Role of fibroblast growth factor receptors 1 and 2 in the ureteric bud

Sea cucumbers: an emerging system in evo-devo

A challenge for evolutionary developmental (evo-devo) biology is to expand the breadth of research organisms used to investigate how animal diversity has evolved through changes in embryonic development. New experimental systems should couple a relevant phylogenetic position with available molecular tools and genomic resources. As a phylum of the sister group to chordates, echinoderms extensively contributed to our knowledge of embryonic patterning, organ development and cell-type evolution. Echinoderms display a variety of larval forms with diverse shapes, making them a suitable group to compare the evolution of embryonic developmental strategies. However, because of the laboratory accessibility and the already available techniques, most studies focus on sea urchins and sea stars mainly. As a comparative approach, the field would benefit from including information on other members of this group, like the sea cucumbers (holothuroids), for which little is known on the molecular basis of their development. Here, we review the spawning and culture methods, the available morphological and molecular information, and the current state of genomic and transcriptomic resources on sea cucumbers. With the goal of making this system accessible to the broader community, we discuss how sea cucumber embryos and larvae can be a powerful system to address the open questions in evo-devo, including understanding the origins of bilaterian structures.

Diverse Fgfr1 signaling pathways and endocytic trafficking regulate early mesoderm development

The Fibroblast growth factor (FGF) pathway is a conserved signaling pathway required for embryonic development. Activated FGF receptor 1 (FGFR1) drives multiple intracellular signaling cascade pathways, including ERK/MAPK and PI3K/AKT, collectively termed canonical signaling. However, unlike Fgfr1 null embryos, embryos containing hypomorphic mutations in Fgfr1 lacking the ability to activate canonical downstream signals are still able to develop to birth, but exhibit severe defects in all mesodermal-derived tissues. The introduction of an additional signaling mutation further reduces the activity of Fgfr1, leading to earlier lethality, reduced somitogenesis, and more severe changes in transcriptional outputs. Genes involved in migration, ECM-interaction, and phosphoinositol signaling were significantly downregulated, proteomic analysis identified changes in interactions with endocytic pathway components, and cells expressing mutant receptors show changes in endocytic trafficking. Together, we identify processes regulating early mesoderm development by mechanisms involving both canonical and non-canonical Fgfr1 pathways, including direct interaction with cell adhesion components and endocytic regulation.

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

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

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

BACKGROUND

The prorenin receptor (PRR) plays a critical role in ureteric bud (UB) branching morphogenesis. DOT1 Like (DOT1L), a histone methyltransferase specific for Histone 3 lysine 79 (H3K79), is important for differentiation of the UB-derived renal collecting duct cells. In this study, we tested whether DOT1L/H3 dimethyl K79 (H3m2K79) are regulated by PRR deletion in the UB and UB-derived collecting ducts in the embryonic mouse kidneys.

METHODS

Mutant Hoxb7Cre+/PRRflox/flox (PRRUB-/-) and control PRRUB+/+, mice were studied on embryonic (E) day E17.5. DOT1L mRNA and protein expression in the kidney was examined by real-time qRT-PCR and immunohistochemistry, respectively. H3m2K79 protein expression was determined by immunohistochemistry and Western blot analysis.

RESULTS

DOT1L mRNA levels were decreased in mutant compared to control mice (0.68 ± 0.06 vs. 1.0 ± 0.01, p < 0.01). DOT1L and H3m2K79 immunostaining was reduced in the mutant vs. control kidneys (Dot1: 0.62 ± 0.03 vs. 1.0 ± 0.01, p < 0.05; H3m2K79: 0.64 ± 0.04 vs.1.1 ± 0.01. p < 0.05.). Western blot analysis revealed decreased H3m2K79 protein levels in mutant compared to control kidneys (1.0 ± 0.06 vs. 1.5 ± 0.02, p < 0.05).

CONCLUSION

Targeted deletion of the PRR in the UB and UB-derived collecting ducts results in reduced DOT1L gene/protein and H3m2K79 protein expression in the embryonic mouse metanephroi in vivo.

IMPACT

The role of histone methylation in mediating the effect of the prorenin receptor on the ureteric bud branching (UB) morphogenesis and urine acidification during kidney development is unknown. We demonstrate that histone H3 lysine (K) 79 dimethylation by methyltransferase Dot1 is reduced in the embryonic kidney of mice that lack the prorenin receptor in the UB lineage.

Aberrant centrosome biogenesis disrupts nephron and collecting duct progenitor growth and fate resulting in fibrocystic kidney disease

Mutations that disrupt centrosome biogenesis or function cause congenital kidney developmental defects and fibrocystic pathologies. Yet how centrosome dysfunction results in the kidney disease phenotypes remains unknown. Here, we examined the consequences of conditional knockout of the ciliopathy gene Cep120, essential for centrosome duplication, in the nephron and collecting duct progenitor niches of the mouse embryonic kidney. Cep120 loss led to reduced abundance of both cap mesenchyme and ureteric bud populations, due to a combination of delayed mitosis, increased apoptosis and premature differentiation of progenitor cells. These defects resulted in dysplastic kidneys at birth, which rapidly formed cysts, displayed increased interstitial fibrosis and decline in kidney function. RNA sequencing of embryonic and postnatal kidneys from Cep120-null mice identified changes in the pathways essential for development, fibrosis and cystogenesis. Our study defines the cellular and developmental defects caused by centrosome dysfunction during kidney morphogenesis and identifies new therapeutic targets for patients with renal centrosomopathies.

ASH2L Controls Ureteric Bud Morphogenesis through the Regulation of RET/GFRA1 Signaling Activity in a Mouse Model

SIGNIFICANCE STATEMENT

Causes of congenital anomalies of the kidney and urinary tract (CAKUT) remain unclear. The authors investigated whether and how inactivation of Ash2l -which encodes a subunit of the COMPASS methyltransferase responsible for genome-wide histone H3 lysine K4 (H3K4) methylation-might contribute to CAKUT. In a mouse model, inactivation of Ash2l in the ureteric bud (UB) lineage led to CAKUT-like phenotypes. Removal of ASH2L led to deficient H3K4 trimethylation, which slowed cell proliferation at the UB tip, delaying budding and impairing branching morphogenesis. The absence of ASH2L also downregulated the expression of Ret , Gfra1 , and Wnt11 genes involved in RET/GFRA1 signaling. These findings identify ASH2L-mediated H3K4 methylation as an upstream epigenetic regulator of signaling crucial for UB morphogenesis and indicate that deficiency or dysregulation of these processes may lead to CAKUT.

BACKGROUND

Ureteric bud (UB) induction and branching morphogenesis are fundamental to the establishment of the renal architecture and are key determinants of nephron number. Defective UB morphogenesis could give rise to a spectrum of malformations associated with congenital anomalies of the kidney and urinary tract (CAKUT). Signaling involving glial cell line-derived neurotrophic factor and its receptor rearranged during transfection (RET) and coreceptor GFRA1 seems to be particularly important in UB development. Recent epigenome profiling studies have uncovered dynamic changes of histone H3 lysine K4 (H3K4) methylation during metanephros development, and dysregulated H3K4 methylation has been associated with a syndromic human CAKUT.

