Deregulation of Pax-2 expression in transgenic mice generates severe kidney abnormalities

Mice with a Pax2 missense variant display impaired glomerular repair

PAX2 regulates kidney development, and its expression persists in parietal epithelial cells (PECs), potentially serving as a podocyte reserve. We hypothesized that mice with a Pax2 pathogenic missense variant (Pax2A220G/+) have impaired PEC-mediated podocyte regeneration. Embryonic wild-type mouse kidneys showed overlapping expression of PAX2/Wilms' tumor-1 (WT-1) until PEC and podocyte differentiation, reflecting a close lineage relationship. Embryonic and adult Pax2A220G/+ mice have reduced nephron number but demonstrated no glomerular disease under baseline conditions. Pax2A220G/+ mice compared with wild-type mice were more susceptible to glomerular disease after adriamycin (ADR)-induced podocyte injury, as demonstrated by worsened glomerular scarring, increased podocyte foot process effacement, and podocyte loss. There was a decrease in PAX2-expressing PECs in wild-type mice after adriamycin injury accompanied by the occurrence of PAX2/WT-1-coexpressing glomerular tuft cells. In contrast, Pax2A220G/+ mice showed no changes in the numbers of PAX2-expressing PECs after adriamycin injury, associated with fewer PAX2/WT-1-coexpressing glomerular tuft cells compared with injured wild-type mice. A subset of PAX2-expressing glomerular tuft cells after adriamycin injury was increased in Pax2A220G/+ mice, suggesting a pathological process given the worse outcomes observed in this group. Finally, Pax2A220G/+ mice have increased numbers of glomerular tuft cells expressing Ki-67 and cleaved caspase-3 compared with wild-type mice after adriamycin injury, consistent with maladaptive responses to podocyte loss. Collectively, our results suggest that decreased glomerular numbers in Pax2A220G/+ mice are likely compounded with the inability of their mutated PECs to regenerate podocyte loss, and together these two mechanisms drive the worsened focal segmental glomerular sclerosis phenotype in these mice.NEW & NOTEWORTHY Congenital anomalies of the kidney and urinary tract comprise some of the leading causes of kidney failure in children, but our previous study showed that one of its genetic causes, PAX2, is also associated with adult-onset focal segmental glomerular sclerosis. Using a clinically relevant model, our present study demonstrated that after podocyte injury, parietal epithelial cells expressing PAX2 are deployed into the glomerular tuft to assist in repair in wild-type mice, but this mechanism is impaired in Pax2A220G/+ mice.

Shared features in ear and kidney development - implications for oto-renal syndromes

The association between ear and kidney anomalies has long been recognized. However, little is known about the underlying mechanisms. In the last two decades, embryonic development of the inner ear and kidney has been studied extensively. Here, we describe the developmental pathways shared between both organs with particular emphasis on the genes that regulate signalling cross talk and the specification of progenitor cells and specialised cell types. We relate this to the clinical features of oto-renal syndromes and explore links to developmental mechanisms.

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3′,5′-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

PAX8 in the Junction between Development and Tumorigenesis

Normal processes of embryonic development and abnormal transformation to cancer have many parallels, and in fact many aberrant cancer cell capabilities are embryonic traits restored in a distorted, unorganized way. Some of these capabilities are cell autonomous, such as proliferation and resisting apoptosis, while others involve a complex interplay with other cells that drives significant changes in neighboring cells. The correlation between embryonic development and cancer is driven by shared proteins. Some embryonic proteins disappear after embryogenesis in adult differentiated cells and are restored in cancer, while others are retained in adult cells, acquiring new functions upon transformation to cancer. Many embryonic factors embraced by cancer cells are transcription factors; some are master regulators that play a major role in determining cell fate. The paired box (PAX) domain family of developmental transcription factors includes nine members involved in differentiation of various organs. All paired box domain proteins are involved in different cancer types carrying pro-tumorigenic or anti-tumorigenic roles. This review focuses on PAX8, a master regulator of transcription in embryonic development of the thyroid, kidney, and male and female genital tracts. We detail the role of PAX8 in each of these organ systems, describe its role during development and in the adult if known, and highlight its pro-tumorigenic role in cancers that emerge from PAX8 expressing organs.

Factors influencing the development of Multicystic Dysplastic Kidney (MCDK) following urinary tract obstruction in the fetal lamb

BACKGROUND

Creating obstructive uropathy (OU) during glomerulogenesis in the fetal lamb results in multicystic dysplastic kidney (MCDK) at term. We explored this using immunohistochemical techniques.

METHOD

OU was created in fetal lambs at 60-day gestation, ligating the urethra and urachus. The kidneys of MCDK lambs, 60-day gestation fetal lambs, full-term lamb (145 days), term sham-operated lambs, and adult ewes were evaluated by HE staining, and immunohistochemistry with paired box genes 2 (PAX2) and CD10.

RESULTS

Multiple cysts were found in the MCDK model. CD10 was expressed in proximal tubular epithelial cells, glomerular epithelial cells, and medullary stromal cells in the kidneys of 60-day gestation fetal lambs and full-term lambs and adult ewes. PAX2 expression was found in ureteric buds, C- and S-shaped bodies, epithelial cells of collecting ducts, and Bowman's capsule of fetal kidneys at 60-day gestation, but only in the collecting ducts of full-term fetal lambs and adult ewes. Both CD10 and PAX2 were expressed in the cystic epithelial cells of the MCDK model.

DISCUSSION

PAX2 expression in cystic epithelial cells suggests that cyst formation is associated with disturbed down-regulation of PAX2 in the nephrogenic zone epithelial cells during the renal development in the OU model.

Identification of Pax protein inhibitors that suppress target gene expression and cancer cell proliferation

The Pax family of developmental control genes are frequently deregulated in human disease. In the kidney, Pax2 is expressed in developing nephrons but not in adult proximal and distal tubules, whereas polycystic kidney epithelia or renal cell carcinoma continues to express high levels. Pax2 reduction in mice or cell culture can slow proliferation of cystic epithelial cells or renal cancer cells. Thus, inhibition of Pax activity may be a viable, cell-type-specific therapy. We designed an unbiased, cell-based, high-throughput screen that identified triazolo pyrimidine derivatives that attenuate Pax transactivation ability. We show that BG-1 inhibits Pax2-positive cancer cell growth and target gene expression but has little effect on Pax2-negative cells. Chromatin immunoprecipitation suggests that these inhibitors prevent Pax protein interactions with the histone H3K4 methylation complex at Pax target genes in renal cells. Thus, these compounds may provide structural scaffolds for kidney-specific inhibitors with therapeutic potential.

