Islet1 deletion causes kidney agenesis and hydroureter resembling CAKUT

The role of mesenchymal estrogen receptor 1 in mouse uterus in response to estrogen

Estrogens play important roles in uterine growth and homeostasis through estrogen receptors (ESR1 and ESR2). To address the role of ESR1-mediated tissue events in the murine uterus, we analyzed mice with a mesenchymal tissue-specific knockout of Esr1. Isl1-driven Cre expression generated Esr1 deletion in the uterine stroma and endometrium (Isl-Esr1KO). We showed that overall structure of the Isl1-Esr1KO mouse uterus developed normally, but estrogen responsiveness and subsequent growth were defective, suggesting that mesenchymal ESR1 is necessary for both epithelial and mesenchymal cell proliferation. Furthermore, RNA-seq analysis revealed that the majority of estrogen-induced genes were regulated by stromal ESR1. In control mice, E2 administration induced 9476 up-regulated differentially expressed genes (DEGs), whereas only 1801 up-regulated DEGs were induced by E2 in Isl1-Esr1KO mice. We further showed that stromal ESR1-regulated genes in the mouse uterus included several growth factors and cytokines, which are potential factors that regulate epithelial and stromal tissue interaction, and also genes involved in lipid homeostasis. Therefore, we infer that stromal ESR1 expression is indispensable for most estrogen actions in the mouse uterus and the current results provide new insights into estrogen-mediated homeostasis in female reproductive organs.

Rathke's cleft-like cysts arise from Isl1 deletion in murine pituitary progenitors

The transcription factor ISL1 is expressed in pituitary gland stem cells and the thyrotrope and gonadotrope lineages. Pituitary-specific Isl1 deletion causes hypopituitarism with increased stem cell apoptosis, reduced differentiation of thyrotropes and gonadotropes, and reduced body size. Conditional Isl1 deletion causes development of multiple Rathke's cleft-like cysts, with 100% penetrance. Foxa1 and Foxj1 are abnormally expressed in the pituitary gland and associated with a ciliogenic gene-expression program in the cysts. We confirmed expression of FOXA1, FOXJ1, and stem cell markers in human Rathke's cleft cyst tissue, but not craniopharyngiomas, which suggests these transcription factors are useful, pathological markers for diagnosis of Rathke's cleft cysts. These studies support a model whereby expression of ISL1 in pituitary progenitors drives differentiation into thyrotropes and gonadotropes and without it, activation of FOXA1 and FOXJ1 permits development of an oral epithelial cell fate with mucinous cysts. This pituitary-specific Isl1 mouse knockout sheds light on the etiology of Rathke's cleft cysts and the role of ISL1 in normal pituitary development.

Renal agenesis associated with contralateral ectopic ureter and hydroureteronephrosis

Congenital anomalies of the kidney and the urinary tract such as renal agenesis and ectopic ureter have complex development. These anomalies have variable presentations and associations. In this report, we highlight the case of a young man with congenital renal agenesis presenting for a urinary tract infection. Abdominal and pelvic computed tomography imaging revealed the rare association of renal agenesis with contralateral ectopic ureter and subsequent hydroureteronephrosis. A urinary tract infection can be the presenting complication of such association, and a long follow-up is needed to anticipate the management.

Molecular detection of maturation stages in the developing kidney

Recent advances in stem cell biology have enabled the generation of kidney organoids in vitro, and further maturation of these organoids is observed after experimental transplantation. However, the current organoids remain immature and their precise maturation stages are difficult to determine because of limited information on developmental stage-dependent gene expressions in the kidney in vivo. To establish relevant molecular coordinates, we performed single-cell RNA sequencing (scRNA-seq) on developing kidneys at different stages in the mouse. By selecting genes that exhibited upregulation at birth compared with embryonic day 15.5 as well as cell lineage-specific expression, we generated gene lists correlated with developmental stages in individual cell lineages. Application of these lists to transplanted embryonic kidneys revealed that most cell types, other than the collecting ducts, exhibited similar maturation to kidneys at the neonatal stage in vivo, revealing non-synchronous maturation across the cell lineages. Thus, our scRNA-seq data can serve as useful molecular coordinates to assess the maturation of developing kidneys and eventually of kidney organoids.

