Wnt-4 is a mesenchymal signal for epithelial transformation of metanephric mesenchyme in the developing kidney

Nephron progenitor fate is modulated by angiotensin type 1 receptor signaling in human kidney organoids

The renin-angiotensin system (RAS) is essential for normal kidney development. Dysregulation of the RAS during embryogenesis can result in kidney abnormalities. To explore how angiotensin type 1 receptor (AT1R) signaling modulates nephron progenitor (NP) fate specification, we used induced pluripotent stem cell (iPSC) derived human kidney organoids treated with angiotensin II (Ang II) or the AT1R blocker losartan during differentiation. Ang II promoted NP proliferation and differentiation preferentially toward a podocyte fate, depleted the podocyte precursor population, and accelerated glomerular maturation. By contrast, losartan expanded the podocyte precursor population, delayed podocyte differentiation, and regressed the transcriptional signature to a more immature fetal state. Overall, using various in silico approaches with validation by RNAscope, we identified a role for AT1R signaling in regulating NP fate during nephrogenesis in kidney organoids. Our work supports the use of RAS modulators to improve organoid maturation and suggests that RAS may be a determinant of nephron endowment in vivo.

Three-dimensional rosettes in epithelial formation

Epithelia are ubiquitous tissues with essential structural, signaling, and barrier functions. How cells transition from individual to collective behaviors as they build and remodel epithelia throughout development is a fundamental question in developmental biology. Recent studies show that three-dimensional multicellular rosettes are key intermediates that provide a solution to the challenge of building tissue-scale epithelia by coordinating local interactions in small groups of cells. These radially polarized rosette structures facilitate epithelial formation by providing a protected environment for cells to acquire apical-basal polarity, establish cell adhesion, and coordinate intercellular signaling. Once formed, rosettes can dynamically expand, move, coalesce, and interact with surrounding tissues to generate a wide range of structures with specialized functions, including epithelial sheets, tubes, cavities, and branched networks. In this review, we describe the mechanisms that regulate rosette assembly and dynamics, and discuss how rosettes serve as versatile intermediates in epithelial morphogenesis. In addition, we present open questions about the molecular, cellular, and biophysical mechanisms that drive rosette behaviors, and discuss the implications of this widely used mode of epithelial formation for understanding embryonic development and human disease.

Wilms tumor primary cultures capture phenotypic heterogeneity and facilitate preclinical screening

Wilms tumors (WT) are characterized by variable contributions of blastemal, epithelial and stromal elements, reflecting their diverse cellular origins and genetic drivers. In vitro models remain rare, despite a growing need to better characterize tumor biology and evaluate new treatments. Using three approaches, we have now established a large collection of long-term cultures that represent this diversity. Adherent WT cultures are predominated by stromal cells, 3D spheroids model blastema, and patient-derived organoid cultures of both tumor and healthy kidney tissue result in the preferential growth of epithelial cells. Adherent, spheroid and organoid cultures are also clearly distinguishable by their transcriptome. Preclinical drug screening experiments revealed sensitivity to a range of inhibitors, that are highly effective in other childhood solid tumors. Sensitivity was related to MYCN status, a marker associated with adverse outcome across human cancers including WT. The combination of the three culture techniques represents a promising tool to both explore tumor heterogeneity in vitro and to facilitate characterization of candidate driver genes, in order to improve treatment regimens in the future.

Deciphering the cellular and molecular landscapes of Wnt/β-catenin signaling in mouse embryonic kidney development

Background

The Wnt/β-catenin signaling pathway is critical in kidney development, yet its specific effects on gene expression in different embryonic kidney cell types are not fully understood.

Methods

Wnt/β-catenin signaling was activated in mouse E12.5 kidneys in vitro using CHIR99021, with RNA sequencing performed afterward, and the results were compared to DMSO controls (dataset GSE131240). Differential gene expression in ureteric buds and cap mesenchyme following pathway activation (datasets GSE20325 and GSE39583) was analyzed. Single-cell RNA-seq data from the Mouse Cell Atlas was used to link differentially expressed genes (DEGs) with kidney cell types. β-catenin ChIP-seq data (GSE39837) identified direct transcriptional targets.

Results

Activation of Wnt/β-catenin signaling led to 917 significant DEGs, including the upregulation of Notum and Apcdd1 and the downregulation of Crym and Six2. These DEGs were involved in kidney development and immune response. Single-cell analysis identified 787 DEGs across nineteen cell subtypes, with Macrophage_Apoe high cells showing the most pronounced enrichment of Wnt/β-catenin-activated genes. Gene expression profiles in ureteric buds and cap mesenchyme differed significantly upon β-catenin manipulation, with cap mesenchyme showing a unique set of DEGs. Analysis of β-catenin ChIP-seq data revealed 221 potential direct targets, including Dpp6 and Fgf12.

Conclusion

This study maps the complex gene expression driven by Wnt/β-catenin signaling in embryonic kidney cell types. The identified DEGs and β-catenin targets elucidate the molecular details of kidney development and the pathway's role in immune processes, providing a foundation for further research into Wnt/β-catenin signaling in kidney development and disease.

Wnt/β-Catenin Signaling and Congenital Abnormalities of Kidney and Urinary Tract

Background

Precise regulation of cell-cell communication is vital for cell survival and normal function during embryogenesis. The Wnt protein family, a highly conserved and extensively studied group, plays a crucial role in key cell-cell signaling events essential for development and regeneration. Congenital anomalies of the kidney and urinary tract (CAKUT) represent a leading cause of chronic kidney disease in children and young adults, and include a variety of birth abnormalities resulting from disrupted genitourinary tract development during embryonic development. The incidence and progression of CAKUT may be related to the Wnt signal transduction mechanism.

Summary

This review provides a comprehensive overview of the classical Wnt signaling pathway's role in CAKUT, explores related molecular mechanisms and provides new targets and intervention methods for the future treatment of the disease.

Key Messages

The Wnt signal is intricately engaged in a variety of differentiation processes throughout kidney development.

Next generation sequencing identifies WNT signalling as a significant pathway in Autosomal Recessive Polycystic Kidney Disease (ARPKD) manifestation and may be linked to disease severity

INTRODUCTION

Autosomal Recessive Polycystic Kidney Disease (ARPKD) is a rare paediatric disease primarily caused by sequence variants in PKHD1. ARPKD presents with considerable clinical variability relating to the type of PKHD1 sequence variant, but not its position. Animal models of Polycystic Kidney Disease (PKD) suggest a complex genetic landscape, with genetic modifiers as a potential cause of disease variability.

METHODS

To investigate in an unbiased manner the molecular mechanisms of ARPKD and identify potential indicators of disease severity, Whole Exome Sequencing (WES) and RNA-Sequencing (RNA-Seq) were employed on human ARPKD kidneys and age-matched healthy controls.

RESULTS

WES confirmed the clinical diagnosis of ARPKD in our patient cohort consisting of ten ARPKD kidneys. Sequence variant type, nor position of PKHD1 sequence variants, was linked to disease severity. Sequence variants in genes associated with other ciliopathies were detected in the ARPKD cohort, but only PKD1 could be linked to disease severity. Transcriptomic analysis on a subset of four ARPKD kidneys representing severe and moderate ARPKD, identified a significant number of genes relating to WNT signalling, cellular metabolism and development. Increased expression of WNT signalling-related genes was validated by RT-qPCR in severe and moderate ARPKD kidneys. Two individuals in our cohort with the same PKHD1 sequence variants but different rates of kidney disease progression, with displayed transcriptomic differences in the expression of WNT signalling genes.