Kidney developmental effects of metal-herbicide mixtures: Implications for chronic kidney disease of unknown etiology

Chronic kidney disease of unknown etiology (CKDu) is an emerging global concern affecting several agricultural communities in the Americas and South Asia. Environmental contaminants such as heavy metals (e.g., Cd, As, Pb, and V) and organic pesticides (e.g., glyphosate) in the drinking water have been hypothesized to play a role in childhood onset and progression of this disease. However, a comprehensive analysis of chemical contaminants in the drinking water and effects of these compounds and their mixtures on kidney development and function remains unknown. Here, we conducted targeted and non-targeted chemical analyses of sediment and drinking water in CKDu affected regions in Sri Lanka, one of the most affected countries. Using zebrafish Danio rerio, a toxicology and kidney disease model, we then examined kidney developmental effects of exposure to (i) environmentally derived samples from CKDu endemic and non-endemic regions and (ii) Cd, As, V, Pb, and glyphosate as individual compounds and in mixtures. We found that drinking water is contaminated with various organic chemicals including nephrotoxic compounds as well as heavy metals, but at levels considered safe for drinking. Histological studies and gene expression analyses examining markers of kidney development (pax2a) and kidney injury (kim1) showed novel metal and glyphosate-metal mixture specific effects on kidney development. Mitochondrial dysfunction is directly linked to kidney failure, and examination of mixture specific mitochondrial toxicity showed altered mitochondrial function following treatment with environmental samples from endemic regions. Collectively, we show that metals in drinking water, even at safe levels, can impede kidney development at an early age, potentiating increased susceptibility to other agrochemicals such as glyphosate. Drinking water contaminant effects on mitochondria can further contribute to progression of kidney dysfunction and our mitochondrial assay may help identify regions at risk of CKDu.

Dominant PAX2 mutations may cause steroid-resistant nephrotic syndrome and FSGS in children

BACKGROUND

Heterozygous PAX2 mutations cause renal coloboma syndrome (RCS) [OMIM no. 120330]. RCS is a renal syndromic disease encompassing retinal coloboma and sensorineural hearing loss. Recently, a causative role for PAX2 was reported in adult-onset nephrotic syndrome secondary to focal segmental glomerulosclerosis (FSGS). However, the prevalence of PAX2 mutations among large cohort of children with steroid-resistant nephrotic syndrome (SRNS) and FSGS has not been systematically studied.

METHODS

We employed whole-exome sequencing (WES) to identify the percentage of SRNS cases explained by monogenic mutations in known genes of SRNS/FSGS. As PAX2 mutations are not an established cause of childhood FSGS, we evaluated a cohort of 215 unrelated families with SRNS, in whom no underlying genetic etiology had been previously established.

RESULTS

Using WES, we identified 3 novel causative heterozygous PAX2 mutations in 3 out of the 215 unrelated index cases studied (1.3%). All three cases were detected in individuals from families with more than one affected and compatible with an autosomal dominant mode of inheritance (3/57 familial cases studied (5.2%)). The clinical diagnosis in three out of four pediatric index patients was done during routine medical evaluation.

CONCLUSIONS

Our findings demonstrate high frequency of PAX2 mutations in familial form of SRNS (5.2%) and further expand the phenotypic spectrum of PAX2 heterozygous mutations to include autosomal dominant childhood-onset FSGS. These results highlight the importance of including PAX2 in the list of genes known to cause FSGS in children.

We, the developing rete testis, efferent ducts, and Wolffian duct, all hereby agree that we need to connect

BACKGROUND

The mechanisms by which the rete testis joins the efferent ducts, which joins the Wolffian duct during development, are not known. Mouse and chick models have been helpful in identifying genes that are important for the development of each part, but genes have not been identified as to those that play a role in the joining of each part. Clinical implications of the failure of the male reproductive tract to form a fully functional conduit for spermatozoa are not trivial. Epididymal disjunction, the failure of the efferent ducts to join the testis, is one of several epididymal anomalies that have been observed in some boys who were cryptorchid at birth.

OBJECTIVE

A systematic review of studies focusing on the morphogenesis of the mesonephric duct and mesonephric tubules in different species, and identification of clinical issues should there be failure of these tissues to develop.

DESIGN

PubMed and GUDMAP databases, and review of books on kidney development were searched for studies reporting on the mechanisms of morphogenesis of the kidney and epididymis.

MAIN OUTCOMES MEASURE(S)

Gaps in our knowledge were identified, and hypotheses coupled with suggestions for future experiments were presented.

RESULTS

A total of 64 papers were identified as relevant, of which 53 were original research articles and 11 were book chapters and reviews covering morphogenesis and clinical issues. Investigators utilized multiple species including, human, mouse, chick, Xenopus, bovine, and sheep.

CONCLUSION

Fundamental understanding of the morphogenesis of the male reproductive tract is limited, especially the morphogenesis of the rete testis and efferent ducts. Therefore, it is not surprising that we do not understand how each part unites to form a whole. Only one mechanism of joining of one part of the tract to another was identified: the joining of the Wolffian duct to the cloaca via controlled apoptosis.

TranscriptAchilles: a genome-wide platform to predict isoform biomarkers of gene essentiality in cancer

BACKGROUND

Aberrant alternative splicing plays a key role in cancer development. In recent years, alternative splicing has been used as a prognosis biomarker, a therapy response biomarker, and even as a therapeutic target. Next-generation RNA sequencing has an unprecedented potential to measure the transcriptome. However, due to the complexity of dealing with isoforms, the scientific community has not sufficiently exploited this valuable resource in precision medicine.

FINDINGS

We present TranscriptAchilles, the first large-scale tool to predict transcript biomarkers associated with gene essentiality in cancer. This application integrates 412 loss-of-function RNA interference screens of >17,000 genes, together with their corresponding whole-transcriptome expression profiling. Using this tool, we have studied which are the cancer subtypes for which alternative splicing plays a significant role to state gene essentiality. In addition, we include a case study of renal cell carcinoma that shows the biological soundness of the results. The databases, the source code, and a guide to build the platform within a Docker container are available at GitLab. The application is also available online.

CONCLUSIONS

TranscriptAchilles provides a user-friendly web interface to identify transcript or gene biomarkers of gene essentiality, which could be used as a starting point for a drug development project. This approach opens a wide range of translational applications in cancer.

NeuroD2 controls inhibitory circuit formation in the molecular layer of the cerebellum

The cerebellar cortex is involved in the control of diverse motor and non-motor functions. Its principal circuit elements are the Purkinje cells that integrate incoming excitatory and local inhibitory inputs and provide the sole output of the cerebellar cortex. However, the transcriptional control of circuit assembly in the cerebellar cortex is not well understood. Here, we show that NeuroD2, a neuronal basic helix-loop-helix (bHLH) transcription factor, promotes the postnatal survival of both granule cells and molecular layer interneurons (basket and stellate cells). However, while NeuroD2 is not essential for the integration of surviving granule cells into the excitatory circuit, it is required for the terminal differentiation of basket cells. Axons of surviving NeuroD2-deficient basket cells follow irregular trajectories and their inhibitory terminals are virtually absent from Purkinje cells in Neurod2 mutants. As a result inhibitory, but not excitatory, input to Purkinje cells is strongly reduced in the absence of NeuroD2. Together, we conclude that NeuroD2 is necessary to instruct a terminal differentiation program in basket cells that regulates targeted axon growth and inhibitory synapse formation. An imbalance of excitation and inhibition in the cerebellar cortex affecting Purkinje cell output may underlay impaired adaptive motor learning observed in Neurod2 mutants.