Mouse Models of Congenital Kidney Anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects, which cause the majority of chronic kidney diseases in children. CAKUT covers a wide range of malformations that derive from deficiencies in embryonic kidney and lower urinary tract development, including renal aplasia, hypodysplasia, hypoplasia, ectopia, and different forms of ureter abnormalities. The majority of the genetic causes of CAKUT remain unknown. Research on mutant mice has identified multiple genes that critically regulate renal differentiation. The data generated from this research have served as an excellent resource to identify the genetic bases of human kidney defects and have led to significantly improved diagnostics. Furthermore, genetic data from human CAKUT studies have also revealed novel genes regulating kidney differentiation.

Islet1 and Brn3 Expression Pattern Study in Human Retina and hiPSC-Derived Retinal Organoid

This study was conducted to determine the dynamic Islet1 and Brn3 (POU4F) expression pattern in the human fetal retina and human-induced pluripotent stem cell- (hiPSC-) derived retinal organoid. Human fetal eyes from 8 to 27 fetal weeks (Fwks), human adult retina, hiPSC-derived retinal organoid from 7 to 31 differentiation weeks (Dwks), and rhesus adult retina were collected for cyrosectioning. Immunofluorescence analysis showed that Islet1 was expressed in retinal ganglion cells in the fetal retina, human adult retina, and retinal organoids. Unexpectedly, after Fwk 20, Brn3 expression gradually decreased in the fetal retina. In the midstage of development, Islet1 was detected in bipolar and developing horizontal cells. As the photoreceptor developed, the Islet1-positive cone precursors gradually became Islet1-negative/S-opsin-positive cones. This study highlights the distinguishing characteristics of Islet1 dynamic expression in human fetal retina development and proposes more concerns which should be taken regarding Brn3 as a cell-identifying marker in mature primate retina.

LIM homeodomain transcription factor Isl1 affects urethral epithelium differentiation and apoptosis via Shh

Urethral hypoplasia, including failure of urethral tube closure, is one of the common phenotypes observed in hereditary human disorders, the mechanism of which remains unclear. The present study was thus designed to study the expression, functions, and related mechanisms of the LIM homeobox transcription factor Isl1 throughout mouse urethral development. Results showed that Isl1 was highly expressed in urethral epithelial cells and mesenchymal cells of the genital tubercle (GT). Functional studies were carried out by utilizing the tamoxifen-inducible Isl1-knockout mouse model. Histological and morphological results indicated that Isl1 deletion caused urethral hypoplasia and inhibited maturation of the complex urethral epithelium. In addition, we show that Isl1-deleted mice failed to maintain the progenitor cell population required for renewal of urethral epithelium during tubular morphogenesis and exhibited significantly increased cell death within the urethra. Dual-Luciferase reporter assays and yeast one-hybrid assays showed that ISL1 was essential for normal urethral development by directly targeting the Shh gene. Collectively, results presented here demonstrated that Isl1 plays a crucial role in mouse urethral development, thus increasing our potential for understanding the mechanistic basis of hereditary urethral hypoplasia.

Isl1 mediates mesenchymal expansion in the developing external genitalia via regulation of Bmp4, Fgf10 and Wnt5a

Genital malformations are among the most common human birth defects, and both genetic and environmental factors can contribute to these malformations. Development of the external genitalia in mammals relies on complex signaling networks, and disruption of these signaling pathways can lead to genital defects. Islet-1 (ISL1), a member of the LIM/Homeobox family of transcription factors, has been identified as a major susceptibility gene for classic bladder exstrophy in humans, a common form of the bladder exstrophy-epispadias complex (BEEC), and is implicated in a role in urinary tract development. We report that deletion of Isl1 from the genital mesenchyme in mice led to hypoplasia of the genital tubercle and prepuce, with an ectopic urethral opening and epispadias-like phenotype. These mice also developed hydroureter and hydronephrosis. Identification of ISL1 transcriptional targets via ChIP-Seq and expression analyses revealed that Isl1 regulates several important signaling pathways during embryonic genital development, including the BMP, WNT, and FGF cascades. An essential function of Isl1 during development of the external genitalia is to induce Bmp4-mediated apoptosis in the genital mesenchyme. Together, these studies demonstrate that Isl1 plays a critical role during development of the external genitalia and forms the basis for a greater understanding of the molecular mechanisms underlying the pathogenesis of BEEC and urinary tract defects in humans.

