Fras1, a basement membrane-associated protein mutated in Fraser syndrome, mediates both the initiation of the mammalian kidney and the integrity of renal glomeruli

Appendage-resident epithelial cells expedite wound healing response in adult zebrafish

Adult zebrafish are able to heal large-sized cutaneous wounds in hours with little to no scarring. This rapid re-epithelialization is crucial for preventing infection and jumpstarting the subsequent regeneration of damaged tissues. Despite significant progress in understanding this process, it remains unclear how vast numbers of epithelial cells are orchestrated on an organismic scale to ensure the timely closure of millimeter-sized wounds. Here, we report an unexpected role of adult zebrafish appendages (fins) in accelerating the re-epithelialization process. Through whole-body monitoring of single-cell dynamics in live animals, we found that fin-resident epithelial cells (FECs) are highly mobile and migrate to cover wounds in nearby body regions. Upon injury, FECs readily undergo organ-level mobilization, allowing for coverage of body surfaces of up to 4.78 mm2 in less than 8 h. Intriguingly, long-term fate-tracking experiments revealed that the migratory FECs are not short-lived at the wound site; instead, the cells can persist on the body surface for more than a year. Our experiments on "fin-less" and "fin-gaining" individuals demonstrated that the fin structures are not only capable of promoting rapid re-epithelialization but are also necessary for the process. We further found that fin-enriched extracellular matrix laminins promote the active migration of FECs by facilitating lamellipodia formation. These findings lead us to conclude that appendage structures in regenerative vertebrates, such as fins, may possess a previously unrecognized function beyond serving as locomotor organs. The appendages may also act as a massive reservoir of healing cells, which speed up wound closure and tissue repair.

The Landscape of Point Mutations in Human Protein Coding Genes Leading to Pregnancy Loss

Pregnancy loss is the most frequent complication of a pregnancy which is devastating for affected families and poses a significant challenge for the health care system. Genetic factors are known to play an important role in the etiology of pregnancy loss; however, despite advances in diagnostics, the causes remain unexplained in more than 30% of cases. In this review, we aggregated the results of the decade-long studies into the genetic risk factors of pregnancy loss (including miscarriage, termination for fetal abnormality, and recurrent pregnancy loss) in euploid pregnancies, focusing on the spectrum of point mutations associated with these conditions. We reviewed the evolution of molecular genetics methods used for the genetic research into causes of pregnancy loss, and collected information about 270 individual genetic variants in 196 unique genes reported as genetic cause of pregnancy loss. Among these, variants in 18 genes have been reported by multiple studies, and two or more variants were reported as causing pregnancy loss for 57 genes. Further analysis of the properties of all known pregnancy loss genes showed that they correspond to broadly expressed, highly evolutionary conserved genes involved in crucial cell differentiation and developmental processes and related signaling pathways. Given the features of known genes, we made an effort to construct a list of candidate genes, variants in which may be expected to contribute to pregnancy loss. We believe that our results may be useful for prediction of pregnancy loss risk in couples, as well as for further investigation and revealing genetic etiology of pregnancy loss.

Genetic and epigenetic background of diabetic kidney disease

Diabetic kidney disease (DKD) is a severe diabetic complication that affects up to half of the individuals with diabetes. Elevated blood glucose levels are a key underlying cause of DKD, but DKD is a complex multifactorial disease, which takes years to develop. Family studies have shown that inherited factors also contribute to the risk of the disease. During the last decade, genome-wide association studies (GWASs) have emerged as a powerful tool to identify genetic risk factors for DKD. In recent years, the GWASs have acquired larger number of participants, leading to increased statistical power to detect more genetic risk factors. In addition, whole-exome and whole-genome sequencing studies are emerging, aiming to identify rare genetic risk factors for DKD, as well as epigenome-wide association studies, investigating DNA methylation in relation to DKD. This article aims to review the identified genetic and epigenetic risk factors for DKD.

Foxc1 and Foxc2 are indispensable for maintenance of progenitors of nephron and stroma in the developing kidney

Nephron development proceeds with reciprocal interactions among three layers: nephron progenitors (NPs), ureteric buds, and stromal progenitors (SPs). We found Foxc1 and Foxc2 (Foxc1/2) expression in NPs and SPs. Systemic deletion of Foxc1/2 two days after the onset of metanephros development (E13.5) resulted in epithelialization of NPs and ectopic formation of renal vesicles. NP-specific deletion did not cause these phenotypes, indicating that Foxc1/2 in other cells (likely in SPs) contributed to the maintenance of NPs. Single-cell RNA-seq analysis revealed NP and SP subpopulations, the border between committed NPs and renewing NPs, and similarity among cortical interstitium and vascular smooth muscle type cells. Integrated analysis of the control and knockout data indicated transformation of some NPs to strange cells expressing markers of vascular endothelium, reduced numbers of self-renewing NP and SP populations, downregulation of crucial genes for kidney development such as Fgf20 and Frem1 in NPs, and Foxd1 and Sall1 in SPs. It also revealed upregulation of genes that were not usually expressed in NPs and SPs. Thus, Foxc1/2 maintains NPs and SPs by regulating the expression of multiple genes.

Disease mechanisms of monogenic congenital anomalies of the kidney and urinary tract American Journal of Medical Genetics Part C

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) is a developmental disorder of the kidney and/or genito-urinary tract that results in end stage kidney disease (ESKD) in up to 50% of children. Despite the congenital nature of the disease, CAKUT accounts for almost 10% of adult onset ESKD. Multiple lines of evidence suggest that CAKUT is a Mendelian disorder, including the observation of familial clustering of CAKUT. Pathogenesis in CAKUT is embryonic in origin, with disturbances of kidney and urinary tract development resulting in a heterogeneous range of disease phenotypes. Despite polygenic and environmental factors being implicated, a significant proportion of CAKUT is monogenic in origin, with studies demonstrating single gene defects in 10%-20% of patients with CAKUT. Here, we review monogenic disease causation with emphasis on the etiological role of gene developmental pathways in CAKUT.

SLC4A4, FRAS1, and SULT1A1 Genetic Variations Associated With Dabigatran Metabolism in a Healthy Chinese Population

Background: The purpose of this study was to identify genetic variations associated with the metabolism of dabigatran in healthy Chinese subjects, with particular focus given to pharmacokinetics (PK) and pharmacodynamics (PD).

Methods: Healthy Chinese adults aged 18–65 years with unknown genotypes from a bioequivalence trial were included according to the protocol registered at ClinicalTrial.org (NCT03161496). All subjects received a single dose (150 mg) of dabigatran etexilate. PK (main outcomes: area under the concentration-time, AUC0-t, of total and free dabigatran) and PD (main outcomes: anti-FIIa activity, APTT, and PT) parameters were evaluated. Whole-exome sequencing and genome-wide association analyses were performed. Additionally, candidate gene association analyses related to dabigatran were conducted.

