Sall genes regulate hindlimb initiation in mouse embryos

Vertebrate limbs start to develop as paired protrusions from the lateral plate mesoderm at specific locations of the body with forelimb buds developing anteriorly and hindlimb buds posteriorly. During the initiation process, limb progenitor cells maintain active proliferation to form protrusions and start to express Fgf10, which triggers molecular processes for outgrowth and patterning. Although both processes occur in both types of limbs, forelimbs (Tbx5), and hindlimbs (Isl1) utilize distinct transcriptional systems to trigger their development. Here, we report that Sall1 and Sall4, zinc finger transcription factor genes, regulate hindlimb initiation in mouse embryos. Compared to the 100% frequency loss of hindlimb buds in TCre; Isl1 conditional knockouts, Hoxb6Cre; Isl1 conditional knockout causes a hypomorphic phenotype with only approximately 5% of mutants lacking the hindlimb. Our previous study of SALL4 ChIP-seq showed SALL4 enrichment in an Isl1 enhancer, suggesting that SALL4 acts upstream of Isl1. Removing 1 allele of Sall4 from the hypomorphic Hoxb6Cre; Isl1 mutant background caused loss of hindlimbs, but removing both alleles caused an even higher frequency of loss of hindlimbs, suggesting a genetic interaction between Sall4 and Isl1. Furthermore, TCre-mediated conditional double knockouts of Sall1 and Sall4 displayed a loss of expression of hindlimb progenitor markers (Isl1, Pitx1, Tbx4) and failed to develop hindlimbs, demonstrating functional redundancy between Sall1 and Sall4. Our data provides genetic evidence that Sall1 and Sall4 act as master regulators of hindlimb initiation.

Sall4 regulates posterior trunk mesoderm development by promoting mesodermal gene expression and repressing neural genes in the mesoderm

The trunk axial skeleton develops from paraxial mesoderm cells. Our recent study demonstrated that conditional knockout of the stem cell factor Sall4 in mice by TCre caused tail truncation and a disorganized axial skeleton posterior to the lumbar level. Based on this phenotype, we hypothesized that, in addition to the previously reported role of Sall4 in neuromesodermal progenitors, Sall4 is involved in the development of the paraxial mesoderm tissue. Analysis of gene expression and SALL4 binding suggests that Sall4 directly or indirectly regulates genes involved in presomitic mesoderm differentiation, somite formation and somite differentiation. Furthermore, ATAC-seq in TCre; Sall4 mutant posterior trunk mesoderm shows that Sall4 knockout reduces chromatin accessibility. We found that Sall4-dependent open chromatin status drives activation and repression of WNT signaling activators and repressors, respectively, to promote WNT signaling. Moreover, footprinting analysis of ATAC-seq data suggests that Sall4-dependent chromatin accessibility facilitates CTCF binding, which contributes to the repression of neural genes within the mesoderm. This study unveils multiple mechanisms by which Sall4 regulates paraxial mesoderm development by directing activation of mesodermal genes and repression of neural genes.

Kidney Bioengineering for Transplantation

The kidney is an important organ for maintenance of homeostasis in the human body. As renal failure progresses, renal replacement therapy becomes necessary. However, there is a chronic shortage of kidney donors, creating a major problem for transplantation. To solve this problem, many strategies for the generation of transplantable kidneys are under investigation. Since the first reports describing that nephron progenitors could be induced from human induced pluripotent stem cells, kidney organoids have been attracting attention as tools for studying human kidney development and diseases. Because the kidney is formed through the interactions of multiple renal progenitors, current studies are investigating ways to combine these progenitors derived from human induced pluripotent stem cells for the generation of transplantable kidney organoids. Other bioengineering strategies, such as decellularization and recellularization of scaffolds, 3-dimensional bioprinting, interspecies blastocyst complementation and progenitor replacement, and xenotransplantation, also have the potential to generate whole kidneys, although each of these strategies has its own challenges. Combinations of these approaches will lead to the generation of bioengineered kidneys that are transplantable into humans.