CONCLUSION

ARPKD kidney transcriptomics highlights changes in WNT signalling as potentially significant in ARPKD manifestation and severity, providing indicators for slowing down the progression of ARPKD.

The mRNA and microRNA Landscape of the Blastema Niche in Regenerating Newt Limbs

Newts are excellent vertebrate models for investigating tissue regeneration due to their remarkable regenerative capabilities. To investigate the mRNA and microRNAs (miRNAs) profiles within the blastema niche of regenerating newt limbs, we amputated the limbs of Chinese fire belly newts (Cynops orientalis) and conducted comprehensive analyses of the transcriptome and microRNA profiles at five distinct time points post-amputation (0 hours, 1 day, 5 days 10 days and 20 days). We identified 24 significantly differentially expressed (DE) genes and 20 significantly DE miRNAs. Utilizing weighted gene co-expression network analysis (WGCNA) and gene ontology (GO) enrichment analysis, we identified four genes likely to playing crucial roles in the early stages of limb regeneration: Cemip, Rhou, Gpd2 and Pcna. Moreover, mRNA-miRNA integration analysis uncovered seven human miRNAs (miR-19b-1, miR-19b-2, miR-21-5p, miR-127-5p, miR-150-5p, miR-194-5p, and miR-210-5p) may regulate the expression of these four key genes. The temporal expression patterns of these key genes and miRNAs further validated the robustness of the identified mRNA-miRNA landscape. Our study successfully identified candidate key genes and elucidated a portion of the genetic regulatory mechanisms involved in newt limb regeneration. These findings offer valuable insights for further exploration of the intricate processes of tissue regeneration.

The Impact of Low Protein Diet on the Molecular and Cellular Development of the Fetal Kidney

Background

Low nephron number has a direct impact on the development of hypertension and chronic kidney disease later in life. While intrauterine growth restriction caused by maternal low protein diet (LPD) is thought to be a significant cause of reduced nephron endowment in impoverished communities, its influence on the cellular and molecular processes which drive nephron formation are poorly understood.

Methods

We conducted a comprehensive characterization of the impact of LPD on kidney development using tomographic and confocal imaging to quantify changes in branching morphogenesis and the cellular and morphological features of nephrogenic niches across development. These analyses were paired with single-cell RNA sequencing to dissect the transcriptional changes that LPD imposes during renal development to affect nephron number.

Results

Single cell analysis at E14.5 and P0 revealed differences in the expression of genes and pathways involved in metabolism, cell cycle, epigenetic regulators and reciprocal inductive signals in most cell types analyzed, yielding imbalances and shifts in cellular energy production and cellular trajectories. In the nephron progenitor cells, LPD impeded cellular commitment and differentiation towards pre-tubular and renal vesicle structures. Confocal microscopy revealed a reduction in the number of pre-tubular aggregates and proliferation in nephron progenitor cells. We also found changes in branching morphogenesis, with a reduction in cell proliferation in the ureteric tips as well as reduced tip and tip parent lengths by optical projection tomography which causes patterning defects.

Conclusions

This unique profiling demonstrates how a fetal programming defect leads to low nephron endowment which is intricately linked to changes in both branching morphogenesis and the commitment of nephron progenitor cells. The commitment of progenitor cells is pivotal for nephron formation and is significantly influenced by nutritional factors, with a low protein diet driving alterations in this program which directly results in a reduced nephron endowment.

Significance Statement

While a mother's diet can negatively impact the number of nephrons in the kidneys of her offspring, the root cellular and molecular drivers of these deficits have not been rigorously explored. In this study we use advanced imaging and gene expression analysis in mouse models to define how a maternal low protein diet, analogous to that of impoverished communities, results in reduced nephron endowment. We find that low protein diet has pleiotropic effects on metabolism and the normal developmental programs of gene expression. These profoundly impact the process of branching morphogenesis necessary to establish niches for nephron generation and change cell behaviors which regulate how and when nephron progenitor cells commit to differentiation.

Generating kidney organoids based on developmental nephrology

Over the past decade, the induction protocols for the two types of kidney organoids (nephron organoids and ureteric bud organoids) from pluripotent stem cells (PSCs) have been established based on the knowledge gained in developmental nephrology. Kidney organoids are now used for disease modeling and drug screening, but they also have potential as tools for clinical transplantation therapy. One of the options to achieve this goal would be to assemble multiple renal progenitor cells (nephron progenitor, ureteric bud, stromal progenitor) to reproduce the organotypic kidney structure from PSCs. At least from mouse PSCs, all the three progenitors have been induced and assembled into such "higher order" kidney organoids. We will provide an overview of the developmental nephrology required for the induction of renal progenitors and discuss recent advances and remaining challenges of kidney organoids for clinical transplantation therapy.

Calcium signaling induces partial EMT and renal fibrosis in a Wnt4mCherry knock-in mouse model

The renal tubular epithelial cells (TEC) have a strong capacity for repair after acute injury, but when this mechanism becomes uncontrollable, it leads to chronic kidney diseases (CKD). Indeed, in progress toward CKDs, the TECs may dedifferentiate, undergo epithelial-to-mesenchyme transition (EMT), and promote inflammation and fibrosis. Given the critical role of Wnt4 signaling in kidney ontogenesis, we addressed whether changes in this signaling are connected to renal inflammation and fibrosis by taking advantage of a knock-in Wnt4mCh/mCh mouse. While the Wnt4mCh/mCh embryos appeared normal, the corresponding mice, within one month, developed CKD-related phenotypes, such as pro-inflammatory responses including T-cell/macrophage influx, expression of fibrotic markers, and epithelial cell damage with a partial EMT. The Wnt signal transduction component β-catenin remained unchanged, while calcium signaling is induced in the injured TECs involving Nfat and Tfeb transcription factors. We propose that the Wnt4 signaling pathway is involved in repairing the renal injury, and when the signal is overdriven, CKD is established.

Implication of transcription factor FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below age 30 years. Many monogenic forms have been discovered due to comprehensive genetic testing like exome sequencing. However, disease-causing variants in known disease-associated genes only explain a proportion of cases. Here, we aim to unravel underlying molecular mechanisms of syndromic CAKUT in three unrelated multiplex families with presumed autosomal recessive inheritance. Exome sequencing in the index individuals revealed three different rare homozygous variants in FOXD2, encoding a transcription factor not previously implicated in CAKUT in humans: a frameshift in the Arabic and a missense variant each in the Turkish and the Israeli family with segregation patterns consistent with autosomal recessive inheritance. CRISPR/Cas9-derived Foxd2 knockout mice presented with a bilateral dilated kidney pelvis accompanied by atrophy of the kidney papilla and mandibular, ophthalmologic, and behavioral anomalies, recapitulating the human phenotype. In a complementary approach to study pathomechanisms of FOXD2-dysfunction-mediated developmental kidney defects, we generated CRISPR/Cas9-mediated knockout of Foxd2 in ureteric bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important for kidney/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a shift toward a stromal cell identity. Histology of Foxd2 knockout mouse kidneys confirmed increased fibrosis. Further, genome-wide association studies suggest that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Thus, our studies help in genetic diagnostics of monogenic CAKUT and in understanding of monogenic and multifactorial kidney diseases.