Results: A total of 118 healthy Chinese subjects were enrolled in this study. According to the p-value suggestive threshold (1.0 × 10−4), the following three SNPs were found to be associated with the AUC0–t of total dabigatran: SLC4A4 SNP rs138389345 (p = 5.99 × 10−5), FRAS1 SNP rs6835769 (p = 6.88 × 10−5), and SULT1A1 SNP rs9282862 (p = 7.44 × 10−5). Furthermore, these SNPs were also found to have significant influences on the AUC0–t of free dabigatran, maximum plasma concentration, and anti-FIIa activity (p < 0.05). Moreover, we identified 30 new potential SNPs of 13 reported candidate genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP1A2, CYP2C19, CYP3A5, CES1, SLCO1B1, SLC22A1, UGT1A1, UGT1A9, and UGT2B7) that were associated with drug metabolism.

Conclusion: Genetic variations were indeed found to impact dabigatran metabolism in a population of healthy Chinese subjects. Further research is needed to explore the more detailed functions of these SNPs. Additionally, our results should be verified in studies that use larger sample sizes and investigate other ethnicities.

Genome-wide gene-air pollution interaction analysis of lung function in 300,000 individuals

BACKGROUND

Impaired lung function is predictive of mortality and is a key component of chronic obstructive pulmonary disease. Lung function has a strong genetic component but is also affected by environmental factors such as increased exposure to air pollution, but the effect of their interactions is not well understood.

OBJECTIVES

To identify interactions between genetic variants and air pollution measures which affect COPD risk and lung function. Additionally, to determine whether previously identified lung function genetic association signals showed evidence of interaction with air pollution, considering both individual effects and combined effects using a genetic risk score (GRS).

METHODS

We conducted a genome-wide gene-air pollution interaction analysis of spirometry measures with three measures of air pollution at home address: particulate matter (PM2.5 & PM10) and nitrogen dioxide (NO2), in approximately 300,000 unrelated European individuals from UK Biobank. We explored air pollution interactions with previously identified lung function signals and determined their combined interaction effect using a GRS.

RESULTS

We identified seven new genome-wide interaction signals (P<5×10-8), and a further ten suggestive interaction signals (P<5×10-7). Additionally, we found statistical evidence of interaction for FEV1/FVC between PM2.5 and previously identified lung function signal, rs10841302, near AEBP2, suggesting increased susceptibility as copies of the G allele increased (but size of the impact was small - interaction beta: -0.363 percentage points, 95% CI: -0.523, -0.203 per 5 µg/m3). There was no observed interaction between air pollutants and the weighted GRS.

DISCUSSION

We carried out the largest genome-wide gene-air pollution interaction study of lung function and identified potential effects of clinically relevant size and significance. We observed up to 440 ml lower lung function for certain genotypes when exposed to mean levels of outdoor air pollution, which is approximately equivalent to nine years of average normal loss of lung function in adults.

The term CAKUT has outlived its usefulness: the case for the prosecution

CAKUT stands for Congenital Anomalies of the Kidney and Urinary Tract, and the acronym first appeared in a review article published in 1998. Since then, CAKUT has become a familiar term encountered in the medical literature, especially in nephrology journals. I reason that the term CAKUT was conceived as not a simple description of various diseases, but more as shorthand for a bold conceptual package that linked the occurrence of diverse types of anatomical malformations with insights from genetic and developmental biology research. Moreover, the angiotensin II receptor type 2 was seen as a paradigmatic molecule in the pathobiology of CAKUT. I contend that the acronym, while appearing as an intellectually good idea at the time it was conceived, has outlived its usefulness. To reach these conclusions, I focus on the complex of research observations that led to the theory behind CAKUT, and then question whether these scientific foundations still stand firm. In addition, it is noted that not all clinicians have adopted the acronym, and I speculate why this is the case. I proceed to demonstrate that there is an incompatibility between the semantic meaning of CAKUT and the diseases for which the term was originally conceived. Instead, I suggest the acronym UTM, standing for Urinary Tract Malformation, is a simpler and less ambiguous one to use. Finally, I contend that the continued use of the acronym is a regressive step for the disciplines of nephrology and urology, taking us back two centuries when all kidney diseases were simply called Bright's disease.

Tissue-specific parameters for the design of ECM-mimetic biomaterials

The extracellular matrix (ECM) is a complex network of biomolecules that mechanically and biochemically directs cell behavior and is crucial for maintaining tissue function and health. The heterogeneous organization and composition of the ECM varies within and between tissue types, directing mechanics, aiding in cell-cell communication, and facilitating tissue assembly and reassembly during development, injury and disease. As technologies like 3D printing rapidly advance, researchers are better able to recapitulate in vivo tissue properties in vitro; however, tissue-specific variations in ECM composition and organization are not given enough consideration. This is in part due to a lack of information regarding how the ECM of many tissues varies in both homeostatic and diseased states. To address this gap, we describe the components and organization of the ECM, and provide examples for different tissues at various states of disease. While many aspects of ECM biology remain unknown, our goal is to highlight the complexity of various tissues and inspire engineers to incorporate unique components of the native ECM into in vitro platform design and fabrication. Ultimately, we anticipate that the use of biomaterials that incorporate key tissue-specific ECM will lead to in vitro models that better emulate human pathologies. STATEMENT OF SIGNIFICANCE: Biomaterial development primarily emphasizes the engineering of new materials and therapies at the expense of identifying key parameters of the tissue that is being emulated. This can be partially attributed to the difficulty in defining the 3D composition, organization, and mechanics of the ECM within different tissues and how these material properties vary as a function of homeostasis and disease. In this review, we highlight a range of tissues throughout the body and describe how ECM content, cell diversity, and mechanical properties change in diseased tissues and influence cellular behavior. Accurately mimicking the tissue of interest in vitro by using ECM specific to the appropriate state of homeostasis or pathology in vivo will yield results more translatable to humans.

Human disease-associated extracellular matrix orthologs ECM3 and QBRICK regulate primary mesenchymal cell migration in sea urchin embryos

Sea urchin embryos have been one of model organisms to investigate cellular behaviors because of their simple cell composition and transparent body. They also give us an opportunity to investigate molecular functions of human proteins of interest that are conserved in sea urchin. Here we report that human disease-associated extracellular matrix orthologues ECM3 and QBRICK are necessary for mesenchymal cell migration during sea urchin embryogenesis. Immunofluorescence has visualized the colocalization of QBRICK and ECM3 on both apical and basal surface of ectoderm. On the basal surface, QBRICK and ECM3 constitute together a mesh-like fibrillar structure along the blastocoel wall. When the expression of ECM3 was knocked down by antisense-morpholino oligonucleotides, the ECM3-QBRICK fibrillar structure completely disappeared. When QBRICK was knocked down, the ECM3 was still present, but the basally localized fibers became fragmented. The ingression and migration of primary mesenchymal cells were not critically affected, but their migration at later stages was severely affected in both knock-down embryos. As a consequence of impaired primary mesenchymal cell migration, improper spicule formation was observed. These results indicate that ECM3 and QBRICK are components of extracellular matrix, which play important role in primary mesenchymal cell migration, and that sea urchin is a useful experimental animal model to investigate human disease-associated extracellular matrix proteins.

