The GDNF target Vsnl1 marks the ureteric tip

Analysis of Acute and Chronic Methamphetamine Treatment in Mice on Gdnf System Expression Reveals a Potential Mechanism of Schizophrenia Susceptibility

The increase in presynaptic striatal dopamine is the main dopaminergic abnormality in schizophrenia (SCZ). SCZ is primarily treated by modulating the activity of monoamine systems, with a focus on dopamine and serotonin receptors. Glial cell line-derived neurotrophic factor (GDNF) is a strong dopaminergic factor, that recently was shown to correlate with SCZ in human CSF and in striatal tissue. A 2-3-fold increase in GDNF in the brain was sufficient to induce SCZ-like dopaminergic and behavioural changes in mice. Here, we analysed the effect of acute, chronic, and embryonic methamphetamine, a drug known to enhance the risk of psychosis, on Gdnf and its receptors, Gfra1 and Ret, as well as on monoamine metabolism-related gene expression in the mouse brain. We found that acute methamphetamine application increases Gdnf expression in the striatum and chronic methamphetamine decreases the striatal expression of GDNF receptors Gfra1 and Ret. Both chronic and acute methamphetamine treatment upregulated the expression of genes related to dopamine and serotonin metabolism in the striatum, prefrontal cortex, and substantia nigra. Our results suggest a potential mechanism as to how methamphetamine elicits individual psychosis risk in young adults-variation in initial striatal GDNF induction and subsequent GFRα1 and RET downregulation may determine individual susceptibility to psychosis. Our results may guide future experiments and precision medicine development for methamphetamine-induced psychosis using GDNF/GFRa1/RET antagonists.

Opposing Spatially Segregated Function of Endogenous GDNF-RET Signaling in Cocaine Addiction

Cocaine addiction is a serious condition with potentially lethal complications and no current pharmacological approaches towards treatment. Perturbations of the mesolimbic dopamine system are crucial to the establishment of cocaine-induced conditioned place preference and reward. As a potent neurotrophic factor modulating the function of dopamine neurons, glial cell line-derived neurotrophic factor (GDNF) acting through its receptor RET on dopamine neurons may provide a novel therapeutic avenue towards psychostimulant addiction. However, current knowledge on endogenous GDNF and RET function after the onset of addiction is scarce. Here, we utilized a conditional knockout approach to reduce the expression of the GDNF receptor tyrosine kinase RET from dopamine neurons in the ventral tegmental area (VTA) after the onset of cocaine-induced conditioned place preference. Similarly, after establishing cocaine-induced conditioned place preference, we studied the effect of conditionally reducing GDNF in the ventral striatum nucleus accumbens (NAc), the target of mesolimbic dopaminergic innervation. We find that the reduction of RET within the VTA hastens cocaine-induced conditioned place preference extinction and reduces reinstatement, while the reduction of GDNF within the NAc does the opposite: prolongs cocaine-induced conditioned place preference and increases preference during reinstatement. In addition, the brain-derived neurotrophic factor (BDNF) was increased and key dopamine-related genes were reduced in the GDNF cKO mutant animals after cocaine administration. Thus, RET antagonism in the VTA coupled with intact or enhanced accumbal GDNF function may provide a new approach towards cocaine addiction treatment.

Visinin-like 1, a novel target gene of the Wnt/β-catenin signaling pathway, is involved in apoptosis resistance in colorectal cancer

BACKGROUND

Abnormal activation of Wnt/β-catenin signaling is associated with various aspects of cancer development. This study explored the roles of novel target genes of the Wnt/β-catenin signaling pathway in cancer cells.

METHODS

Using the haploid chronic myelogenous leukemia cell line HAP1, RNA sequencing (RNA-seq) was performed to identify genes whose expression was increased by APC disruption and reversed by β-catenin knockdown (KD). The regulatory mechanism and function of one of the candidate genes was investigated in colorectal cancer (CRC) cells.