METHODS

To investigate whether and how inactivation of Ash2l , which encodes a subunit of the COMPASS methyltransferase responsible for genome-wide H3K4 methylation, might contribute to CAKUT, we inactivated Ash2l specifically from the UB lineage in C57BL/6 mice and examined the effects on genome-wide H3K4 methylation and metanephros development. Genes and epigenome changes potentially involved in these effects were screened using RNA-seq combined with Cleavage Under Targets and Tagmentation sequencing.

RESULTS

UB-specific inactivation of Ash2l caused CAKUT-like phenotypes mainly involving renal dysplasia at birth, which were associated with deficient H3K4 trimethylation. Ash2l inactivation slowed proliferation of cells at the UB tip, delaying budding and impairing UB branching morphogenesis. These effects were associated with downregulation of Ret , Gfra1 , and Wnt11 , which participate in RET/GFRA1 signaling.

CONCLUSIONS

These experiments identify ASH2L-dependent H3K4 methylation in the UB lineage as an upstream epigenetic regulator of RET/GFRA1 signaling in UB morphogenesis, which, if deficient, may lead to CAKUT.

Aberrations in FGFR1, FGFR2, and RIP5 Expression in Human Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)

This study aimed to explore the spatio-temporal expression patterns of congenital anomalies of kidney and urinary tract (CAKUT) candidate genes, Fibroblast Growth Factor Receptor 1 (FGFR1), Fibroblast Growth Factor Receptor 2 (FGFR2) and Receptor-Interacting Protein Kinase 5 (RIP5), in human fetal kidney development (CTRL) and kidneys affected with CAKUT. Human fetal kidneys from the 22nd to 41st developmental week (duplex, hypoplastic, dysplastic, and controls) were stained with antibodies and analyzed by epifluorescence microscopy and RT-qPCR. The effect of CAKUT candidate genes on kidney nephrogenesis and function is confirmed by statistically significant variations in the spatio-temporal expression patterns of the investigated markers. The nuclear localization of FGFR1, elevated expression score of FGFR1 mRNA, the increased area percentage of FGFR1-positive cells in the kidney cortex, and the overall decrease in the expression after the peak at the 27th developmental week in dysplastic kidneys (DYS), suggest an altered expression pattern and protein function in response to CAKUT pathophysiology. The RT-qPCR analysis revealed a significantly higher FGFR2 mRNA expression score in the CAKUT kidneys compared to the CTRL. This increase could be due to the repair mechanism involving the downstream mediator, Extracellular Signal-Regulated Kinase 1/2 (ERK1/2). The expression of RIP5 during normal human kidney development was reduced temporarily, due to urine production and increased later since it undertakes additional functions in the maturation of the postnatal kidney and homeostasis, while the expression dynamics in CAKUT-affected kidneys exhibited a decrease in the percentage of RIP5-positive cells during the investigated developmental period. Our findings highlight the importance of FGFR1, FGFR2, and RIP5 as markers in normal and pathological kidney development.

Rac1 deficiency impairs postnatal development of the renal papilla

Development of the renal medulla continues after birth to form mature renal papilla and obtain urine-concentrating ability. Here, we found that a small GTPase, Rac1, plays a critical role in the postnatal development of renal papilla. Mice with distal tubule-specific deletion of Rac1 reached adulthood but showed polydipsia and polyuria with an impaired ability to concentrate urine. The elongation of renal papilla that occurs in the first weeks after birth was impaired in the Rac1-deficient infants, resulting in shortening and damage of the renal papilla. Moreover, the osmoprotective signaling mediated by nuclear factor of activated T cells 5, which is a key molecule of osmotic response to osmotic stress in renal medulla, was significantly impaired in the kidneys of the Rac1-deficient infants. These results demonstrate that Rac1 plays an important role in the development of renal papilla in the postnatal period, and suggested a potential link between Rac1 and osmotic response.

Comparative whole-genome transcriptome analysis in renal cell populations reveals high tissue specificity of MAPK/ERK targets in embryonic kidney

Background

MAPK/ERK signaling is a well-known mediator of extracellular stimuli controlling intracellular responses to growth factors and mechanical cues. The critical requirement of MAPK/ERK signaling for embryonic stem cell maintenance is demonstrated, but specific functions in progenitor regulation during embryonic development, and in particular kidney development remain largely unexplored. We previously demonstrated MAPK/ERK signaling as a key regulator of kidney growth through branching morphogenesis and normal nephrogenesis where it also regulates progenitor expansion. Here, we performed RNA sequencing-based whole-genome expression analysis to identify transcriptional MAPK/ERK targets in two distinct renal populations: the ureteric bud epithelium and the nephron progenitors.

Results

Our analysis revealed a large number (5053) of differentially expressed genes (DEGs) in nephron progenitors and significantly less (1004) in ureteric bud epithelium, reflecting likely heterogenicity of cell types. The data analysis identified high tissue-specificity, as only a fraction (362) of MAPK/ERK targets are shared between the two tissues. Tissue-specific MAPK/ERK targets participate in the regulation of mitochondrial energy metabolism in nephron progenitors, which fail to maintain normal mitochondria numbers in the MAPK/ERK-deficient tissue. In the ureteric bud epithelium, a dramatic decline in progenitor-specific gene expression was detected with a simultaneous increase in differentiation-associated genes, which was not observed in nephron progenitors. Our experiments in the genetic model of MAPK/ERK deficiency provide evidence that MAPK/ERK signaling in the ureteric bud maintains epithelial cells in an undifferentiated state. Interestingly, the transcriptional targets shared between the two tissues studied are over-represented by histone genes, suggesting that MAPK/ERK signaling regulates cell cycle progression and stem cell maintenance through chromosome condensation and nucleosome assembly.

Conclusions

Using tissue-specific MAPK/ERK inactivation and RNA sequencing in combination with experimentation in embryonic kidneys, we demonstrate here that MAPK/ERK signaling maintains ureteric bud tip cells, suggesting a regulatory role in collecting duct progenitors. We additionally deliver new mechanistic information on how MAPK/ERK signaling regulates progenitor maintenance through its effects on chromatin accessibility and energy metabolism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01309-z.

Immunohistochemical Expression Pattern of FGFR1, FGFR2, RIP5, and HIP2 in Developing and Postnatal Kidneys of Dab1-/- (yotari) Mice

This study aimed to explore how Dab1 gene functional silencing influences the spatial and temporal expression patterns of fibroblast growth factor receptor 1 (FGFR1), fibroblast growth factor receptor 2 (FGFR2), receptor-interacting protein kinase 5 (RIP5), and huntingtin-interacting protein 2 (HIP2) in the developing and postnatal kidneys of the yotari mice as potential determinants of normal kidney formation and function. Dab1^-/- animal kidneys exhibit diminished FGFR1/FGFR2 expression in all examined developmental stages, whereas RIP5 cell immunoreactivity demonstrated negligible variation. The HIP2 expression revealed a discernible difference during the postnatal period, where we noted a significant decrease in almost all the observed kidney structures of yotari animals. An extracellular signal-regulated kinase (Erk1/2) and mammalian target of rapamycin (mTOR) expression in yotari kidneys decreased in embryonic and postnatal developmental phases for which we can hypothesize that the Erk1/2 signaling pathway in the yotari mice kidneys is dependent on Reelin with Dab1 only partially implicated in Reelin-mediated MEK/Erk1/2 activation. The impairment of FGFR1 and FGFR2 expression suggests the involvement of the observed markers in generating the CAKUT phenotype resulting in renal hypoplasia. Our study demonstrates the critical role of HIP2 in reducing cell death throughout nephrogenesis and maturation in wild-type mice and indicates a possible connection between decreased HIP2 expression in postnatal kidney structures and observed podocyte injury in yotari. Our results emphasize the crucial function of the examined markers throughout normal kidney development and their potential participation in kidney pathology and diagnostics, where they might serve as biomarkers and therapeutic targets.