Sall4 restricts glycolytic metabolism in limb buds through transcriptional regulation of glycolytic enzyme genes

Recent studies illustrate the importance of regulation of cellular metabolism, especially glycolysis and pathways branching from glycolysis, during vertebrate embryo development. For example, glycolysis generates cellular energy ATP. Glucose carbons are also directed to the pentose phosphate pathway, which is needed to sustain anabolic processes in the rapidly growing embryos. However, our understanding of the exact status of glycolytic metabolism as well as genes that regulate glycolytic metabolism are still incomplete. Sall4 is a zinc finger transcription factor that is highly expressed in undifferentiated cells in developing mouse embryos, such as blastocysts and the post-implantation epiblast. TCre; Sall4 conditional knockout mouse embryos exhibit various defects in the posterior part of the body, including hindlimbs. Using transcriptomics approaches, we found that many genes encoding glycolytic enzymes are upregulated in the posterior trunk, including the hindlimb-forming region, of Sall4 conditional knockout mouse embryos. In situ hybridization and qRT-PCR also confirmed upregulation of expression of several glycolytic genes in hindlimb buds. A fraction of those genes are bound by SALL4 at the promoters, gene bodies or distantly-located regions, suggesting that Sall4 directly regulates expression of several glycolytic enzyme genes in hindlimb buds. To further gain insight into the metabolic status associated with the observed changes at the transcriptional level, we performed a comprehensive analysis of metabolite levels in limb buds in wild type and Sall4 conditional knockout embryos by high-resolution mass spectrometry. We found that the levels of metabolic intermediates of glycolysis are lower, but glycolytic end-products pyruvate and lactate did not exhibit differences in Sall4 conditional knockout hindlimb buds. The increased expression of glycolytic genes would have caused accelerated glycolytic flow, resulting in low levels of intermediates. This condition may have prevented intermediates from being re-directed to other pathways, such as the pentose phosphate pathway. Indeed, the change in glycolytic metabolite levels is associated with reduced levels of ATP and metabolites of the pentose phosphate pathway. To further test whether glycolysis regulates limb patterning downstream of Sall4, we conditionally inactivated Hk2, which encodes a rate-limiting enzyme gene in glycolysis and is regulated by Sall4. The TCre; Hk2 conditional knockout hindlimb exhibited a short femur, and a lack of tibia and anterior digits in hindlimbs, which are defects similarly found in the TCre; Sall4 conditional knockout. The similarity of skeletal defects in Sall4 mutants and Hk2 mutants suggests that regulation of glycolysis plays a role in hindlimb patterning. These data suggest that Sall4 restricts glycolysis in limb buds and contributes to patterning and regulation of glucose carbon flow during development of limb buds.

Advances and challenges toward developing kidney organoids for clinical applications

Kidney organoids have enabled modeling of human development and disease. While methods of generating the nephron lineage are well established, new protocols to induce another lineage, the ureteric bud/collecting duct, have been reported in the past 5 years. Many reports have described modeling of various hereditary kidney diseases, with polycystic kidney disease serving as the archetypal disease, by using patient-derived or genome-edited kidney organoids. The generation of more organotypic kidneys is also becoming feasible. In this review, I also discuss the significant challenges for more sophisticated disease modeling and for realizing the ambitious goal of generating transplantable synthetic kidneys.

Loss of phosphatase CTDNEP1 potentiates aggressive medulloblastoma by triggering MYC amplification and genomic instability

MYC-driven medulloblastomas are highly aggressive childhood brain tumors, however, the molecular and genetic events triggering MYC amplification and malignant transformation remain elusive. Here we report that mutations in CTDNEP1, a CTD nuclear-envelope-phosphatase, are the most significantly enriched recurrent alterations in MYC-driven medulloblastomas, and define high-risk subsets with poorer prognosis. Ctdnep1 ablation promotes the transformation of murine cerebellar progenitors into Myc-amplified medulloblastomas, resembling their human counterparts. CTDNEP1 deficiency stabilizes and activates MYC activity by elevating MYC serine-62 phosphorylation, and triggers chromosomal instability to induce p53 loss and Myc amplifications. Further, phosphoproteomics reveals that CTDNEP1 post-translationally modulates the activities of key regulators for chromosome segregation and mitotic checkpoint regulators including topoisomerase TOP2A and checkpoint kinase CHEK1. Co-targeting MYC and CHEK1 activities synergistically inhibits CTDNEP1-deficient MYC-amplified tumor growth and prolongs animal survival. Together, our studies demonstrate that CTDNEP1 is a tumor suppressor in highly aggressive MYC-driven medulloblastomas by controlling MYC activity and mitotic fidelity, pointing to a CTDNEP1-dependent targetable therapeutic vulnerability.

Disease modeling of ADAMTS9-related nephropathy using kidney organoids reveals its roles in tubular cells and podocytes

Introduction

Mutations in ADAMTS9 cause nephronophthisis-related ciliopathies (NPHP-RC), which are characterized by multiple developmental defects and kidney diseases. Patients with NPHP-RC usually have normal glomeruli and negligible or no proteinuria. Herein, we identified novel compound-heterozygous ADAMTS9 variants in two siblings with NPHP-RC who had glomerular manifestations, including proteinuria.

