Deletion of the prorenin receptor in the ureteric bud in mice inhibits Dot1/H3K79 pathway.

BACKGROUND: The prorenin receptor (PRR) plays a critical role in ureteric bud (UB) branching morphogenesis. DOT1 Like (DOT1L), a histone methyltransferase specific for Histone 3 lysine 79 (H3K79), is important for differentiation of the UB-derived renal collecting duct cells. In this study, we tested whether DOT1L/H3 dimethyl K79 (H3m2K79) are regulated by PRR deletion in the UB and UB-derived collecting ducts in the embryonic mouse kidneys. METHODS: Mutant Hoxb7Cre+/PRRflox/flox (PRRUB-/-) and control PRRUB+/+, mice were studied on embryonic (E) day E17.5. DOT1L mRNA and protein expression in the kidney was examined by real-time qRT-PCR and immunohistochemistry, respectively. H3m2K79 protein expression was determined by immunohistochemistry and Western blot analysis. RESULTS: DOT1L mRNA levels were decreased in mutant compared to control mice (0.68 ± 0.06 vs. 1.0 ± 0.01, p < 0.01). DOT1L and H3m2K79 immunostaining was reduced in the mutant vs. control kidneys (Dot1: 0.62 ± 0.03 vs. 1.0 ± 0.01, p < 0.05; H3m2K79: 0.64 ± 0.04 vs.1.1 ± 0.01. p < 0.05.). Western blot analysis revealed decreased H3m2K79 protein levels in mutant compared to control kidneys (1.0 ± 0.06 vs. 1.5 ± 0.02, p < 0.05). CONCLUSION: Targeted deletion of the PRR in the UB and UB-derived collecting ducts results in reduced DOT1L gene/protein and H3m2K79 protein expression in the embryonic mouse metanephroi in vivo. IMPACT: The role of histone methylation in mediating the effect of the prorenin receptor on the ureteric bud branching (UB) morphogenesis and urine acidification during kidney development is unknown. We demonstrate that histone H3 lysine (K) 79 dimethylation by methyltransferase Dot1 is reduced in the embryonic kidney of mice that lack the prorenin receptor in the UB lineage.

Cytogenomic aberrations in isolated multicystic dysplastic kidney in children.

BACKGROUND: Multicystic dysplastic kidney (MCDK) is a common form of congenital kidney anomaly. The cause of MCDK is unknown. We investigated whether MCDK in children is linked to cytogenomic aberrations. METHODS: We conducted array comparative genomic hybridization (aCGH) in ten unrelated children with MCDK. The pattern of inheritance was determined by real-time PCR in patients and their biological parents. RESULTS: Pathogenic aberrations were detected in three patients: a deletion at 7p14.3 with a size of 2.07 Mb housing 12 genes, including BBS9 (Bardet-Biedl syndrome 9) and BMPER (BMP binding endothelial regulator); a duplication at 16p13.11p12.3 with a size of 3.28 Mb that included >20 genes; and monosomy X for a female patient. The deletion at 7p14.3 was inherited from the patient's father, while the duplication at 16p13.11p12.3 was derived from the patient's mother. CONCLUSIONS: Up to 30% of patients with MCDK possess cytogenomic aberrations. BBS9 and BMPER variants have been reported to result in cystic kidney dysplasia, suggesting a possible pathogenic function for the deletion at 7p14.3 in children with MCDK. The duplication at 16p13.11p12.3 was not reported previously to associate with MCDK. Both variations were inherited from parents, indicating hereditary contributions in MCDK. Thus, aCGH is an informative tool to unravel the pathogenic mechanisms of MCDK. IMPACT: Cytogenomic aberrations are common in children with MCDK. Cytogenomic aberrations are inherited from parents, indicating hereditary contributions in MCDK. aCGH is a valuable tool to reveal pathogenic mechanisms of MCDK.

Self-adhesive protein/polypyrrole hybrid film for flexible electronic sensors in physiological signal monitoring.