FGFR2 signaling enhances the SHH-BMP4 signaling axis in early ureter development

The patterned array of basal, intermediate and superficial cells in the urothelium of the mature ureter arises from uncommitted epithelial progenitors of the distal ureteric bud. Urothelial development requires signaling input from surrounding mesenchymal cells, which, in turn, depend on cues from the epithelial primordium to form a layered fibro-muscular wall. Here, we have identified FGFR2 as a crucial component in this reciprocal signaling crosstalk in the murine ureter. Loss of Fgfr2 in the ureteric epithelium led to reduced proliferation, stratification, intermediate and basal cell differentiation in this tissue, and affected cell survival and smooth muscle cell differentiation in the surrounding mesenchyme. Loss of Fgfr2 impacted negatively on epithelial expression of Shh and its mesenchymal effector gene Bmp4. Activation of SHH or BMP4 signaling largely rescued the cellular defects of mutant ureters in explant cultures. Conversely, inhibition of SHH or BMP signaling in wild-type ureters recapitulated the mutant phenotype in a dose-dependent manner. Our study suggests that FGF signals from the mesenchyme enhance, via epithelial FGFR2, the SHH-BMP4 signaling axis to drive urothelial and mesenchymal development in the early ureter.

Fibroblast growth factor and kidney disease: Updates for emerging novel therapeutics

The discovery of fibroblast growth factors (FGFs) and fibroblast growth factor receptors (FGFRs) provided a profound new insight into physiological and metabolic functions. FGF has a large family by having divergent structural elements and enable functional divergence and specification. FGF and FGFRs are highly expressed during kidney development. Signals from the ureteric bud regulate morphogenesis, nephrogenesis, and nephron progenitor survival. Thus, FGF signaling plays an important role in kidney progenitor cell aggregation at the sites of new nephron formation. This review will summarize the current knowledge about functions of FGF signaling in kidney development and their ability to promote regeneration in injured kidneys and its use as a biomarker and therapeutic target in kidney diseases. Further studies are essential to determine the predictive significance of the various FGF/FGFR deviations and to integrate them into clinical algorithms.

Organ-Specific Branching Morphogenesis

A common developmental process, called branching morphogenesis, generates the epithelial trees in a variety of organs, including the lungs, kidneys, and glands. How branching morphogenesis can create epithelial architectures of very different shapes and functions remains elusive. In this review, we compare branching morphogenesis and its regulation in lungs and kidneys and discuss the role of signaling pathways, the mesenchyme, the extracellular matrix, and the cytoskeleton as potential organ-specific determinants of branch position, orientation, and shape. Identifying the determinants of branch and organ shape and their adaptation in different organs may reveal how a highly conserved developmental process can be adapted to different structural and functional frameworks and should provide important insights into epithelial morphogenesis and developmental disorders.

Planar cell polarity pathway in kidney development, function and disease

Planar cell polarity (PCP) refers to the coordinated orientation of cells in the tissue plane. Originally discovered and studied in Drosophila melanogaster, PCP is now widely recognized in vertebrates, where it is implicated in organogenesis. Specific sets of PCP genes have been identified. The proteins encoded by these genes become asymmetrically distributed to opposite sides of cells within a tissue plane and guide many processes that include changes in cell shape and polarity, collective cell movements or the uniform distribution of cell appendages. A unifying characteristic of these processes is that they often involve rearrangement of actomyosin. Mutations in PCP genes can cause malformations in organs of many animals, including humans. In the past decade, strong evidence has accumulated for a role of the PCP pathway in kidney development including outgrowth and branching morphogenesis of ureteric bud and podocyte development. Defective PCP signalling has been implicated in the pathogenesis of developmental kidney disorders of the congenital anomalies of the kidney and urinary tract spectrum. Understanding the origins, molecular constituents and cellular targets of PCP provides insights into the involvement of PCP molecules in normal kidney development and how dysfunction of PCP components may lead to kidney disease.

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.

Targeted disruption of the histone lysine 79 methyltransferase Dot1L in nephron progenitors causes congenital renal dysplasia

The epigenetic regulator Dot1, the only known histone H3K79 methyltransferase, has a conserved role in organismal development and homoeostasis. In yeast, Dot1 is required for telomeric silencing and genomic integrity. In Drosophila, Dot1 (Grappa) regulates homoeotic gene expression. Dysregulation of DOT1L (human homologue of Dot1) causes leukaemia and is implicated in dilated cardiomyopathy. In mice, germline disruption of Dot1L and loss of H3K79me2 disrupt vascular and haematopoietic development. Targeted inactivation of Dot1L in principal cells of the mature collecting duct affects terminal differentiation and cell type patterning. However, the role of H3K79 methylation in mammalian tissue development has been questioned, as it is dispensable in the intestinal epithelium, a rapidly proliferating tissue. Here, we used lineage-specific Cre recombinase to delineate the role of Dot1L methyltransferase activity in the mouse metanephric kidney, an organ that develops via interactions between ureteric epithelial (Hoxb7) and mesenchymal (Six2) cell lineages. The results demonstrate that Dot1L^Hoxb7 is dispensable for ureteric bud branching morphogenesis. In contrast, Dot1L^Six2 is critical for the maintenance and differentiation of Six2+ progenitors into epithelial nephrons. Dot1LSix2 mutant kidneys exhibit congenital nephron deficit and cystic dysplastic kidney disease. Molecular analysis implicates defects in key renal developmental regulators, such as Lhx1, Pax2 and Notch. We conclude that the developmental functions of Dot1L-H3K79 methylation in the kidney are lineage-restricted. The link between H3K79me and renal developmental pathways reaffirms the importance of chromatin-based mechanisms in organogenesis.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Mdm4 controls ureteric bud branching via regulation of p53 activity

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

Tubule-Specific Mst1/2 Deficiency Induces CKD via YAP and Non-YAP Mechanisms

BACKGROUND

The serine/threonine kinases MST1 and MST2 are core components of the Hippo pathway, which has been found to be critically involved in embryonic kidney development. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are the pathway's main effectors. However, the biologic functions of the Hippo/YAP pathway in adult kidneys are not well understood, and the functional role of MST1 and MST2 in the kidney has not been studied.

METHODS

We used immunohistochemistry to examine expression in mouse kidneys of MST1 and MST2, homologs of Hippo in Drosophila. We generated mice with tubule-specific double knockout of Mst1 and Mst2 or triple knockout of Mst1, Mst2, and Yap. PCR array and mouse inner medullary collecting duct cells were used to identify the primary target of Mst1/Mst2 deficiency.