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.

Gata6 restricts Isl1 to the posterior of nascent hindlimb buds through Isl1 cis-regulatory modules

Isl1 is required for two processes during hindlimb development: initiation of the processes directing hindlimb development in the lateral plate mesoderm and configuring posterior hindlimb field in the nascent hindlimb buds. During these processes, Isl1 expression is restricted to the posterior mesenchyme of hindlimb buds. How this dynamic change in Isl1 expression is regulated remains unknown. We found that two evolutionarily conserved sequences, located 3' to the Isl1 gene, regulate LacZ transgene expression in the hindlimb-forming region in mouse embryos. Both sequences contain GATA binding motifs, and expression pattern analysis identified that Gata6 is expressed in the flank and the anterior portion of nascent hindlimb buds. Recent studies have shown that conditional inactivation of Gata6 in mice causes hindlimb-specific pre-axial polydactyly, indicating a role of Gata6 in anterior-posterior patterning of hindlimbs. We studied whether Gata6 restricts Isl1 in the nascent hindlimb bud through the cis-regulatory modules. In vitro experiments demonstrate that GATA6 binds to the conserved GATA motifs in the cis-regulatory modules. GATA6 repressed expression of a luciferase reporter that contains the cis-regulatory modules by synergizing with Zfpm2. Analyses of Gata6 mutant embryos showed that ISL1 levels are higher in the anterior of nascent hindlimb buds than in wild type. Moreover, we detected a greater number of Isl1-transcribing cells in the anterior of nascent hindlimb buds in Gata6 mutants. Our results support a model in which Gata6 contributes to repression of Isl1 expression in the anterior of nascent hindlimb buds.

Non-muscle myosin II deletion in the developing kidney causes ureter-bladder misconnection and apical extrusion of the nephric duct lineage epithelia

In kidney development, connection of the nephric duct (ND) to the cloaca and subsequent sprouting of the ureteric bud (UB) from the ND are important for urinary exit tract formation. Although the roles of Ret signaling are well established, it remains unclear how intracellular cytoskeletal proteins regulate these morphogenetic processes. Myh9 and Myh10 encode two different non-muscle myosin II heavy chains, and Myh9 mutations in humans are implicated in congenital kidney diseases. Here we report that ND/UB lineage-specific deletion of Myh9/Myh10 in mice caused severe hydroureter/hydronephrosis at birth. At mid-gestation, the mutant ND/UB epithelia exhibited aberrant basal protrusion and ectopic UB formation, which likely led to misconnection of the ureter to the bladder. In addition, the mutant epithelia exhibited apical extrusion followed by massive apoptosis in the lumen, which could be explained by reduced apical constriction and intercellular adhesion mediated by E-cadherin. These phenotypes were not ameliorated by genetic reduction of the tyrosine kinase receptor Ret. In contrast, ERK was activated in the mutant cells and its chemical inhibition partially ameliorated the phenotypes. Thus, myosin II is essential for maintaining the apicobasal integrity of the developing kidney epithelia independently of Ret signaling.

ISL1 is a major susceptibility gene for classic bladder exstrophy and a regulator of urinary tract development

Previously genome-wide association methods in patients with classic bladder exstrophy (CBE) found association with ISL1, a master control gene expressed in pericloacal mesenchyme. This study sought to further explore the genetics in a larger set of patients following-up on the most promising genomic regions previously reported. Genotypes of 12 markers obtained from 268 CBE patients of Australian, British, German Italian, Spanish and Swedish origin and 1,354 ethnically matched controls and from 92 CBE case-parent trios from North America were analysed. Only marker rs6874700 at the ISL1 locus showed association (p = 2.22 × 10⁻⁰⁸). A meta-analysis of rs6874700 of our previous and present study showed a p value of 9.2 × 10⁻¹⁹. Developmental biology models were used to clarify the location of ISL1 activity in the forming urinary tract. Genetic lineage analysis of Isl1-expressing cells by the lineage tracer mouse model showed Isl1-expressing cells in the urinary tract of mouse embryos at E10.5 and distributed in the bladder at E15.5. Expression of isl1 in zebrafish larvae staged 48 hpf was detected in a small region of the developing pronephros. Our study supports ISL1 as a major susceptibility gene for CBE and as a regulator of urinary tract development.

