An ovine hepatorenal fibrocystic model of a Meckel-like syndrome associated with dysmorphic primary cilia and TMEM67 mutations.

Meckel syndrome (MKS) is an inherited autosomal recessive hepatorenal fibrocystic syndrome, caused by mutations in TMEM67, characterized by occipital encephalocoele, renal cysts, hepatic fibrosis, and polydactyly. Here we describe an ovine model of MKS, with kidney and liver abnormalities, without polydactyly or occipital encephalocoele. Homozygous missense p.(Ile681Asn; Ile687Ser) mutations identified in ovine TMEM67 were pathogenic in zebrafish phenotype rescue assays. Meckelin protein was expressed in affected and unaffected kidney epithelial cells by immunoblotting, and in primary cilia of lamb kidney cyst epithelial cells by immunofluorescence. In contrast to primary cilia of relatively consistent length and morphology in unaffected kidney cells, those of affected cyst-lining cells displayed a range of short and extremely long cilia, as well as abnormal morphologies, such as bulbous regions along the axoneme. Putative cilia fragments were also consistently located within the cyst luminal contents. The abnormal ciliary phenotype was further confirmed in cultured interstitial fibroblasts from affected kidneys. These primary cilia dysmorphologies and length control defects were significantly greater in affected cells compared to unaffected controls. In conclusion, we describe abnormalities involving primary cilia length and morphology in the first reported example of a large animal model of MKS, in which we have identified TMEM67 mutations.

Biallelic DICER1 mutations occur in Wilms tumours.

DICER1 is an endoribonuclease central to the generation of microRNAs (miRNAs) and short interfering RNAs (siRNAs). Germline mutations in DICER1 have been associated with a pleiotropic tumour predisposition syndrome and Wilms tumour (WT) is a rare manifestation of this syndrome. Three WTs, each in a child with a deleterious germline DICER1 mutation, were screened for somatic DICER1 mutations and were found to bear specific mutations in either the RNase IIIa (n = 1) or the RNase IIIb domain (n = 2). In the two latter cases, we demonstrate that the germline and somatic DICER1 mutations were in trans, suggesting that the two-hit hypothesis of tumour formation applies for these examples of WT. Among 191 apparently sporadic WTs, we identified five different missense or deletion somatic DICER1 mutations (2.6%) in four individual WTs; one tumour had two very likely deleterious somatic mutations in trans in the RNase IIIb domain (c.5438A>G and c.5452G>A). In vitro studies of two somatic single-base substitutions (c.5429A>G and c.5438A>G) demonstrated exon 25 skipping from the transcript, a phenomenon not previously reported in DICER1. Further we show that DICER1 transcripts lacking exon 25 can be translated in vitro. This study has demonstrated that a subset of WTs exhibits two 'hits' in DICER1, suggesting that these mutations could be key events in the pathogenesis of these tumours.

PAX2 is an antiapoptotic molecule with deregulated expression in medulloblastoma.

PAX2 is a paired box transcription factor possessing a fundamental role in the embryogenesis of hindbrain and urinary tract. PAX genes are proto-oncogenes, PAX2 expression may contribute to the pathogenesis of renal cell carcinoma. Because of the expression of PAX2 in the developing hindbrain and its essential role in cerebellar development, it has been hypothesized that PAX2 may also be involved in medulloblastoma tumorigenesis. We investigated the expression pattern of PAX2 and various genes of the neuronal lineage in medulloblastoma and glioma cell lines. We found high expression of PAX2 mRNA and PAX2 protein in medulloblastoma cells and some glioma cell lines independent of their neuronal lineage gene expression signature. Gene suppression of PAX2 decreased the expression of the PAX2 transcriptional target GDNF in Daoy cells and had a profound cytotoxic effect in vitro on Daoy medulloblastoma and T98G glioma cells. Expression of PAX2 was then assessed in two separate medulloblastoma tissue microarrays with a total of 61 patient samples by immunohistochemistry. PAX2 expression was detected in the majority of medulloblastoma samples and correlated with less differentiated histology. Therefore, PAX2 is a biomarker for a more aggressive medulloblastoma phenotype and may represent a novel therapeutic target.

PAX8 promotes tumor cell growth by transcriptionally regulating E2F1 and stabilizing RB protein.