Developmental pathology of congenital kidney and urinary tract anomalies

Congenital anomalies of the kidneys or lower urinary tract (CAKUT) are the most common causes of renal failure in children and account for 25% of end-stage renal disease in adults. The spectrum of anomalies includes renal agenesis; hypoplasia; dysplasia; supernumerary, ectopic or fused kidneys; duplication; ureteropelvic junction obstruction; primary megaureter or ureterovesical junction obstruction; vesicoureteral reflux; ureterocele; and posterior urethral valves. CAKUT originates from developmental defects and can occur in isolation or as part of other syndromes. In recent decades, along with better understanding of the pathological features of the human congenital urinary tract defects, researchers using animal models have provided valuable insights into the pathogenesis of these diseases. However, the genetic causes and etiology of many CAKUT cases remain unknown, presenting challenges in finding effective treatment. Here we provide an overview of the critical steps of normal development of the urinary system, followed by a description of the pathological features of major types of CAKUT with respect to developmental mechanisms of their etiology.

New PAX2 heterozygous mutation in a child with chronic kidney disease: a case report and review of the literature

BACKGROUND

We herein report a 3-year-old boy presented with chronic kidney disease (CKD) due to PAX2 missense mutation (C to G transversion at position 418 in exon 4).

CASE PRESENTATION

He attended our clinic with a 3-month history of foamy urine. Upon examination, he had reduced estimated glomerular filtration rate (GFR) and renal atrophy. Genetic investigations revealed that he has inherited a mutated PAX2 gene from his father, who had renal failure at the age of 20. We searched the literature and confirmed that this mutation site has not been reported by any other group before.

CONCLUSIONS

Although renal coloboma syndrome (RCS) with simultaneous kidney and eye involvement is the most common phenotype of PAX2 mutations, current literature supports that such mutations may have profuse clinical manifestations and renal hypoplasia is one distinct entity in the spectrum.

SMAD proteins directly suppress PAX2 transcription downstream of transforming growth factor-beta 1 (TGF-β1) signalling in renal cell carcinoma

Canonical TGF-β1 signalling promotes tumor progression by facilitating invasion and metastasis, whereby release of TGF-β1, by (for example) infiltrating immune cells, induces epithelial to mesenchymal transition (EMT). PAX2, a member of the Paired box family of transcriptional regulators, is normally expressed during embryonic development, including in the kidney, where it promotes mesenchymal to epithelial transition (MET). PAX2 expression is silenced in many normal adult tissues. However, in contrast, PAX2 is expressed in several cancer types, including kidney, prostate, breast, and ovarian cancer. While multiple studies have implicated TGF-β superfamily members in modulating expression of Pax genes during embryonic development, few have investigated direct regulation of Pax gene expression by TGF-β1. Here we have investigated direct regulation of PAX2 expression by TGF-β1 in clear cell renal cell carcinoma (CC-RCC) cell lines. Treatment of PAX2-expressing 786-O and A498 CC-RCC cell lines with TGF-β1 resulted in inhibition of endogenous PAX2 mRNA and protein expression, as well as expression from transiently transfected PAX2 promoter constructs; this inhibition was abolished in the presence of expression of the inhibitory SMAD, SMAD7. Using ChIP-PCR we showed TGF-β1 treatment induced SMAD3 protein phosphorylation in 786-O cells, and direct SMAD3 binding to the human PAX2 promoter, which was inhibited by SMAD7 over-expression. Overall, these data suggest that canonical TGF-β signalling suppresses PAX2 transcription in CC-RCC cells due to the direct binding of SMAD proteins to the PAX2 promoter. These studies improve our understanding of tumor progression and epithelial to mesenchyme transition (EMT) in CC-RCC and in other PAX2-expressing cancer types.

Establishment of a large panel of patient-derived preclinical models of human renal cell carcinoma

The objective of the present work was to establish a large panel of preclinical models of human renal cell carcinoma (RCC) directly from patients, faithfully reproducing the biological features of the original tumor. RCC tissues (all stages/subtypes) were collected for 8 years from 336 patients undergoing surgery, xenografted subcutaneously in nude mice, and serially passaged into new mice up to 13 passages. Tissue samples from the primary tumor and tumors grown in mice through passages were analyzed for biological tissue stability by histopathology, mRNA profiling, von Hippel-Lindau gene sequencing, STR fingerprinting, growth characteristics and response to current therapies. Metastatic models were also established by orthotopic implantation and analyzed by imagery. We established a large panel of 30 RCC models (passage > 3, 8.9% success rate). High tumor take rate was associated with high stage and grade. Histopathologic, molecular and genetic characteristics were preserved between original tumors and case-matched xenografts. The models reproduced the sensitivity to targeted therapies observed in the clinic. Overall, these models constitute an invaluable tool for the clinical design of efficient therapies, the identification of predictive biomarkers and translational research.

Nephron number, hypertension, and CKD: physiological and genetic insight from humans and animal models

The kidneys play a vital role in the excretion of waste products and the regulation of electrolytes, maintenance of acid-base balance, regulation of blood pressure, and production of several hormones. Any alteration in the structure of the nephron (basic functional unit of the kidney) can have a major impact on the kidney's ability to work efficiently. Progressive decline in kidney function can lead to serious illness and ultimately death if not treated by dialysis or transplantation. While there have been numerous studies that implicate lower nephron numbers as being an important factor in influencing susceptibility to developing hypertension and chronic kidney disease, a direct association has been difficult to establish because of three main limitations: 1) the large variation in nephron number observed in the human population; 2) no established reliable noninvasive methods to determine nephron complement; and 3) to date, nephron measurements have been done after death, which doesn't adequately account for potential loss of nephrons with age or disease. In this review, we will provide an overview of kidney structure/function, discuss the current literature for both humans and other species linking nephron deficiency and cardio-renal complications, as well as describe the major molecular signaling factors involved in nephrogenesis that modulate variation in nephron number. As more detailed knowledge about the molecular determinants of nephron development and the role of nephron endowment in the cardio-renal system is obtained, it will hopefully provide clinicians the ability to accurately identify people at risk to develop CKD/hypertension and lead to a shift in patient care from disease treatment to prevention.

Transgenic Strategies to Study Podocyte Loss and Regeneration

Podocyte death and regeneration are major topics in kidney research but remain controversial. Data obtained in humans demonstrate the existence of cells sited along Bowman's capsule that behave as podocyte progenitors in vitro and in in vivo mouse models of podocyte injury xenotrasplanted with this human-derived population. However, this podocyte reservoir still remains elusive in murine models, where it could be more easily studied. Transgenic models can be a powerful tool to identify this population and to better understand its dynamics and hierarchies in both physiological and pathological conditions. Indeed, exploiting transgenic approaches allows detecting, at the single cell level, movements, cell death, and replacement. Moreover, through lineage tracing it is now possible to identify specific population increase and to point out clonal expansions during or after the regenerative processes. However, applying transgenic strategies to study glomerular regeneration requires the search of markers to unequivocally identify this progenitor population. Achieving this aim would lead to a deep comprehension of the biological processes that underlie glomerular regeneration and clarify how different cell pools interface during this phase. Here we discuss strategies that have been used and new approaches in transgenic models finalized to study podocyte loss and subsequent replacement.