RESULTS

MST1 and MST2 were predominantly expressed in the tubular epithelial cells of adult kidneys. Deletion of Mst1/Mst2 in renal tubules increased activity of YAP but not TAZ. The kidneys of mutant mice showed progressive inflammation, tubular and glomerular damage, fibrosis, and functional impairment; these phenotypes were largely rescued by deletion of Yap in renal tubules. TNF-α expression was induced via both YAP-dependent and YAP-independent mechanisms, and TNF-α and YAP amplified the signaling activities of each other in the tubules of kidneys with double knockout of Mst1/Mst2.

CONCLUSIONS

Our findings show that tubular Mst1/Mst2 deficiency leads to CKD through both the YAP and non-YAP pathways and that tubular YAP activation induces renal fibrosis. The pathogenesis seems to involve the reciprocal stimulation of TNF-α and YAP signaling activities.

Differential role of planar cell polarity gene Vangl2 in embryonic and adult mammalian kidneys

Planar cell polarity (PCP) pathway is crucial for tissue morphogenesis. Mutations in PCP genes cause multi-organ anomalies including dysplastic kidneys. Defective PCP signaling was postulated to contribute to cystogenesis in polycystic kidney disease. This work was undertaken to elucidate the role of the key PCP gene, Vangl2, in embryonic and postnatal renal tubules and ascertain whether its loss contributes to cyst formation and defective tubular function in mature animals. We generated mice with ubiquitous and collecting duct-restricted excision of Vangl2. We analyzed renal tubules in mutant and control mice at embryonic day E17.5 and postnatal days P1, P7, P30, P90, 6- and 9-month old animals. The collecting duct functions were analyzed in young and adult mutant and control mice. Loss of Vangl2 leads to profound tubular dilatation and microcysts in embryonic kidneys. Mechanistically, these abnormalities are caused by defective convergent extension (larger tubular cross-sectional area) and apical constriction (cuboidal cell shape and a reduction of activated actomyosin at the luminal surface). However, the embryonic tubule defects were rapidly resolved by Vangl2-independent mechanisms after birth. Normal collecting duct architecture and functions were found in young and mature animals. During embryogenesis, Vangl2 controls tubular size via convergent extension and apical constriction. However, rapidly after birth, PCP-dependent control of tubular size is switched to a PCP-independent regulatory mechanism. We conclude that loss of the Vangl2 gene is dispensable for tubular elongation and maintenance postnatally. It does not lead to cyst formation and is unlikely to contribute to polycystic kidney disease.

FGF/FGFR2 Protects against Tubular Cell Death and Acute Kidney Injury Involving Erk1/2 Signaling Activation

Background

Fibroblast growth factors (FGFs) are heparin-binding proteins involved in a variety of biological processes, and part of them may act through binding with cell membrane receptor FGFR2.

Objectives

To clarify the role and mechanisms of FGFR2 signaling in tubular cell survival and acute kidney injury (AKI).

Method

In this study, kidney ischemia/reperfusion (IR) or cisplatin injection was used to induce AKI in mice.

Results

In the kidneys after IR or cisplatin injection, the expression of FGFs and Erk1/2 phosphorylation were elevated. To investigate the role of FGFs in tubular cell survival and AKI, a mouse model with tubular cell specific FGFR2 gene disruption was generated. The knockouts were born normal. At 2 months of age, about one-third of the knockouts developed mild hydronephrosis. Ablation of FGFR2 in tubular cells aggravated acute kidney dysfunction as well as tubular cell apoptosis induced by IR or cisplatin. In addition, Erk1/2 phosphorylation was less in the knockout kidneys than in control littermates at day 1 after cisplatin injection. In cultured NRK-52E cells, recombinant FGF2 protein induced Erk1/2 phosphorylation and inhibited cisplatin-induced cell death. PD98059 abolished Erk1/2 phosphorylation and partly reversed the protective effect of FGF2 on cisplatin-induced cell death.

Conclusions

This study indicates that FGF/FGFR2 signaling plays an important role in protecting against tubular cell death and AKI, which is partly through stimulating Erk1/2 activation.

Immunohistochemical expression pattern of RIP5, FGFR1, FGFR2 and HIP2 in the normal human kidney development

AIM

Present study analyses the co-localisation of RIP5 with FGFR1, FGFR2 and HIP2 in the developing kidney, as RIP5 is a major determinant of urinary tract development, downstream of FGF-signaling.

METHODS

Paraffin embedded human kidney tissues of 16 conceptuses between the 6th-22th developmental week were analysed using double-immunofluorescence method with RIP5/FGFR1/FGFR2 and HIP2 markers. Quantification of positive cells were performed using Kruskal-Wallis test.

RESULTS

In the 6th week of kidney development RIP5 (89.6%) and HIP2 (39.6%) are strongly expressed in the metanephric mesenchyme. FGFR1 shows moderate/strong expression in the developing nephrons (87.3%) and collecting ducts (70.5%) (p < 0.05). RIP5/FGFR1 co-localized at the marginal zone and the ureteric bud with predominant FGFR1 expression. FGFR2 (26.1%) shows similar expression pattern as FGFR1 (70.5%) in the same kidney structures. RIP5/FGFR2 co-localized at the marginal zone and the collecting ducts (predominant expression of FGFR2). HIP2 is strongly expressed in collecting ducts (96.7%), and co-localized with RIP5. In 10th week, RIP5 expression decrease (74.2%), while the pattern of expression of RIP5 and FGFR1 in collecting ducts (33.4% and 91.9%) and developing nephrons (21.9% and 32.4%) (p < 0.05) is similar to that in the 6th developmental week. Ureter is moderately expressing RIP5 while FGFR1 is strongly expressed in the ureteric wall. FGFR2 is strongly expressed in the collecting ducts (84.3%) and ureter. HIP2 have 81.1% positive cells in the collecting duct. RIP5/FGFR1 co-localize in collecting ducts and Henley's loop.

CONCLUSIONS

The expression pattern of RIP5, FGFR1, FGFR2 and HIP2 in the human kidney development might indicate their important roles in metanephric development and ureteric muscle layer differentiation through FGF signaling pathways.

Morphogenesis of the kidney and lung requires branch-tip directed activity of the Adamts18 metalloprotease

Adamts18 encodes a secreted metalloprotease restricted to branch-tip progenitor pools directing the morphogenesis of multiple mammalian organs. Adamts18 was targeted to explore a potential role in branching morphogenesis. In the kidney, an arborized collecting system develops through extensive branching morphogenesis of an initial epithelial outgrowth of the mesonephric duct, the ureteric bud. Adamts18 mutants displayed a weakly penetrant phenotype: duplicated ureteric outgrowths forming enlarged, bi-lobed kidneys with an increased nephron endowment. In contrast, Adamts18 mutants showed a fully penetrant lung phenotype: epithelial growth was markedly reduced and early secondary branching scaled to the reduced length of the primary airways. Furthermore, there was a pronounced delay in the appearance of differentiated cell types in both proximal and distally positions of the developing airways. Adamts18 is closely related to Adamts16. In the kidney but not the lung, broad epithelial Adamts16 expression overlaps Adamts18 in branch tips. However, compound Adamts16/18 mutants displayed a comparable low penetrance duplicated ureteric phenotype, ruling out a possible role for Adamts16 as a functional modifier of the Adamts18 kidney phenotype. Given the predicted action of secreted Adamts18 metalloprotease, and broad expression of Adamts18 in branching organ systems, these findings suggest distinct requirements for matrix modelling in the morphogenesis of epithelial networks.