Flexible electronic sensors composed of conductive material and flexible film have attracted increasing attention in decades due to its commercial, medical and scientific value. However, the poor interfacial bonding robustness between conductive materials and flexible film influences widely practical application of sensors. It is still a great challenge to fabricate a self-adhesive conductive film. Herein, we report a freestanding and self-adhesive bovine serum albumin/polypyrrole (BSA/PPy) hybrid film at the air/water interface. It is discovered that the PPy nanoparticles aggregate uniformly on the BSA film that is formed by amyloid-like BSA aggregation. The BSA/PPy film was integrated with polydimethylsiloxane (PDMS) film to fabricate flexible electronic sensors. The test indicates that the BSA/PPy film-based sensor could tolerate 500 cycles of bending without the resistance performance variation. The BSA/PPy film functions as a key mediator to dynamically tune the PPy conductance in response to external pressures and strains. The sensors exhibit ability for detecting tiny acoustic vibration, real-time human motion, physiological behavior and for differentiating various breathing pattern. Our strategy may open a pathway to readily construct flexible electronic sensors toward practical applications.

Sequence variants in the renin-angiotensin system genes are associated with isolated multicystic dysplastic kidney in children.

BACKGROUND: Multicystic dysplastic kidney (MCDK) is a common form of congenital cystic kidney disease in children. The etiology of MCDK remains unclear. Given an important role of the renin-angiotensin system in normal kidney development, we explored whether MCDK in children is associated with variants in the genes encoding renin-angiotensin system components by Sanger sequencing. METHODS: The coding regions of renin (REN), angiotensinogen (AGT), ACE, and angiotensin 1 receptor (AGTR1) genes were amplified by PCR. The effect of DNA sequence variants on protein function was predicted with PolyPhen-2 software. RESULTS: 3 novel and known AGT variants were found. 1 variant was probably damaging, 1 was possibly damaging and one was benign. Out of 7 REN variants, 4 were probably damaging and 3 were benign. Of 6 ACE variants, 3 were probably damaging and 3-benign. 3 AGTR1 variants were found. 2 variants were possibly damaging, and one was benign. CONCLUSION: We report novel associations of sequence variants in REN, AGT, ACE, or AGTR1 genes in children with isolated MCDK in the United States. Our findings suggest a recessive disease model and support the hypothesis of multiple renin-angiotensin system gene involvement in MCDK. IMPACT: Discovery of novel gene variants in renin-angiotensin genes in children with MCDK. Novel possibly damaging gene variants discovered. Multiple renin-angiotensin system gene variants are involved in MCDK.

(Pro)renin receptor regulates lung development via the Wnt/ß-catenin signaling pathway.

The (pro)renin receptor [(P)RR] binds to prorenin to activate the renin-angiotensin system and is essential for the development of many different organ systems. Whether the (P)RR also plays a role in lung development is unknown. Immunostaining was used to determine the spatial-temporal distribution of (P)RR in the embryonic, postnatal, and adult lungs. We created a lung-specific (P)RR knockout mouse [Foxd1cre/+-(P)RRflox/flox] and assessed changes in lung morphology, cell proliferation, and apoptosis using immunohistochemistry and TUNEL staining. (P)RR function was confirmed by using siRNA to knock down (P)RR in human bronchial epithelial cells (HBECs) and then using the CCK-8 assay and flow cytometry to assess cell proliferation and apoptosis. Gene expression changes after knockdown were assessed by RT-PCR and Western blotting. (P)RR is expressed in the club cells of the bronchial epithelium, and expression increases throughout development. Lung-specific (P)RR knockout disrupted branching morphogenesis, leading to lung hypoplasia and neonatal mortality. These defects were associated with increased apoptosis and decreased proliferation of the pulmonary epithelial and mesenchymal cells and may be mediated by downregulation of Wnt11, ß-catenin, and Axin2. (P)RR regulates lung development through canonical Wnt/ß-catenin signaling and may present a new target for strategies to treat lung hypoplasia.

Defining the dynamic chromatin landscape of mouse nephron progenitors.