3D Mapping Reveals a Complex and Transient Interstitial Matrix During Murine Kidney Development

BACKGROUND

The extracellular matrix (ECM) is a network of proteins and glycosaminoglycans that provides structural and biochemical cues to cells. In the kidney, the ECM is critical for nephrogenesis; however, the dynamics of ECM composition and how it relates to 3D structure during development is unknown.

METHODS

Using embryonic day 14.5 (E14.5), E18.5, postnatal day 3 (P3), and adult kidneys, we fractionated proteins based on differential solubilities, performed liquid chromatography-tandem mass spectrometry, and identified changes in ECM protein content (matrisome). Decellularized kidneys were stained for ECM proteins and imaged in 3D using confocal microscopy.

RESULTS

We observed an increase in interstitial ECM that connects the stromal mesenchyme to the basement membrane (TNXB, COL6A1, COL6A2, COL6A3) between the embryo and adult, and a transient elevation of interstitial matrix proteins (COL5A2, COL12A1, COL26A1, ELN, EMID1, FBN1, LTBP4, THSD4) at perinatal time points. Basement membrane proteins critical for metanephric induction (FRAS1, FREM2) were highest in abundance in the embryo, whereas proteins necessary for integrity of the glomerular basement membrane (COL4A3, COL4A4, COL4A5, LAMB2) were more abundant in the adult. 3D visualization revealed a complex interstitial matrix that dramatically changed over development, including the perinatal formation of fibrillar structures that appear to support the medullary rays.

CONCLUSION

By correlating 3D ECM spatiotemporal organization with global protein abundance, we revealed novel changes in the interstitial matrix during kidney development. This new information regarding the ECM in developing kidneys offers the potential to inform the design of regenerative scaffolds that can guide nephrogenesis in vitro.

Studying Müllerian duct anomalies - from cataloguing phenotypes to discovering causation

Müllerian duct anomalies (MDAs) are developmental disorders of the Müllerian duct, the embryonic anlage of most of the female reproductive tract. The prevalence of MDAs is 6.7% in the general female population and 16.7% in women who exhibit recurrent miscarriages. Individuals affected by these anomalies suffer from high rates of infertility, first-trimester pregnancy losses, premature labour, placental retention, foetal growth retardation and foetal malpresentations. The aetiology of MDAs is complex and heterogeneous, displaying a range of clinical pictures that generally lack a direct genotype-phenotype correlation. De novo and familial cases sharing the same genomic lesions have been reported. The familial cases follow an autosomal-dominant inheritance, with reduced penetrance and variable expressivity. Furthermore, few genetic factors and molecular pathways underpinning Müllerian development and dysregulations causing MDAs have been identified. The current knowledge in this field predominantly derives from loss-of-function experiments in mouse and chicken models, as well as from human genetic association studies using traditional approaches, such as microarrays and Sanger sequencing, limiting the discovery of causal factors to few genetic entities from the coding genome. In this Review, we summarise the current state of the field, discuss limitations in the number of studies and patient samples that have stalled progress, and review how the development of new technologies provides a unique opportunity to overcome these limitations. Furthermore, we discuss how these new technologies can improve functional validation of potential causative alterations in MDAs.

Summary: Here, we review the current knowledge about Müllerian duct anomalies in the context of new high-throughput technologies and model systems and their implications in the prevention of these disorders.

Novel Linkage Peaks Discovered for Diabetic Nephropathy in Individuals With Type 1 Diabetes

Genome-wide association studies (GWAS) and linkage studies have had limited success in identifying genome-wide significantly linked regions or risk loci for diabetic nephropathy (DN) in individuals with type 1 diabetes (T1D). As GWAS cohorts have grown, they have also included more documented and undocumented familial relationships. Here we computationally inferred and manually curated pedigrees in a study cohort of >6,000 individuals with T1D and their relatives without diabetes. We performed a linkage study for 177 pedigrees consisting of 452 individuals with T1D and their relatives using a genome-wide genotyping array with >300,000 single nucleotide polymorphisms and PSEUDOMARKER software. Analysis resulted in genome-wide significant linkage peaks on eight chromosomal regions from five chromosomes (logarithm of odds score >3.3). The highest peak was localized at the HLA region on chromosome 6p, but whether the peak originated from T1D or DN remained ambiguous. Of other significant peaks, the chromosome 4p22 region was localized on top of ARHGAP24, a gene associated with focal segmental glomerulosclerosis, suggesting this gene may play a role in DN as well. Furthermore, rare variants have been associated with DN and chronic kidney disease near the 4q25 peak, localized on top of CCSER1.

Development of the metanephric kidney

The kidney plays an integral role in filtering the blood-removing metabolic by-products from the body and regulating blood pressure. This requires the establishment of large numbers of efficient and specialized blood filtering units (nephrons) that incorporate a system for vascular exchange and nutrient reabsorption as well as a collecting duct system to remove waste (urine) from the body. Kidney development is a dynamic process which generates these structures through a delicately balanced program of self-renewal and commitment of nephron progenitor cells that inhabit a constantly evolving cellular niche at the tips of a branching ureteric "tree." The former cells build the nephrons and the latter the collecting duct system. Maintaining these processes across fetal development is critical for establishing the normal "endowment" of nephrons in the kidney and perturbations to this process are associated both with mutations in integral genes and with alterations to the fetal environment.

Towards Modelling Genetic Kidney Diseases with Human Pluripotent Stem Cells

BACKGROUND

Kidney disease causes major suffering and premature mortality worldwide. With no cure for kidney failure currently available, and with limited options for treatment, there is an urgent need to develop effective pharmaceutical interventions to slow or prevent kidney disease progression.

SUMMARY

In this review, we consider the feasibility of using human pluripotent stem cell-derived kidney tissues, or organoids, to model genetic kidney disease. Notable successes have been made in modelling genetic tubular diseases (e.g., cystinosis), polycystic kidney disease, and medullary cystic kidney disease. Organoid models have also been used to test novel therapies that ameliorate aberrant cell biology. Some progress has been made in modelling congenital glomerular disease, even though glomeruli within organoids are developmentally immature. Less progress has been made in modelling structural kidney malformations, perhaps because sufficiently mature metanephric mesenchyme-derived nephrons, ureteric bud-derived branching collecting ducts, and a prominent stromal cell population are not generated together within a single protocol. Key Messages: We predict that the field will advance significantly if organoids can be generated with a full complement of cell lineages and with kidney components displaying key physiological functions, such as glomerular filtration. The future economic upscaling of reproducible organoid generation will facilitate more widespread research applications, including the potential therapeutic application of these stem cell-based technologies.