Generating Genetic Mosaic Mouse Embryos or Organoids for Studies of Kidney Development

For studies of gene function during development, it can be very useful to generate mosaic embryos in which a small subset of cells in a given cell lineage lacks a gene of interest and carries a marker that allows the mutant cells to be specifically visualized and compared to wild-type cells. Several methods have been used to generate genetically mosaic mouse kidneys for such studies. These include (1) chimeric embryos generated using embryonic stem cells, (2) chimeric renal organoids generated by dissociation and reaggregation of the fetal kidneys, (3) generation of a knockout allele with a built-in reporter gene, (4) mosaic analysis with double markers (MADM), and (5) mosaic mutant analysis with spatial and temporal control of recombination (MASTR). In this chapter, these five methods are described, and their advantages and disadvantages are discussed.

Fibroblast growth factor signaling mediates progenitor cell aggregation and nephron regeneration in the adult zebrafish kidney

The zebrafish kidney regenerates after injury by development of new nephrons from resident adult kidney stem cells. Although adult kidney progenitor cells have been characterized by transplantation and single cell RNA seq, signals that stimulate new nephron formation are not known. Here we demonstrate that fibroblast growth factors and FGF signaling is rapidly induced after kidney injury and that FGF signaling is required for recruitment of progenitor cells to sites of new nephron formation. Chemical or dominant negative blockade of Fgfr1 prevented formation of nephron progenitor cell aggregates after injury and during kidney development. Implantation of FGF soaked beads induced local aggregation of lhx1a:EGFP  ​+ ​kidney progenitor cells. Our results reveal a previously unexplored role for FGF signaling in recruitment of renal progenitors to sites of new nephron formation and suggest a role for FGF signaling in maintaining cell adhesion and cell polarity in newly forming kidney epithelia.

Roscovitine blocks collecting duct cyst growth in Cep164-deficient kidneys

Nephronophthisis is an autosomal recessive kidney disease with high genetic heterogeneity. Understanding the functions of the individual genes contributing to this disease is critical for delineating the pathomechanisms of this disorder. Here, we investigated kidney function of a novel gene associated with nephronophthisis, CEP164, coding a centriolar distal appendage protein, using a Cep164 knockout mouse model. Collecting duct-specific deletion of Cep164 abolished primary cilia from the collecting duct epithelium and led to rapid postnatal cyst growth in the kidneys. Cell cycle and biochemical studies revealed that tubular hyperproliferation is the primary mechanism that drives cystogenesis in the kidneys of these mice. Administration of roscovitine, a cell cycle inhibitor, blocked cyst growth in the cortical collecting ducts and preserved kidney parenchyma in Cep164 knockout mice. Thus, our findings provide evidence that therapeutic modulation of cell cycle activity can be an effective approach to prevent cyst progression in the kidney.

MAPK/ERK Signaling in Regulation of Renal Differentiation

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

Development of the urogenital system is regulated via the 3'UTR of GDNF

Mechanisms controlling ureter lenght and the position of the kidney are poorly understood. Glial cell-line derived neurotrophic factor (GDNF) induced RET signaling is critical for ureteric bud outgrowth, but the function of endogenous GDNF in further renal differentiation and urogenital system development remains discursive. Here we analyzed mice where 3′ untranslated region (UTR) of GDNF is replaced with sequence less responsive to microRNA-mediated regulation, leading to increased GDNF expression specifically in cells naturally transcribing Gdnf. We demonstrate that increased Gdnf leads to short ureters in kidneys located in an abnormally caudal position thus resembling human pelvic kidneys. High GDNF levels expand collecting ductal progenitors at the expense of ureteric trunk elongation and result in expanded tip and short trunk phenotype due to changes in cell cycle length and progenitor motility. MEK-inhibition rescues these defects suggesting that MAPK-activity mediates GDNF’s effects on progenitors. Moreover, Gdnf   ^hyper mice are infertile likely due to effects of excess GDNF on distal ureter remodeling. Our findings suggest that dysregulation of GDNF levels, for example via alterations in 3′UTR, may account for a subset of congenital anomalies of the kidney and urinary tract (CAKUT) and/or congenital infertility cases in humans and pave way to future studies.

FAT4 Fine-Tunes Kidney Development by Regulating RET Signaling

FAT4 mutations lead to several human diseases that disrupt the normal development of the kidney. However, the underlying mechanism remains elusive. In studying the duplex kidney phenotypes observed upon deletion of Fat4 in mice, we have uncovered an interaction between the atypical cadherin FAT4 and RET, a tyrosine kinase receptor essential for kidney development. Analysis of kidney development in Fat4^-/- kidneys revealed abnormal ureteric budding and excessive RET signaling. Removal of one copy of the RET ligand Gdnf rescues Fat4^-/- kidney development, supporting the proposal that loss of Fat4 hyperactivates RET signaling. Conditional knockout analyses revealed a non-autonomous role for Fat4 in regulating RET signaling. Mechanistically, we found that FAT4 interacts with RET through extracellular cadherin repeats. Importantly, expression of FAT4 perturbs the assembly of the RET-GFRA1-GDNF complex, reducing RET signaling. Thus, FAT4 interacts with RET to fine-tune RET signaling, establishing a juxtacrine mechanism controlling kidney development.

Mathematical Approaches of Branching Morphogenesis

Many organs require a high surface to volume ratio to properly function. Lungs and kidneys, for example, achieve this by creating highly branched tubular structures during a developmental process called branching morphogenesis. The genes that control lung and kidney branching share a similar network structure that is based on ligand-receptor reciprocal signalling interactions between the epithelium and the surrounding mesenchyme. Nevertheless, the temporal and spatial development of the branched epithelial trees differs, resulting in organs of distinct shape and size. In the embryonic lung, branching morphogenesis highly depends on FGF10 signalling, whereas GDNF is the driving morphogen in the kidney. Knockout of Fgf10 and Gdnf leads to lung and kidney agenesis, respectively. However, FGF10 plays a significant role during kidney branching and both the FGF10 and GDNF pathway converge on the transcription factors ETV4/5. Although the involved signalling proteins have been defined, the underlying mechanism that controls lung and kidney branching morphogenesis is still elusive. A wide range of modelling approaches exists that differ not only in the mathematical framework (e.g., stochastic or deterministic) but also in the spatial scale (e.g., cell or tissue level). Due to advancing imaging techniques, image-based modelling approaches have proven to be a valuable method for investigating the control of branching events with respect to organ-specific properties. Here, we review several mathematical models on lung and kidney branching morphogenesis and suggest that a ligand-receptor-based Turing model represents a potential candidate for a general but also adaptive mechanism to control branching morphogenesis during development.