Methods

To investigate whether ADAMTS9 dysfunction causes NPHP and glomerulopathy, we differentiated ADAMTS9 knockout human induced pluripotent stem cells (hiPSCs) into kidney organoids. Single-cell RNA sequencing was utilized to elucidate the gene expression profiles from the ADAMTS9 knockout kidney organoids.

Results

ADAMTS9 knockout had no effect on nephron differentiation; however, it reduced the number of primary cilia, thereby recapitulating renal ciliopathy. Single-cell transcriptomics revealed that podocyte clusters express the highest levels of ADAMTS9, followed by the proximal tubules. Loss of ADAMTS9 increased the activity of multiple signaling pathways, including the Wnt/PCP signaling pathway, in podocyte clusters.

Conclusions

Mutations in ADMATS9 cause a glomerulotubular nephropathy in kidney and our study provides insights into the functional roles of ADMATS9 in glomeruli and tubules.

Functional renal collecting ducts from human PSCs

Collecting ducts in the kidney control the balance of water and electrolytes, as well as pH of the urine to maintain body homeostasis. Shi et al.¹ recently reported in Nature Biotechnology a protocol to generate functional collecting duct cells from human pluripotent stem cells.

Kif26b contributes to the progression of interstitial fibrosis via migration and myofibroblast differentiation in renal fibroblast

Kinesin family member 26b (Kif26b) is essential for kidney development, and its deletion in mice leads to kidney agenesis. However, the roles of this gene in adult settings remain elusive. Thus, this study aims to investigate the role of Kif26b in the progression of renal fibrosis. A renal fibrosis model with adenine administration using Kif26b heterozygous mice and wild-type mice was established. Renal fibrosis and the underlying mechanism were investigated. The underlying pathways and functions of Kif26b were evaluated in an in vitro model using primary renal fibroblasts. Kif26b heterozygous mice were protected from renal fibrosis with adenine administration. Renal expressions of connective tissue growth factor (CTGF) and myofibroblast accumulation were reduced in Kif26b heterozygous mice. The expression of nonmuscle myosin heavy chain II (NMHCII), which binds to the C-terminus of Kif26b protein, was also suppressed in Kif26b heterozygous mice. The in vitro study revealed reduced expressions of CTGF, α-smooth muscle actin, and myosin heavy chain 9 (Myh9) via transfection with siRNAs targeting Kif26b in renal fibroblasts (RFB). RFBs, which were transfected by the expression vector of Kif26b, demonstrated higher expressions of these genes than non-transfected cells. Finally, Kif26b suppression and NMHCII blockage led to reduced abilities of migration and collagen gel contraction in renal fibroblasts. Taken together, Kif26b contributes to the progression of interstitial fibrosis via migration and myofibroblast differentiation through Myh9 in the renal fibrosis model. Blockage of this pathway at appropriate timing might be a therapeutic approach for renal fibrosis.

Building kidney organoids from pluripotent stem cells

PURPOSE OF REVIEW

During embryogenesis, the kidney is mainly generated from three progenitor cells; nephron progenitors, ureteric bud progenitors and stromal progenitors. Mutual interactions of the all three progenitor populations are essential to form a functional kidney with the higher-order structure. Pluripotent stem cells have potential to differentiate into all cell types of the animal body, including the kidney. In this review, we will summarize recent advances in reconstructing kidney organoids from pluripotent stem cells.

RECENT FINDINGS

In the past years, major advances were reported to induce nephron and ureteric bud progenitors from pluripotent stem cells in mice and humans, and to create kidney organoids of nephron and/or ureteric bud-derived collecting duct tissues in vitro. These kidney organoid technologies were applied to high-throughput genetic screenings and small chemical screenings to identify key factors for kidney development and disease. Furthermore, a novel method was established to induce stromal progenitors from pluripotent stem cells, leading to creation of kidney organoids with the higher-order structures completely derived from pluripotent stem cells.

SUMMARY

These advances in kidney organoids from pluripotent stem cells should lay a foundation to establish a novel therapy for kidney disease, which ultimately eliminate the need of dialysis and kidney transplantation for patients with kidney disease in the future.

The zinc finger transcription factor Sall1 is required for the early developmental transition of microglia in mouse embryos

Microglia play many critical roles in neural development. Recent single-cell RNA-sequencing studies have found diversity of microglia both across different stages and within the same stage in the developing brain. However, how such diversity is controlled during development is poorly understood. In this study, we first found the expression of the macrophage mannose receptor CD206 in early-stage embryonic microglia on mouse brain sections. This expression showed a sharp decline between E12.5 and E13.5 across the central nervous system. We next tested the roles of the microglia-expressed zinc finger transcription factor SALL1 in this early transition of gene expression. By deleting Sall1 specifically in microglia, we found that many microglia continued to express CD206 when it is normally downregulated. In addition, the mutant microglia continued to show less ramified morphology in comparison with controls even into postnatal stages. Thus, SALL1 is required for early microglia to transition into a more mature status during development.