The retinoblastoma protein (RB)-E2F1 pathway has a central role in regulating the cell cycle. Several PAX proteins (tissue-specific developmental regulators), including PAX8, interact with the RB protein, and thus regulate the cell cycle directly or indirectly. Here, we report that PAX8 expression is frequent in renal cell carcinoma, bladder, ovarian and thyroid cancer cell lines, and that silencing of PAX8 in cancer cell lines leads to a striking reduction in the expression of E2F1 and its target genes, as well as a proteasome-dependent destabilization of RB protein, with the RB1 mRNA level remaining unaffected. Cancer cells expressing PAX8 undergo a G(1)/S arrest and eventually senesce following PAX8 silencing. We demonstrate that PAX8 transcriptionally regulates the E2F1 promoter directly, and E2F1 transcription is enhanced after RB depletion. RB is recruited to the PAX8-binding site, and is involved in PAX8-mediated E2F1 transcription in cancer cells. Therefore, our results suggest that, in cancer, frequent and persistent expression of PAX8 is required for cell growth control through transcriptional activation of E2F1 expression and upregulation of the RB-E2F1 pathway.

Congenital polycystic kidney disease in lambs.

AIM: To describe the pathology and inheritance of a congenital polycystic kidney disease (PKD) of sheep. METHODS: Mode of inheritance of PKD was investigated by evaluation of results of the disorder from planned matings in two consecutive years within subsets of a flock that had a high prevalence of PKD in lambs. Gross pathological and histopathological studies were based on tissues derived from this study. Haematoxylin and eosin (H&E)-stained paraffin sections of kidney, liver, extrahepatic biliary and pancreatic ducts, pancreas and epididymis were used to describe the lesions. RESULTS: Twenty-five lambs affected by PKD, of both sexes, were born, numbers in accord with those expected for an autosomal recessive disorder in the population studied. In all cases for which tissues were available, the renal, bile ductal (intrahepatic and extrahepatic), pancreatic and epididymal tissues had widespread dysplastic changes and associated cyst formation. CONCLUSIONS: The findings of renal cysts in conjunction with cysts in other organs are unifying features in many of the human and animal forms of PKD and suggest a related pathogenic and genetic base consistent with an autosomal recessive disorder.

PAX2 mutations in renal-coloboma syndrome: mutational hotspot and germline mosaicism.

The renal-coloboma syndrome (RCS, MIM 120330) is an autosomal dominant disorder caused by PAX2 gene mutations. We screened the entire coding sequence of the PAX2 gene for mutations in nine patients with RCS. We found five heterozygous PAX2 gene mutations: a dinucleotide insertion (2G) at position 619 in one sporadic RCS case, a single nucleotide insertion (619 + G) in three unrelated cases, and a single nucleotide deletion in a familial case. In this familial case, three affected sibs showed a striking ocular phenotypic variability. Each of the sibs carried a 619insG mutation, whilst unaffected parents did not, suggesting the presence of germline mosaicism. Interestingly, the 619insG mutation has been previously reported in several patients and is also responsible for the Pax21Neu mouse mutant, an animal model of human RCS. This study confirms the critical role of the PAX2 gene in human renal and ocular development. In addition, it emphasises the high variability of ocular defects associated with PAX2 mutations ranging from subtle optic disc anomalies to microphthalmia. Finally, the presence of PAX2 germline mosaicism highlights the difficulties associated with genetic counselling for PAX2 mutations.

Imprinting of insulin-like growth factor 2 is modulated during hematopoiesis.

The transcription of insulin-like growth factor 2 (IGF-2) is affected by genomic imprinting, a multistep process through which the parental origin of a gene influences its transcription. The maternal copy of IGF-2 is silenced in most human tissues, but in the choroid plexus and the adult liver both alleles of IGF-2 are expressed. This study shows that though in peripheral blood mononuclear cells IGF-2 shows paternal allele-specific expression, in total bone marrow both alleles are transcribed. This modulation of imprinting is not attributable to use of the P1 promoter, because transcription from the P3 promoter occurred from both alleles. These results suggest that transcriptional recognition of the IGF-2 imprint can be modulated during hematopoiesis and may facilitate the development of in vitro model systems to study the transcriptional recognition of a genomic imprint.

The genetics of primary vesico-ureteric reflux.