Pax8 and Pax2 are specifically required at different steps of Xenopus pronephros development

The respective role of Pax2 and Pax8 in early kidney development in vertebrates is poorly understood. In this report, we have studied the roles of Pax8 and Pax2 in Xenopus pronephros development using a loss-of-function approach. Our results highlight a differential requirement of these two transcription factors for proper pronephros formation. Pax8 is necessary for the earliest steps of pronephric development and its depletion leads to a complete absence of pronephric tubule. Pax2 is required after the establishment of the tubule pronephric anlage, for the expression of several terminal differentiation markers of the pronephric tubule. Neither Pax2 nor Pax8 is essential to glomus development. We further show that Pax8 controls hnf1b, but not lhx1 and Osr2, expression in the kidney field as soon as the mid-neurula stage. Pax8 is also required for cell proliferation of pronephric precursors in the kidney field. It may exert its action through the wnt/beta-catenin pathway since activation of this pathway can rescue MoPax8 induced proliferation defect and Pax8 regulates expression of the wnt pathway components, dvl1 and sfrp3. Finally, we observed that loss of pronephros in Pax8 morphants correlates with an expanded vascular/blood gene expression domain indicating that Pax8 function is important to delimit the blood/endothelial genes expression domain in the anterior part of the dorso-lateral plate.

Pax2 may play a role in kidney development by regulating the expression of TBX1

Renal anomaly is commonly found among patients with loss of TBX1 gene, encoding an important transcriptional factor implicated in numerous developmental processes. Pax2 is a member of the "paired-box" (PAX) family of homeotic genes that orchestrates the patterns of gene expression in specific cells during nephrogenesis. In this study, we hypothesized that Pax2 might activate expression of TBX1, a member of T-box family that closely involving in kidney development. Immunohistochemical and immunofluorescence staining was performed to detect TBX1 expression in E16.5 embryonic rat kidney, while luciferase assay, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) assay were used to confirm the interaction between the Pax2 protein and TBX1 genes. TBX1 was expressed in the cytoplasm of renal tubular epithelial cells in the cortex of E16.5 fetal rat kidney. Inspection of the 5'-flanking sequence of the TBX1 gene identified a putative Pax2 recognition motif (TBX1-577). Luciferase assay and EMSA confirmed this novel promoter region of TBX1 that directly interacted with Pax2, and a site mutation could abolish the transcriptional activation of the TBX1 promoter by Pax2. ChIP assay of the Pax2-TBX1 promoter complex from human kidney epithelial cells further confirmed that endogenous Pax2 interacted with TBX1 promoter region. Thus, Pax2 directly regulates TBX1 expression in vivo. These findings suggest that Pax2 may regulate the TBX1 expression through specific binding to the TBX1 promoter, which may shed light on the potential mechanism of Pax2 and TBX1 in nephrogenesis and renal malformations.

PAX genes in childhood oncogenesis: developmental biology gone awry?

Childhood solid tumors often arise from embryonal-like cells, which are distinct from the epithelial cancers observed in adults, and etiologically can be considered as 'developmental patterning gone awry'. Paired-box (PAX) genes encode a family of evolutionarily conserved transcription factors that are important regulators of cell lineage specification, migration and tissue patterning. PAX loss-of-function mutations are well known to cause potent developmental phenotypes in animal models and underlie genetic disease in humans, whereas dysregulation and/or genetic modification of PAX genes have been shown to function as critical triggers for human tumorigenesis. Consequently, exploring PAX-related pathobiology generates insights into both normal developmental biology and key molecular mechanisms that underlie pediatric cancer, which are the topics of this review.

Genome-wide analysis of gestational gene-environment interactions in the developing kidney

The G protein-coupled bradykinin B2 receptor (Bdkrb2) plays an important role in regulation of blood pressure under conditions of excess salt intake. Our previous work has shown that Bdkrb2 also plays a developmental role since Bdkrb2(-/-) embryos, but not their wild-type or heterozygous littermates, are prone to renal dysgenesis in response to gestational high salt intake. Although impaired terminal differentiation and apoptosis are consistent findings in the Bdkrb2(-/-) mutant kidneys, the developmental pathways downstream of gene-environment interactions leading to the renal phenotype remain unknown. Here, we performed genome-wide transcriptional profiling on embryonic kidneys from salt-stressed Bdkrb2(+/+) and Bdkrb2(-/-) embryos. The results reveal significant alterations in key pathways regulating Wnt signaling, apoptosis, embryonic development, and cell-matrix interactions. In silico analysis reveal that nearly 12% of differentially regulated genes harbor one or more Pax2 DNA-binding sites in their promoter region. Further analysis shows that metanephric kidneys of salt-stressed Bdkrb2(-/-) have a significant downregulation of Pax2 gene expression. This was corroborated in Bdkrb2(-/-);Pax2(GFP+/tg) mice, demonstrating that Pax2 transcriptional activity is significantly repressed by gestational salt-Bdkrb2 interactions. We conclude that gestational gene (Bdkrb2) and environment (salt) interactions cooperate to impact gene expression programs in the developing kidney. Suppression of Pax2 likely contributes to the defects in epithelial survival, growth, and differentiation in salt-stressed BdkrB2(-/-) mice.

Chromatin dynamics in kidney development and function

Epigenetic mechanisms are fundamental key features of developing cells connecting developmental regulatory factors to chromatin modification. Changes in the environment during renal development can have long-lasting effects on the permanent tissue structure and the level of expression of important functional genes. These changes are believed to contribute to kidney disease occurrence and progression. Although the mechanisms of early patterning and cell fate have been well described for renal development, little is known about associated epigenetic modifications and their impact on how genes interact to specify the renal epithelial cells of nephrons and how this specification is relevant to maintaining normal renal function. A better understanding of the renal cell-specific epigenetic modifications and the interaction of different cell types to form this highly complex organ will not only help to better understand developmental defects and early loss of kidney function in children, but also help to understand and improve chronic disease progression, cell regeneration and renal aging.

MicroRNAs: potential regulators of renal development genes that contribute to CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) are the leading cause of childhood chronic kidney disease (CKD). While mutations in several renal development genes have been identified as causes for CAKUT, most cases have not yet been linked to known mutations. Furthermore, the genotype-phenotype correlation is variable, suggesting that there might be additional factors that have an impact on the severity of CAKUT. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level, and are involved in many developmental processes. Although little is known about the function of specific miRNAs in kidney development, several have recently been shown to regulate the expression of, and/or are regulated by, crucial renal development genes present in other organ systems. In this review, we discuss how miRNA regulation of common developmental signaling pathways may be applicable to renal development. We focus on genes that are known to contribute to CAKUT in humans, for which miRNA interactions in other contexts have been identified, with miRNAs that are present in the kidney. We hypothesize that miRNA-mediated processes might play a role in kidney development through similar mechanisms, and speculate that genotypic variations in these small RNAs or their targets could be associated with CAKUT.

