confirmed that 6HIS-ZN-wt1 has higher DNA binding affinity than 6HIS-ZN+wt1.

Novel familial WT1 read-through mutation associated with Wilms tumor and slow progressive nephropathy

Wilms tumor gene 1 (WT1) is essential for normal urogenital development. Mutations in WT1 are involved in Wilms tumorigenesis and several associated syndromes, such as Denys-Drash, Frasier, or Wilms tumor, aniridia, genitourinary anomalies, and mental retardation syndrome. We report a novel familial WT1 point mutation in the stop codon of exon 10 (1730A/G; X450W) in 3 members of 1 family. The index patient is a 22-year-old woman in whom Wilms tumor and ureter duplex were diagnosed at the age of 9 years and who subsequently developed slow progressive nephropathy. Her mother also had late-onset nephropathy that led to end-stage renal failure, whereas renal function in 1 brother of the index patient was not impaired. We hypothesize that this type of mutation (read-through), which leads to an elongated, but otherwise unchanged, WT1 protein, may be associated with incomplete penetrance and a relatively late onset of both Wilms tumor and nephropathy in this family.

WT1 Induces Apoptosis through Transcriptional Regulation of the Proapoptotic Bcl-2 Family Member Bak

Wilms' tumor or nephroblastoma is believed to arise from embryonic nephrogenic rests of multipotent cells that fail to terminally differentiate into epithelium and continue to proliferate. The WT1 tumor suppressor gene, a transcription factor controlling the mesenchymal-epithelial transition in renal development, is mutated in 10% to 15% of Wilms' tumors. This potentially explains the disordered differentiation and proliferation program of a subset of Wilms' tumors. To elucidate the role of mutations of WT1 in the etiology of Wilms' tumor, we used an inducible cellular system for expressing wild-type and tumor-derived missense mutant WT1 proteins. Expression of wild-type WT1, but not mutant proteins, blocked cellular proliferation and DNA synthesis and rapidly induced apoptosis. We showed that wild-type WT1 induced transcription of one of the seven studied proapoptotic genes, Bak. Furthermore, WT1 protein bound to specific DNA-binding sites located in the Bak promoter and Bak was critical to WT1-mediated apoptosis, as overexpression of VDAC2, a specific Bak inhibitor, attenuated WT1-mediated cell death. These data support the hypothesis that Wilms' tumors arise, in part, because WT1 mutant proteins fail to promote programmed cell death during kidney development.

Congenital nephrotic syndrome responsive to angiotensin-converting enzyme inhibition

Congenital nephrotic syndrome is a severe disorder caused by increased permeability of the glomerular capillary leading to massive proteinuria. Typically, this disorder presents in the first three months and is caused by inherited mutations in genes encoding structural proteins of the podocyte slit membrane and, as such, is usually irreversible. Medical management is often insufficient to stem the enormous losses of protein, and the patients require nephrectomies. Here, we present results for a patient with congenital nephrotic syndrome of unknown etiology which responded to treatment with an angiotensin-converting enzyme inhibitor alone. The patient's proteinuria relapsed when the medication was stopped, but went into complete remission after restarting treatment. This remarkable response is discussed in the light of recent investigations into the effect of angiotensin II on podocyte integrity.

Genetics of idiopathic nephrotic syndrome

Nephrotic syndrome (NS) is a pathological entity characterized by massive proteinuria and has diverse etiology. Although it is one of the most common renal diseases in children, the etiological factors responsible for idiopathic NS/FSGS remain largely unknown. Previous studies had implicated a variety of factors including genetic factors, although NS is generally regarded as a sporadic disease. Familial cases of NS have however been reported periodically, and both autosomal dominant and recessive forms have been identified. Studies of familial NS/FSGS have led to the discovery of several genes that are expressed in podocytes and are associated with proteinuria. These discoveries have shifted the focus from glomerular basement membrane (GBM) to recognition of the central role of podocytes in maintaining glomerular perm selectivity and pathogenesis of NS/FSGS. Associations with various genes (NPHS1, ACTN4, NPHS2, WT-1) and linkage to several chromosomal regions (such as 19q13, 11q21, 11q24) have been reported in patients with familial NS/FSGS.

Wilms' tumour: connecting tumorigenesis and organ development in the kidney

Wilms' tumour, or nephroblastoma, is a common childhood tumour that is intimately linked to early kidney development and is often associated with persistent embryonic renal tissue and other kidney abnormalities. WT1, the first gene found to be inactivated in Wilms' tumour, encodes a transcription factor that functions as both a tumour suppressor and a critical regulator of renal organogenesis. Our understanding of the roles of WT1 in tumour formation and organogenesis have advanced in parallel, providing a striking example of the intersection between tumour biology, cellular differentiation and normal organogenesis.