Regulation of Renal Differentiation by Trophic Factors

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

Expression of ILK in renal stroma is essential for multiple aspects of renal development

Kidney development involves reciprocal and inductive interactions between the ureteric bud (UB) and surrounding metanephric mesenchyme. Signals from renal stromal lineages are essential for differentiation and patterning of renal epithelial and mesenchymal cell types and renal vasculogenesis; however, underlying mechanisms remain not fully understood. Integrin-linked kinase (ILK), a key component of integrin signaling pathway, plays an important role in kidney development. However, the role of ILK in renal stroma remains unknown. Here, we ablated ILK in renal stromal lineages using a platelet-derived growth factor receptor B ( Pdgfrb) -Cre mouse line, and the resulting Ilk mutant mice presented postnatal growth retardation and died within 3 wk of age with severe renal developmental defects. Pdgfrb-Cre;Ilk mutant kidneys exhibited a significant decrease in UB branching and disrupted collecting duct formation. From E16.5 onward, renal interstitium was disorganized, forming medullary interstitial pseudocysts. Pdgfrb-Cre;Ilk mutants exhibited renal vasculature mispatterning and impaired glomerular vascular differentiation. Impaired glial cell-derived neurotrophic factor/Ret and bone morphogenetic protein 7 signaling pathways were observed in Pdgfrb-Cre;Ilk mutant kidneys. Furthermore, phosphoproteomic and Western blot analyses revealed a significant dysregulation of a number of key signaling pathways required for kidney morphogenesis, including PI3K/AKT and MAPK/ERK in Pdgfrb-Cre;Ilk mutants. Our results revealed a critical requirement for ILK in renal-stromal and vascular development, as well as a noncell autonomous role of ILK in UB branching morphogenesis.

Hedgehog-GLI signaling in Foxd1-positive stromal cells promotes murine nephrogenesis via TGFβ signaling

Normal kidney function depends on the proper development of the nephron: the functional unit of the kidney. Reciprocal signaling interactions between the stroma and nephron progenitor compartment have been proposed to control nephron development. Here, we show that removal of hedgehog intracellular effector smoothened (Smo-deficient mutants) in the cortical stroma results in an abnormal renal capsule, and an expanded nephron progenitor domain with an accompanying decrease in nephron number via a block in epithelialization. We show that stromal-hedgehog-Smo signaling acts through a GLI3 repressor. Whole-kidney RNA sequencing and analysis of FACS-isolated stromal cells identified impaired TGFβ2 signaling in Smo-deficient mutants. We show that neutralization and knockdown of TGFβ2 in explants inhibited nephrogenesis. In addition, we demonstrate that concurrent deletion of Tgfbr2 in stromal and nephrogenic cells in vivo results in decreased nephron formation and an expanded nephrogenic precursor domain similar to that observed in Smo-deficient mutant mice. Together, our data suggest a mechanism whereby a stromal hedgehog-TGFβ2 signaling axis acts to control nephrogenesis.

Centrosome amplification disrupts renal development and causes cystogenesis

Supernumerary centrosomes are commonly observed in cystic kidneys, but whether they are a cause or consequence of cystogenesis is unknown. Dionne et al. demonstrate that centrosome amplification disrupts renal development and is sufficient to induce cystogenesis in vivo.

Centrosome number is tightly controlled to ensure proper ciliogenesis, mitotic spindle assembly, and cellular homeostasis. Centrosome amplification (the formation of excess centrosomes) has been noted in renal cells of patients and animal models of various types of cystic kidney disease. Whether this defect plays a causal role in cystogenesis remains unknown. Here, we investigate the consequences of centrosome amplification during kidney development, homeostasis, and after injury. Increasing centrosome number in vivo perturbed proliferation and differentiation of renal progenitors, resulting in defective branching morphogenesis and renal hypoplasia. Centrosome amplification disrupted mitotic spindle morphology, ciliary assembly, and signaling pathways essential for the function of renal progenitors, highlighting the mechanisms underlying the developmental defects. Importantly, centrosome amplification was sufficient to induce rapid cystogenesis shortly after birth. Finally, we discovered that centrosome amplification sensitized kidneys in adult mice, causing cystogenesis after ischemic renal injury. Our study defines a new mechanism underlying the pathogenesis of renal cystogenesis, and identifies a potentially new cellular target for therapy.

Protein Kinase 2β Is Expressed in Neural Crest-Derived Urinary Pacemaker Cells and Required for Pyeloureteric Contraction

Nonobstructive hydronephrosis, defined as dilatation of the renal pelvis with or without dilatation of the ureter, is the most common antenatal abnormality detected by fetal ultrasound. Yet, the etiology of nonobstructive hydronephrosis is poorly defined. We previously demonstrated that defective development of urinary tract pacemaker cells (utPMCs) expressing hyperpolarization-activated cyclic nucleotide-gated channel 3 (HCN3) and the stem cell marker cKIT causes abnormal ureteric peristalsis and nonobstructive hydronephrosis. However, further investigation of utPMC development and function is limited by lack of knowledge regarding the embryonic derivation, development, and molecular apparatus of these cells. Here, we used lineage tracing in mice to identify cells that give rise to utPMCs. Neural crest cells (NCCs) indelibly labeled with tdTomato expressed HCN3 and cKIT. Furthermore, purified HCN3+ and cKIT+ utPMCs were enriched in Sox10 and Tfap-2α, markers of NCCs. Sequencing of purified RNA from HCN3+ cells revealed enrichment of a small subset of RNAs, including RNA encoding protein kinase 2β (PTK2β), a Ca²⁺-dependent tyrosine kinase that regulates ion channel activity in neurons. Immunofluorescence analysis in situ revealed PTK2β expression in NCCs as early as embryonic day 12.5 and in HCN3+ and cKIT+ utPMCs as early as embryonic day 15.5, with sustained expression in HCN3+ utPMCs until postnatal week 8. Pharmacologic inhibition of PTK2β in murine pyeloureteral tissue explants inhibited contraction frequency. Together, these results demonstrate that utPMCs are derived from NCCs, identify new markers of utPMCs, and demonstrate a functional contribution of PTK2β to utPMC function.

GRHL2 Is Required for Collecting Duct Epithelial Barrier Function and Renal Osmoregulation

Collecting ducts make up the distal-most tubular segments of the kidney, extending from the cortex, where they connect to the nephron proper, into the medulla, where they release urine into the renal pelvis. During water deprivation, body water preservation is ensured by the selective transepithelial reabsorption of water into the hypertonic medullary interstitium mediated by collecting ducts. The collecting duct epithelium forms tight junctions composed of barrier-enforcing claudins and exhibits a higher transepithelial resistance than other segments of the renal tubule exhibit. However, the functional relevance of this strong collecting duct epithelial barrier is unresolved. Here, we report that collecting duct-specific deletion of an epithelial transcription factor, grainyhead-like 2 (GRHL2), in mice led to reduced expression of tight junction-associated barrier components, reduced collecting duct transepithelial resistance, and defective renal medullary accumulation of sodium and other osmolytes. In vitro, Grhl2-deficient collecting duct cells displayed increased paracellular flux of sodium, chloride, and urea. Consistent with these effects, Grhl2-deficient mice had diabetes insipidus, produced dilute urine, and failed to adequately concentrate their urine after water restriction, resulting in susceptibility to prerenal azotemia. These data indicate a direct functional link between collecting duct epithelial barrier characteristics, which appear to prevent leakage of interstitial osmolytes into urine, and body water homeostasis.