RESULTS

In total, 64 candidate genes whose expression was regulated by Wnt/β-catenin signaling were identified. Of these candidate genes, the expression levels of six were reduced by β-catenin KD in HCT116 CRC cells in our previous microarray. One of these genes was Visinin-like 1 ( VSNL1 ), which belongs to the neuronal calcium-sensor gene family. The expression of VSNL1 was regulated by the β-catenin/TCF7L2 complex via two TCF7L2-binding elements in intron 1. VSNL1 KDinduced apoptosis in VSNL1-positive CRC cells. Additionally, forced expression of wild-type VSNL1, but not a myristoylation, Ca²⁺ -binding, or dimerization-defective mutant, suppressed the apoptosis induced by camptothecin and doxorubicin in VSNL1-negative CRC cells.

CONCLUSION

Our findings suggest that VSNL1 , a novel target gene of the Wnt/β-catenin signaling pathway, is associated with apoptosis resistance in CRC cells.

Mapping of the amniotic fluid proteome of fetuses with congenital anomalies of the kidney and urinary tract identifies plastin 3 as a protein involved in glomerular integrity

Congenital anomalies of the kidney and the urinary tract (CAKUT) are the first cause of chronic kidney disease in childhood. Several genetic and environmental origins are associated with CAKUT, but most pathogenic pathways remain elusive. Considering the amniotic fluid (AF) composition as a proxy for fetal kidney development, we analyzed the AF proteome from non-severe CAKUT (n = 19), severe CAKUT (n = 14), and healthy control (n = 22) fetuses using LC-MS/MS. We identified 471 significant proteins that discriminated the three AF groups with 81% precision. Among them, eight proteins independent of gestational age (CSPG4, LMAN2, ENDOD1, ANGPTL2, PRSS8, NGFR, ROBO4, PLS3) were associated with both the presence and the severity of CAKUT. Among those, five were part of a protein-protein interaction network involving proteins previously identified as being potentially associated with CAKUT. The actin-bundling protein PLS3 (plastin 3) was the only protein displaying a gradually increased AF abundance from control, via non-severe, to severe CAKUT. Immunohistochemistry experiments showed that PLS3 was expressed in the human fetal as well as in both the fetal and the postnatal mouse kidney. In zebrafish embryos, depletion of PLS3 led to a general disruption of embryonic growth including reduced pronephros development. In postnatal Pls3-knockout mice, kidneys were macroscopically normal, but the glomerular ultrastructure showed thickening of the basement membrane and fusion of podocyte foot processes. These structural changes were associated with albuminuria and decreased expression of podocyte markers including Wilms' tumor-1 protein, nephrin, and podocalyxin. In conclusion, we provide the first map of the CAKUT AF proteome that will serve as a reference for future studies. Among the proteins strongly associated with CAKUT, PLS3 did surprisingly not specifically affect nephrogenesis but was found as a new contributor in the maintenance of normal kidney function, at least in part through the control of glomerular integrity. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Postnatal prolongation of mammalian nephrogenesis by excess fetal GDNF

Nephron endowment, defined during the fetal period, dictates renal and related cardiovascular health throughout life. We show here that, despite its negative effects on kidney growth, genetic increase of GDNF prolongs the nephrogenic program beyond its normal cessation. Multi-stage mechanistic analysis revealed that excess GDNF maintains nephron progenitors and nephrogenesis through increased expression of its secreted targets and augmented WNT signaling, leading to a two-part effect on nephron progenitor maintenance. Abnormally high GDNF in embryonic kidneys upregulates its known targets but also Wnt9b and Axin2, with concomitant deceleration of nephron progenitor proliferation. Decline of GDNF levels in postnatal kidneys normalizes the ureteric bud and creates a permissive environment for continuation of the nephrogenic program, as demonstrated by morphologically and molecularly normal postnatal nephron progenitor self-renewal and differentiation. These results establish that excess GDNF has a bi-phasic effect on nephron progenitors in mice, which can faithfully respond to GDNF dosage manipulation during the fetal and postnatal period. Our results suggest that sensing the signaling activity level is an important mechanism through which GDNF and other molecules contribute to nephron progenitor lifespan specification.