[Denys-Drash syndrome. Experience gathered in Erlangen illustrated by two case reports]

Denys-Drash syndrome is a rare symptom complex associated with obligatory childhood nephrotic syndrome, male pseudohermaphroditism, and Wilms' tumor. The etiology of Denys-Drash syndrome is attributed to a mutation of the WT1 gene. We report on two cases of Deny-Drash syndrome confirmed by genetic testing. Rapidly evolving terminal renal insufficiency was detected in both patients necessitating bilateral nephrectomies with prophylactic intent. In one of the patients, a Wilms' tumor had already been verified in one kidney so that chemotherapy had to be initiated.The risk of Wilms' tumor is very high in patients with a WT1 mutation, which leads to the need for removal of both kidneys during or before transplantation. It would be important to perform a diagnostic work-up for WT1 gene mutation in children who develop renal failure in the 1st year of life.

High incidence of malformation syndromes in a series of 1,073 children with cancer

Constitutional molecular defects are known to play a role in oncogenesis, as shown by the increased incidence of embryonic cancers in children with Beckwith-Wiedemann syndrome (BWS) or of leukemia in children with Down syndrome. To establish the incidence and spectrum of malformation syndromes associated with childhood cancer we performed a clinical morphological examination on a series of 1,073 children with cancer. We diagnosed a syndrome in 42 patients (3.9%) and suspected the presence of a syndrome in another 35 patients (3.3%), for a total of 7.2%. This incidence of patients with a proven or suspected syndrome is high, and points to a possible association. We describe new syndrome-tumor associations in several entities: cleidocranial dysostosis (Wilms tumor), Bardet-Biedl syndrome (BBS) (acute lymphoblastic leukemia), Kabuki syndrome (neuroblastoma), LEOPARD syndrome (neuroblastoma), Poland anomaly (osteosarcoma; Hodgkin disease), and blepharophimosis epicanthus inversus syndrome (Burkitt lymphoma). Twenty of the 42 syndrome diagnoses were not recognized in the patients prior to this study, indicating that these diagnoses are commonly missed. We propose that all children with a malignancy should be examined by a clinical geneticist or a pediatrician skilled in clinical morphology to determine if the patients have a malformation syndrome.

Congenital diaphragmatic hernia in WAGR syndrome

Wilms tumor, aniridia, genitourinary anomalies, and mental retardation (WAGR) syndrome is a contiguous gene deletion syndrome involving the Wilms tumor 1 gene (WT1), the paired box gene 6 (PAX6), and possibly other genes on chromosome 11p13. WT1 is required for normal formation of the genitourinary system and the high incidence of Wilms tumor and genitourinary anomalies found in patients with WAGR are attributed to haploinsufficiency of this gene. It has been hypothesized that WT1 also plays an important role in the development of the diaphragm. During mammalian embryonic development, WT1 is expressed in the pleural and abdominal mesothelium that forms part of the diaphragm. Furthermore, mice that are homozygous for a deletion in the mouse homolog of WT1 have diaphragmatic hernias. Case reports describing congenital diaphragmatic hernias in infants with Denys-Drash and Frasier syndromes, both of which can be caused by mutations in WT1, provide additional support for this hypothesis. We report an infant with aniridia, bilateral cryptorchidism, vesicoureteral reflux, and a right-sided Morgagni-type diaphragmatic hernia. G-banded chromosome analysis revealed a deletion of 11p12-p15.1. Breakpoint regions were refined by fluorescence in situ hybridization (FISH) and deletion of the WAGR critical region, including WT1, was confirmed. A review of the medical literature identified a second patient with a deletion of 11p13, a left-sided Bochdalek-type diaphragmatic hernia, and anomalies that suggest a diagnosis of WAGR including bilateral microphthalmia, a small penis, bilateral cryptorchidism, and a hypoplastic scrotum. These cases demonstrate that congenital diaphragmatic hernia can be associated with WAGR syndrome and suggest that deletions of WT1 may predispose individuals to develop congenital diaphragmatic hernia.

Childhood solid tumours: a developmental disorder

Several lines of evidence demonstrate that the biology, genetics and environment of childhood solid tumours (CSTs) sets them apart from adult solid tumours. The nature of the progenitor cells from which these tumours arise, and their immature tissue environment, allows CSTs to develop with fewer defects in cell regulatory processes than adult cancers. These differences could explain why CSTs are more susceptible to therapeutic intervention than adult tumours. How does the aetiology of these cancers differ from those occurring in adults and how might this affect the development of more effective therapies?