The presence of xanthine dehydrogenase is crucial for the maturation of the rat kidneys

The development of the kidney involves essential cellular processes, such as cell proliferation and differentiation, which are led by interactions between multiple signaling pathways. Xanthine dehydrogenase (XDH) catalyzes the reaction producing uric acid in the purine catabolism, which plays a multifaceted role in cellular metabolism. Our previous study revealed that the genetic ablation of the Xdh gene in rats leads to smaller kidneys, kidney damage, decline of renal functions, and failure to thrive. Rats, unlike humans, continue their kidney development postnatally. Therefore, we explored whether XDH plays a critical role in kidney development using SS-/- rats during postnatal development phase. XDH expression was significantly increased from postnatal day 5 to 15 in wild-type but not homozygote rat kidneys. The transcriptomic profile of renal tissue revealed several dysregulated pathways due to the lack of Xdh expression with the remodeling in inflammasome, purinergic signaling, and redox homeostasis. Further analysis suggested that lack of Xdh affects kidney development, likely via dysregulation of epidermal growth factor and its downstream STAT3 signaling. The present study showed that Xdh is essential for kidney maturation. Our data, alongside the previous research, suggests that loss of Xdh function leads to developmental issues, rendering them vulnerable to kidney diseases in adulthood.

MAP3K1 regulates female reproductive tract development

Mitogen-activated protein 3 kinase 1 (MAP3K1) has a plethora of cell type-specific functions not yet fully understood. Herein, we describe a role for MAP3K1 in female reproductive tract (FRT) development. MAP3K1 kinase domain-deficient female mice exhibited an imperforate vagina, labor failure and infertility. These defects corresponded with shunted Müllerian ducts (MDs), the embryonic precursors of FRT, that manifested as a contorted caudal vagina and abrogated vaginal-urogenital sinus fusion in neonates. The MAP3K1 kinase domain is required for optimal activation of the Jun-N-terminal kinase (JNK) and cell polarity in the MD epithelium, and for upregulation of WNT signaling in the mesenchyme surrounding the caudal MD. The MAP3K1-deficient epithelial cells and MD epithelium had reduced expression of WNT7B ligands. Correspondingly, conditioned media derived from MAP3K1-competent, but not -deficient, epithelial cells activated a TCF/Lef-luciferase reporter in fibroblasts. These observations indicate that MAP3K1 regulates MD caudal elongation and FRT development, in part through the induction of paracrine factors in the epithelium that trans-activate WNT signaling in the mesenchyme.

Wilms' tumor gene 1: lessons from the interface between kidney development and cancer

In 1990, mutations of the Wilms' tumor-1 gene (WT1), encoding a transcription factor in the embryonic kidney, were found in 10-15% of Wilms' tumors; germline WT1 mutations were associated with hereditary syndromes involving glomerular and reproductive tract dysplasia. For more than three decades, these discoveries prompted investigators to explore the embryonic role of WT1 and the mechanisms by which loss of WT1 leads to malignant transformation. Here, we discuss how alternative splicing of WT1 generates isoforms that act in a context-specific manner to activate or repress target gene transcription. WT1 also regulates posttranscriptional regulation, alters the epigenetic landscape, and activates miRNA expression. WT1 functions at multiple stages of kidney development, including the transition from resting stem cells to committed nephron progenitor, which it primes to respond to WNT9b signals from the ureteric bud. WT1 then drives nephrogenesis by activating WNT4 expression and directing the development of glomerular podocytes. We review the WT1 mutations that account for Denys-Drash syndrome, Frasier syndrome, and WAGR syndrome. Although the WT1 story began with Wilms' tumors, an understanding of the pathways that link aberrant kidney development to malignant transformation still has some important gaps. Loss of WT1 in nephrogenic rests may leave these premalignant clones with inadequate DNA repair enzymes and may disturb the epigenetic landscape. Yet none of these observations provide a complete picture of Wilms' tumor pathogenesis. It appears that the WT1 odyssey is unfinished and still holds a great deal of untilled ground to be explored.

Geometric effects position renal vesicles during kidney development

During kidney development, reciprocal signaling between the epithelium and the mesenchyme coordinates nephrogenesis with branching morphogenesis of the collecting ducts. The mechanism that positions the renal vesicles, and thus the nephrons, relative to the branching ureteric buds has remained elusive. By combining computational modeling and experiments, we show that geometric effects concentrate the key regulator, WNT9b, at the junctions between parent and daughter branches where renal vesicles emerge, even when uniformly expressed in the ureteric epithelium. This curvature effect might be a general paradigm to create non-uniform signaling in development.

Altered binding affinity of SIX1-Q177R correlates with enhanced WNT5A and WNT pathway effector expression in Wilms tumor

Wilms tumors present as an amalgam of varying proportions of tissues located within the developing kidney, one being the nephrogenic blastema comprising multipotent nephron progenitor cells (NPCs). The recurring missense mutation Q177R in NPC transcription factors SIX1 and SIX2 is most correlated with tumors of blastemal histology and is significantly associated with relapse. Yet, the transcriptional regulatory consequences of SIX1/2-Q177R that might promote tumor progression and recurrence have not been investigated extensively. Utilizing multiple Wilms tumor transcriptomic datasets, we identified upregulation of the gene encoding non-canonical WNT ligand WNT5A in addition to other WNT pathway effectors in SIX1/2-Q177R mutant tumors. SIX1 ChIP-seq datasets from Wilms tumors revealed shared binding sites for SIX1/SIX1-Q177R within a promoter of WNT5A and at putative distal cis-regulatory elements (CREs). We demonstrate colocalization of SIX1 and WNT5A in Wilms tumor tissue and utilize in vitro assays that support SIX1 and SIX1-Q177R activation of expression from the WNT5A CREs, as well as enhanced binding affinity within the WNT5A promoter that may promote the differential expression of WNT5A and other WNT pathway effectors associated with SIX1-Q177R tumors.

Long-term viable chimeric nephrons generated from progenitor cells are a reliable model in cisplatin-induced toxicity

Kidney organoids have shown promise as evaluation tools, but their in vitro maturity remains limited. Transplantation into adult mice has aided in maturation; however, their lack of urinary tract connection limits long-term viability. Thus, long-term viable generated nephrons have not been demonstrated. In this study, we present an approachable method in which mouse and rat renal progenitor cells are injected into the developing kidneys of neonatal mice, resulting in the generation of chimeric nephrons integrated with the host urinary tracts. These chimeric nephrons exhibit similar maturation to the host nephrons, long-term viability with excretion and reabsorption functions, and cisplatin-induced renal injury in both acute and chronic phases, as confirmed by single-cell RNA-sequencing. Additionally, induced human nephron progenitor cells differentiate into nephrons within the neonatal kidneys. Collectively, neonatal injection represents a promising approach for in vivo nephron generation, with potential applications in kidney regeneration, drug screening, and pathological analysis.

Hand2 represses non-cardiac cell fates through chromatin remodeling at cis- regulatory elements

Developmental studies have revealed the importance of the transcription factor Hand2 in cardiac development. Hand2 promotes cardiac progenitor differentiation and epithelial maturation, while repressing other tissue types. The mechanisms underlying the promotion of cardiac fates are far better understood than those underlying the repression of alternative fates. Here, we assess Hand2-dependent changes in gene expression and chromatin remodeling in cardiac progenitors of zebrafish embryos. Cell-type specific transcriptome analysis shows a dual function for Hand2 in activation of cardiac differentiation genes and repression of pronephric pathways. We identify functional cis- regulatory elements whose chromatin accessibility are increased in hand2 mutant cells. These regulatory elements associate with non-cardiac gene expression, and drive reporter gene expression in tissues associated with Hand2-repressed genes. We find that functional Hand2 is sufficient to reduce non-cardiac reporter expression in cardiac lineages. Taken together, our data support a model of Hand2-dependent coordination of transcriptional programs, not only through transcriptional activation of cardiac and epithelial maturation genes, but also through repressive chromatin remodeling at the DNA regulatory elements of non-cardiac genes.