Six2+ cap mesenchyme cells, also called nephron progenitor cells (NPC), are precursors of all epithelial cell types of the nephron, the filtering unit of the kidney. Current evidence indicates that perinatal 'old' NPC have a greater tendency to exit the progenitor niche and differentiate into nascent nephrons than their embryonic 'young' counterpart. Understanding the underpinnings of NPC development may offer insights to rejuvenate old NPC and expand the progenitor pool. Here, we compared the chromatin landscape of young and old NPC and found common features reflecting their shared lineage but also intrinsic differences in chromatin accessibility and enhancer landscape supporting the view that old NPC are epigenetically poised for differentiation. Annotation of open chromatin regions and active enhancers uncovered the transcription factor Bach2 as a potential link between the pro-renewal MAPK/AP1 and pro-differentiation Six2/b-catenin pathways that might be of critical importance in regulation of NPC fate. Our data provide the first glimpse of the dynamic chromatin landscape of NPC and serve as a platform for future studies of the impact of genetic or environmental perturbations on the epigenome of NPC.

Stromal prorenin receptor is critical for normal kidney development.

Formation of the metanephric kidney requires coordinated interaction among the stroma, ureteric bud, and cap mesenchyme. The transcription factor Foxd1, a specific marker of renal stromal cells, is critical for normal kidney development. The prorenin receptor (PRR), a receptor for renin and prorenin, is also an accessory subunit of the vacuolar proton pump V-ATPase. Global loss of PRR is embryonically lethal in mice, indicating an essential role of the PRR in embryonic development. Here, we report that conditional deletion of the PRR in Foxd1+ stromal progenitors in mice (cKO) results in neonatal mortality. The kidneys of surviving mice show reduced expression of stromal markers Foxd1 and Meis1 and a marked decrease in arterial and arteriolar development with the subsequent decreased number of glomeruli, expansion of Six2+ nephron progenitors, and delay in nephron differentiation. Intrarenal arteries and arterioles in cKO mice were fewer and thinner and showed a marked decrease in the expression of renin, suggesting a central role for the PRR in the development of renin-expressing cells, which in turn are essential for the proper formation of the renal arterial tree. We conclude that stromal PRR is crucial for the appropriate differentiation of the renal arterial tree, which in turn may restrict excessive expansion of nephron progenitors to promote a coordinated and proper morphogenesis of the nephrovascular structures of the mammalian kidney.

Conditional ablation of the prorenin receptor in nephron progenitor cells results in developmental programming of hypertension.

Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells (NPCs) of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump V-ATPase. Previously, we demonstrated that conditional ablation of the PRR in Six2+ NPCs in mice (Six2PRR-/- ) causes early neonatal death. Here, we identified genes that are regulated by PRR in Six2+ NPCs FACS-isolated from Six2PRR-/- and control kidneys on embryonic day E15.5 using whole-genome expression analysis. Seven genes with expression in CM cells previously shown to direct kidney development, including Notch1, ß-catenin, Lef1, Lhx1, Jag1, and p53, were downregulated. The functional groups within the downregulated gene set included genes involved in embryonic and cellular development, renal regeneration, cellular assembly and organization, cell morphology, death and survival. Double-transgenic Six2PRR-/- /BatGal+ mice, a reporter strain for ß-catenin transcriptional activity, showed decreased ß-catenin activity in the UB in vivo. Reduced PRR gene dosage in heterozygous Six2PRR+/- mice was associated with decreased glomerular number, segmental thickening of the glomerular basement membrane with focal podocyte foot process effacement, development of hypertension and increased soluble PRR (sPRR) levels in the urine at 2 months of age. Together, these data demonstrate that NPC PRR performs essential functions during nephrogenesis via control of hierarchy of genes that regulate critical cellular processes. Both reduced nephron endowment and augmented urine sPRR likely contribute to programming of hypertension in Six2PRR+/- mice.

Foxd1 is an upstream regulator of the renin-angiotensin system during metanephric kidney development.