The endothelial Dll4-muscular Notch2 axis regulates skeletal muscle mass

Adult skeletal muscle is a highly plastic tissue that readily reduces or gains its mass in response to mechanical and metabolic stimulation; however, the upstream mechanisms that control muscle mass remain unclear. Notch signalling is highly conserved, and regulates many cellular events, including proliferation and differentiation of various types of tissue stem cell via cell-cell contact. Here we reveal that multinucleated myofibres express Notch2, which plays a crucial role in disuse- or diabetes-induced muscle atrophy. Mechanistically, in both atrophic conditions, the microvascular endothelium upregulates and releases the Notch ligand, Dll4, which then activates muscular Notch2 without direct cell-cell contact. Inhibition of the Dll4-Notch2 axis substantively prevents these muscle atrophy and promotes mechanical overloading-induced muscle hypertrophy in mice. Our results illuminate a tissue-specific function of the endothelium in controlling tissue plasticity and highlight the endothelial Dll4-muscular Notch2 axis as a central upstream mechanism that regulates catabolic signals from mechanical and metabolic stimulation, providing a therapeutic target for muscle-wasting diseases.

Generation of ovarian follicles from mouse pluripotent stem cells

Oocytes mature in a specialized fluid-filled sac, the ovarian follicle, which provides signals needed for meiosis and germ cell growth. Methods have been developed to generate functional oocytes from pluripotent stem cell-derived primordial germ cell-like cells (PGCLCs) when placed in culture with embryonic ovarian somatic cells. In this study, we developed culture conditions to recreate the stepwise differentiation process from pluripotent cells to fetal ovarian somatic cell-like cells (FOSLCs). When FOSLCs were aggregated with PGCLCs derived from mouse embryonic stem cells, the PGCLCs entered meiosis to generate functional oocytes capable of fertilization and development to live offspring. Generating functional mouse oocytes in a reconstituted ovarian environment provides a method for in vitro oocyte production and follicle generation for a better understanding of mammalian reproduction.

PKD1-Dependent Renal Cystogenesis in Human Induced Pluripotent Stem Cell-Derived Ureteric Bud/Collecting Duct Organoids

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease leading to renal failure, wherein multiple cysts form in renal tubules and collecting ducts derived from distinct precursors: the nephron progenitor and ureteric bud (UB), respectively. Recent progress in induced pluripotent stem cell (iPSC) biology has enabled cyst formation in nephron progenitor-derived human kidney organoids in which PKD1 or PKD2, the major causative genes for ADPKD, are deleted. However, cysts have not been generated in UB organoids, despite the prevalence of collecting duct cysts in patients with ADPKD.

METHODS

CRISPR-Cas9 technology deleted PKD1 in human iPSCs and the cells induced to differentiate along pathways leading to formation of either nephron progenitor or UB organoids. Cyst formation was investigated in both types of kidney organoid derived from PKD1-deleted iPSCs and in UB organoids generated from iPSCs from a patient with ADPKD who had a missense mutation.

RESULTS

Cysts formed in UB organoids with homozygous PKD1 mutations upon cAMP stimulation and, to a lesser extent, in heterozygous mutant organoids. Furthermore, UB organoids generated from iPSCs from a patient with ADPKD who had a heterozygous missense mutation developed cysts upon cAMP stimulation.

CONCLUSIONS

Cysts form in PKD1 mutant UB organoids as well as in iPSCs derived from a patient with ADPKD. The organoids provide a robust model of the genesis of ADPKD.

Development of the Proximal-Anterior Skeletal Elements in the Mouse Hindlimb Is Regulated by a Transcriptional and Signaling Network Controlled by Sall4

The vertebrate limb serves as an experimental paradigm to study mechanisms that regulate development of the stereotypical skeletal elements. In this study, we simultaneously inactivated Sall4 using Hoxb6Cre and Plzf in mouse embryos, and found that their combined function regulates development of the proximal-anterior skeletal elements in hindlimbs. The Sall4; Plzf double knockout exhibits severe defects in the femur, tibia, and anterior digits, distinct defects compared to other allelic series of Sall4; Plzf We found that Sall4 regulates Plzf expression prior to hindlimb outgrowth. Further expression analysis indicated that Hox10 genes and GLI3 are severely downregulated in the Sall4; Plzf double knockout hindlimb bud. In contrast, PLZF expression is reduced but detectable in Sall4; Gli3 double knockout limb buds, and SALL4 is expressed in the Plzf; Gli3 double knockout limb buds. These results indicate that Plzf, Gli3, and Hox10 genes downstream of Sall4, regulate femur and tibia development. In the autopod, we show that Sall4 negatively regulates Hedgehog signaling, which allows for development of the most anterior digit. Collectively, our study illustrates genetic systems that regulate development of the proximal-anterior skeletal elements in hindlimbs.