Podocyte-Parietal Epithelial Cell Interdependence in Glomerular Development and Disease

Podocytes and parietal epithelial cells (PECs) are among the few principal cell types within the kidney glomerulus, the former serving as a crucial constituent of the kidney filtration barrier and the latter representing a supporting epithelial layer that adorns the inner wall of Bowman's capsule. Podocytes and PECs share a circumscript developmental lineage that only begins to diverge during the S-shaped body stage of nephron formation-occurring immediately before the emergence of the fully mature nephron. These two cell types, therefore, share a highly conserved gene expression program, evidenced by recently discovered intermediate cell types occupying a distinct spatiotemporal gene expression zone between podocytes and PECs. In addition to their homeostatic functions, podocytes and PECs also have roles in kidney pathogenesis. Rapid podocyte loss in diseases, such as rapidly progressive GN and collapsing and cellular subtypes of FSGS, is closely allied with PEC proliferation and migration toward the capillary tuft, resulting in the formation of crescents and pseudocrescents. PECs are thought to contribute to disease progression and severity, and the interdependence between these two cell types during development and in various manifestations of kidney pathology is the primary focus of this review.

The Role of MAP3K1 in the Development of the Female Reproductive Tract

Mitogen-Activated Protein 3 Kinase 1 (MAP3K1) is a dynamic signaling molecule with a plethora of cell-type specific functions, most of which are yet to be understood. Here we describe a role for MAP3K1 in the development of female reproductive tract (FRT). MAP3K1 kinase domain-deficient ( Map3k1 ^ΔKD ) females exhibit imperforate vagina, labor failure, and infertility. These defects correspond to a shunted Müllerian duct (MD), the principle precursor of the FRT, in embryos, while they manifest as a contorted caudal vagina with abrogated vaginal-urogenital sinus fusion in neonates. In epithelial cells, MAP3K1 acts through JNK and ERK to activate WNT, yet in vivo MAP3K1 is crucial for WNT activity in mesenchyme associated with the caudal MD. Expression of Wnt7b is high in wild type, but low in Map3k1 knockout MD epithelium and MAP3K1-deficient keratinocytes. Correspondingly, conditioned media derived from MAP3K1-competent epithelial cells activate TCF/Lef-luciferase reporter in fibroblasts, suggesting that MAP3K1-induced factors released from epithelial cells trans-activate WNT signaling in fibroblasts. Our results reveal a temporal-spatial and paracrine MAP3K1-WNT crosstalk contributing to MD caudal elongation and FRT development.

Highlights

MAP3K1 deficient female mice exhibit imperforate vagina and infertilityLoss of MAP3K1 kinase activity impedes Müllerian duct (MD) caudal elongation and fusion with urogenital sinus (UGS) in embryogenesisThe MAP3K1-MAPK pathway up-regulates WNT signaling in epithelial cellsMAP3K1 deficiency down-regulates Wnt7b expression in the MD epithelium and prevents WNT activity in mesenchyme of the caudal MD.

A morphogenetic wave in the chick embryo lateral mesoderm generates mesenchymal-epithelial transition through a 3D-rosette intermediate

Formation of epithelia through mesenchymal-epithelial transition (MET) is essential for embryonic development and for many physiological and pathological processes. This study investigates MET in vivo in the chick embryo lateral mesoderm, where a multilayered mesenchyme transforms into two parallel epithelial sheets that constitute the coelomic lining of the embryonic body cavity. Prior to MET initiation, mesenchymal cells exhibit non-polarized distribution of multiple polarity markers, albeit not aPKC. We identified an epithelializing wave that sweeps across the lateral mesoderm, the wavefront of which is characterized by the accumulation of basal fibronectin and a network of 3D rosettes composed of polarized, wedge-shaped cells surrounding a central focus of apical markers, now including aPKC. Initiation of the MET process is dependent on extracellular matrix-integrin signaling acting through focal adhesion kinase and talin, whereas progression through the rosette phase requires aPKC function. We present a stepwise model for MET, comprising polarization, 3D-rosette, and epithelialization stages.

Implication of FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT)

Background

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below 30 years of age. Many monogenic forms have been discovered mainly due to comprehensive genetic testing like exome sequencing (ES). However, disease-causing variants in known disease-associated genes still only explain a proportion of cases. Aim of this study was to unravel the underlying molecular mechanism of syndromic CAKUT in two multiplex families with presumed autosomal recessive inheritance.

Methods and Results

ES in the index individuals revealed two different rare homozygous variants in FOXD2, a transcription factor not previously implicated in CAKUT in humans: a frameshift in family 1 and a missense variant in family 2 with family segregation patterns consistent with autosomal-recessive inheritance. CRISPR/Cas9-derived Foxd2 knock-out (KO) mice presented with bilateral dilated renal pelvis accompanied by renal papilla atrophy while extrarenal features included mandibular, ophthalmologic, and behavioral anomalies, recapitulating the phenotype of humans with FOXD2 dysfunction. To study the pathomechanism of FOXD2-dysfunction-mediated developmental renal defects, in a complementary approach, we generated CRISPR/Cas9-mediated KO of Foxd2 in ureteric-bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important in renal/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a cell identity shift towards a stromal cell identity. Histology of Foxd2 KO mouse kidneys confirmed increased fibrosis. Further, GWAS data (genome-wide association studies) suggests that FOXD2 could play a role for maintenance of podocyte integrity during adulthood.

Conclusions

In summary, our data implicate that FOXD2 dysfunction is a very rare cause of autosomal recessive syndromic CAKUT and suggest disturbances of the PAX2-WNT4 cell signaling axis contribute to this phenotype.

Planar cell polarity regulators in asymmetric organogenesis during development and disease

The phenomenon of planar cell polarity is critically required for a myriad of morphogenetic processes in metazoan and is accurately controlled by several conserved modules. Six "core" proteins, including Frizzled, Flamingo (Celsr), Van Gogh (Vangl), Dishevelled, Prickle, and Diego (Ankrd6), are major components of the Wnt/planar cell polarity pathway. The Fat/Dchs protocadherins and the Scrib polarity complex also function to instruct cellular polarization. In vertebrates, all these pathways are essential for tissue and organ morphogenesis, such as neural tube closure, left-right symmetry breaking, heart and gut morphogenesis, lung and kidney branching, stereociliary bundle orientation, and proximal-distal limb elongation. Mutations in planar polarity genes are closely linked to various congenital diseases. Striking advances have been made in deciphering their contribution to the establishment of spatially oriented pattern in developing organs and the maintenance of tissue homeostasis. The challenge remains to clarify the complex interplay of different polarity pathways in organogenesis and the link of cell polarity to cell fate specification. Interdisciplinary approaches are also important to understand the roles of mechanical forces in coupling cellular polarization and differentiation. This review outlines current advances on planar polarity regulators in asymmetric organ formation, with the aim to identify questions that deserve further investigation.

Urinary Extracellular Vesicles in Chronic Kidney Disease: From Bench to Bedside?