Mutations in PAX2 associate with adult-onset FSGS

FSGS is characterized by the presence of partial sclerosis of some but not all glomeruli. Studies of familial FSGS have been instrumental in identifying podocytes as critical elements in maintaining glomerular function, but underlying mutations have not been identified for all forms of this genetically heterogeneous condition. Here, exome sequencing in members of an index family with dominant FSGS revealed a nonconservative, disease-segregating variant in the PAX2 transcription factor gene. Sequencing in probands of a familial FSGS cohort revealed seven rare and private heterozygous single nucleotide substitutions (4% of individuals). Further sequencing revealed seven private missense variants (8%) in a cohort of individuals with congenital abnormalities of the kidney and urinary tract. As predicted by in silico structural modeling analyses, in vitro functional studies documented that several of the FSGS-associated PAX2 mutations perturb protein function by affecting proper binding to DNA and transactivation activity or by altering the interaction of PAX2 with repressor proteins, resulting in enhanced repressor activity. Thus, mutations in PAX2 may contribute to adult-onset FSGS in the absence of overt extrarenal manifestations. These results expand the phenotypic spectrum associated with PAX2 mutations, which have been shown to lead to congenital abnormalities of the kidney and urinary tract as part of papillorenal syndrome. Moreover, these results indicate PAX2 mutations can cause disease through haploinsufficiency and dominant negative effects, which could have implications for tailoring individualized drug therapy in the future.

Hepatocyte nuclear factor 1β controls nephron tubular development

Nephron morphogenesis is a complex process that generates blood-filtration units (glomeruli) connected to extremely long and patterned tubular structures. Hepatocyte nuclear factor 1β (HNF1β) is a divergent homeobox transcription factor that is expressed in kidney from the first steps of nephrogenesis. Mutations in HNF1B (OMIM #137920) are frequently found in patients with developmental renal pathologies, the mechanisms of which have not been completely elucidated. Here we show that inactivation of Hnf1b in the murine metanephric mesenchyme leads to a drastic tubular defect characterized by the absence of proximal, distal and Henle's loop segments. Nephrons were eventually characterized by glomeruli, with a dilated urinary space, directly connected to collecting ducts via a primitive and short tubule. In the absence of HNF1β early nephron precursors gave rise to deformed S-shaped bodies characterized by the absence of the typical bulge of epithelial cells at the bend between the mid and lower segments. The lack of this bulge eventually led to the absence of proximal tubules and Henle's loops. The expression of several genes, including Irx1, Osr2 and Pou3f3, was downregulated in the S-shaped bodies. We also observed decreased expression of Dll1 and the consequent defective activation of Notch in the prospective tubular compartment of comma- and S-shaped bodies. Our results reveal a novel hierarchical relationship between HNF1β and key genes involved in renal development. In addition, these studies define a novel structural and functional component of S-shaped bodies at the origin of tubule formation.

PAX2 and PAX8 Expression in Primary and Metastatic Renal Tumors: A Comprehensive Comparison

Context.—The diagnosis of renal cell carcinoma (RCC) remains problematic, especially in the context of metastasis or small-needle biopsies. PAX2 and PAX8 transcription factors are known to be expressed by several histologic types of renal neoplasms.

Objective.—To evaluate the diagnostic utility of PAX2 and PAX8 relative to one another, which has not been studied.

Design.—Consecutive tissue sections from the archival samples of 243 primary and 99 metastatic renal neoplasms were submitted to PAX2 and PAX8 immunostain.

Results.—Within the primary neoplasms, PAX2 versus PAX8 expression was noted in 90 of 95 (95%) versus 92 of 95 (97%) for clear cell RCC, 29 of 38 (76%) versus 38 of 38 (100%) for papillary RCC, 14 of 25 (56%) versus 22 of 25 (88%) for chromophobe RCC, 3 of 7 (43%) versus 5 of 7 (71%) for collecting duct RCC, 6 of 8 (75%) versus 8 of 8 (100%) for acquired cystic kidney disease–related RCC, and 7 of 13 (54%) versus 11 of 13 (85%) for oncocytoma. Regardless of histologic subtype, PAX8 staining was noted in more cells and with more intense staining than PAX2. Within the metastatic RCCs, PAX8 expression was more frequently positive than PAX2 expression (88 of 99 cases; 89%; versus 75 of 99 cases; 76%).

Conclusions.—Both PAX2 and PAX8 are diagnostically useful markers for both primary and metastatic renal neoplasms of a large variety of histologic types. However, PAX8 appears to be more sensitive than PAX2 in both primary and metastatic settings. PAX8 can be included in any immunohistochemical panel for the diagnosis of primary renal neoplasms. Adding PAX2 should be optional, but this would gain limited further diagnostic yield. In a metastatic setting, both PAX8 and PAX2 can be included in a panel because a small subset of metastatic RCCs are stained only with PAX2.

Renal stem cells and their implications for kidney cancer

The renal cell carcinomas (RCC) denote a diverse set of neoplasias with unique genetic and histological features. The RCCs emanate from the renal tubule, a highly heterogeneous epithelial structure, and depending on which cell is malignified the resulting cancer displays unique characteristics. Notwithstanding this, the cells of origin for the RCC forms are far from established, and only inferred by the accumulated weight of marker similarities, not always providing an unequivocal picture. The tubular epithelium is normally mitotically quiescent, but demonstrates a considerable regenerative capacity upon renal injury. Recently the hypothesis that regeneration is driven by adult stem cells has been added experimental support, providing further complexity to the issue of renal carcinogenesis. Whether these cells are linked to RCC is an open question. In the present review we therefore present the prevailing theories regarding kidney regeneration, since a better understanding of this process might be of relevance when considering the different malignancies that arise from kidney epithelium. Our own results show that papillary renal cell carcinoma displays considerable similarities to proximal tubular progenitor cells and we suggest that this tumor form may develop in a multi-step fashion via benign renal adenomas. The putative connection between renal stem cells and carcinomas is, however, not clarified, since the current understanding of the renal stem cell system is not complete. It is clear that the efforts to isolate and characterize renal progenitor/stem cells suffer from numerous technical limitations and that it remains likely that the kidney harbors different stem cell pools with a restricted differentiation potential.

c-Met and NF-κB-dependent overexpression of Wnt7a and -7b and Pax2 promotes cystogenesis in polycystic kidney disease

The mechanisms of cystogenesis in autosomal dominant polycystic kidney disease (ADPKD) are not fully understood. Hyperactivation of the tyrosine kinase c-Met contributes to cyst formation, but we do not know the downstream mediators. Here, we found that hyperactivated c-Met led to increased NF-κB signaling, which in turn, drove de novo expression of Wnt7a and overexpression of Wnt7b in Pkd1(-/-) mouse kidneys. Hyperactivated Wnt signaling increased expression of the transcription factor Pax2 in the cells lining cysts. Furthermore, blocking Wnt signaling with DKK1 decreased cyst formation in an organ culture model of ADPKD. In summary, these results suggest that the c-Met/NF-κB/Wnt/Pax2 signaling transduction axis may provide pharmacological targets for the treatment of ADPKD.

The role of Pax2 in mouse prostate development

BACKGROUND

Loss-of-function of Pax2 results in severe defects of the male reproductive system, and Pax2 expression is detected in mouse prostate lobes and human prostatic cancers. However, the role for Pax2 in prostate development remains poorly understood.

METHODS

The expression of Pax2 was examined by in situ hybridization at various developmental stages. Urogenital sinuses were dissected out at E18.5 from mouse Pax2 mutants and controls, cultured in vitro or grafted under the renal capsule of CD1 nude mice. The expression of prostate developmental regulatory factors was analyzed by semi-quantitative real-time PCR or immuohistochemistry.