Yap and Taz are required for Ret-dependent urinary tract morphogenesis

Despite the high occurrence of congenital abnormalities of the lower urinary tract in humans, the molecular, cellular and morphological aspects of their development are still poorly understood. Here, we use a conditional knockout approach to inactivate within the nephric duct (ND) lineage the two effectors of the Hippo pathway, Yap and Taz. Deletion of Yap leads to hydronephrotic kidneys with blind-ending megaureters at birth. In Yap mutants, the ND successfully migrates towards, and contacts, the cloaca. However, close analysis reveals that the tip of the Yap(-/-) ND forms an aberrant connection with the cloaca and does not properly insert into the cloaca, leading to later detachment of the ND from the cloaca. Taz deletion from the ND does not cause any defect, but analysis of Yap(-/-);Taz(-/-) NDs indicates that both genes play partially redundant roles in ureterovesical junction formation. Aspects of the Yap(-/-) phenotype resemble hypersensitivity to RET signaling, including excess budding of the ND, increased phospho-ERK and increased expression of Crlf1, Sprouty1, Etv4 and Etv5. Importantly, the Yap(ND) (-/-) ND phenotype can be largely rescued by reducing Ret gene dosage. Taken together, these results suggest that disrupting Yap/Taz activities enhances Ret pathway activity and contributes to pathogenesis of lower urinary tract defects in human infants.

Genome-wide association study and meta-analysis identify ISL1 as genome-wide significant susceptibility gene for bladder exstrophy

The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the uro-rectal malformation spectrum, and is thought to result from aberrant embryonic morphogenesis of the cloacal membrane and the urorectal septum. The most common form of BEEC is isolated classic bladder exstrophy (CBE). To identify susceptibility loci for CBE, we performed a genome-wide association study (GWAS) of 110 CBE patients and 1,177 controls of European origin. Here, an association was found with a region of approximately 220kb on chromosome 5q11.1. This region harbors the ISL1 (ISL LIM homeobox 1) gene. Multiple markers in this region showed evidence for association with CBE, including 84 markers with genome-wide significance. We then performed a meta-analysis using data from a previous GWAS by our group of 98 CBE patients and 526 controls of European origin. This meta-analysis also implicated the 5q11.1 locus in CBE risk. A total of 138 markers at this locus reached genome-wide significance in the meta-analysis, and the most significant marker (rs9291768) achieved a P value of 2.13 × 10-12. No other locus in the meta-analysis achieved genome-wide significance. We then performed murine expression analyses to follow up this finding. Here, Isl1 expression was detected in the genital region within the critical time frame for human CBE development. Genital regions with Isl1 expression included the peri-cloacal mesenchyme and the urorectal septum. The present study identified the first genome-wide significant locus for CBE at chromosomal region 5q11.1, and provides strong evidence for the hypothesis that ISL1 is the responsible candidate gene in this region.

Functional models for congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) constitute one of the most common developmental diseases in humans; however, the cause for most patients remains unknown. Efforts to identify novel genetic causes for CAKUT through next-generation sequencing techniques have led to the discovery of new genes and risk factors. Concomitantly, these same efforts have generated large gene candidate lists requiring individual functional characterization. Appropriate model systems are needed to assess the functionality of genes and pathogenicity of genetic variants discovered in CAKUT patients. In this review, we discuss how cellular, animal, and personal (human) models are being used to study CAKUT candidate genes and what their major advantages and disadvantages are with respect to relevance and throughput.