Summary: Dosage of neurotropic factor GDNF regulates nephron progenitors and in utero growth factor augmentation can extend postnatal lifespan and differentiation of nephron progenitors.

Mdm4 controls ureteric bud branching via regulation of p53 activity

The antagonism between Mdm2 and its close homolog Mdm4 (also known as MdmX) and p53 is vital for embryogenesis and organogenesis. Previously, we demonstrated that targeted disruption of Mdm2 in the Hoxb7+ ureteric bud (Ub) lineage, which gives rise to the renal collecting system, causes renal hypodysplasia culminating in perinatal lethality. In this study, we examine the unique role of Mdm4 in establishing the collecting duct system of the murine kidney. Hoxb7Cre driven loss of Mdm4 in the Ub lineage (Ub^Mdm4-/-) disrupts branching morphogenesis and triggers UB cell apoptosis. Ub^Mdm4-/- kidneys exhibit abnormally dilated Ub tips while the medulla is hypoplastic. These structural alterations result in secondary depletion of nephron progenitors and nascent nephrons. As a result, newborn Ub^Mdm4-/- mice have hypo-dysplastic kidneys. Transcriptional profiling revealed downregulation of the Ret-tyrosine kinase pathway components, Gdnf, Wnt11, Sox8, Etv4 and Cxcr4 in the Ub^Mdm4-/- mice relative to controls. Moreover, the expression levels of the canonical Wnt signaling members Axin2 and Wnt9b are downregulated. Mdm4 deletion upregulated p53 activity and p53-target gene expression including Cdkn1a (p21), Gdf15, Ccng1, PERP, and Fas. Germline loss of p53 in Ub^Mdm4-/- mice largely rescues kidney development and terminal differentiation of the collecting duct. We conclude that Mdm4 plays a unique and vital role in Ub branching morphogenesis and collecting system development.

Cellular and Molecular Mechanisms of Kidney Development: From the Embryo to the Kidney Organoid

Development of the metanephric kidney is strongly dependent on complex signaling pathways and cell-cell communication between at least four major progenitor cell populations (ureteric bud, nephron, stromal, and endothelial progenitors) in the nephrogenic zone. In recent years, the improvement of human-PSC-derived kidney organoids has opened new avenues of research on kidney development, physiology, and diseases. Moreover, the kidney organoids provide a three-dimensional (3D) in vitro model for the study of cell-cell and cell-matrix interactions in the developing kidney. In vitro re-creation of a higher-order and vascularized kidney with all of its complexity is a challenging issue; however, some progress has been made in the past decade. This review focuses on major signaling pathways and transcription factors that have been identified which coordinate cell fate determination required for kidney development. We discuss how an extensive knowledge of these complex biological mechanisms translated into the dish, thus allowed the establishment of 3D human-PSC-derived kidney organoids.

MAPK/ERK Signaling in Regulation of Renal Differentiation

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects derived from abnormalities in renal differentiation during embryogenesis. CAKUT is the major cause of end-stage renal disease and chronic kidney diseases in children, but its genetic causes remain largely unresolved. Here we discuss advances in the understanding of how mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) activity contributes to the regulation of ureteric bud branching morphogenesis, which dictates the final size, shape, and nephron number of the kidney. Recent studies also demonstrate that the MAPK/ERK pathway is directly involved in nephrogenesis, regulating both the maintenance and differentiation of the nephrogenic mesenchyme. Interestingly, aberrant MAPK/ERK signaling is linked to many cancers, and recent studies suggest it also plays a role in the most common pediatric renal cancer, Wilms' tumor.

Regulation of Renal Differentiation by Trophic Factors

Classically, trophic factors are considered as proteins which support neurons in their growth, survival, and differentiation. However, most neurotrophic factors also have important functions outside of the nervous system. Especially essential renal growth and differentiation regulators are glial cell line-derived neurotrophic factor (GDNF), bone morphogenetic proteins (BMPs), and fibroblast growth factors (FGFs). Here we discuss how trophic factor-induced signaling contributes to the control of ureteric bud (UB) branching morphogenesis and to maintenance and differentiation of nephrogenic mesenchyme in embryonic kidney. The review includes recent advances in trophic factor functions during the guidance of branching morphogenesis and self-renewal versus differentiation decisions, both of which dictate the control of kidney size and nephron number. Creative utilization of current information may help better recapitulate renal differentiation in vitro, but it is obvious that significantly more basic knowledge is needed for development of regeneration-based renal therapies.