Extracellular vesicles are a diverse group of particles that include exosomes, microvesicles, and apoptotic bodies and are defined by size, composition, site of origin, and density. They incorporate various bioactive molecules from their cell of origin during formation, such as soluble proteins, membrane receptors, nucleic acids (mRNAs and miRNAs), and lipids, which can then be transferred to target cells. Extracellular vesicles/exosomes have been extensively studied as a critical factor in pathophysiological processes of human diseases. Urinary extracellular vesicles could be a promising liquid biopsy for determining the pattern and/or severity of kidney histologic injury. The signature of urinary extracellular vesicles may pave the way for noninvasive methods to supplement existing testing methods for diagnosing kidney diseases. We discuss the potential role of urinary extracellular vesicles in various chronic kidney diseases in this review, highlighting open questions and discussing the potential for future research.

Renal interstitial cells promote nephron regeneration by secreting prostaglandin E2

In organ regeneration, progenitor and stem cells reside in their native microenvironment, which provides dynamic physical and chemical cues essential to their survival, proliferation, and differentiation. However, the types of cells that form the native microenvironment for renal progenitor cells (RPCs) have not been clarified. Here, single-cell sequencing of zebrafish kidney reveals fabp10a as a principal marker of renal interstitial cells (RICs), which can be specifically labeled by GFP under the control of fabp10a promoter in the fabp10a:GFP transgenic zebrafish. During nephron regeneration, the formation of nephrons is supported by RICs that form a network to wrap the RPC aggregates. RICs that are in close contact with RPC aggregates express cyclooxygenase 2 (Cox2) and secrete prostaglandin E2 (PGE2). Inhibiting PGE2 production prevents nephrogenesis by reducing the proliferation of RPCs. PGE2 cooperates with Wnt4a to promote nephron maturation by regulating β-catenin stability of RPC aggregates. Overall, these findings indicate that RICs provide a necessary microenvironment for rapid nephrogenesis during nephron regeneration.

Histone deacetylases 1 and 2 target gene regulatory networks of nephron progenitors to control nephrogenesis

Our studies demonstrated the critical role of Histone deacetylases (HDACs) in the regulation of nephrogenesis. To better understand the key pathways regulated by HDAC1/2 in early nephrogenesis, we performed chromatin immunoprecipitation sequencing (ChIP-Seq) of HDAC1/2 on isolated nephron progenitor cells (NPCs) from mouse E16.5 kidneys. Our analysis revealed that 11,802 (40.4%) of HDAC1 peaks overlap with HDAC2 peaks, further demonstrates the redundant role of HDAC1 and HDAC2 during nephrogenesis. Common HDAC1/2 peaks are densely concentrated close to the transcriptional start site (TSS). GREAT Gene Ontology analysis of overlapping HDAC1/2 peaks reveals that HDAC1/2 are associated with metanephric nephron morphogenesis, chromatin assembly or disassembly, as well as other DNA checkpoints. Pathway analysis shows that negative regulation of Wnt signaling pathway is one of HDAC1/2's most significant function in NPCs. Known motif analysis indicated that Hdac1 is enriched in motifs for Six2, Hox family, and Tcf family members, which are essential for self-renewal and differentiation of nephron progenitors. Interestingly, we found the enrichment of HDAC1/2 at the enhancer and promoter regions of actively transcribed genes, especially those concerned with NPC self-renewal. HDAC1/2 simultaneously activate or repress the expression of different genes to maintain the cellular state of nephron progenitors. We used the Integrative Genomics Viewer to visualize these target genes associated with each function and found that HDAC1/2 co-bound to the enhancers or/and promoters of genes associated with nephron morphogenesis, differentiation, and cell cycle control. Taken together, our ChIP-Seq analysis demonstrates that HDAC1/2 directly regulate the molecular cascades essential for nephrogenesis.

Myelin and lymphocyte protein serves as a prognostic biomarker and is closely associated with the tumor microenvironment in the nephroblastoma

Nephroblastoma, also known as Wilms' tumor (WT), is the most common renal tumor that occurs in children. Although the efficacy of treatment has been significantly improved by a series of comprehensive treatments, some patients still have poor prognosis. Myelin and lymphocyte (MAL) protein, a highly hydrophobic integrated membrane‐bound protein, has been implicated in many tumors and is also closely linked to kidney development. However, the relationship between MAL and WT has not yet been elucidated. Therefore, we attempted to evaluate the feasibility of MAL as a promising prognosis factor for WT. The differential expression of MAL was investigated using TARGET database and was verified using the Gene Expression Omnibus database and real‐time quantitative PCR. The prognostic ability of MAL was determined using Kaplan–Meier and Cox regression analyses. Pearson correlation analysis was applied to explore the relationship between MAL expression and methylation sites. The ESTIMATE and CIBERSORT algorithms showed that MAL expression was associated with the WT tumor microenvironment. Gene Set Enrichment Analysis (GSEA) indicated that multiple signaling pathways closely associated with tumorigenesis were differentially enriched between the high‐ and low‐MAL groups. In conclusion, our study comprehensively explored the potential of MAL as a prognosis factor for WT. Meanwhile, we also demonstrated that MAL, as a prognostic factor for WT, may be closely related to the tumor microenvironment.

Techniques of fragile renal organoids transplantation in mice

Purpose:

This study aimed to develop a microsurgical technique to transplant extremely fragile renal organoids in vivo, created by in-vitro reaggregation of metanephros from fetal mice. These organoids in reaggregation and development were examined histologically after transplantation under the renal capsule.

Methods:

Initially, metanephros from fetal mice were enzymatically treated to form single cells, and spheroids were generated in vitro. Under a microscope, the renal capsule was detached to avoid bleeding, and the outer cylinder of the indwelling needle was inserted to detach the renal parenchyma from the renal capsule using water pressure. The reaggregated spheroid was aspirated from the culture plate using a syringe with an indwelling needle outer cylinder and carefully extruded under the capsule. Pathological analysis was performed to evaluate changes in reaggregated spheroids over time and the effects of co-culture of spinal cord and subcapsular implantation on maturation.

Results:

In vitro, the formation of luminal structures became clearer on day 5. These fragile organoids were successfully implanted without tissue crapes under the renal capsule and formed glomerular. The effect of spinal cord co-transplant was not obvious histrionically.

Conclusions:

A simple and easy method to transplant fragile spheroids and renal under the renal capsule without damage was developed.

Elevated Wnt2 and Wnt4 activate NF-κB signaling to promote cardiac fibrosis by cooperation of Fzd4/2 and LRP6 following myocardial infarction

Background

Acute myocardial infarction (AMI)-induced excessive myocardial fibrosis exaggerates cardiac dysfunction. However, serum Wnt2 or Wnt4 level in AMI patients, and the roles in cardiac fibrosis are largely unkown.

Methods

AMI and non-AMI patients were enrolled to examine serum Wnt2 and Wnt4 levels by ELISA analysis. The AMI patients were followed-up for one year. MI mouse model was built by ligation of left anterior descending branch (LAD).

Findings

Serum Wnt2 or Wnt4 level was increased in patients with AMI, and the elevated Wnt2 and Wnt4 were correlated to adverse outcome of these patients. Knockdown of Wnt2 and Wnt4 significantly attenuated myocardial remodeling and cardiac dysfunction following experimental MI. In vitro, hypoxia enhanced the secretion and expression of Wnt2 and Wnt4 in neonatal rat cardiac myocytes (NRCMs) or fibroblasts (NRCFs). Mechanistically, the elevated Wnt2 or Wnt4 activated β-catenin /NF-κB signaling to promote pro-fibrotic effects in cultured NRCFs. In addition, Wnt2 or Wnt4 upregulated the expression of these Wnt co-receptors, frizzled (Fzd) 2, Fzd4 and (ow-density lipoprotein receptor-related protein 6 (LRP6). Further analysis revealed that Wnt2 or Wnt4 activated β-catenin /NF-κB by the co-operation of Fzd4 or Fzd2 and LRP6 signaling, respectively.