BackgroundWe tested the hypothesis that Foxd1, a transcription factor essential for normal kidney development, is an upstream regulator of the renin-angiotensin system (RAS) during ureteric bud (UB)-branching morphogenesis.MethodsUB branching, RAS gene, and protein expression were studied in embryonic mouse kidneys. RAS mRNA expression was studied in mesenchymal MK4 cells.ResultsThe number of UB tips was reduced in Foxd1-/- compared with that in Foxd1+/+ metanephroi on embryonic day E12.5 (14±2.1 vs. 28±1.3, P<0.05). Quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) demonstrated that renin, angiotensin I-converting enzyme (ACE), and angiotensin (Ang) II receptor type 1 (AT1R) mRNA levels were decreased in Foxd1-/- compared with those in Foxd1+/+ E14.5 metanephroi. Western blot analysis and immunohistochemistry showed decreased expression of AGT and renin proteins in Foxd1-/- metanephroi compared with that in Foxd1+/+ metanephroi. Foxd1 overexpression in mesenchymal MK4 cells in vitro increased renin, AGT, ACE, and AT1R mRNA levels. Exogenous Ang II stimulated UB branching equally in whole intact E12.5 Foxd1-/- and Foxd1+/+ metanephroi grown ex vivo (+364±21% vs. +336±18%, P=0.42).ConclusionWe conclude that Foxd1 is an upstream positive regulator of RAS during early metanephric development and propose that the cross-talk between Foxd1 and RAS is essential in UB-branching morphogenesis.

Prorenin receptor controls renal branching morphogenesis via Wnt/ß-catenin signaling.

The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump H+-ATPase. Renal branching morphogenesis, defined as growth and branching of the ureteric bud (UB), is essential for mammalian kidney development. Previously, we demonstrated that conditional ablation of the PRR in the UB in PRRUB-/- mice causes severe defects in UB branching, resulting in marked kidney hypoplasia at birth. Here, we investigated the UB transcriptome using whole genome-based analysis of gene expression in UB cells, FACS-isolated from PRRUB-/-, and control kidneys at birth (P0) to determine the primary role of the PRR in terminal differentiation and growth of UB-derived collecting ducts. Three genes with expression in UB cells that previously shown to regulate UB branching morphogenesis, including Wnt9b, ß-catenin, and Fgfr2, were upregulated, whereas the expression of Wnt11, Bmp7, Etv4, and Gfrα1 was downregulated. We next demonstrated that infection of immortalized UB cells with shPRR in vitro or deletion of the UB PRR in double-transgenic PRRUB-/-/BatGal+ mice, a reporter strain for ß-catenin transcriptional activity, in vivo increases ß-catenin activity in the UB epithelia. In addition to UB morphogenetic genes, the functional groups of differentially expressed genes within the downregulated gene set included genes involved in molecular transport, metabolic disease, amino acid metabolism, and energy production. Together, these data demonstrate that UB PRR performs essential functions during UB branching and collecting duct morphogenesis via control of a hierarchy of genes that control UB branching and terminal differentiation of the collecting duct cells.

Prorenin receptor is critical for nephron progenitors.

Deficient nephrogenesis is the major factor contributing to renal hypoplasia defined as abnormally small kidneys. Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump H(+)-ATPase. Global loss of PRR is lethal in mice and PRR mutations are associated with a high blood pressure, left ventricular hypertrophy and X-linked mental retardation in humans. To circumvent lethality of the ubiquitous PRR mutation in mice and to determine the potential role of the PRR in nephrogenesis, we generated a mouse model with a conditional deletion of the PRR in Six2(+) nephron progenitors and their epithelial derivatives (Six2(PRR-/-)). Targeted ablation of PRR in Six2(+) nephron progenitors caused a marked decrease in the number of developing nephrons, small cystic kidneys and podocyte foot process effacement at birth, and early postnatal death. Reduced congenital nephron endowment resulted from premature depletion of nephron progenitor cell population due to impaired progenitor cell proliferation and loss of normal molecular inductive response to canonical Wnt/ß-catenin signaling within the metanephric mesenchyme. At 2 months of age, heterozygous Six2(PRR+/-) mice exhibited focal glomerulosclerosis, decreased kidney function and massive proteinuria. Collectively, these findings demonstrate a cell-autonomous requirement for the PRR within nephron progenitors for progenitor maintenance, progression of nephrogenesis, normal kidney development and function.