Signaling Networks in Epithelial Tube Formation

Epithelial tubes are crucial to the function of organ systems including the excretory, gastrointestinal, cardiovascular, and pulmonary. Studies in the last two decades using in vitro organotypic systems and a variety of animal models have substantiated a large number of the morphogenetic mechanisms required to form epithelial tubes in development and regeneration. Many of these mechanisms modulate the differentiation and proliferation events necessary for generating the cell movements and changes in cell shape to delineate the wide variety of epithelial tube sizes, lengths, and conformations. For instance, when coupled with oriented cell division, proliferation itself plays a role in changes in tube shape and their directed expansion. Most of these processes are regulated in response to signaling inputs from adjacent cells or soluble factors from the environment. Despite the great deal of recent investigation in this direction, the knowledge we have about the signaling pathways associated with all epithelial tubulogenesis in development and regeneration is still very limited.

Building branched tissue structures: from single cell guidance to coordinated construction

Branched networks are ubiquitous throughout nature, particularly found in tissues that require large surface area within a restricted volume. Many tissues with a branched architecture, such as the vasculature, kidney, mammary gland, lung and nervous system, function to exchange fluids, gases and information throughout the body of an organism. The generation of branched tissues requires regulation of branch site specification, initiation and elongation. Branching events often require the coordination of many cells to build a tissue network for material exchange. Recent evidence has emerged suggesting that cell cooperativity scales with the number of cells actively contributing to branching events. Here, we compare mechanisms that regulate branching, focusing on how cell cohorts behave in a coordinated manner to build branched tissues.This article is part of the themed issue 'Systems morphodynamics: understanding the development of tissue hardware'.

Ablation of FGFR2 in Fibroblasts Ameliorates Kidney Fibrosis after Ischemia/Reperfusion Injury in Mice

Background

Fibroblast growth factors (FGFs) are heparin-binding proteins involved in a variety of biological processes. However, the role and mechanisms of FGF/FGFR2 signaling in fibroblast activation and kidney fibrosis need further investigation.

Methods

In this study, a mouse model with fibroblast-specific FGFR2 gene disruption was generated. The knockouts were born normal and no kidney dysfunction or histological abnormality was found within 2 months after birth. A kidney ischemia/reperfusion injury (IRI) model was created.

Results

Kidney fibrosis was developed in the control littermates within 2 and 4 weeks after IRI, while in the knockouts, total collagen deposition, fibronectin, and alpha smooth muscle actin expression were decreased compared to those in the control littermates. In addition, the numbers of Ki-67-positive interstitial cells as well as TUNEL-positive interstitial cells were lower in the knockout kidneys at 4 weeks after IRI. Phosphorylated extracellular regulated protein kinase 1/2 was decreased in the knockout kidneys at 2 and 4 weeks after IRI compared to those in the control littermates.

Conclusion

These results suggest that FGF/FGFR2 signaling may promote the proliferation and activation of kidney fibroblasts, which contribute to the development of kidney fibrosis.

Higher-Order Kidney Organogenesis from Pluripotent Stem Cells

Organogenesis generates higher-order structures containing functional subunits, connective components, and progenitor niches. Despite recent advances in organoid-based modeling of tissue development, recapitulating these complex configurations from pluripotent stem cells (PSCs) has remained challenging. In this study, we report assembly of kidney organoids that recapitulate embryonic branching morphogenesis. By studying the distinct origins and developmental processes of the ureteric bud, which contains epithelial kidney progenitors that undergo branching morphogenesis and thereby plays a central role in orchestrating organ geometry, and neighboring mesenchymal nephron progenitors, we established a protocol for differential induction of each lineage from mouse and human PSCs. Importantly, reassembled organoids developed the inherent architectures of the embryonic kidney, including the peripheral progenitor niche and internally differentiated nephrons that were interconnected by a ramified ureteric epithelium. This selective induction and reassembly strategy will be a powerful approach to recapitulate organotypic architecture in PSC-derived organoids.

Talin regulates integrin β1-dependent and -independent cell functions in ureteric bud development

Kidney collecting system development requires integrin-dependent cell-extracellular matrix interactions. Integrins are heterodimeric transmembrane receptors consisting of α and β subunits; crucial integrins in the kidney collecting system express the β1 subunit. The β1 cytoplasmic tail has two NPxY motifs that mediate functions by binding to cytoplasmic signaling and scaffolding molecules. Talins, scaffolding proteins that bind to the membrane proximal NPxY motif, are proposed to activate integrins and to link them to the actin cytoskeleton. We have defined the role of talin binding to the β1 proximal NPxY motif in the developing kidney collecting system in mice that selectively express a Y-to-A mutation in this motif. The mice developed a hypoplastic dysplastic collecting system. Collecting duct cells expressing this mutation had moderate abnormalities in cell adhesion, migration, proliferation and growth factor-dependent signaling. In contrast, mice lacking talins in the developing ureteric bud developed kidney agenesis and collecting duct cells had severe cytoskeletal, adhesion and polarity defects. Thus, talins are essential for kidney collecting duct development through mechanisms that extend beyond those requiring binding to the β1 integrin subunit NPxY motif.

Mdm proteins: critical regulators of embry ogenesis and homeostasis

Mdm2 and Mdm4 are negative regulators of the tumor suppressor p53; hence, this relationship is the focus of many cancer related studies. A multitude of experiments across various developmental stages have been conducted to explore the tissue-specific roles of these proteins in the mouse. When Mdm2 or Mdm4 are deleted in the germline or specific tissues, they display different phenotypic defects, some of which lead to embryonic lethality. Mdm2 loss is often more deleterious than loss of its homolog Mdm4 All tissues experience activation of p53 target genes upon loss of Mdm2 or Mdm4; however, the degree to which the p53 pathway is perturbed is highly tissue-specific and does not correlate to the severity of the morphological phenotypes. Therefore, a need for further understanding of how these proteins regulate p53 activity is warranted, as therapeutic targeting of the p53 pathway is rapidly evolving and gaining attention in the field of cancer research. In this review, we discuss the tissue-specificity of Mdm proteins in regulating p53 and expose the need for investigation at the cell-specific level.

Fgfr2 is integral for bladder mesenchyme patterning and function

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor 2 (Fgfr2) is necessary for kidney and ureter mesenchymal development. Our objective was to determine the role of Fgfr2 in bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in bladder mesenchyme (Fgfr2^BM-/-). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblotting, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with controls, embryonic (E) day 16.5 (E16.5) Fgfr2^BM-/- bladders have thin muscle layers with reduced α-smooth muscle actin levels and thickened lamina propria with increased collagen expression that intrudes into muscle. From postnatal (P) day 1 (P1) to P30, Fgfr2^BM-/- bladders demonstrate progressive muscle loss and increased collagen expression. Postnatal Fgfr2^BM-/- bladder sheets exhibit decreased contractility and increased passive stretch tension compared with controls. In vivo cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2^BM-/- bladders compared with controls. Mechanistically, while Shh expression appears normal, mRNA and protein readouts of hedgehog activity are increased in E16.5 Fgfr2^BM-/- bladders compared with controls. Moreover, E16.5Fgfr2^BM-/- bladders exhibit higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, than controls. Fgfr2 is critical for bladder mesenchyme patterning by virtue of its role in modulation of hedgehog signaling.