TRAPγ-CDG shows asymmetric glycosylation and an effect on processing of proteins required in higher organisms

Newly synthesised glycoproteins enter the rough endoplasmic reticulum through a translocation pore. The translocon associated protein (TRAP) complex is located close to the pore. In a patient with a homozygous start codon variant in TRAPγ (SSR3), absence of TRAPγ causes disruption of the TRAP complex, impairs protein translocation into the endoplasmic reticulum and affects transport, for example, into the brush-border membrane. Furthermore, we observed an unbalanced non-occupancy of N-glycosylation sites. The major clinical features are intrauterine growth retardation, facial dysmorphism, congenital diarrhoea, failure to thrive, pulmonary disease and severe psychomotor disability.

Dullard-mediated Smad1/5/8 inhibition controls mouse cardiac neural crest cells condensation and outflow tract septation

The establishment of separated pulmonary and systemic circulation in vertebrates, via cardiac outflow tract (OFT) septation, is a sensitive developmental process accounting for 10% of all congenital anomalies. Neural Crest Cells (NCC) colonising the heart condensate along the primitive endocardial tube and force its scission into two tubes. Here, we show that NCC aggregation progressively decreases along the OFT distal-proximal axis following a BMP signalling gradient. Dullard, a nuclear phosphatase, tunes the BMP gradient amplitude and prevents NCC premature condensation. Dullard maintains transcriptional programs providing NCC with mesenchymal traits. It attenuates the expression of the aggregation factor Sema3c and conversely promotes that of the epithelial-mesenchymal transition driver Twist1. Altogether, Dullard-mediated fine-tuning of BMP signalling ensures the timed and progressive zipper-like closure of the OFT by the NCC and prevents the formation of a heart carrying the congenital abnormalities defining the tetralogy of Fallot.

Compensation of Disabled Organogeneses in Genetically Modified Pig Fetuses by Blastocyst Complementation

We have previously established a concept of developing exogenic pancreas in a genetically modified pig fetus with an apancreatic trait, thereby proposing the possibility of in vivo generation of functional human organs in xenogenic large animals. In this study, we aimed to demonstrate a further proof-of-concept of the compensation for disabled organogeneses in pig, including pancreatogenesis, nephrogenesis, hepatogenesis, and vasculogenesis. These dysorganogenetic phenotypes could be efficiently induced via genome editing of the cloned pigs. Induced dysorganogenetic traits could also be compensated by allogenic blastocyst complementation, thereby proving the extended concept of organ regeneration from exogenous pluripotent cells in empty niches during various organogeneses. These results suggest that the feasibility of blastocyst complementation using genome-edited cloned embryos permits experimentation toward the in vivo organ generation in pigs from xenogenic pluripotent cells.

Monkeys mutant for PKD1 recapitulate human autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) caused by PKD1 mutations is one of the most common hereditary disorders. However, the key pathological processes underlying cyst development and exacerbation in pre-symptomatic stages remain unknown, because rodent models do not recapitulate critical disease phenotypes, including disease onset in heterozygotes. Here, using CRISPR/Cas9, we generate ADPKD models with PKD1 mutations in cynomolgus monkeys. As in humans and mice, near-complete PKD1 depletion induces severe cyst formation mainly in collecting ducts. Importantly, unlike in mice, PKD1 heterozygote monkeys exhibit cyst formation perinatally in distal tubules, possibly reflecting the initial pathology in humans. Many monkeys in these models survive after cyst formation, and cysts progress with age. Furthermore, we succeed in generating selective heterozygous mutations using allele-specific targeting. We propose that our models elucidate the onset and progression of ADPKD, which will serve as a critical basis for establishing new therapeutic strategies, including drug treatments.

How to rebuild the kidney: recent advances in kidney organoids

It is difficult to restore kidney function once it has become severely impaired. Although kidney transplantation is a curative therapy, donor numbers remain limited. Thus, the generation of kidney organoids (mainly comprising glomeruli and renal tubules) from multipotent stem cells represents an important advance in regenerative medicine of the kidney. Recently, a protocol that can generate the higher-order structure of the mouse embryonic kidney was reported. Kidney organoids are now being used for disease modelling, and may eventually be applicable for clinical transplantation. In this review, we summarize the recent advances in kidney organoid research, and discuss the issues to be resolved toward kidney reconstruction.