INTRODUCTION: Vesico-ureteric reflux (VUR), reflux of urine from the bladder into the ureter and towards the kidney, is an important cause of end-stage renal failure in both children and adults. Primary VUR is considered to be a result of a disruption of the normal anti-reflux mechanism of the ureterovesical junction (UVJ). VUR is common, occurring in approximately 1% to 2% of newborns in Caucasian populations. The aetiology of VUR is thought to involve a substantial genetic component, supported by the observation that VUR frequently occurs in multiple members of the same family. The purpose of this article is to review the literature supporting a genetic cause of VUR, and to draw together observations and make suggestions regarding differential diagnosis of VUR, which might help in future studies on the genetic aetiology of VUR. RESULTS: A common theme arising was the notion that VUR may be caused by multiple genes in the population. However, any one individual with VUR may carry a single dominant mutant allele. Overall, progress has been made in mapping putative VUR loci in both humans and mice, although the mode(s) of inheritance and the exact nature of the underlying defect are still poorly understood. CONCLUSIONS: It is likely that over the next few years VUR genes will be mapped and, once identified, the challenge will be to understand how changes in the expression of these genes lead to the underlying defect in VUR.

PAX2 suppresses apoptosis in renal collecting duct cells.

PAX2 is a transcription factor belonging to the evolutionarily conserved paired box family and is required during development of the central nervous system and genitourinary axis. Mutations in the PAX2 gene cause a rare autosomal dominant renal-coloboma syndrome, characterized by optic nerve colobomas and renal hypoplasia. Recent analysis of a spontaneous PAX2 mutant mouse model (1Neu) revealed that the major cause of renal hypoplasia is reduced branching of the ureteric bud (UB) and fewer nephrons. We have observed that this abnormality is associated with a striking increase in the number of UB cells undergoing programmed cell death during nephrogenesis. To ascertain whether apoptosis is directly linked to the level of PAX2 expression, we have studied the role of PAX2 in cultured renal cells. We show that mIMCD-3 cells, a murine collecting duct cell line with high endogenous PAX2 expression, undergo apoptosis when transfected with anti-sense PAX2. In contrast, HEK293 cells expressing exogenous PAX2 are protected against apoptotic death induced by caspase-2. PAX2 has no effect on proliferation of embryonic kidney or in cultured kidney cells. Our observations imply a direct role for PAX2 in survival of ureteric bud cells.

Renal-coloboma syndrome: a multi-system developmental disorder caused by PAX2 mutations.

Optic nerve coloboma combined with renal disease, also called renal-coloboma syndrome ( # 120330 in McKusick's Mendelian Inheritance in Man Online, OMIM), a relatively recently characterized syndrome, results from autosomal dominant mutations in the PAX2 gene. Although renal-coloboma syndrome involves both ocular and renal anomalies, some patients are affected with vesico-ureteral reflux (VUR), high frequency hearing loss, central nervous system (CNS) anomalies, and/or genital anomalies, consistent with the expression of PAX2 in these tissues during development. We review here the clinical features of patients with renal-coloboma syndrome and PAX2 mutation. We also review the PAX2 mutations that have been reported to date, and discuss the possible effect of PAX2 mutations on normal development.

The prevalence of PAX2 mutations in patients with isolated colobomas or colobomas associated with urogenital anomalies.

The PAX2 gene is mutated in patients with ocular colobomas, vesicoureteral reflux (VUR), and kidney anomalies (renal-coloboma syndrome, OMIM 120330). The three abnormalities which make up this syndrome also occur in isolation, but the causal genes are not known. PAX2 encodes a transcription factor of the paired box class of DNA binding proteins, important for the development of the urogenital tract, optic nerve and adjacent retina, inner ear, and CNS. In this paper we have investigated the prevalence of PAX2 mutations in patients with ocular colobomas, microphthalmos, or retinal anomalies, either in isolation or with associated urogenital anomalies. Using PCR-SSCP, most or all exons of PAX2 were examined in blood DNA from 99 patients who have either ocular anomalies alone or a combination of ocular and urogenital conditions. PAX2 mutations were not detected in patients with ocular colobomas, either in isolation or with associated abnormalities, except in one patient with typical renal-coloboma syndrome. We conclude that PAX2 mutations are unlikely to be common in patients with ocular colobomas in isolation or in patients with ocular colobomas and associated anomalies, except for patients with typical renal-coloboma syndrome where PAX2 is known to be the aetiological cause.

Cloning and characterization of the human PAX2 promoter.