Nephron Progenitor Maintenance Is Controlled through Fibroblast Growth Factors and Sprouty1 Interaction

BACKGROUND

Nephron progenitor cells (NPCs) give rise to all segments of functional nephrons and are of great interest due to their potential as a source for novel treatment strategies for kidney disease. Fibroblast growth factor (FGF) signaling plays pivotal roles in generating and maintaining NPCs during kidney development, but little is known about the molecule(s) regulating FGF signaling during nephron development. Sprouty 1 (SPRY1) is an antagonist of receptor tyrosine kinases. Although SPRY1 antagonizes Ret-GDNF signaling, which modulates renal branching, its role in NPCs is not known.

METHODS

Spry1, Fgf9, and Fgf20 compound mutant animals were used to evaluate kidney phenotypes in mice to understand whether SPRY1 modulates FGF signaling in NPCs and whether FGF8 functions with FGF9 and FGF20 in maintaining NPCs.

RESULTS

Loss of one copy of Spry1 counters effects of the loss of Fgf9 and Fgf20, rescuing bilateral renal agenesis premature NPC differentiation, NPC proliferation, and cell death defects. In the absence of SPRY1, FGF9, and FGF20, another FGF ligand, FGF8, promotes nephrogenesis. Deleting both Fgf8 and Fgf20 results in kidney agenesis, defects in NPC proliferation, and cell death. Deleting one copy of Fgf8 reversed the effect of deleting one copy of Spry1, which rescued the renal agenesis due to loss of Fgf9 and Fgf20.

CONCLUSIONS

SPRY1 expressed in NPCs modulates the activity of FGF signaling and regulates NPC stemness. These findings indicate the importance of the balance between positive and negative signals during NPC maintenance.

Novel loss of function variants in FRAS1 AND FREM2 underlie renal agenesis in consanguineous families

INTRODUCTION

Congenital anomalies of the kidney and urinary tract (CAKUT) are a group of abnormalities that affect structure of the kidneys or other structures of the urinary tract. The majority of CAKUT are asymptomatic and are diagnosed prenatally by ultrasound scanning or found incidentally in postnatal life. CAKUT varies in severity and may lead to life-threatening kidney failure and end-stage kidney disease. Renal agenesis, a severe form of CAKUT, is a congenital absence of one or both kidneys. Bilateral renal agenesis belongs to a group of prenatally lethal renal diseases and is often detected on fetal ultrasound scanning during the investigation of oligohydramnios. Approximately 40% of fetuses with bilateral renal agenesis are stillborn or die a few hours postnatally. Mutations in many renal development genes have been shown to be associated with renal agenesis.

METHODS

Six consanguineous Saudi Arabian families were recruited to study the molecular genetic causes of recurrent miscarriages and lost fetuses due to oligohydramnios, renal agenesis and other congenital anomalies. Whole exome sequencing was employed to underlying detect genetic defects.

RESULTS

Novel loss of function variants were detected in FRAS1 and FREM2. In FRAS1, a homozygous splice site variant c.9780+2T>C was found in an affected fetus, segregating form each parent. In addition, in three other families both parents were heterozygous for a frameshift variant (c.8981dupT; p.His2995Profs*3) and splice site variants (c.5217+1G>C and c.8098+2T>A), respectively. In FREM2, a homozygous nonsense variant (c.2303C>G; p.Ser768*) was found in an affected fetus, segregating from both parents. In another family, both parents carried a FREM2 heterozygous frameshift variant (c.3969delC; p.Asn1323Lysfs*5).

CONCLUSION

We describe consanguineous families with clinical features of antenatal oligohydramnios and bilateral renal agenesis, in whom we have identified novel pathogenic variants in FRAS1 and FREM2. These finding highlights the association between mutations in FRAS1 and FREM2 and antenatal/perinatal death.

Fraser syndrome: review of the literature illustrated by a historical adult case

Fraser syndrome (cryptophthalmos-syndactyly syndrome) is a rare autosomal recessive malformation disorder. The first description of the syndrome was reported by George Fraser in 1962. Diagnosis is based on the major and minor criteria established by van Haelst et al. in 2007. Unilateral or bilateral cryptophthalmos, syndactyly, unilateral renal agenesis, and genital anomalies are the most frequent anomalies. Several maxillofacial, oro-dental, ear-nose-throat, hormonal, and anorectal disorders are reported. Cardiac malformations and musculoskeletal anomalies are uncommon. The syndrome is related to mutations in three different genes (FRAS1, FREM2, and GRIP1) resulting in failure of the apoptosis program and disruption of the epithelial-mesenchymal interactions during embryonic development. Prenatal diagnosis is based on the detection of renal agenesis and laryngeal atresia, together with a family history. Most foetuses with severe anomalies are terminated or are stillborn. All patients or pregnancies with a diagnosis of Fraser syndrome should be referred to expert centres. A collaborative approach including anaesthetists, ENT specialists, maxillofacial surgeons, and geneticists is necessary for the management of this syndrome. In vivo and in vitro research models are available to better understand the underlying aetiology.

Overactivity or blockade of transforming growth factor-β each generate a specific ureter malformation

Transforming growth factor-β (TGFβ) has been reported to be dysregulated in malformed ureters. There exists, however, little information on whether altered TGFβ levels actually perturb ureter development. We therefore hypothesised that TGFβ has functional effects on ureter morphogenesis. Tgfb1, Tgfb2 and Tgfb3 transcripts coding for TGFβ ligands, as well as Tgfbr1 and Tgfbr2 coding for TGFβ receptors, were detected by quantitative polymerase chain reaction in embryonic mouse ureters collected over a wide range of stages. As assessed by in situ hybridisation and immunohistochemistry, the two receptors were detected in embryonic urothelia. Next, TGFβ1 was added to serum-free cultures of embryonic day 15 mouse ureters. These organs contain immature smooth muscle and urothelial layers and their in vivo potential to grow and acquire peristaltic function can be replicated in serum-free organ culture. Such organs therefore constitute a suitable developmental stage with which to define roles of factors that affect ureter growth and functional differentiation. Exogenous TGFβ1 inhibited growth of the ureter tube and generated cocoon-like dysmorphogenesis. RNA sequencing suggested that altered levels of transcripts encoding certain fibroblast growth factors (FGFs) followed exposure to TGFβ. In serum-free organ culture exogenous FGF10 but not FGF18 abrogated certain dysmorphic effects mediated by exogenous TGFβ1. To assess whether an endogenous TGFβ axis functions in developing ureters, embryonic day 15 explants were exposed to TGFβ receptor chemical blockade; growth of the ureter was enhanced, and aberrant bud-like structures arose from the urothelial tube. The muscle layer was attenuated around these buds, and peristalsis was compromised. To determine whether TGFβ effects were limited to one stage, explants of mouse embryonic day 13 ureters, more primitive organs, were exposed to exogenous TGFβ1, again generating cocoon-like structures, and to TGFβ receptor blockade, again generating ectopic buds. As for the mouse studies, immunostaining of normal embryonic human ureters detected TGFβRI and TGFβRII in urothelia. Collectively, these observations reveal unsuspected regulatory roles for endogenous TGFβ in embryonic ureters, fine-tuning morphogenesis and functional differentiation. Our results also support the hypothesis that the TGFβ up-regulation reported in ureter malformations impacts on pathobiology. Further experiments are needed to unravel the intracellular signalling mechanisms involved in these dysmorphic responses. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