Interpretation

Elevated Wnt2 and Wnt4 activate β-catenin/NF-κB signaling to promote cardiac fibrosis by cooperation of Fzd4/2 and LRP6 in fibroblasts, which contributes to adverse outcome of patients with AMI, suggesting that systemic inhibition of Wnt2 and Wnt4 may improve cardiac dysfunction after MI.

Opposing effects of Wnt/β-catenin signaling on epithelial and mesenchymal cell fate in the developing cochlea

During embryonic development, the otic epithelium and surrounding periotic mesenchymal cells originate from distinct lineages and coordinate to form the mammalian cochlea. Epithelial sensory precursors within the cochlear duct first undergo terminal mitosis before differentiating into sensory and non-sensory cells. In parallel, periotic mesenchymal cells differentiate to shape the lateral wall, modiolus and pericochlear spaces. Previously, Wnt activation was shown to promote proliferation and differentiation of both otic epithelial and mesenchymal cells. Here, we fate-mapped Wnt-responsive epithelial and mesenchymal cells in mice and found that Wnt activation resulted in opposing cell fates. In the post-mitotic cochlear epithelium, Wnt activation via β-catenin stabilization induced clusters of proliferative cells that dedifferentiated and lost epithelial characteristics. In contrast, Wnt-activated periotic mesenchyme formed ectopic pericochlear spaces and cell clusters showing a loss of mesenchymal and gain of epithelial features. Finally, clonal analyses via multi-colored fate-mapping showed that Wnt-activated epithelial cells proliferated and formed clonal colonies, whereas Wnt-activated mesenchymal cells assembled as aggregates of mitotically quiescent cells. Together, we show that Wnt activation drives transition between epithelial and mesenchymal states in a cell type-dependent manner.

Summary: The developing cochlea comprises spatially and lineally distinct populations of epithelial and mesenchymal cells. This study shows the opposing effects of aberrant Wnt/β-catenin signaling on cell fates of cochlear epithelial and mesenchymal cells.

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.

Identification of candidate PAX2-regulated genes implicated in human kidney development

PAX2 is a transcription factor essential for kidney development and the main causative gene for renal coloboma syndrome (RCS). The mechanisms of PAX2 action during kidney development have been evaluated in mice but not in humans. This is a critical gap in knowledge since important differences have been reported in kidney development in the two species. In the present study, we hypothesized that key human PAX2-dependent kidney development genes are differentially expressed in nephron progenitor cells from induced pluripotent stem cells (iPSCs) in patients with RCS relative to healthy individuals. Cap analysis of gene expression revealed 189 candidate promoters and 71 candidate enhancers that were differentially activated by PAX2 in this system in three patients with RCS with PAX2 mutations. By comparing this list with the list of candidate Pax2-regulated mouse kidney development genes obtained from the Functional Annotation of the Mouse/Mammalian (FANTOM) database, we prioritized 17 genes. Furthermore, we ranked three genes-PBX1, POSTN, and ITGA9-as the top candidates based on closely aligned expression kinetics with PAX2 in the iPSC culture system and susceptibility to suppression by a Pax2 inhibitor in cultured mouse embryonic kidney explants. Identification of these genes may provide important information to clarify the pathogenesis of RCS, human kidney development, and kidney regeneration.

WT1-Mutant Wilms Tumor Progression Is Associated With Diverting Clonal Mutations of CTNNB1

WT1-mutant Wilms tumors exhibit a high rate of concomitant CTNNB1 mutations, associated with activated Wnt signaling. Here, we show by laser and manual microdissection of different histologic cell types from 6 WT1-mutant tumor samples that 1 patient's tumor can contain up to 4 distinct mutations in CTNNB1 and/or WTX. Consecutive sections may also harbor different CTNNB1 mutations. The variability of activating CTNNB1 mutations demonstrates the multifocal nature of WT1-mutant Wilms tumors. As multiple independent tumors can occur in patients with constitutional WT1 mutations, they need to be surveyed more closely for tumor development.

Wnt signaling in kidney: the initiator or terminator?

The kidney is a key organ in the human body that excretes toxins and sustains the water-electrolyte balance. During embryonic development and disease progression, the kidney undergoes enormous changes in macrostructure, accompanied by a variety of microstructural histological changes, such as glomerular formation and sclerosis, tubule elongation and atrophy, interstitial establishment, and fibrosis progression. All of these rely on the frequent occurrence of cell death and growth. Notably, to overcome disease, some cells regenerate through self-repair or progenitor cell differentiation. However, the signaling mechanisms underlying kidney development and regeneration have not been elucidated. Recently, Wnt signaling has been noted to play an important role. Although it is a well-known developmental signal, the role of Wnt signaling in kidney development and regeneration is not well recognized. In this review, we review the role of Wnt signaling in kidney embryonic development, tissue repair, cell division, and progenitor cell differentiation after injury. Moreover, we briefly highlight advances in our understanding of the pathogenic mechanisms of Wnt signaling in mediating cellular senescence in kidney parenchymal and stem cells, an irreversible arrest of cell proliferation blocking tissue repair and regeneration. We also highlight the therapeutic targets of Wnt signaling in kidney diseases and provide important clues for clinical strategies.

Combined Omics Approaches Reveal the Roles of Non-canonical WNT7B Signaling and YY1 in the Proliferation of Human Pancreatic Progenitor Cells

The proliferation of human pancreatic progenitor cells (PPCs) is critical for developing cell therapies for diabetes. Here, using transcriptome analysis combined with small interfering RNA (siRNA) screening, we revealed that WNT7B is a downstream growth factor of AT7867, a compound known to promote the proliferation of PPCs generated from human pluripotent stem cells. Feeder cell lines stably expressing mouse Wnt7a or Wnt7b, but not other Wnts, enhanced PPC proliferation in the absence of AT7867. Importantly, Wnt7a/b ligands did not activate the canonical Wnt pathway, and PPC proliferation depended on the non-canonical Wnt/PKC pathway. A comparison of the phosphoproteome in response to AT7867 or a newly synthesized AT7867 derivative uncovered the function of YY1 as a transcriptional regulator of WNT7B. Overall, our data highlight unknown roles of non-canonical WNT7B/PKC signaling and YY1 in human PPC proliferation and will contribute to the stable supply of a cell source for pancreatic disease modeling and therapeutic applications.

The struggle to equilibrate outer and inner milieus: Renal evolution revisited

The journey of life, from primordial protoplasm to a complex vertebrate form, is a tale of survival against incessant alterations in climate, surface topography, food chain, and chemistry of the external environment. Kidneys present with an ensemble embodiment of the adaptations devised by diverse life-forms to cope with such challenges and maintain a chemical equilibrium of water and solutes, both in and outside the body. This minireview revisits renal evolution utilizing the classic: From Fish to Philosopher; the story of our internal environment, by Prof. Homer W. Smith (1895-1962) as a template. Prof. Smith's views exemplified the invention of glomeruli, or its abolishment, as a mechanism to filter water. Moreover, with the need to preserve water, as in reptiles, the loop of Henle was introduced to concentrate urine. When compared to smaller mammals, the larger ones, albeit having loops of Henle of similar lengths, demonstrated a distinct packing of the nephrons in kidneys. Moreover, the renal portal system degenerated in mammals, while still present in other vertebrates. This account will present with a critique of the current concepts of renal evolution while examining how various other factors, including the ones that we know more about now, such as genetic factors, synchronize to achieve renal development. Finally, it will try to assess the validity of ideas laid by Prof. Smith with the knowledge that we possess now, and understand the complex architecture that evolution has imprinted on the kidneys during its struggle to survive over epochs.