Sall4 regulates neuromesodermal progenitors and their descendants during body elongation in mouse embryos

Bi-potential neuromesodermal progenitors (NMPs) produce both neural and paraxial mesodermal progenitors in the trunk and tail during vertebrate body elongation. We show that Sall4, a pluripotency-related transcription factor gene, has multiple roles in regulating NMPs and their descendants in post-gastrulation mouse embryos. Sall4 deletion using TCre caused body/tail truncation, reminiscent of early depletion of NMPs, suggesting a role of Sall4 in NMP maintenance. This phenotype became significant at the time of the trunk-to-tail transition, suggesting that Sall4 maintenance of NMPs enables tail formation. Sall4 mutants exhibit expanded neural and reduced mesodermal tissues, indicating a role of Sall4 in NMP differentiation balance. Mechanistically, we show that Sall4 promotion of WNT/β-catenin signaling contributes to NMP maintenance and differentiation balance. RNA-Seq and SALL4 ChIP-Seq analyses support the notion that Sall4 regulates both mesodermal and neural development. Furthermore, in the mesodermal compartment, genes regulating presomitic mesoderm differentiation are downregulated in Sall4 mutants. In the neural compartment, we show that differentiation of NMPs towards post-mitotic neuron is accelerated in Sall4 mutants. Our results collectively provide evidence supporting the role of Sall4 in regulating NMPs and their descendants.

Podocyte development, disease, and stem cell research

The glomerular podocyte is one of the major targets of kidney research. Recent establishment of kidney organoids from pluripotent stem cells has enabled the detailed analysis of human podocytes in both development and disease. The podocytes in organoids express slit diaphragm-related genes and proteins and exhibit characteristic morphology, especially upon experimental transplantation. Organoid technology is now used to reproduce hereditary podocyte diseases, and selective podocyte induction methods have also been reported. Moreover, single-cell RNA-sequencing of human fetal and adult kidneys has revealed the detailed molecular features of this cell lineage, as well as serving as references for kidney organoids in which podocytes are still immature. Here, we discuss the recent progress and limitations of podocyte research from the viewpoint of developmental biology and kidney organoids.

Mesenchymal actomyosin contractility is required for androgen-driven urethral masculinization in mice

The morphogenesis of mammalian embryonic external genitalia (eExG) shows dynamic differences between males and females. In genotypic males, eExG are masculinized in response to androgen signaling. Disruption of this process can give rise to multiple male reproductive organ defects. Currently, mechanisms of androgen-driven sexually dimorphic organogenesis are still unclear. We show here that mesenchymal-derived actomyosin contractility, by MYH10, is essential for the masculinization of mouse eExG. MYH10 is expressed prominently in the bilateral mesenchyme of male eExG. Androgen induces MYH10 protein expression and actomyosin contractility in the bilateral mesenchyme. Inhibition of actomyosin contractility through blebbistatin treatment and mesenchymal genetic deletion induced defective urethral masculinization with reduced mesenchymal condensation. We also suggest that actomyosin contractility regulates androgen-dependent mesenchymal directional cell migration to form the condensation in the bilateral mesenchyme leading to changes in urethral plate shape to accomplish urethral masculinization. Thus, mesenchymal-derived actomyosin contractility is indispensable for androgen-driven urethral masculinization.

From organoids to transplantable artificial kidneys

It is difficult to restore kidney function following chronic kidney damage. Although dialysis is currently used to treat patients with chronic kidney disease, it does not cure the disease, while severely restricting the patient's daily and social activities. Kidney transplantation is an alternative and curative therapy, but donor numbers remain limited. However, the generation of kidney organoids from human induced pluripotent stem cells represents an important recent advance in regenerative medicine. Kidney organoids are expected to be used for disease modeling and drug discovery, and may eventually be applicable for transplantation. In this review, we describe the current status of kidney organoids and discuss the hurdles that need to be overcome to generate transplantable artificial kidneys.

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.

Generation of Three-Dimensional Nephrons from Mouse and Human Pluripotent Stem Cells

Nephrons, the functional units of the kidney, are derived from nephron progenitor cells (NPCs). Here, we describe methods to reconstruct nephron tissue via induction of NPCs from mouse and human pluripotent stem cells, which mimic multistep developmental signals in vivo. Induced NPCs differentiate into three-dimensional nephron structures, including glomerular podocytes and nephric tubules, which are useful for studying early stages of kidney specification and morphogenetic processes in the context of normal development or disease.