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.

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

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

Inactivation of the tumor suppressor gene von Hippel-Lindau (VHL) in granulocytes contributes to development of liver hemangiomas in a mouse model

Background

Mutations in the tumor suppressor gene von Hippel-Lindau (VHL) underlie a hereditary cancer syndrome—VHL disease—and are also frequently observed in sporadic renal cell carcinoma of the clear cell type (ccRCC). VHL disease is characterized by malignant and benign tumors in a few specific tissues, including ccRCC, hemangioblastoma and pheochromocytoma. The etiology of these tumors remains unresolved.

Methods

Conditional inactivation of the VHL gene in mouse (Vhlh) was generated to examine the pathophysiological role of the VHL gene function. Specific cell populations were isolated by fluorescence-activated cell sorting (FACS) and bone marrow transplants were performed to identify the Vhlh-inactivated cells responsible for the phenotype.

Results

Previously we showed that inactivation of Vhlh in a subpopulation of kidney distal tubule cells resulted in hyperplastic clear-cell lesions and severe inflammation and fibrosis. Here, we show that this knockout mouse strain also develops Hif-2α-dependent vascular overgrowth (hemangioma) and extramedullary erythropoiesis in the liver. However, Vhlh inactivation was not detected in the liver parenchyma. We instead demonstrate that in these mice, Vhlh is inactivated in liver granulocytes and that hemangiomas are partially rescued in knockout mice reconstituted with wild-type hematopoietic stem cells, indicating the involvement of bone-marrow-derived leukocyte. Interestingly, bone marrow from knockout mice failed to generate the liver phenotype in wild-type recipients, suggesting that an additional cell type that is not derived from the bone marrow is involved in the development of the hemangioma phenotype.

Conclusion

These results support the idea that the development of a full-blown VHL disease phenotype requires inactivation of the VHL gene not only in the tumor proper, but also in the stromal compartment.

Understanding kidney morphogenesis to guide renal tissue regeneration

The treatment of renal failure has seen little change in the past 70 years. Patients with end-stage renal disease (ESRD) are treated with renal replacement therapy, including dialysis or organ transplantation. The growing imbalance between the availability of donor organs and prevalence of ESRD is pushing an increasing number of patients to undergo dialysis. Although the prospect of new treatment options for patients through regenerative medicine has long been suggested, advances in the generation of human kidney cell types through the directed differentiation of human pluripotent stem cells over the past 2 years have brought this prospect closer to delivery. These advances are the result of careful research into mammalian embryogenesis. By understanding the decision points made within the embryo to pattern the kidney, it is now possible to recreate self-organizing kidney tissues in vitro. In this Review, we describe the key decision points in kidney development and how these decisions have been mimicked experimentally. Recreation of human nephrons from human pluripotent stem cells opens the door to patient-derived disease models and personalized drug and toxicity screening. In the long term, we hope that these efforts will also result in the generation of bioengineered organs for the treatment of kidney disease.

Sonic hedgehog protein regulates fibroblast growth factor 8 expression in metanephric explant culture from BALB/c mice: Possible mechanisms associated with renal morphogenesis

The sonic hedgehog (SHH) morphogen regulates cell differentiation and controls a number of genes during renal morphogenesis. To date, the effects of SHH on fibroblast growth factors (Fgfs) in embryonic kidney development remain unclear. In the present study, explants of BALB/c mouse embryonic kidney tissues were used to investigate the role of exogenous SHH on Fgf8 and Fgf10 expression levels ex vivo. Ureteric bud branches and epithelial metanephric derivatives were used to determine the renal morphogenesis with Dolichos biflorus agglutinin or hematoxylin‑eosin staining. mRNA expression levels were determined using reverse transcription‑quantitative polymerase chain reaction, while the protein expression levels were examined using immunohistochemistry and western blot analysis. During the initial stages of metanephric development, low levels of SHH, Fgf8, and Fgf10 expression were observed, which were found to increase significantly during more advanced stages of metanephric development. In addition, exogenous SHH protein treatment increased the number of ureteric bud branches and enhanced the formation of nephrons. Exogenous SHH reduced the Fgf8 mRNA and protein expression levels, whereas cyclopamine (an SHH‑smoothened receptor inhibitor) interfered with SHH‑mediated downregulation of Fgf8 expression. By contrast, exogenous SHH protein was not found to modulate Fgf10 mRNA and protein expression levels. In conclusion, these results indicate that the modulatory effects of SHH on BALB/c mouse metanephric explant cultures may involve the regulation of Fgf8 expression but not Fgf10 expression, which provides evidence for the functional role of Fgf proteins in renal morphogenesis.

Genetic insights into the mechanisms of Fgf signaling

The fibroblast growth factor (Fgf) family of ligands and receptor tyrosine kinases is required throughout embryonic and postnatal development and also regulates multiple homeostatic functions in the adult. Here, Brewer et al. review the mechanisms of Fgf signaling by focusing on genetic strategies that enable in vivo analysis.

The fibroblast growth factor (Fgf) family of ligands and receptor tyrosine kinases is required throughout embryonic and postnatal development and also regulates multiple homeostatic functions in the adult. Aberrant Fgf signaling causes many congenital disorders and underlies multiple forms of cancer. Understanding the mechanisms that govern Fgf signaling is therefore important to appreciate many aspects of Fgf biology and disease. Here we review the mechanisms of Fgf signaling by focusing on genetic strategies that enable in vivo analysis. These studies support an important role for Erk1/2 as a mediator of Fgf signaling in many biological processes but have also provided strong evidence for additional signaling pathways in transmitting Fgf signaling in vivo.

A critical role for NF2 and the Hippo pathway in branching morphogenesis

Branching morphogenesis is a complex biological process common to the development of most epithelial organs. Here we demonstrate that NF2, LATS1/2 and YAP play a critical role in branching morphogenesis in the mouse kidney. Removal of Nf2 or Lats1/2 from the ureteric bud (UB) lineage causes loss of branching morphogenesis that is rescued by loss of one copy of Yap and Taz, and phenocopied by YAP overexpression. Mosaic analysis demonstrates that cells with high YAP expression have reduced contribution to UB tips, similar to Ret^−/− cells, and that YAP suppresses RET signalling and tip identity. Conversely, Yap/Taz UB-deletion leads to cyst-like branching and expansion of UB tip markers, suggesting a shift towards tip cell identity. Based on these data we propose that NF2 and the Hippo pathway locally repress YAP/TAZ activity in the UB to promote subsequent splitting of the tip to allow branching morphogenesis.

Branching morphogenesis is essential for the formation of most epithelial organs. Here, the authors show that Neurofibromatosis 2 (NF2), the Hippo pathway kinases LATS1 and LATS2, and the transcriptional co-activators YAP and TAZ control tip identity, RET signalling and branching morphogenesis in the mouse kidney.