RESULTS

Pax2 is expressed in the epithelial cells of prostate buds. Loss-of-function of Pax2 does not affect the initiation of prostatic buds, but in vitro culture assays show that the prostates of Pax2 mutants are hypomorphic and branching is severely disrupted compared to controls. RT-PCR data from Pax2 mutant prostates demonstrate increased expression levels of dorsolateral prostate marker MSMB and ventral prostate marker SBP and dramatically reduced expression levels of anterior prostate marker TGM4.

CONCLUSIONS

Pax2 is essential for mouse prostate development and regulates prostatic ductal growth, branching, and lobe-specific identity. These findings are important for understanding the molecular regulatory mechanisms in prostate development.

The leucine zipper putative tumor suppressor 2 protein LZTS2 regulates kidney development

Members of the leucine zipper putative tumor suppressor (LZTS) family play crucial roles in transcription modulation and cell cycle control. We previously demonstrated that LZTS2 functions as a novel β-catenin-interacting protein and represses β-catenin-mediated transcription on T-cell factor/lymphoid enhancing factor. Here, we investigate the biological role of LZTS2 using newly established Lzts2 KO mice. Homozygosity for loss-of-function of the Lzts2-targeted allele resulted in severe kidney and urinary tract developmental defects, including renal/ureteral duplication, hydroureter, and hydronephrosis, which were visible prenatally. Altered ureteric bud outgrowth was identified in Lzts2 null embryos. Further analysis indicated that β-catenin subcellular localization was altered in fibroblasts isolated from Lzts2 null embryos. In addition, Wnt growth factor-induced β-catenin-mediated transcriptional activity was increased in Lzts2 null fibroblasts, suggesting a direct role for Lzts2 in the Wnt signaling pathway. These data demonstrate a critical role of LZTS2 in renal development and implicate LZTS2 as a critical regulator of β-catenin-mediated nephrogenesis.

Patterning and early cell lineage decisions in the developing kidney: the role of Pax genes

Specification of the intermediate mesoderm and the epithelial derivatives that will make the mammalian kidney depends on the concerted action of many transcription factors and signaling proteins. Among the earliest genes expressed in the nephric duct and surrounding mesenchyme is Pax2, whose function is essential for making and maintaining the epithelium. The Pax2 protein is subject to phosphorylation in response to signals that activate the c-Jun N-terminal kinase pathway, including Wnts and BMPs. In cell culture systems, Pax2 is know to recruit components of a histone H3 lysine 4 methyltransferase complex to specific DNA sites to alter the pattern of histone modifications and determine gene expression. This epigenetic function may underlie the ability of Pax2 and similar proteins to maintain cell lineages during development.

The transcription factor PAX2 regulates ADAM10 expression in renal cell carcinoma

ADAM10 is a metalloprotease that plays an important role in the progression and metastasis of various cancers. In the present study, we present compelling evidence that PAX2 can bind to the promotor of ADAM10 and regulate ADAM10 protein expression in renal cancer cells. We further show that ADAM10 is the major sheddase for the constitutive cleavage of L1-CAM and c-Met, two important proteins involved in the progression of renal cancer. The downregulation of ADAM10 led to a more scattered cell phenotype, which was accompanied by the induction of Slug and the loss of E-cadherin, which is observed during epithelial-to-mesenchymal transition (EMT). In addition, the downregulation of ADAM10 reduced the proliferation but induced the migration of renal cancer cells. Notably, the downregulation of PAX2 led to an increased L1-CAM expression, which was accompanied by a massive metalloprotease-mediated release of soluble L1-CAM. Importantly, soluble L1-CAM induced the proliferation of endothelial cells and the migration of renal cancer cells. Finally, we can demonstrate that the silencing of PAX2 led to an L1-CAM-dependent activation of the PI3K/Akt pathway, one important pathway mediating cancer cell survival. In summary, we identified PAX2 as a regulator of L1-CAM and ADAM10, which play crucial roles in the progression of various cancers including renal cell carcinoma and the downregulation of ADAM10 maybe an earlier step in renal cancer development as it seems to be involved in processes of EMT.

Increased hedgehog signaling in postnatal kidney results in aberrant activation of nephron developmental programs

Hedgehog (Hh) is a core signaling pathway implicated in fundamental processes during embryonic kidney development. We previously found that loss-of-function mutations in the transcription factor GLIS2, a putative vertebrate ortholog of Drosophila Ci, cause nephronophthisis type 7 in humans and mice. Kidney tubular cells in Glis2-knockout mice acquire mesenchymal phenotype, but the cellular mechanisms of this transition are unknown. Here, we demonstrate that Glis2 is a functional component of Hh signaling and is necessary to suppress this pathway in the postnatal kidney. In the epithelial compartment, Glis2 opposes Gli1 activity by binding cis-acting regulatory sequences in the 5' flanking regions of Snai1 and Wnt4, thereby inhibiting de-differentiation of tubular cells. We conclude that Glis2 is necessary to inhibit Hh signaling and to maintain the mature tubular epithelial phenotype in the adult kidney. This is the first description of a molecular mechanism that links the Hh signaling pathway to cystic kidney diseases and can open new avenues for the treatment of diverse ciliopathies.

Glomerular proteinuria: a complex interplay between unique players

Protein leak in the urine is a harbinger of disruption of the glomerular filtration barrier. It also correlates with disease progression and development of ESRD. At present, therapies are aimed at decreasing proteinuria to decrease further damage to the filter and as a marker of remission. Understanding the mechanism of molecular events that lead to protein leak is vital to developing new therapeutic interventions. There has been tremendous progress over the last decade in identifying gene defects which result in hereditary proteinuric defects. This has led to identifying pathways by which these genes regulate the structure and function of the components of the filtration barrier, namely the podocytes, mesangial cells, endothelial cells, and the basement membrane. Using gene knockout mouse models, a role of tubular cells in regulating proteinuria is also emerging. In this review, we have attempted to present some of the prevailing understanding of the underlying mechanisms and physiology of proteinuria.