Deletion of the prorenin receptor from the ureteric bud causes renal hypodysplasia.

The role of the prorenin receptor (PRR) in the regulation of ureteric bud (UB) branching morphogenesis is unknown. Here, we investigated whether PRR acts specifically in the UB to regulate UB branching, kidney development and function. We demonstrate that embryonic (E) day E13.5 mouse metanephroi, isolated intact E11.5 UBs and cultured UB cells express PRR mRNA. To study its role in UB development, we conditionally ablated PRR in the developing UB (PRR (UB-/-)) using Hoxb7 (Cre) mice. On E12.5, PRR (UB-/-) mice had decreased UB branching and increased UB cell apoptosis. These defects were associated with decreased expression of Ret, Wnt11, Etv4/Etv5, and reduced phosphorylation of Erk1/2 in the UB. On E18.5, mutants had marked kidney hypoplasia, widespread apoptosis of medullary collecting duct cells and decreased expression of Foxi1, AE1 and H(+)-ATPase α4 mRNA. Ultimately, they developed occasional small cysts in medullary collecting ducts and had decreased nephron number. To test the functional consequences of these alterations, we determined the ability of PRR (UB-/-) mice to acidify and concentrate the urine on postnatal (P) day P30. PRR (UB-/-) mice were polyuric, had lower urine osmolality and a higher urine pH following 48 hours of acidic loading with NH4Cl. Taken together, these data show that PRR present in the UB epithelia performs essential functions during UB branching morphogenesis and collecting duct development via control of Ret/Wnt11 pathway gene expression, UB cell survival, activation of Erk1/2, terminal differentiation and function of collecting duct cells needed for maintaining adequate water and acid-base homeostasis. We propose that mutations in PRR could possibly cause renal hypodysplasia and renal tubular acidosis in humans.

Ontogeny of the (pro)renin receptor.

BACKGROUND: This study examined temporal expression of the (pro)renin receptor ((P)RR), during renal, heart, lung, and brain organogenesis in the mouse. METHODS: (P)RR expression was determined by quantitative reverse-transcription PCR, western blotting, and immunohistochemistry. RESULTS: Brain, kidney, and lung (P)RR mRNA levels increased progressively during gestation and peak on postnatal day (P)10. (P)RR protein contents were high during gestation in all organs studied and declined with maturation. Brain (P)RR was expressed most prominently in the ependymal lining of the ventricles. In the embryonic day (E)16.5 and E18.5 metanephros, (P)RR was present in the ureteric bud and ureteric bud-derived collecting ducts. In the fetal heart, (P)RR was expressed diffusely in the myocardium, whereas pulmonary (P)RR was detected at highest levels in the epithelium of branching airways. Treatment of newborn kidneys with the angiotensin (Ang) II type 1 receptor (AT1R) antagonist candesartan increased (P)RR mRNA levels. CONCLUSION: (P)RR gene and protein expressions in the brain, kidney, heart, and lung are developmentally regulated in a tissue-specific manner. Endogenous Ang II, acting via the AT1R, exerts a negative feedback on (P)RR in the newborn kidney. These findings suggest that high (P)RR protein levels observed during gestation may play a role in brain, kidney, heart, and lung organogenesis.

Ontogeny of angiotensin-converting enzyme 2.

INTRODUCTION: This study examined the temporal expression of angiotensin (Ang)-converting enzyme 2 (ACE2) during renal, heart, lung, and brain organogenesis in the mouse. RESULTS: We demonstrate that kidney ACE2 mRNA levels are low on embryonic day (E) 12.5, increase fourfold during development, and decline in adulthood. In extrarenal tissues, ACE2 mRNA levels are also low during early gestation, increase in perinatal period, and peak in adulthood. The lung shows the highest age-related increase in ACE2 mRNA levels followed by the brain, kidney, and heart. ACE2 protein levels and enzymatic activity are high in all organs studied during gestation and decline postnatally. Ang II decreases ACE2 mRNA levels and enzymatic activity in kidneys grown ex vivo. These effects of Ang II are blocked by the specific Ang II AT(1) receptor (AT(1)R) antagonist candesartan, but not by the AT(2) receptor (AT(2)R) antagonist PD123319. DISCUSSION: We conclude that ACE2 gene and protein expression and enzymatic activity are developmentally regulated in a tissue-specific manner. Ang II, acting through AT(1)R, exerts a negative feedback on ACE2 during kidney development. We postulate that relatively high ACE2 protein levels and enzymatic activity observed during gestation may play a role in kidney, lung, brain, and heart organogenesis.