3D organoid-derived human glomeruli for personalised podocyte disease modelling and drug screening

The podocytes within the glomeruli of the kidney maintain the filtration barrier by forming interdigitating foot processes with intervening slit diaphragms, disruption in which results in proteinuria. Studies into human podocytopathies to date have employed primary or immortalised podocyte cell lines cultured in 2D. Here we compare 3D human glomeruli sieved from induced pluripotent stem cell-derived kidney organoids with conditionally immortalised human podocyte cell lines, revealing improved podocyte-specific gene expression, maintenance in vitro of polarised protein localisation and an improved glomerular basement membrane matrisome compared to 2D cultures. Organoid-derived glomeruli retain marker expression in culture for 96 h, proving amenable to toxicity screening. In addition, 3D organoid glomeruli from a congenital nephrotic syndrome patient with compound heterozygous NPHS1 mutations reveal reduced protein levels of both NEPHRIN and PODOCIN. Hence, human iPSC-derived organoid glomeruli represent an accessible approach to the in vitro modelling of human podocytopathies and screening for podocyte toxicity.

Studies examining human podocytopathies have utilised 2D cultured primary or immortalised podocyte cell lines. Here, the authors demonstrate that 3D human glomeruli sieved from induced pluripotent stem cell-derived kidney organoids retain an improved podocyte identity in vitro facilitating disease modelling and toxicity testing.

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.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

Novel Insights into the Pathogenesis of Monogenic Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidneys and urinary tract (CAKUT) comprise a large spectrum of congenital malformations ranging from severe manifestations, such as renal agenesis, to potentially milder conditions, such as vesicoureteral reflux. CAKUT causes approximately 40% of ESRD that manifests within the first three decades of life. Several lines of evidence indicate that CAKUT is often caused by recessive or dominant mutations in single (monogenic) genes. To date, approximately 40 monogenic genes are known to cause CAKUT if mutated, explaining 5%-20% of patients. However, hundreds of different monogenic CAKUT genes probably exist. The discovery of novel CAKUT-causing genes remains challenging because of this pronounced heterogeneity, variable expressivity, and incomplete penetrance. We here give an overview of known genetic causes for human CAKUT and shed light on distinct renal morphogenetic pathways that were identified as relevant for CAKUT in mice and humans.

Renal development in the fetus and premature infant

Congenital abnormalities of the kidney and urinary tract (CAKUT) are one of the leading congenital defects to be identified on prenatal ultrasound. CAKUT represent a broad spectrum of abnormalities, from transient hydronephrosis to severe bilateral renal agenesis. CAKUT are a major contributor to chronic and end stage kidney disease (CKD/ESKD) in children. Prenatal imaging is useful to identify CAKUT, but will not detect all defects. Both genetic abnormalities and the fetal environment contribute to CAKUT. Monogenic gene mutations identified in human CAKUT have advanced our understanding of molecular mechanisms of renal development. Low nephron number and solitary kidneys are associated with increased risk of adult onset CKD and ESKD. Premature and low birth weight infants represent a high risk population for low nephron number. Additional research is needed to identify biomarkers and appropriate follow-up of premature and low birth weight infants into adulthood.

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.

Genetic Syndromes Affecting Kidney Development

Renal anomalies are common birth defects that may manifest as a wide spectrum of anomalies from hydronephrosis (dilation of the renal pelvis and calyces) to renal aplasia (complete absence of the kidney(s)). Aneuploidies and mosaicisms are the most common syndromes associated with CAKUT. Syndromes with single gene and renal developmental defects are less common but have facilitated insight into the mechanism of renal and other organ development. Analysis of underlying genetic mutations with transgenic and mutant mice has also led to advances in our understanding of mechanisms of renal development.

Pharyngeal morphogenesis requires fras1-itga8-dependent epithelial-mesenchymal interaction

Both Fras1 and Itga8 connect mesenchymal cells to epithelia by way of an extracellular 'Fraser protein complex' that functions in signaling and adhesion; these proteins are vital to the development of several vertebrate organs. We previously found that zebrafish fras1 mutants have craniofacial defects, specifically, shortened symplectic cartilages and cartilage fusions that spare joint elements. During a forward mutagenesis screen, we identified a new zebrafish mutation, b1161, that we show here disrupts itga8, as confirmed using CRISPR-generated itga8 alleles. fras1 and itga8 single mutants and double mutants have similar craniofacial phenotypes, a result expected if loss of either gene disrupts function of the Fraser protein complex. Unlike fras1 mutants or other Fraser-related mutants, itga8 mutants do not show blistered tail fins. Thus, the function of the Fraser complex differs in the craniofacial skeleton and the tail fin. Focusing on the face, we find that itga8 mutants consistently show defective outpocketing of a late-forming portion of the first pharyngeal pouch, and variably express skeletal defects, matching previously characterized fras1 mutant phenotypes. In itga8 and fras1 mutants, skeletal severity varies markedly between sides, indicating that both mutants have increased developmental instability. Whereas fras1 is expressed in epithelia, we show that itga8 is expressed complementarily in facial mesenchyme. Paired with the observed phenotypic similarity, this expression indicates that the genes function in epithelial-mesenchymal interactions. Similar interactions between Fras1 and Itga8 have previously been found in mouse kidney, where these genes both regulate Nephronectin (Npnt) protein abundance. We find that zebrafish facial tissues express both npnt and the Fraser gene fibrillin2b (fbn2b), but their transcript levels do not depend on fras1 or itga8 function. Using a revertible fras1 allele, we find that the critical window for fras1 function in the craniofacial skeleton is between 1.5 and 3 days post fertilization, which coincides with the onset of fras1-dependent and itga8-dependent morphogenesis. We propose a model wherein Fras1 and Itga8 interact during late pharyngeal pouch morphogenesis to sculpt pharyngeal arches through epithelial-mesenchymal interactions, thereby stabilizing the developing craniofacial skeleton.

Syndactyly in a novel Fras1(rdf) mutant results from interruption of signals for interdigital apoptosis

BACKGROUND

Fras1 encodes an extracellular matrix protein that is critical for the establishment of the epidermal basement membrane during gestation. In humans, mutations in FRAS1 cause Fraser Syndrome (FS), a pleiotropic condition with many clinical presentations such as limb, eye, kidney, and craniofacial deformations. Many of these defects are mimicked by loss of Fras1 in mice, and are preceded by the formation of epidermal blisters in utero.