Concepts for a therapeutic prolongation of nephrogenesis in preterm and low-birth-weight babies must correspond to structural-functional properties in the nephrogenic zone

Numerous investigations are dealing with anlage of the mammalian kidney and primary development of nephrons. However, only few information is available about the last steps in kidney development leading at birth to a downregulation of morphogen activity in the nephrogenic zone and to a loss of stem cell niches aligned beyond the organ capsule. Surprisingly, these natural changes in the developmental program display similarities to processes occurring in the kidneys of preterm and low-birth-weight babies. Although those babies are born at a time with a principally intact nephrogenic zone and active niches, a high proportion of them suffers on impairment of nephrogenesis resulting in oligonephropathy, formation of atypical glomeruli, and immaturity of parenchyma. The setting points out that up to date not identified noxae in the nephrogenic zone hamper primary steps of parenchyma development. In this situation, a possible therapeutic aim is to prolong nephrogenesis by medications. However, actual data provide information that administration of drugs is problematic due to an unexpectedly complex microanatomy of the nephrogenic zone, in niches so far not considered textured extracellular matrix and peculiar contacts between mesenchymal cell projections and epithelial stem cells via tunneling nanotubes. Thus, it remains to be figured out whether disturbance of morphogen signaling altered synthesis of extracellular matrix, disturbed cell-to-cell contacts, or modified interstitial fluid impair nephrogenic activity. Due to most unanswered questions, search for eligible drugs prolonging nephrogenesis and their reliable administration is a special challenge for the future.

Ret and Etv4 Promote Directed Movements of Progenitor Cells during Renal Branching Morphogenesis

Branching morphogenesis of the epithelial ureteric bud forms the renal collecting duct system and is critical for normal nephron number, while low nephron number is implicated in hypertension and renal disease. Ureteric bud growth and branching requires GDNF signaling from the surrounding mesenchyme to cells at the ureteric bud tips, via the Ret receptor tyrosine kinase and coreceptor Gfrα1; Ret signaling up-regulates transcription factors Etv4 and Etv5, which are also critical for branching. Despite extensive knowledge of the genetic control of these events, it is not understood, at the cellular level, how renal branching morphogenesis is achieved or how Ret signaling influences epithelial cell behaviors to promote this process. Analysis of chimeric embryos previously suggested a role for Ret signaling in promoting cell rearrangements in the nephric duct, but this method was unsuited to study individual cell behaviors during ureteric bud branching. Here, we use Mosaic Analysis with Double Markers (MADM), combined with organ culture and time-lapse imaging, to trace the movements and divisions of individual ureteric bud tip cells. We first examine wild-type clones and then Ret or Etv4 mutant/wild-type clones in which the mutant and wild-type sister cells are differentially and heritably marked by green and red fluorescent proteins. We find that, in normal kidneys, most individual tip cells behave as self-renewing progenitors, some of whose progeny remain at the tips while others populate the growing UB trunks. In Ret or Etv4 MADM clones, the wild-type cells generated at a UB tip are much more likely to remain at, or move to, the new tips during branching and elongation, while their Ret-/- or Etv4-/- sister cells tend to lag behind and contribute only to the trunks. By tracking successive mitoses in a cell lineage, we find that Ret signaling has little effect on proliferation, in contrast to its effects on cell movement. Our results show that Ret/Etv4 signaling promotes directed cell movements in the ureteric bud tips, and suggest a model in which these cell movements mediate branching morphogenesis.