Regenerative potential of induced pluripotent stem cells derived from patients undergoing haemodialysis in kidney regeneration

Kidney regeneration from pluripotent stem cells is receiving a lot of attention because limited treatments are currently available for chronic kidney disease (CKD). It has been shown that uremic state in CKD is toxic to somatic stem/progenitor cells, such as endothelial progenitor and mesenchymal stem cells, affecting their differentiation and angiogenic potential. Recent studies reported that specific abnormalities caused by the non-inherited disease are often retained in induced pluripotent stem cell (iPSC)-derived products obtained from patients. Thus, it is indispensable to first assess whether iPSCs derived from patients with CKD due to non-inherited disease (CKD-iPSCs) have the ability to generate kidneys. In this study, we generated iPSCs from patients undergoing haemodialysis due to diabetes nephropathy and glomerulonephritis (HD-iPSCs) as representatives of CKD-iPSCs or from healthy controls (HC-iPSCs). HD-iPSCs differentiated into nephron progenitor cells (NPCs) with similar efficiency to HC-iPSCs. Additionally, HD-iPSC-derived NPCs expressed comparable levels of NPC markers and differentiated into vascularised glomeruli upon transplantation into mice, as HC-iPSC-derived NPCs. Our results indicate the potential of HD-iPSCs as a feasible cell source for kidney regeneration. This is the first study paving the way for CKD patient-stem cell-derived kidney regeneration, emphasising the potential of CKD-iPSCs.

Organoids from Nephrotic Disease-Derived iPSCs Identify Impaired NEPHRIN Localization and Slit Diaphragm Formation in Kidney Podocytes

Mutations in the NPHS1 gene, which encodes NEPHRIN, cause congenital nephrotic syndrome, resulting from impaired slit diaphragm (SD) formation in glomerular podocytes. However, methods for SD reconstitution have been unavailable, thereby limiting studies in the field. In the present study, we established human induced pluripotent stem cells (iPSCs) from a patient with an NPHS1 missense mutation, and reproduced the SD formation process using iPSC-derived kidney organoids. The mutant NEPHRIN failed to become localized on the cell surface for pre-SD domain formation in the induced podocytes. Upon transplantation, the mutant podocytes developed foot processes, but exhibited impaired SD formation. Genetic correction of the single amino acid mutation restored NEPHRIN localization and phosphorylation, colocalization of other SD-associated proteins, and SD formation. Thus, these kidney organoids from patient-derived iPSCs identified SD abnormalities in the podocytes at the initial phase of congenital nephrotic disease.

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iPSCs are established from a patient with a missense NPHS1 mutation

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The induced podocytes exhibit impaired NEPHRIN localization

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The slit diaphragm is lacking in the mutant podocytes

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Genetic correction of the point mutation restores the phenotypes

Dullard deficiency causes hemorrhage in the adult ovarian follicles

In mammals, the ovarian follicles are regulated at least in part by bone morphogenetic protein (BMP) family members. Dullard (also known as Ctdnep1) gene encodes a phosphatase that suppresses BMP signaling by inactivating or degrading BMP receptors. Here we report that the Col1a1-Cre-induced Dullard mutant mice displayed hemorrhagic ovarian cysts, with red blood cells accumulated in the follicles, resulting in infertility. Cells expressing Cre driven by Col1a1 2.3-kb promoter and their descendants were found in granulosa cells in the ovary and in Sertoli cells in the testis. DullardmRNA was localized to granulosa cells in the ovary. Genes involved in steroid hormone genesis including Cyp11a1, Hsd3b1 and Star were reduced, whereas expression of Smad6 and Smad7, BMP-inducible inhibitory Smads, was up-regulated in the Dullard mutant ovaries. Tamoxifen-inducible Dullard deletion in the whole body using Rosa26-CreER mice also resulted in hemorrhagic ovarian cysts in 2 weeks, which was rescued by administration of LDN-193189, a chemical inhibitor of BMP receptor kinase, suggesting that the hemorrhage in the Dullard-deficient ovarian follicles might be caused by increased BMP signaling. Thus, we conclude that Dullard is essential for ovarian homeostasis at least in part via suppression of BMP signaling.

Sall1 Regulates Microglial Morphology Cell Autonomously in the Developing Retina

Retinal degeneration often accompanies microglial activation and infiltration of monocyte-derived macrophages into the retina, resulting in the coexistence of microglia and monocyte-derived macrophages in the retina. We previously showed that the Sall1 zinc-finger transcriptional factor is expressed specifically in microglia within the retinal phagocyte pool, and analyses of Sall1 knockout mice revealed that microglial morphology changed from a ramified to a more amoeboid appearance in the developing retina. To investigate further whether Sall1 functions autonomously in microglia, we generated Sall1 conditional knockout mice, in which Sall1 was depleted specifically in the Cx3cr1+ microglial compartment of the developing retina. Sall1-deficient microglia exhibited morphological abnormalities on embryonic day 18 that strikingly resembled the phenotype observed in Sall1 knockout mice, demonstrating that Sall1 regulates microglial morphology cell autonomously. Analysis of the postnatal retina revealed that Sall1-deficient microglia extended their processes and their morphology became comparable to that of wild-type microglia on postnatal day 21, indicating that Sall1 is essential for microglial ramification in the developing retina, but not in the postnatal retina.