PAX 8 expression in non-neoplastic tissues, primary tumors, and metastatic tumors: a comprehensive immunohistochemical study

PAX 8 is a transcription factor that is essential for embryonic development of the kidney, Müllerian organs, and thyroid. It may also have a role in tumor development in these organs. The diagnostic utility of PAX 8 has not been comprehensively studied. Formalin-fixed, paraffin-embedded tissue samples for non-neoplastic tissues (n=1601), primary neoplasms (n=933), and metastatic neoplasms (n=496) were subjected to PAX 8 immunostain. In non-neoplastic tissues, PAX 8 was consistently noted in glomerular parietal epithelial cells, renal collecting ductal cells, atrophic renal tubular epithelial cells regardless of nephronic segments, and epithelial cells of the endocervix, endometrium, fallopian tube, seminal vesicle, epidydimis, thyroid, pancreatic islet cells, and lymphoid cells. PAX 8 was not seen in the rest of the tissue samples. In primary neoplasms, PAX 8 was expressed by 194 of 240 (89%) renal cell neoplasms, by 238 of 267 (89%) Müllerian-type neoplasms, by 65 of 65 (100%) thyroid follicular cell neoplasms, by 8 of 8 (100%) nephrogenic adenomas, and by 17 of 17 (100%) lymphomas. Weak focal staining was noted in 5 of 12 (42%) cases of parathyroid hyperplasia/adenoma and in 6 of 17 (35%) well-differentiated neuroendocrine tumors of the pancreas. PAX 8 was not seen in other neoplasms. In metastatic neoplasms, PAX 8 was expressed by 90 of 102 (88%) metastatic renal cell carcinomas, by 57 of 63 metastatic Müllerian tumors (90%), and by 6 of 6 metastatic papillary thyroid carcinomas (100%). There was also weak focal staining for 1 of 15 metastatic small cell carcinomas and for 1 of 9 metastatic well-differentiated neuroendocrine carcinomas. PAX 8 was not seen in other metastatic neoplasms. It can be successfully identified in routinely processed tissue samples, and its expression is mostly nuclear. PAX 8 expression in non-neoplastic mature tissues is limited to the organs, the embryonic development of which depends on this transcription factor. This tissue/cell-specific expression is maintained during both neoplastic transformation and metastasis. PAX 8 is a sensitive and specific marker for tumors of renal, Müllerian, or thyroid origin in both primary and metastatic sites.

PAX2 gene mutations in pediatric and young adult transplant recipients: kidney and urinary tract malformations without ocular anomalies

Heterozygous humans for PAX2 mutations show autosomal dominant papillorenal syndrome (PRS), consisting of ocular colobomas, renal hypo/dysplasia and progressive renal failure in childhood. PAX2 mutations have also been identified in patients with isolated renal hypo/dysplasia. Twenty unrelated children and young adults with kidney and urinary tract malformations and no ocular abnormalities were retrospectively recruited for PAX2 mutational analysis. All patients had undergone renal transplantation after end-stage renal disease. We identified two new sequence variations: (i) a deletion causing a frameshift (c.69delC) and (ii) a nucleotide substitution determining a splice site mutation (c.410+5 G/A) by predictive analysis. Therefore, we suggest PAX2 molecular analysis to be extended to all patients with congenital malformations of kidney and urinary tract (CAKUT).

The Opdc missense mutation of Pax2 has a milder than loss-of-function phenotype

Renal-coloboma syndrome, also known as papillorenal syndrome, is an autosomal dominant human disorder in which optic disc coloboma is associated with kidney abnormalities. Mutations in the paired domain transcription factor PAX2 have been found to be the underlying cause of this disease. Disease severity varies between patients, and in some cases, renal hypoplasia has been found in the absence of any retinal defects. Here we report an N-ethyl-N-nitrosourea-induced mouse mutation, Opdc, which is an isoleucinetothreonine missense mutation, I40T, in the first α-helix of the Pax2 paired domain. The mutant protein binds target DNA sequences less strongly than the wild-type protein and acts poorly to transactivate target promoters in culture. The phenotypic consequence of this mutation on the development of the eye and ear is similar to that reported for null alleles of Pax2. However, in homozygotes, cerebellar development is normal on a genetic background in which loss of Pax2 results in failure of cerebellar formation. Moreover, there is a genetic background effect on the heterozygous phenotype such that on some strain backgrounds, kidney development is unaffected. Opdc is the first hypomorphic mutation reported for Pax2 that differs in phenotype from loss-of-function mutations. These results suggest that PAX2 is a strong candidate gene for cases in which human patients have optic disc coloboma not associated with renal dysplasia.

Cyclic stretch induces proliferation and TGF-β1-mediated apoptosis via p38 and ERK in ureteric bud cells

We previously reported that p38 mitogen-activated protein kinase (p38) and phosphorylated ERK are upregulated in cyst epithelium of human renal dysplasia and obstructive uropathy in fetal lambs (Omori S, Fukuzawa R, Hida M, Awazu M. Kidney Int 61: 899–906, 2002; Omori S, Kitagawa H, Koike J, Fujita H, Hida M, Pringle KC, Awazu M. Kidney Int 73: 1031–1037, 2008). Dysplastic epithelium is characterized by proliferation, apoptosis, and upregulation of Pax2 and transforming growth factor (TGF)-β1. In the present study, we investigated whether cyclic mechanical stretching of ureteric bud cells, a mimic of the hydrodynamic derangement after fetal urinary tract obstruction, reproduces events seen in vivo. Cyclic stretch activated p38 and ERK and upregulated Pax2 expression in a time-dependent manner in ureteric bud cells. Stretch-stimulated Pax2 expression was suppressed by a p38 inhibitor, SB203580, or a MEK inhibitor, PD98059. 5-Deoxyuridine incorporation was increased by stretch at 24 h, which was also abolished by SB203580 or PD98059. On the other hand, apoptosis was not induced at 24 h by stretch but was significantly increased at 48 h. TGF-β1 secretion was increased by stretch at 24 h, which was inhibited by SB203580 or PD98059. Inhibition of p38 or ERK as well as anti-TGF-β antibody abolished the stretch-induced apoptosis. Finally, exogenous TGF-β1 induced apoptosis of ureteric bud cells, which was inhibited by SB203580 and PD98059. In conclusion, cyclic stretch induces Pax2 upregulation, proliferation, and TGF-β1-mediated apoptosis, features characteristic of dysplastic epithelium, via p38 and ERK in ureteric bud cells.

PAX-2 is a helpful marker for diagnosing metastatic renal cell carcinoma: comparison with the renal cell carcinoma marker antigen and kidney-specific cadherin

CONTEXT

The diagnosis of metastatic renal cell carcinoma (RCC) remains problematic.

OBJECTIVE

To evaluate the role of PAX-2, a renal tubular cell transcription factor, in the diagnosis of metastatic RCC. PAX-2 expression in metastatic RCC was compared with that of the renal cell carcinoma marker antigen (RCCM) and kidney-specific cadherin (KSC), which are 2 known markers for RCC.

DESIGN

Immunostaining for PAX-2, RCCM, and KSC was performed on consecutive tissue sections of 95 metastatic RCCs (77 clear cell, 8 papillary, 5 sarcomatoid, and 5 collecting duct) and 183 metastatic tumors other than RCC.

RESULTS

For PAX-2, positive immunoreactivity was detected in 77% clear cell, 75% papillary, 100% collecting duct, and 0% sarcomatoid metastatic RCCs. For RCCM, positive immunoreactivity was detected in 49% clear cell, 75% papillary, 0% collecting duct, and 0% sarcomatoid metastatic RCCs. For KSC, only 2 metastatic clear cell RCCs (3%) were positive. In combination, all markers were positive in 0% of cases; all markers were negative in 23% of cases (17 clear cell, 1 papillary, and for all 5 sarcomatoid); and at least 1 marker was positive in 76% of cases (PAX-2 only in 28% of cases [21 clear cell, 1 papillary, and 5 collecting duct] and RCCM only in 3% of cases [2 clear, 1 papillary]). Of 183 metastatic tumors other than RCC, 14 were positive for PAX-2 (nodal metastasis of carcinoma of colon [1], breast [1], endometrium [1], and ovary [1]; and omental metastasis of carcinoma of uterus or ovary [10]).