RESULTS

In this study, we identified a novel ENU-derived rounded foot (rdf) mouse mutant with highly penetrant hindlimb soft-tissue syndactyly, among other structural defects. Mapping and sequencing revealed that rdf is a novel loss-of-function nonsense allele of Fras1 (Fras1(rdf)). Focusing on the limb, we found that the Fras1(rdf) syndactyly phenotype originates from loss of interdigital cell death (ICD). Despite normal expression of bone morphogenetic protein (BMP) ligands and their receptors, the BMP downstream target gene Msx2, which is also necessary and sufficient to promote ICD, was down-regulated in the interdigital regions of Fras1(rdf) hindlimb buds.

CONCLUSIONS

The close correlation between limb bud epidermal blistering, decreased Msx2 expression, and reduced ICD in the Fras1(rdf) hindlimb buds suggests that epithelium detachment from the mesenchyme may create a physical gap that interrupts the transmission of BMP, among other signals, resulting in soft tissue syndactyly.

From gene discovery to new biological mechanisms: heparanases and congenital urinary bladder disease

We present a scientific investigation into the pathogenesis of a urinary bladder disease. The disease in question is called urofacial syndrome (UFS), a congenital condition inherited in an autosomal recessive manner. UFS features incomplete urinary bladder emptying and vesicoureteric reflux, with a high risk of recurrent urosepsis and end-stage renal disease. The story starts from a human genomic perspective, then proceeds through experiments that seek to determine the roles of the implicated molecules in embryonic frogs and newborn mice. A future aim would be to use such biological knowledge to intelligently choose novel therapies for UFS. We focus on heparanase proteins and the peripheral nervous system, molecules and tissues that appear to be key players in the pathogenesis of UFS and therefore must also be critical for functional differentiation of healthy bladders. These considerations allow the envisioning of novel biological treatments, although the potential difficulties of targeting the developing bladder in vivo should not be underestimated.

Transcriptional landscape of glomerular parietal epithelial cells

Very little is known about the function of glomerular parietal epithelial cells (PECs). In this study, we performed genome-wide expression analysis on PEC-enriched capsulated vs. PEC-deprived decapsulated rat glomeruli to determine the transcriptional state of PECs under normal conditions. We identified hundreds of differentially expressed genes that mapped to distinct biologic modules including development, tight junction, ion transport, and metabolic processes. Since developmental programs were highly enriched in PECs, we characterized several of their candidate members at the protein level. Collectively, our findings confirm that PECs are multifaceted cells and help define their diverse functional repertoire.

Mild recessive mutations in six Fraser syndrome-related genes cause isolated congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) account for approximately 40% of children with ESRD in the United States. Hitherto, mutations in 23 genes have been described as causing autosomal dominant isolated CAKUT in humans. However, >90% of cases of isolated CAKUT still remain without a molecular diagnosis. Here, we hypothesized that genes mutated in recessive mouse models with the specific CAKUT phenotype of unilateral renal agenesis may also be mutated in humans with isolated CAKUT. We applied next-generation sequencing technology for targeted exon sequencing of 12 recessive murine candidate genes in 574 individuals with isolated CAKUT from 590 families. In 15 of 590 families, we identified recessive mutations in the genes FRAS1, FREM2, GRIP1, FREM1, ITGA8, and GREM1, all of which function in the interaction of the ureteric bud and the metanephric mesenchyme. We show that isolated CAKUT may be caused partially by mutations in recessive genes. Our results also indicate that biallelic missense mutations in the Fraser/MOTA/BNAR spectrum genes cause isolated CAKUT, whereas truncating mutations are found in the multiorgan form of Fraser syndrome. The newly identified recessive biallelic mutations in these six genes represent the molecular cause of isolated CAKUT in 2.5% of the 590 affected families in this study.

Integrin alpha 8 recessive mutations are responsible for bilateral renal agenesis in humans

Renal hypodysplasia (RHD) is a heterogeneous condition encompassing a spectrum of kidney development defects including renal agenesis, hypoplasia, and (cystic) dysplasia. Heterozygous mutations of several genes have been identified as genetic causes of RHD with various severity. However, these genes and mutations are not associated with bilateral renal agenesis, except for RET mutations, which could be involved in a few cases. The pathophysiological mechanisms leading to total absence of kidney development thus remain largely elusive. By using a whole-exome sequencing approach in families with several fetuses with bilateral renal agenesis, we identified recessive mutations in the integrin α8-encoding gene ITGA8 in two families. Itga8 homozygous knockout in mice is known to result in absence of kidney development. We provide evidence of a damaging effect of the human ITGA8 mutations. These results demonstrate that mutations of ITGA8 are a genetic cause of bilateral renal agenesis and that, at least in some cases, bilateral renal agenesis is an autosomal-recessive disease.

PodNet, a protein-protein interaction network of the podocyte

Interactions between proteins crucially determine cellular structure and function. Differential analysis of the interactome may help elucidate molecular mechanisms during disease development; however, this analysis necessitates mapping of expression data on protein-protein interaction networks. These networks do not exist for the podocyte; therefore, we built PodNet, a literature-based mouse podocyte network in Cytoscape format. Using database protein-protein interactions, we expanded PodNet to XPodNet with enhanced connectivity. In order to test the performance of XPodNet in differential interactome analysis, we examined podocyte developmental differentiation and the effect of cell culture. Transcriptomes of podocytes in 10 different states were mapped on XPodNet and analyzed with the Cytoscape plugin ExprEssence, based on the law of mass action. Interactions between slit diaphragm proteins are most significantly upregulated during podocyte development and most significantly downregulated in culture. On the other hand, our analysis revealed that interactions lost during podocyte differentiation are not regained in culture, suggesting a loss rather than a reversal of differentiation for podocytes in culture. Thus, we have developed PodNet as a valuable tool for differential interactome analysis in podocytes, and we have identified established and unexplored regulated interactions in developing and cultured podocytes.