Angiotensin II regulates growth of the developing papillas ex vivo.

We tested the hypothesis that lack of angiotensin (ANG) II production in angiotensinogen (AGT)-deficient mice or pharmacologic antagonism of ANG II AT(1) receptor (AT(1)R) impairs growth of the developing papillas ex vivo, thus contributing to the hypoplastic renal medulla phenotype observed in AGT- or AT(1)R-null mice. Papillas were dissected from Hoxb7(GFP+) or AGT(+/+), (+/-), (-/-) mouse metanephroi on postnatal day P3 and grown in three-dimentional collagen matrix gels in the presence of media (control), ANG II (10(-5) M), or the specific AT(1)R antagonist candesartan (10(-6) M) for 24 h. Percent reduction in papillary length was attenuated in AGT(+/+) and in AGT(+/-) compared with AGT(-/-) (-18.4 ± 1.3 vs. -32.2 ± 1.6%, P < 0.05, -22.8 ± 1.3 vs. -32.2 ± 1.6%, P < 0.05, respectively). ANG II blunted the decrease in papilla length observed in respective media-treated controls in Hoxb7(GFP+) (-1.5 ± 0.3 vs. -10.0 ± 1.4%, P < 0.05) or AGT(+/+), (+/-), and (-/-) papillas (-12.8 ± 0.7 vs. -18.4 ± 1.3%, P < 0.05, -16.8 ± 1.1 vs. -23 ± 1.2%, P < 0.05; -26.2 ± 1.6 vs. -32.2 ± 1.6%, P < 0.05, respectively). In contrast, percent decrease in the length of Hoxb7(GFP+) papillas in the presence of the AT(1)R antagonist candesartan was higher compared with control (-24.3 ± 2.1 vs. -10.5 ± 1.8%, P < 0.05). The number of proliferating phospho-histone H3 (pH3)-positive collecting duct cells was lower, whereas the number of caspase 3-positive cells undergoing apoptosis was higher in candesartan- vs. media-treated papillas (pH3: 12 ± 1.4 vs. 21 ± 2.1, P < 0.01; caspase 3: 3.8 ± 0.5 vs. 1.7 ± 0.2, P < 0.01). Using quantitative RT-PCR, we demonstrate that AT(1)R signaling regulates the expression of genes implicated in morphogenesis of the renal medulla. We conclude that AT(1)R prevents shrinkage of the developing papillas observed ex vivo via control of Wnt7b, FGF7, ß-catenin, calcineurin B1, and α3 integrin gene expression, collecting duct cell proliferation, and survival.

Development of the kidney medulla.

The mature renal medulla, the inner part of the kidney, consists of the medullary collecting ducts, loops of Henle, vasa recta and the interstitium. The unique spatial arrangement of these components is essential for the regulation of urine concentration and other specialized kidney functions. Thus, the proper and timely assembly of medulla constituents is a crucial morphogenetic event leading to the formation of a functioning metanephric kidney. Mechanisms that direct renal medulla formation are poorly understood. This review describes the current understanding of the key molecular and cellular mechanisms underlying morphological aspects of medulla formation. Given that hypoplasia of the renal medulla is a common manifestation of congenital obstructive nephropathy and other types of congenital anomalies of the kidney and urinary tract (CAKUT), better understanding of how disruptions in medulla formation are linked to CAKUT will enable improved diagnosis, treatment and prevention of CAKUT and their associated morbidity.

Angiotensin II stimulates in vitro branching morphogenesis of the isolated ureteric bud.