Advances in understanding vertebrate nephrogenesis

The kidney is a complex organ that performs essential functions such as blood filtration and fluid homeostasis, among others. Recent years have heralded significant advancements in our knowledge of the mechanisms that control kidney formation. Here, we provide an overview of vertebrate renal development with a focus on nephrogenesis, the process of generating the epithelialized functional units of the kidney. These steps begin with intermediate mesoderm specification and proceed all the way to the terminally differentiated nephron cell, with many detailed stages in between. The establishment of nephron architecture with proper cellular barriers is vital throughout these processes. Continuously striving to gain further insights into nephrogenesis can ultimately lead to a better understanding and potential treatments for developmental maladies such as Congenital Anomalies of the Kidney and Urinary Tract (CAKUT).

Noncanonical Wnt planar cell polarity signaling in lung development and disease

The planar cell polarity (PCP) signaling pathway is a potent developmental regulator of directional cell behaviors such as migration, asymmetric division and morphological polarization that are critical for shaping the body axis and the complex three-dimensional architecture of tissues and organs. PCP is considered a noncanonical Wnt pathway due to the involvement of Wnt ligands and Frizzled family receptors in the absence of the beta-catenin driven gene expression observed in the canonical Wnt cascade. At the heart of the PCP mechanism are protein complexes capable of generating molecular asymmetries within cells along a tissue-wide axis that are translated into polarized actin and microtubule cytoskeletal dynamics. PCP has emerged as an important regulator of developmental, homeostatic and disease processes in the respiratory system. It acts along other signaling pathways to create the elaborately branched structure of the lung by controlling the directional protrusive movements of cells during branching morphogenesis. PCP operates in the airway epithelium to establish and maintain the orientation of respiratory cilia along the airway axis for anatomically directed mucociliary clearance. It also regulates the establishment of the pulmonary vasculature. In adult tissues, PCP dysfunction has been linked to a variety of chronic lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary arterial hypertension, stemming chiefly from the breakdown of proper tissue structure and function and aberrant cell migration during regenerative wound healing. A better understanding of these (impaired) PCP mechanisms is needed to fully harness the therapeutic opportunities of targeting PCP in chronic lung diseases.

Wnt family member 4 (WNT4) and WNT3A activate cell-autonomous Wnt signaling independent of porcupine O-acyltransferase or Wnt secretion

Porcupine O-acyltransferase (PORCN) is considered essential for Wnt secretion and signaling. However, we observed that PORCN inhibition does not phenocopy the effects of WNT4 knockdown in WNT4-dependent breast cancer cells. This suggests a unique relationship between PORCN and WNT4 signaling. To examine the role of PORCN in WNT4 signaling, here we overexpressed WNT4 or WNT3A in breast cancer, ovarian cancer, and fibrosarcoma cell lines. Conditioned media from these lines and co-culture systems were used to assess the dependence of Wnt secretion and activity on the critical Wnt secretion proteins PORCN and Wnt ligand secretion (WLS) mediator. We observed that WLS is universally required for Wnt secretion and paracrine signaling. In contrast, the dependence of WNT3A secretion and activity on PORCN varied across the cell lines, and WNT4 secretion was PORCN-independent in all models. Surprisingly, WNT4 did not exhibit paracrine activity in any tested context. Absent the expected paracrine activity of secreted WNT4, we identified cell-autonomous Wnt signaling activation by WNT4 and WNT3A, independent of PORCN or Wnt secretion. The PORCN-independent, cell-autonomous Wnt signaling demonstrated here may be critical in WNT4-driven cellular contexts or in those that are considered to have dysfunctional Wnt signaling.

Pre-marked chromatin and transcription factor co-binding shape the pioneering activity of Foxa2

Pioneer transcription factors (PTF) can recognize their binding sites on nucleosomal DNA and trigger chromatin opening for recruitment of other non-pioneer transcription factors. However, critical properties of PTFs are still poorly understood, such as how these transcription factors selectively recognize cell type-specific binding sites and under which conditions they can initiate chromatin remodelling. Here we show that early endoderm binding sites of the paradigm PTF Foxa2 are epigenetically primed by low levels of active chromatin modifications in embryonic stem cells (ESC). Priming of these binding sites is supported by preferential recruitment of Foxa2 to endoderm binding sites compared to lineage-inappropriate binding sites, when ectopically expressed in ESCs. We further show that binding of Foxa2 is required for chromatin opening during endoderm differentiation. However, increased chromatin accessibility was only detected on binding sites which are synergistically bound with other endoderm transcription factors. Thus, our data suggest that binding site selection of PTFs is directed by the chromatin environment and that chromatin opening requires collaboration of PTFs with additional transcription factors.

Omega-3 attenuates high fat diet-induced kidney injury of female rats and renal programming of their offsprings

Context: Maternal diet composition could influence fetal organogenesis. Objective: We investigated effects of high fat diet (HFD) intake alone or combined with omega 3 during pregnancy, lactation and early days of weaning on nephrogenesis of pups and maternal renal function and morphology. Material and methods: Mothers and their pups included in each group were supplied with the same diet composition. Rats were divided into group I, II and III supplied with chow of either 10 kcal%, 45 kcal% or 45 kcal% from fat together with omega-3 respectively. Results: Group II showed increased serum urea and creatinine, renal TNF-α, IL1β. Structural injury was observed in mothers and their pups as Bowman's capsule and tubular dilatation and increased expression of PCNA that were decreased following omega-3 supplementation added to down regulation of Wnt4, Pax2 gene and podocin expression. Discussion and conclusion: Omega-3 supplementation improves lipid nephrotoxicity observed in mothers and their pups.

Macrophages as an Emerging Source of Wnt Ligands: Relevance in Mucosal Integrity

The Wnt signaling pathway is a conserved pathway involved in important cellular processes such as the control of embryonic development, cellular polarity, cellular migration, and cell proliferation. In addition to playing a central role during embryogenesis, this pathway is also an essential part of adult homeostasis. Indeed, it controls the proliferation of epithelial cells in different organs such as intestine, lung, and kidney, and guarantees the maintenance of the mucosa in physiological conditions. The origin of this molecular pathway is the binding between Wnt ligands (belonging to a family of 19 different homologous secreted glycoproteins) and their specific membrane receptors, from the Frizzled receptor family. This specific interaction triggers the activation of the signaling cascade, which in turn activates or suppresses the expression of different genes in order to change the behavior of the cell. On the other hand, alterations of this pathway have been described in pathological conditions such as inflammation, fibrosis, and cancer. In recent years, macrophages-among other cell types-have emerged as a potential source of Wnt ligands. Due to their high plasticity, macrophages, which are central to the innate immune response, are capable of adopting different phenotypes depending on their microenvironment. In the past, two different phenotypes were described: a proinflammatory phenotype-M1 macrophages-and an anti-inflammatory phenotype-M2 macrophages-and a selective expression of Wnt ligands has been associated with said phenotypes. However, nowadays it is assumed that macrophages in vivo move through a continual spectrum of functional phenotypes. In both physiological and pathological (inflammation, fibrosis and cancer) conditions, the accumulation and polarization of macrophages conditions the future of the tissue, facilitating various scenarios, such as resolution of inflammation, activation of fibrosis, and cancer development due to the modulation of the Wnt signaling pathway, in autocrine and paracrine manner. In this work, we provide an overview of studies that have explored the role of macrophages and how they act as a source of Wnt ligands and as mediators of mucosal integrity.