CONCLUSIONS

PAX-2 is a sensitive and specific marker for metastatic RCC. The diagnostic yield would be marginally increased by adding RCCM, but not KSC, as an immunomarker.

Genetics of kidney development: pathogenesis of renal anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) account for more than 50% of abdominal masses found in neonates and involve about 0.5% of all pregnancies. CAKUT has a major role in renal failure, and increasing evidence suggests that certain abnormalities predispose to the development of hypertension and cardiovascular disease in adulthood. To understand the pathogenesis of human renal anomalies, understanding the development of kidney is important. Diverse anomalies of the kidney corresponding to defects at a particular stage of development have been documented recently; however, more research is required to understand the molecular networks underlying kidney development, and such an investigation will provide a clue to the therapeutic intervention for CAKUT.

The developmental expression profile of PAX2 in the murine prostate

BACKGROUND

Nine transcription factors comprise the PAX gene family that regulate organogenesis. The urogenital system of PAX2 null male mice fails to develop properly. PAX2 is overexpressed in PC3 cells. Therefore, PAX2 is implicated in both prostate organogenesis and cancer. However, the expression pattern/profile of PAX2 in the prostate is unknown.

METHODS

PAX2/5/8 expression was surveyed in E16.5 male urogenital sinus (UGS) by RT-PCR. Prostate samples from 10 developmental stages in C3H male mice were used in quantitative reverse-transcript PCR (Q-PCR) and Western blotting (WB). RT-PCR and WB measured PAX2 expression in prostatic lobes or UGS layers, to identify local-regional expression patterns. Cytoplasmic versus nuclear expression was examined by WB. A castration series in adult C3H male mice and R1881 treatment in serum-free LNCaP cells examined androgen control of PAX2.

RESULTS

PAX2 mRNA levels are higher in early developmental stages as compared to postpubertal prostates. RT-PCR and/or WB indicated a dorsal epithelial-nuclear localization of PAX2. PAX2 mRNA and protein increase postcastration. R1881 decreases expression of PAX2 mRNA in LNCaP cells as compared to controls.

CONCLUSIONS

The expression profile of PAX2 indicates that it may regulate early, androgen-independent stages of murine prostate development, particularly for dorsally derived prostate glands. PAX2 expression appears to be associated with a dorsally localized epithelial cell population that is castration insensitive and retains proliferative and differentiative potential. Such a population of cells may represent a subset of stem-like cells having some characteristics in common with castrate-resistant prostate cancer cells.

Lrp4 regulates initiation of ureteric budding and is crucial for kidney formation--a mouse model for Cenani-Lenz syndrome

Background

Development of the kidney is initiated when the ureteric bud (UB) branches from the Wolffian duct and invades the overlying metanephric mesenchyme (MM) triggering the mesenchymal/epithelial interactions that are the basis of organ formation. Multiple signaling pathways must be integrated to ensure proper timing and location of the ureteric bud formation.

Methods and Principal Findings

We have used gene targeting to create an Lrp4 null mouse line. The mutation results in early embryonic lethality with a subpenetrant phenotype of kidney agenesis. Ureteric budding is delayed with a failure to stimulate the metanephric mesenchyme in a timely manner, resulting in failure of cellular differentiation and resulting absence of kidney formation in the mouse as well as comparable malformations in humans with Cenani-Lenz syndrome.

Conclusion

Lrp4 is a multi-functional receptor implicated in the regulation of several molecular pathways, including Wnt and Bmp signaling. Lrp4^−/− mice show a delay in ureteric bud formation that results in unilateral or bilateral kidney agenesis. These data indicate that Lrp4 is a critical regulator of UB branching and lack of Lrp4 results in congenital kidney malformations in humans and mice.

Angiotensin II AT2 receptor regulates ureteric bud morphogenesis

ANG II AT2 receptor (AT2R)-deficient mice exhibit abnormal ureteric bud (UB) budding, increased incidence of double ureters, and vesicoureteral reflux. However, the role of the AT2R during UB morphogenesis and the mechanisms by which aberrant AT2R signaling disrupts renal collecting system development have not been fully defined. In this study, we mapped the expression of the AT2R during mouse metanephric development, examined the impact of disrupted AT2R signaling on UB branching, cell proliferation, and survival, and investigated the cross talk of the AT2R with the glial-derived neurotrophic factor (GDNF)/c-Ret/Wnt11 signaling pathway. Embryonic mouse kidneys express AT2R in the branching UB and the mesenchyme. Treatment of embryonic day 12.5 (E12.5) metanephroi with the AT2R antagonist PD123319 or genetic inactivation of the AT2R in mice inhibits UB branching, decreasing the number of UB tips compared with control (34 +/- 1.0 vs. 43 +/- 0.6, P < 0.01; 36 +/- 1.8 vs. 48 +/- 1.3, P < 0.01, respectively). In contrast, treatment of metanephroi with the AT2R agonist CGP42112 increases the number of UB tips compared with control (48 +/- 1.8 vs. 39 +/- 12.3, P < 0.05). Using real-time quantitative RT-PCR and whole mount in situ hybridization, we demonstrate that PD123319 downregulates the expression of GDNF, c-Ret, Wnt11, and Spry1 mRNA levels in E12.5 metanephroi grown ex vivo. AT(2)R blockade or genetic inactivation of AT2R stimulates apoptosis and inhibits proliferation of the UB cells in vivo. We conclude that AT2R performs essential functions during UB branching morphogenesis via control of the GDNF/c-Ret/Wnt11 signaling pathway, UB cell proliferation, and survival.

Trps1 functions downstream of Bmp7 in kidney development

During embryonic development, the mesenchyme of the lungs, gut, kidneys, and other tissues expresses Trps1, an atypical member of the GATA-type family of transcription factors. Our previous work suggested the possibility that Trps1 acts downstream of bone morphogenic protein 7 (Bmp7), which is essential for normal renal development. To examine the role of Trps1 during early renal development, we generated Trps1-deficient mice and examined their renal histology. Compared with wild-type mice, Trps1-deficient newborn mice had fewer tubules and glomeruli, an expanded renal interstitium, and numerous uninduced metanephric mesenchymal cells, which resulted in fewer nephrons. In wild-type kidneys, Trps1 expression was present in ureteric buds, cap mesenchyme, and renal vesicles, whereas Trps1 was virtually absent in Bmp7-deficient kidneys. Furthermore, Trps1-deficient kidneys had low levels of Pax2 and Wt1, which are markers of condensed mesenchymal cells, suggesting that a lack of Trps1 affects the differentiation of cap mesenchyme to renal vesicles. In cultured metanephric mesenchymal cells, Bmp7 induced Trps1 and E-cadherin and downregulated vimentin. Knockdown of Trps1 with small interference RNA inhibited this Bmp7-induced mesenchymal-to-epithelial transition. Last, whole-mount in situ hybridization of Wnt9b and Wnt4 demonstrated prolonged branching of ureteric buds and sparse cap mesenchyme in the kidneys of Trps1-deficient mice. Taken together, these findings suggest that normal formation of nephrons requires Trps1, which mediates mesenchymal-to-epithelial transition and ureteric bud branching during early renal development.