Evidence for intermediate mesoderm and kidney progenitor cell specification by Pax2 and PTIP dependent mechanisms

Activation of the Pax2 gene marks the intermediate mesoderm shortly after gastrulation, as the mesoderm becomes compartmentalized into paraxial, intermediate, and lateral plate. Using an EGFP knock-in allele of Pax2 to identify and sort cells of the intermediate mesodermal lineage, we compared gene expression patterns in EGFP positive cells that were heterozygous or homozygous null for Pax2. Thus, we identified critical regulators of intermediate mesoderm and kidney development whose expression depended on Pax2 function. In cell culture models, Pax2 is thought to recruit epigenetic modifying complex to imprint activating histone methylation marks through interactions with the adaptor protein PTIP. In kidney organ culture, conditional PTIP deletion showed that many Pax2 target genes, which were activated early in renal progenitor cells, remained on once activated, whereas Pax2 target genes expressed later in kidney development were unable to be fully activated without PTIP. In Pax2 mutants, we also identified a set of genes whose expression was up-regulated in EGFP positive cells and whose expression was consistent with a cell fate transformation to paraxial mesoderm and its derivatives. These data provide evidence that Pax2 specifies the intermediate mesoderm and renal epithelial cells through epigenetic mechanisms and in part by repressing paraxial mesodermal fate.

Visinin-like peptide 1 in adrenal gland of the rat. Gene expression and its hormonal control

VSNL1 encodes the calcium-sensor protein visinin-like 1 and was identified previously as an upregulated gene in a sample set of aldosterone-producing adenomas. Recently, by means of microarray studies we demonstrated high expression of Vsnl1 gene in rat adrenal zona glomerulosa (ZG). Only scanty data are available on the role of this gene in adrenal function as well as on regulation of its expression by factors affecting adrenal cortex structure and function. Therefore we performed relevant studies aimed at clarifying some of the above issues. By Affymetrix(®) Rat Gene 1.1 ST Array Strip, QPCR and immunohistochemistry we demonstrated that expression levels of Vsnl1 in the rat adrenal ZG are notably higher than in the fasciculata/reticularis zone. In QPCR assay this difference was approximately 10 times higher. Expression of this gene in the rat adrenal gland or adrenocortical cells was acutely down regulated by ACTH, while chronic administration of corticotrophin or dexamethasone did not change Vsnl1 mRNA levels. In enucleation-induced adrenocortical regeneration expression levels of both Vsnl1 and Cyp11b2 were notably lowered and positively correlated. Despite these findings, the physiological significance of adrenal Vsnl1 remains unclear, and requires further investigation.

Mitogen-activated protein kinase (MAPK) pathway regulates branching by remodeling epithelial cell adhesion

Although the growth factor (GF) signaling guiding renal branching is well characterized, the intracellular cascades mediating GF functions are poorly understood. We studied mitogen-activated protein kinase (MAPK) pathway specifically in the branching epithelia of developing kidney by genetically abrogating the pathway activity in mice lacking simultaneously dual-specificity protein kinases Mek1 and Mek2. Our data show that MAPK pathway is heterogeneously activated in the subset of G1- and S-phase epithelial cells, and its tissue-specific deletion results in severe renal hypodysplasia. Consequently to the deletion of Mek1/2, the activation of ERK1/2 in the epithelium is lost and normal branching pattern in mutant kidneys is substituted with elongation-only phenotype, in which the epithelium is largely unable to form novel branches and complex three-dimensional patterns, but able to grow without primary defects in mitosis. Cellular characterization of double mutant epithelium showed increased E-cadherin at the cell surfaces with its particular accumulation at baso-lateral locations. This indicates changes in cellular adhesion, which were revealed by electron microscopic analysis demonstrating intercellular gaps and increased extracellular space in double mutant epithelium. When challenged to form monolayer cultures, the mutant epithelial cells were impaired in spreading and displayed strong focal adhesions in addition to spiky E-cadherin. Inhibition of MAPK activity reduced paxillin phosphorylation on serine 83 while remnants of phospho-paxillin, together with another focal adhesion (FA) protein vinculin, were augmented at cell surface contacts. We show that MAPK activity is required for branching morphogenesis, and propose that it promotes cell cycle progression and higher cellular motility through remodeling of cellular adhesions.