Novel frem1-related mouse phenotypes and evidence of genetic interactions with gata4 and slit3

The FRAS1-related extracellular matrix 1 (FREM1) gene encodes an extracellular matrix protein that plays a critical role in the development of multiple organ systems. In humans, recessive mutations in FREM1 cause eye defects, congenital diaphragmatic hernia, renal anomalies and anorectal malformations including anteriorly placed anus. A similar constellation of findings-microphthalmia, cryptophthalmos, congenital diaphragmatic hernia, renal agenesis and rectal prolapse-have been described in FREM1-deficient mice. In this paper, we identify a homozygous Frem1 missense mutation (c.1687A>T, p.Ile563Phe) in an N-ethyl-N-nitrosourea (ENU)-derived mouse strain, crf11, with microphthalmia, cryptophthalmos, renal agenesis and rectal prolapse. This mutation affects a highly conserved residue in FREM1's third CSPG domain. The p.Ile563Phe change is predicted to be deleterious and to cause decreased FREM1 protein stability. The crf11 allele also fails to complement the previously described eyes2 allele of Frem1 (p.Lys826*) providing further evidence that the crf11 phenotype is due to changes affecting Frem1 function. We then use mice bearing the crf11 and eyes2 alleles to identify lung lobulation defects and decreased anogenital distance in males as novel phenotypes associated with FREM1 deficiency in mice. Due to phenotypic overlaps between FREM1-deficient mice and mice that are deficient for the retinoic acid-responsive transcription factor GATA4 and the extracellular matrix protein SLIT3, we also perform experiments to look for in vivo genetic interactions between the genes that encode these proteins. These experiments reveal that Frem1 interacts genetically with Gata4 in the development of lung lobulation defects and with Slit3 in the development of renal agenesis. These results demonstrate that FREM1-deficient mice faithfully recapitulate many of the phenotypes seen in individuals with FREM1 deficiency and that variations in GATA4 and SLIT3 expression modulate some FREM1-related phenotypes in mice.

Cell biology of ureter development

The mammalian ureter contains two main cell types: a multilayered water-tight epithelium called the urothelium, surrounded by smooth muscle layers that, by generating proximal to distal peristaltic waves, pump urine from the renal pelvis toward the urinary bladder. Here, we review the cellular mechanisms involved in the development of these tissues, and the molecules that control the process. We consider the relevance of these biologic findings for understanding the pathogenesis of human ureter malformations.

Sprouty1 haploinsufficiency prevents renal agenesis in a model of Fraser syndrome

Deficiency of the extracellular matrix molecule FRAS1, normally expressed by the ureteric bud, leads to bilateral renal agenesis in humans with Fraser syndrome and blebbed (Fras1(bl/bl)) mice. The metanephric mesenchyme of these mutants fails to express sufficient Gdnf, which activates receptor tyrosine kinase (RTK) signalling, contributing to the phenotype. To determine whether modulating RTK signalling may overcome the abnormal nephrogenesis characteristic of Fraser syndrome, we introduced a single null Sprouty1 allele into Fras1(bl/bl) mice, thereby reducing the ureteric bud's expression of this anti-branching molecule and antagonist of RTK signalling. This prevented renal agenesis in Fras1(bl/bl) mice, permitting kidney development and postnatal survival. We found that fibroblast growth factor (FGF) signalling contributed to this genetic rescue, and exogenous FGF10 rescued defects in Fras1(bl/bl) rudiments in vitro. Whereas wild-type metanephroi expressed FRAS1 and the related proteins FREM1 and FREM2, FRAS1 was absent and the other proteins were downregulated in rescued kidneys, consistent with a reciprocally stabilized FRAS1/FREM1/FREM2 complex. In addition to contributing to knowledge regarding events during nephrogenesis, the demonstrated rescue of renal agenesis in a model of a human genetic disease raises the possibility that enhancing growth factor signaling might be a therapeutic approach to ameliorate this devastating malformation.

Generation of mice with a conditional null Fraser syndrome 1 (Fras1) allele

Fraser syndrome (FS) is an autosomal recessive disease characterized by skin lesions and kidney and upper airway malformations. Fraser syndrome 1 (FRAS1) is an extracellular matrix protein, and FRAS1 homozygous mutations occur in some FS individuals. FRAS1 is expressed at the epithelial-mesenchymal interface in embryonic skin and kidney. blebbed mice have a null Fras1 mutation and phenocopy human FS. Like humans with FS, they exhibit a high fetal and neonatal mortality, precluding studies of FRAS1 functions in later life. We generated conditional Fras1 null allele mice. Cre-mediated generalized deletion of this allele generated embryonic skin blisters and renal agenesis characteristic of blebbed mice and human FS. Targeted deletion of Fras1 in kidney podocytes circumvented skin blistering, renal agenesis, and early death. FRAS1 expression was downregulated in maturing glomeruli which then became sclerotic. The data are consistent with the hypothesis that locally produced FRAS1 has roles in glomerular maturation and integrity. This conditional allele will facilitate study of possible role for FRAS1 in other tissues such as the skin.

Expression of Fraser syndrome genes in normal and polycystic murine kidneys

BACKGROUND

Fraser syndrome (FS) features renal agenesis and cystic kidneys. Mutations of FRAS1 (Fraser syndrome 1)and FREM2 (FRAS1-related extracellular matrix protein 2)cause FS. They code for basement membrane proteins expressed in metanephric epithelia where they mediate epithelial/mesenchymal signalling. Little is known about whether and where these molecules are expressed in more mature kidneys.

METHODS

In healthy and congenital polycystic kidney (cpk)mouse kidneys we sought Frem2 expression using a LacZ reporter gene and quantified Fras family transcripts. Fras1 immunohistochemistry was undertaken in cystic kidneys from cpk mice and PCK (Pkhd1 mutant) rats (models of autosomal recessive polycystic kidney disease) and in wildtype metanephroi rendered cystic by dexamethasone.

RESULTS

Nascent nephrons transiently expressed Frem2 in both tubule and podocyte epithelia. Maturing and adult collecting ducts also expressed Frem2. Frem2 was expressed in cpk cystic epithelia although Frem2 haploinsufficiency did not significantly modify cystogenesis in vivo. Fras1 transcripts were significantly upregulated, and Frem3 downregulated, in polycystic kidneys versus the non-cystic kidneys of littermates. Fras1 was immunodetected in cpk, PCK and dexamethasone-induced cystepithelia.

CONCLUSIONS

These descriptive results are consistent with the hypothesis that Fras family molecules play diverse roles in kidney epithelia. In future, this should be tested by conditional deletion of FS genes in nephron segments and collecting ducts.

Basement membrane assembly of the integrin α8β1 ligand nephronectin requires Fraser syndrome-associated proteins

QBRICK facilitates the integrin α8β1–dependent interactions of cells with basement membranes by regulating the basement membrane assembly of nephronectin.

Dysfunction of the basement membrane protein QBRICK provokes Fraser syndrome, which results in renal dysmorphogenesis, cryptophthalmos, syndactyly, and dystrophic epidermolysis bullosa through unknown mechanisms. Here, we show that integrin α8β1 binding to basement membranes was significantly impaired in Qbrick-null mice. This impaired integrin α8β1 binding was not a direct consequence of the loss of QBRICK, which itself is a ligand of integrin α8β1, because knock-in mice with a mutation in the integrin-binding site of QBRICK developed normally and do not exhibit any defects in integrin α8β1 binding. Instead, the loss of QBRICK significantly diminished the expression of nephronectin, an integrin α8β1 ligand necessary for renal development. In vivo, nephronectin associated with QBRICK and localized at the sublamina densa region, where QBRICK was also located. Collectively, these findings indicate that QBRICK facilitates the integrin α8β1–dependent interactions of cells with basement membranes by regulating the basement membrane assembly of nephronectin and explain why renal defects occur in Fraser syndrome.