PAX2, a member of the PAX gene family of developmental transcription factors, is expressed at high levels in the developing eyes, ears, central nervous and urogenital systems, as well as in Wilms' tumor and renal cell carcinoma. Expression of PAX2 in the urogenital system is associated with proliferating cells of the ureteric bud and the differentiating nephrogenic mesenchyme. To date, little is known about the molecular mechanisms controlling the regulation of PAX2 expression. This report describes the cloning and characterization of the human PAX2 gene promoter and localization of the transcription start sites in fetal kidney and Wilms' tumor. We identified two transcription start sites in a Wilms' tumor sample, which were found to be different from that in fetal kidney. The activity of a deletion series of the PAX2 promoter was assessed in NIH-3T3, COS-7, 293, and Madin-Darby canine kidney cells. Although some differences were observed in the activity of each promoter construct, the profile of activity for the promoter fragment series was similar in each experiment, regardless of cell type. The WT1 tumor suppressor protein, which has previously been shown to repress murine Pax2 expression in vitro, was shown to also repress expression from the human PAX2 promoter.

Absence of PAX2 gene mutations in patients with primary familial vesicoureteric reflux.

Vesicoureteric reflux (VUR) is a common childhood condition characterised by regurgitation of urine from the bladder to the kidney. It is the commonest cause of end stage renal failure in children and an important cause in adults. Primary VUR is often familial, suggesting that genetic factors play an important role in its aetiology. Recently, VUR was observed as part of a syndrome, involving optic nerve colobomas and renal anomalies, caused by mutations of the PAX2 gene. PAX2 is a member of the paired box family of genes and is expressed in the ureteric bud and differentiating nephrogenic mesenchyme of the developing kidney. PAX2 has been shown to play a critical role in the development of both the kidney and the ureter. The occurrence of VUR in one family with the PAX2 mutation, and the expression pattern of PAX2 in developing ureteric bud, strongly suggested that PAX2 could be the cause of primary familial VUR. Single strand conformational polymorphism (SSCP) analysis of 23 affected subjects in eight families with primary familial VUR showed no alterations in exons 2-5 of the PAX2 gene. In addition, a polymorphic dinucleotide repeat marker located within the PAX2 gene segregated independently of the disease trait in one large family who primarily had VUR or reflux nephropathy. These results suggest that PAX2 is not a major cause of primary familial reflux.

The role of PAX2 in normal and abnormal development of the urinary tract.

The molecular etiology of many urinary tract abnormalities in children remains unknown, but a number of genes with a key role in urogenital development have now been identified. PAX2, one such gene, encodes a transcription factor which is critically required for epithelial differentiation within the urogenital tract. Recent studies suggest that PAX2 mutations lead to urological abnormalities and renal failure, while overexpression of PAX2 in the kidneys of mice causes multifocal microcystic tubular dilatation. In humans persistent PAX2 expression has been identified in multicystic dysplastic kidneys. In this review, recent research on the developmental gene, PAX2, and its involvement in normal and abnormal kidney development is summarized. In addition, an overview of the phenotypes associated with either loss-of-function PAX2 mutations or PAX2 overexpression is presented. A brief summary of factors that are known to regulate PAX2 and genes that may be regulated by PAX2 protein is also included.

Differential regulation of the human Wilms tumour suppressor gene (WT1) promoter by two isoforms of PAX2.

PAX2 is a member of the paired box family of genes with an important role in kidney, genital tract and eye development. Another gene essential for kidney and genital tract development is the Wilms tumour gene, WT1. PAX2 and WT1 encode transcription factors expressed during fetal kidney development in patterns that overlap both spatially and temporally. The overlap of PAX2 and WT1 expression in fetal kidney prompted us to determine whether PAX2 regulates the WT1 gene. To investigate this possibility, the WT1 promoter and a series of WT1 promoter deletion fragments were cloned into a luciferase reporter vector, and used in co-transfection experiments with PAX2 expression constructs. PAX2 transactivated the WT1 promoter up to 35-fold in CHO-K1 cells, and from four- to sevenfold in 293 cells. Two regions of the WT1 promoter were required in the same promoter construct for efficient transactivation by PAX2 in CHO-K1 cells, and purified recombinant PAX2 protein was found to bind to two sites in the WT1 promoter, at -205/-230 and +377/+402. Removal of WT1 promoter sequences containing the -205/-230, or +377/+402 binding sites abolished transactivation of the WT1 promoter by PAX2 in CHO-K1 cells, and had a differential effect on transactivation of the WT1 promoter in 293 cells, depending on the PAX2 isoform used. A fragment containing the -205/-230 site alone could be transactivated by PAX2. These findings suggest that PAX2 is a tissue-specific modulator of WT1 expression, and is involved in cell growth control via WT1.