Renal branching morphogenesis: morphogenetic and signaling mechanisms

The human kidney is composed of an arborized network of collecting ducts, calyces and urinary pelvis that facilitate urine excretion and regulate urine composition. The renal collecting system is formed in utero, completed by the 34th week of gestation in humans, and dictates final nephron complement. The renal collecting system arises from the ureteric bud, a derivative of the intermediate-mesoderm derived nephric duct that responds to inductive signals from adjacent tissues via a process termed ureteric induction. The ureteric bud subsequently undergoes a series of iterative branching and remodeling events in a process called renal branching morphogenesis. Altered signaling that disrupts patterning of the nephric duct, ureteric induction, or renal branching morphogenesis leads to varied malformations of the renal collecting system collectively known as congenital anomalies of the kidney and urinary tract (CAKUT) and is the most frequently detected congenital renal aberration in infants. Here, we describe critical morphogenetic and cellular events that govern nephric duct specification, ureteric bud induction, renal branching morphogenesis, and cessation of renal branching morphogenesis. We also highlight salient molecular signaling pathways that govern these processes, and the investigative techniques used to interrogate them.

Next-generation sequencing for research and diagnostics in kidney disease

The advent of next-generation sequencing technologies has enabled genetic nephrology research to move beyond single gene analysis to the simultaneous investigation of hundreds of genes and entire pathways. These new sequencing approaches have been used to identify and characterize causal factors that underlie inherited heterogeneous kidney diseases such as nephronophthisis and congenital anomalies of the kidney and urinary tract. In this Review, we describe the development of next-generation sequencing in basic and clinical research and discuss the implementation of this novel technology in routine patient management. Widespread use of targeted and nontargeted approaches for gene identification in clinical practice will require consistent phenotyping, appropriate disease modelling and collaborative efforts to combine and integrate data analyses. Next-generation sequencing is an exceptionally promising technique that has the potential to improve the management of patients with inherited kidney diseases. However, identifying the molecular mechanisms that lead to renal developmental disorders and ciliopathies is difficult. A major challenge in the near future will be how best to integrate data obtained using next-generation sequencing with personalized medicine, including use of high-throughput disease modelling as a tool to support the clinical diagnosis of kidney diseases.

Role of Wnt5a-Ror2 signaling in morphogenesis of the metanephric mesenchyme during ureteric budding

Development of the metanephric kidney begins with the induction of a single ureteric bud (UB) on the caudal Wolffian duct (WD) in response to GDNF (glial cell line-derived neurotrophic factor) produced by the adjacent metanephric mesenchyme (MM). Mutual interaction between the UB and MM maintains expression of GDNF in the MM, thereby supporting further outgrowth and branching morphogenesis of the UB, while the MM also grows and aggregates around the branched tips of the UB. Ror2, a member of the Ror family of receptor tyrosine kinases, has been shown to act as a receptor for Wnt5a to mediate noncanonical Wnt signaling. We show that Ror2 is predominantly expressed in the MM during UB induction and that Ror2- and Wnt5a-deficient mice exhibit duplicated ureters and kidneys due to ectopic UB induction. During initial UB formation, these mutant embryos show dysregulated positioning of the MM, resulting in spatiotemporally aberrant interaction between the MM and WD, which provides the WD with inappropriate GDNF signaling. Furthermore, the numbers of proliferating cells in the mutant MM are markedly reduced compared to the wild-type MM. These results indicate an important role of Wnt5a-Ror2 signaling in morphogenesis of the MM to ensure proper epithelial tubular formation of the UB required for kidney development.

BMP signaling and its modifiers in kidney development

The kidney develops through mutual interactions between the metanephric mesenchyme and the ureteric bud, the former of which contains nephron progenitors that give rise to glomeruli and renal tubules. Bone morphogenetic protein (BMP) signaling and its modifiers play important roles in many steps of kidney development. BMP4 inhibits ureteric bud attraction, and the BMP antagonist Gremlin is essential for the initial stage of ureteric budding. During mid-gestation, BMP7 maintains the nephron progenitors and, at the same time, sensitizes them to the ureteric bud-derived differentiation signal. Crossveinless2 is a pro-BMP factor, and its absence leads to kidney hypoplasia. After birth, when nephron progenitors have disappeared, Dullard, a phosphatase that inactivates BMP receptors, keeps BMP signaling at an appropriate level. Deletion of Dullard results in excessive BMP signaling and apoptosis of the postnatal nephrons. In this review I discuss the similarities and differences of BMP functions in kidney development, as well as in diseases.