Mutations in the renin-angiotensin system (RAS) genes are associated with congenital anomalies of the kidney and urinary tract (CAKUT). As angiotensin (Ang) II, the principal effector peptide growth factor of the RAS, stimulates ureteric bud (UB) branching in whole intact embryonic (E) metanephroi, defects in UB morphogenesis may be causally linked to CAKUT observed under conditions of disrupted RAS. In the present study, using the isolated intact UB (iUB) assay, we tested the hypothesis that Ang II stimulates UB morphogenesis by directly acting on the UB, identified Ang II target genes in the iUB by microarray and examined the effect of Ang II on UB cell migration in vitro. We show that isolated E11.5 mouse iUBs express Ang II AT(1) and AT(2) receptor mRNA. Treatment of E11.5 iUBs grown in collagen matrix gels with Ang II (10(-5)M) increases the number of iUB tips after 48h of culture compared to control (4.8±0.4 vs. 2.4±0.2, p<0.01). A number of genes required for UB branching as well as novel genes whose role in UB development is currently unknown are targets of Ang II signaling in the iUB. In addition, Ang II increases UB cell migration (346±5.1 vs. 275±4.4, p<0.01) in vitro. In summary, Ang II stimulates UB cell migration and directly induces morphogenetic response in the iUB. We conclude that Ang II-regulated genes in the iUB may be important mediators of Ang II-induced UB branching. We hypothesize that Ang II-dependent cell movements play an important role in UB branching morphogenesis.

(Pro)renin Receptor in Kidney Development and Disease.

The renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the developing metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans are associated with a broad spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). These forms of CAKUT include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, and aberrant glomerulogenesis. Emerging evidence indicates that (pro)renin receptor (PRR), a novel component of the RAS, is essential for proper kidney development and that aberrant PRR signaling is causally linked to cardiovascular and renal disease. This paper describes the role of the RAS in kidney development and highlights emerging insights into the cellular and molecular mechanisms by which the PRR may regulate this critical morphogenetic process.

Receptor tyrosine kinases in kidney development.

The kidney plays a fundamental role in the regulation of arterial blood pressure and fluid/electrolyte homeostasis. As congenital anomalies of the kidney and urinary tract (CAKUT) constitute one of the most common human birth defects, improved understanding of the cellular and molecular mechanisms that lead to CAKUT is critical. Accumulating evidence indicates that aberrant signaling via receptor tyrosine kinases (RTKs) is causally linked to CAKUT. Upon activation by their ligands, RTKs dimerize, undergo autophosphorylation on specific tyrosine residues, and interact with adaptor proteins to activate intracellular signal transduction pathways that regulate diverse cell behaviours such as cell proliferation, survival, and movement. Here, we review the current understanding of role of RTKs and their downstream signaling pathways in the pathogenesis of CAKUT.

Genetics of congenital anomalies of the kidney and urinary tract.

Congenital anomalies of the kidney and urinary tract (CAKUT) occur in 1 in 500 births and are a major cause of morbidity in children. Notably, CAKUT account for the most cases of pediatric end-stage renal disease and predispose the individual to hypertension and cardiovascular disease throughout life. Although some forms of CAKUT are a part of a syndrome or are associated with a positive family history, most cases of renal system anomalies are sporadic and isolated to the urinary tract. Broad phenotypic spectrum of CAKUT and variability in genotype-phenotype correlation indicate that pathogenesis of CAKUT is a complex process that depends on interplay of many factors. This review focuses on the genetic mechanisms (single-gene mutations, modifier genes) leading to renal system anomalies in humans and discusses emerging insights into the role of epigenetics, in utero environmental factors, and micro-RNAs (miRNAs) in the pathogenesis of CAKUT. Common gene networks that function in defined temporospatial fashion to orchestrate renal system morphogenesis are highlighted. Derangements in cellular, molecular, and morphogenetic mechanisms that direct normal renal system development are emphasized as a major cause of CAKUT. Integrated understanding of how morphogenetic process disruptions are linked to CAKUT will enable improved diagnosis, treatment, and prevention of congenital renal system anomalies and their consequences.