Identification of two novel CAKUT-causing genes by massively parallel exon resequencing of candidate genes in patients with unilateral renal agenesis

Congenital abnormalities of the kidney and urinary tract (CAKUT) are the most frequent cause of chronic kidney disease in children, accounting for about half of all cases. Although many forms of CAKUT are likely caused by single-gene defects, mutations in only a few genes have been identified. In order to detect new contributing genes we pooled DNA from 20 individuals to amplify all 313 exons of 30 CAKUT candidate genes by PCR analysis and massively parallel exon resequencing. Mutation carriers were identified by Sanger sequencing. We repeated the analysis with 20 new patients to give a total of 29 with unilateral renal agenesis and 11 with other CAKUT phenotypes. Five heterozygous missense mutations were detected in 2 candidate genes (4 mutations in FRAS1 and 1 in FREM2) not previously implicated in non-syndromic CAKUT in humans. All of these mutations were absent from 96 healthy control individuals and had a PolyPhen score over 1.4, predicting possible damaging effects of the mutation on protein function. Recessive truncating mutations in FRAS1 and FREM2 were known to cause Fraser syndrome in humans and mice; however, a phenotype in heterozygous carriers has not been described. Thus, heterozygous missense mutations in FRAS1 and FREM2 cause non-syndromic CAKUT in humans.

Basement membranes in development and disease

Basement membranes (BMs) are specializations of the extracellular matrix that act as key mediators of development and disease. Their sheet like protein matrices typically serve to separate epithelial or endothelial cell layers from underlying mesenchymal tissues, providing both a biophysical support to overlying tissue as well as a hub to promote and regulate cell-cell and cell-protein interactions. In the latter context, the BM is increasingly being recognized as a mediator of growth factor interactions during development. In this review, we discuss recent findings regarding the structure of the BM and its roles in mediating the normal development of the embryo, and we examine congenital diseases affecting the BM which impact embryonic development and health in later life.

Renal malformations associated with mutations of developmental genes: messages from the clinic

Renal tract malformations (RTMs) account for about 40% of children with end-stage renal failure. RTMs can be caused by mutations of genes normally active in the developing kidney and lower renal tract. Moreover, some RTMs occur in the context of multi-organ malformation syndromes. For these reasons, and because genetic testing is becoming more widely available, pediatric nephrologists should work closely with clinical geneticists to make genetic diagnoses in children with RTMs, followed by appropriate family counseling. Here we highlight families with renal cysts and diabetes, renal coloboma and Fraser syndromes, and a child with microdeletion of chromosome 19q who had a rare combination of malformations. Such diagnoses provide families with often long-sought answers to the question "why was our child born with kidney disease". Precise genetic diagnoses will also help to define cohorts of children with RTMs for long-term clinical outcome studies.

Ureter myogenesis: putting Teashirt into context

After the basic shape of the mammalian ureter is established, its epithelia mature and a coat of smooth muscle cells differentiate around nascent urothelia. The ureter actively propels tubular fluid from the renal pelvis to the bladder, and this peristalsis, which starts in the fetal period, requires coordinated smooth muscle contraction. Teashirt-3 (Tshz3) is expressed in smooth muscle cell precursors that form the wall of the forming mammalian ureter. The Teashirt gene family was first identified in Drosophila where Teashirt (Tsh) protein acts as a transcription factor directing embryonic anterior-posterior patterning and leg and eye development. In fly embryonic renal tubules, Tsh is expressed in mesodermally derived stellate cells intercalating between principal cells, and a paralogue, tiptop, is expressed in forming tubules. Teashirt is a component of several gene networks in flies and it is notable that similar networks control mammalian renal tract development. Null mutation of Tshz3 in mice leads to failure of functional muscularization in the top of the ureter and this is followed by congenital hydronephrosis. A signaling pathway can be envisaged, starting with sonic hedgehog secreted by the nascent ureteric urothelium and ending with ureteric smooth muscle cell differentiation, with Tshz3 downstream of bone morphogenetic protein 4 and upstream of myocardin and smooth muscle cell contractile protein synthesis. The phenotype of Tshz3 mutant mice resembles that of human congenital pelviureteric junction obstruction, and we suggest these individuals may have mutations of genes encoding molecules in the differentiation pathway mediated by Tshz3.

Plumbing in the embryo: developmental defects of the urinary tracts

Kidney and urinary tract malformations are among the most frequent developmental defects identified in newborns. Ranging from asymptomatic to neonatal lethal, these malformations represent an important clinical challenge. Recent progress in understanding the developmental origin of urinary tract defects in the mouse and other animal models suggests a new framework for the interpretation of these defects in humans. Gene inactivation studies in mice provided invaluable information on the formation of the Wolffian duct, a central component of embryonic renal development, on ureter and kidney induction as well as on distal ureter maturation. All three developmental processes are crucial for normal urinary tract morphogenesis. A failure to complete these developmental steps is responsible for a spectrum of kidney and urinary tract malformations including renal agenesis, renal dysplasia, vesicoureteral reflux, hydroureter, hydronephrosis and ureterocele. Surprisingly, distal ureter maturation, the process by which the ureter is displaced from the Wolffian duct to its final position within the bladder wall, has only recently been characterized at the morphological level. Anomalies in this process are emerging as a major source of urinary tract developmental defects. This review is aimed at bridging the current knowledge on the morphological and molecular events identified in the mouse, together with clinical observations of urinary tract malformation in humans.

Genetic analyses reveal a requirement for Dicer1 in the mouse urogenital tract

Despite the increasing interest in other classes of small RNAs, microRNAs (miRNAs) remain the most widely investigated and have been shown to play a role in a number of different processes in mammals. Many studies investigating miRNA function focus on the processing enzyme Dicer1, which is an RNAseIII protein essential for the biogenesis of active miRNAs through its cleavage of precursor RNA molecules. General deletion of Dicer1 in the mouse confirms that miRNAs are essential for development because embryos lacking Dicer1 fail to reach the end of gastrulation. Here we investigate the role of Dicer1 in urogenital tract development. We utilised a conditional allele of the Dicer1 gene and two Cre-expressing lines, driven by HoxB7 and Amhr2, to investigate the effect of Dicer1 deletion on both male and female reproductive tract development. Data presented here highlight an essential role for Dicer1 in the correct morphogenesis and function of the female reproductive tract and confirm recent findings that suggest Dicer1 is required for female fertility. In addition, HoxB7:Cre-mediated deletion in ureteric bud derivatives leads to a spectrum of anomalies in both males and females, including hydronephrotic kidneys and kidney parenchymal cysts. Male reproductive tract development, however, remains largely unaffected in the absence of Dicer1. Thus, Dicer1 is required for development of the female reproductive tract and also normal kidney morphogenesis.