Kidney Regeneration in Later-Stage Mouse Embryos via Transplanted Renal Progenitor Cells

BACKGROUND

The limited availability of donor kidneys for transplantation has spurred interest in investigating alternative strategies, such as regenerating organs from stem cells transplanted into animal embryos. However, there is no known method for transplanting cells into later-stage embryos, which may be the most suitable host stages for organogenesis, particularly into regions useful for kidney regeneration.

METHODS

We demonstrated accurate transplantation of renal progenitor cells expressing green fluorescent protein to the fetal kidney development area by incising the opaque uterine muscle layer but not the transparent amniotic membrane. We allowed renal progenitor cell-transplanted fetuses to develop for 6 days postoperatively before removal for analysis. We also transplanted renal progenitor cells into conditional kidney-deficient mouse embryos. We determined growth and differentiation of transplanted cells in all cases.

RESULTS

Renal progenitor cell transplantation into the retroperitoneal cavity of fetuses at E13-E14 produced transplant-derived, vascularized glomeruli with filtration function and did not affect fetal growth or survival. Cells transplanted to the nephrogenic zone produced a chimera in the cap mesenchyme of donor and host nephron progenitor cells. Renal progenitor cells transplanted to conditional kidney-deficient fetuses induced the formation of a new nephron in the fetus that is connected to the host ureteric bud.

CONCLUSIONS

We developed a cell transplantation method for midstage to late-stage fetuses. In vivo kidney regeneration from renal progenitor cells using the renal developmental environment of the fetus shows promise. Our findings suggest that fetal transplantation methods may contribute to organ regeneration and developmental research.

The Telocytes in the Subepicardial Niche

A great interest has developed over the last several years in research on interstitial Cajal-like cells (ICLCs), later renamed to telocytes (TCs). Such studies are restricted by diverse limitations. We aimed to critically review (sub)epicardial ICLCs/TCs and to bring forward supplemental immunohistochemical evidence on (sub)epicardial stromal niche inhabitants. We tested the epicardial expressions of CD117/c-kit, CD34, Cytokeratin 7 (CK7), Ki67, Platelet-Derived Growth Factor Receptor (PDGFR)-α and D2-40 in adult human cardiac samples. The mesothelial epicardial cells expressed D2-40, CK7, CD117/c-kit and PDGFR-α. Subepicardial D2-40-positive lymphatic vessels and isolated D2-40-positive and CK7-positive subepicardial cells were also found. Immediate submesothelial spindle-shaped cells expressed Ki-67. Submesothelial stromal cells and endothelial tubes were PDGFR-α-positive and CD34-positive. The expression of CD34 was pan-stromal, so a particular stromal cell type could not be distinguished. The stromal expression of CD117/c-kit was also noted. It seems that epicardial TCs could not be regarded as belonging to a unique cell type until (pre)lymphatic endothelial cells are inadequately excluded. Markers such as CD117/c-kit or CD34 seem to be improper for identifying TCs as a distinctive cell type. Care should be taken when using the immunohistochemical method and histological interpretations, as they may not produce accurate results.

Induction of human pluripotent stem cells into kidney tissues by synthetic mRNAs encoding transcription factors

The derivation of kidney tissues from human pluripotent stem cells (hPSCs) and its application for replacement therapy in end-stage renal disease have been widely discussed. Here we report that consecutive transfections of two sets of synthetic mRNAs encoding transcription factors can induce rapid and efficient differentiation of hPSCs into kidney tissues, termed induced nephron-like organoids (iNephLOs). The first set - FIGLA, PITX2, ASCL1 and TFAP2C, differentiated hPSCs into SIX2+SALL1+ nephron progenitor cells with 92% efficiency within 2 days. Subsequently, the second set - HNF1A, GATA3, GATA1 and EMX2, differentiated these cells into PAX8+LHX1+ pretubular aggregates in another 2 days. Further culture in both 2-dimensional and 3-dimensional conditions produced iNephLOs containing cells characterized as podocytes, proximal tubules, and distal tubules in an additional 10 days. Global gene expression profiles showed similarities between iNephLOs and the human adult kidney, suggesting possible uses of iNephLOs as in vitro models for kidneys.

Nephron progenitor commitment is a stochastic process influenced by cell migration

Progenitor self-renewal and differentiation is often regulated by spatially restricted cues within a tissue microenvironment. Here, we examine how progenitor cell migration impacts regionally induced commitment within the nephrogenic niche in mice. We identify a subset of cells that express Wnt4, an early marker of nephron commitment, but migrate back into the progenitor population where they accumulate over time. Single cell RNA-seq and computational modelling of returning cells reveals that nephron progenitors can traverse the transcriptional hierarchy between self-renewal and commitment in either direction. This plasticity may enable robust regulation of nephrogenesis as niches remodel and grow during organogenesis.

Manipulation of Nephron-Patterning Signals Enables Selective Induction of Podocytes from Human Pluripotent Stem Cells

BACKGROUND

Previous research has elucidated the signals required to induce nephron progenitor cells (NPCs) from pluripotent stem cells (PSCs), enabling the generation of kidney organoids. However, selectively controlling differentiation of NPCs to podocytes has been a challenge.

METHODS

We investigated the effects of various growth factors in cultured mouse embryonic NPCs during three distinct steps of nephron patterning: from NPC to pretubular aggregate, from the latter to epithelial renal vesicle (RV), and from RV to podocyte. We then applied the findings to human PSC-derived NPCs to establish a method for selective induction of human podocytes.

RESULTS

Mouse NPC differentiation experiments revealed that phase-specific manipulation of Wnt and Tgf-β signaling is critical for podocyte differentiation. First, optimal timing and intensity of Wnt signaling were essential for mesenchymal-to-epithelial transition and podocyte differentiation. Then, inhibition of Tgf-β signaling supported domination of the RV proximal domain. Inhibition of Tgf-β signaling in the third phase enriched the podocyte fraction by suppressing development of other nephron lineages. The resultant protocol enabled successful induction of human podocytes from PSCs with >90% purity. The induced podocytes exhibited global gene expression signatures comparable to those of adult human podocytes, had podocyte morphologic features (including foot process-like and slit diaphragm-like structures), and showed functional responsiveness to drug-induced injury.

CONCLUSIONS

Elucidation of signals that induce podocytes during the nephron-patterning process enabled us to establish a highly efficient method for selective induction of human podocytes from PSCs. These PSC-derived podocytes show molecular, morphologic, and functional characteristics of podocytes, and offer a new resource for disease modeling and nephrotoxicity testing.

Experimental Tubulogenesis Induction Model in the Mouse

Kidney development and induction of tubulogenesis have been studied for almost seven decades. The experimental setup of metanephric mesenchyme induction ex vivo allows to control the environment, to perform cellular manipulations, and to learn about renal development. Since the establishment of the ex vivo kidney culture technique in 1953, the method was modified to suit well the progress in biological and medical fields and still today present many advantages over the traditional in vivo studies.