Molecular and clinical studies of three cases of female pseudohermaphroditism with caudal dysplasia suggest multiple etiologies.

Female pseudohermaphroditism with caudal dysplasia is a clinical entity in which normal-appearing male genitalia may occur in the apparent absence of testosterone or the sex-determining gene (SR Y). We have extended observations of two previously reported cases, and report a third case, which strongly suggests multiple etiologies. The first case was one of identical twins. The other identical twin did not show female pseudohermaphroditism with caudal dysplasia, but both patients had the rare birth defect of neonatal cataracts. We have explored skewed X-inactivation as a possible difference between the two twins, with a negative result. The second case had a deletion at 10q25.3-->ter. This is near the location of PAX2, and we searched for mutations in PAX2 in both this and the first case, with negative results. Neither patient had a scrotal raphe, suggesting that a failure of division of the cloacal membrane was an important step in their development of female pseudohermaphroditism. The final case is newly described and differed from the above two in the presence of a scrotal raphe and an elevated testosterone level. Although no source for the testosterone was found, this case suggests that the etiology in this patient was different and that the presence of a scrotal raphe can be used to distinguish between at least two etiologies.

Further delineation of renal-coloboma syndrome in patients with extreme variability of phenotype and identical PAX2 mutations.

Renal-coloboma syndrome is a recently described autosomal dominant syndrome of abnormal optic nerve and renal development. Two families have been reported with renal-coloboma syndrome and mutations of the PAX2 gene. The PAX2 gene, which encodes a DNA-binding protein, is expressed in the developing ear, CNS, eye, and urogenital tract. Ocular and/or renal abnormalities have been consistently noted in the five reports of patients with renal-coloboma syndrome, to date, but PAX2 expression patterns suggest that auditory and CNS abnormalities may be additional features of renal-coloboma syndrome. To determine whether additional clinical features are associated with PAX2 mutations, we have used PCR-SSCP to identify PAX2 gene mutations in patients. We report here four patients with mutations in exon 2, one of whom has severe ocular and renal disease, microcephaly, and retardation, and another who has ocular and renal disease with high-frequency hearing loss. Unexpectedly, extreme variability in clinical presentation was observed between a mother, her son, and an unrelated patient, all of whom had the same PAX2 mutation as previously described in two siblings with renal-coloboma syndrome. These results suggest that a sequence of seven Gs in PAX2 exon 2 may be particularly prone to mutation.

Localisation of a 10q breakpoint within the PAX2 gene in a patient with a de novo t(10;13) translocation and optic nerve coloboma-renal disease.

We describe a 5 year old boy with a de novo t(10;13) translocation and optic nerve coloboma-renal disease (ONCR). On the basis of GTG banding analysis of prometaphase chromosomes, the patient's karyotype was interpreted as either 46,XY,t(10;13)(q24.3;q12.3) or t(10;13) (q25.2;q14.1). Fluorescence in situ hybridisation (FISH) studies using a YAC clone containing the PAX2 gene and YAC clones adjoining FRA10B at 10q25.2 showed that the 10q breakpoint had occurred just within the PAX2 gene and was proximal to FRA10B. These FISH results suggest that the translocation causes a disruption of the PAX2 gene and leads to ONCR, in agreement with the recent reports of PAX2 mutations in two unrelated families with ONCR. Furthermore, we refined the regional mapping of the human PAX2 gene to the junction of bands 10q24.3 and 10q25.1.

Genomic structure of the human PAX2 gene.

PAX2 is one of nine PAX genes that have been described in vertebrates. Each PAX gene contains a conserved paired box domain that was first identified in Drosophila. PAX2 encodes a transcription factor that has a critical role in the development of the urogenital tract, the eyes, and the CNS. Recently, we reported a mutation of PAX2 in patients with optic nerve coloboma, vesicoureteric reflux, and renal anomalies. To facilitate further analysis of PAX2 mutations in human disease, we have now determined the complete structure of the human PAX2 gene. Five genomic lambda clones containing human PAX2 gene sequences were isolated. Sequencing and restriction mapping of these clones showed that human PAX2 was composed of 12 exons spanning approximately 70 kb. Two alternatively spliced exons and a dinuclotide repeat polymorphism were also determined in PAX2. These data will be useful in characterizing the role of PAX2 in human disease.