Genetic controls and cellular behaviors in branching morphogenesis of the renal collecting system

The mammalian kidney, which at maturity contains thousands of nephrons joined to a highly branched collecting duct (CD) system, is an important model system for studying the development of a complex organ. Furthermore, congenital anomalies of the kidney and urinary tract, often resulting from defects in ureteric bud branching morphogenesis, are relatively common human birth defects. Kidney development is initiated by interactions between the nephric duct and the metanephric mesenchyme, leading to the outgrowth and repeated branching of the ureteric bud epithelium, which gives rise to the entire renal CD system. Meanwhile, signals from the ureteric bud induce the mesenchyme cells to form the nephron epithelia. This review focuses on development of the CD system, with emphasis on the mouse as an experimental system. The major topics covered include the origin and development of the nephric duct, formation of the ureteric bud, branching morphogenesis of the ureteric bud, and elongation of the CDs. The signals, receptors, transcription factors, and other regulatory molecules implicated in these processes are discussed. In addition, our current knowledge of cellular behaviors that are controlled by these genes and underlie development of the collecting system is reviewed.

MicroRNAs that target Ca(2+) transporters are involved in vascular smooth muscle cell calcification

The role of microRNAs (miRNAs) in vascular calcification is currently unclear. To examine how miRNAs are involved in vascular smooth muscle cell (VSMC) calcification, we explored the alteration of miRNAs in VSMC calcification in vitro and in vivo. Klotho homozygous mutant mice (kl/kl) display vascular calcification and have perturbations of calcium handling. We therefore hypothesized that the calcium perturbations in VSMCs could be mediated by miRNAs. Using an miRNA array analysis, we demonstrated that miRNAs are aberrantly expressed in the aortic media of 3-week-old kl/kl mice compared with wild-type (WT) mice. The expression levels of miR-135a(*), miR-762, miR-714, and miR-712(*) in the aortic media of kl/kl mice were significantly higher than in WT mice. We used quantitative real-time reverse transcriptase polymerase chain reaction to further confirm that these miRNAs were increased in the aortic media of kl/kl mice and in cultured VSMCs treated with high phosphate and calcium. A search of the miRNA database indicated that the Ca(2+) efflux proteins NCX1, PMCA1, and NCKX4 frequently appeared as potential targets of these miRNAs. The transfection of miRNA mimics into cultured VSMCs reduced the protein levels of each potential target. Conversely, miRNA inhibitors reduced phosphate and calcium-induced VSMC calcification. Furthermore, these inhibitors decreased the intracellular Ca(2+) concentration in cultured VSMCs after treatment with phosphate and calcium. Our results suggest that increased expression of miR-135a(*), miR-762, miR-714, and miR-712(*) in VSMCs may be involved in VSMC calcification by disrupting Ca(2+) efflux proteins.

The expression of Visinin-like 1 during mouse embryonic development

Visinin like 1 (Vsnl1) encodes a calcium binding protein which is well conserved between species. It was originally found in the brain and its biological functions in central nervous system have been addressed in several studies. Low expression levels have also been found in some peripheral organs, but very little information is available regarding its physiological roles in non-neuronal tissues. Except for the kidney, the expression pattern of Vsnl1 mRNA and protein has not yet been addressed during embryogenesis. By in situ hybridization and immunolabeling we have extensively analyzed the expression pattern of Vsnl1 during murine development. Vsnl1 specifies the cardiac primordia and its expression becomes restricted to the atrial myocardium after heart looping. However, in the adult heart, Vsnl1 is expressed by all four cardiac chambers. It also serves as a specific marker for the cardiomyocyte-derived structures in the systemic and pulmonary circulation. Vsnl1 is dynamically expressed also by many other organs during development e.g. taste buds, cochlea, thyroid, tooth, salivary and adrenal gland. The stage specific expression pattern of Vsnl1 makes it a potentially useful marker particularly in studies of cardiac and vascular morphogenesis.

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.