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.

Re-expression of Sall1 in podocytes protects against adriamycin-induced nephrosis

The highly conserved spalt (sal) gene family members encode proteins characterized by multiple double zinc finger motifs of the C2H2 type. Humans and mice each have four known Sal-like genes (SALL1-4 in humans and Sall1-4 in mice). Sall1 is known to have a crucial role in kidney development. To explore the significance of Sall1 in differentiated podocytes, we investigated podocyte-specific Sall1-deficient mice (Sall1 KO^p°^d°^/p°^d°) using a podocin-Cre/loxP system and siRNA Sall1 knockdown (Sall1 KD) podocytes. Under physiological conditions, Sall1 KO^p°^d°^/p°^d° mice exhibited no proteinuria during their lifetime, but foot-process effacement was detected in some of the podocytes. To elucidate the role of Sall1 in injured podocytes, we used an adriamycin (ADR)-induced model of nephrosis and glomerulosclerosis. Surprisingly, the expression of Sall1 was elevated in control mice on day 14 after ADR injection. On day 28 after ADR injection, Sall1 KO^p°^d°^/p°^d° mice exhibited significantly higher levels of proteinuria and higher numbers of sclerotic glomeruli. Differentiated Sall1 KD podocytes showed a loss of synaptopodin, suppressed stress fiber formation, and, ultimately, impaired directed cell migration. In addition, the loss of Sall1 increased the number of apoptotic podocytes following ADR treatment. These results indicated that Sall1 has a protective role in podocytes; thus, we investigated the endoplasmic reticulum stress marker GRP78. GRP78 expression was higher in ADR-treated Sall1 KO^p°^d°^/p°^d° mice than in control mice. Sall1 appeared to influence the expression of GRP78 in injured podocytes. These results suggest that Sall1 is associated with actin reorganization, endoplasmic reticulum stress, and apoptosis in injured podocytes. These protective aspects of Sall1 re-expression in injured podocytes may have the potential to reduce apoptosis and possibly glomerulosclerosis.

Expanding nephron progenitors in vitro: a step toward regenerative medicine in nephrology

With recent success in directed differentiation of nephron progenitors from mouse embryonic stem cells or human-induced pluripotent stem cells, the ability to expand these nephron progenitors is an important step toward regenerative medicine in nephrology. A recent publication reports the first successful attempt to propagate human nephron progenitors while retaining their potential to form both glomeruli and renal tubules.

Embryonic Intra-Aortic Clusters Undergo Myeloid Differentiation Mediated by Mesonephros-Derived CSF1 in Mouse

The aorta-gonad-mesonephros (AGM) region contains intra-aortic clusters (IACs) thought to have acquired hematopoietic stem cell (HSC) potential in vertebrate embryos. To assess extrinsic regulation of IACs in the AGM region, we employed mouse embryos harboring a Sall1-GFP reporter gene, which allows identification of mesonephros cells based on GFP expression. Analysis of AGM region tissue sections confirmed mesonephros GFP expression. Mesonephric cells sorted at E10.5 expressed mRNA encoding Csf1, a hematopoietic cytokine, and corresponding protein, based on real-time PCR and immunocytochemistry, respectively. Further analysis indicated that some IACs express the CSF1 receptor, CSF1R. Expression of Cebpa and Irf8 mRNAs was higher in CSF1R-positive IACs, whereas that of Cebpε and Gfi1 mRNAs was lower relative to CSF1R-negative IACs, suggesting that CSF1/CSF1R signaling functions in IAC myeloid differentiation by modulating expression of these transcription factors. Colony formation assays using CSF1R-positive IACs revealed increased numbers of myeloid colonies in the presence of CSF1. Analysis using an intra-cellular signaling array indicated the greatest fold increase of Cleaved Caspase-3 in AGM cells in the presence of CSF1. Immunohistochemistry revealed that Cleaved Caspase-3 is primarily expressed in IACs in the AGM region, and incubation of IACs with CSF1 up-regulated Cleaved Caspase-3. Overall, our findings suggest that CSF1 secreted from mesonephros accelerates IAC myeloid differentiation in the AGM region, possibly via Caspase-3 cleavage.

Kinesin superfamily protein Kif26b links Wnt5a-Ror signaling to the control of cell and tissue behaviors in vertebrates

Wnt5a-Ror signaling constitutes a developmental pathway crucial for embryonic tissue morphogenesis, reproduction and adult tissue regeneration, yet the molecular mechanisms by which the Wnt5a-Ror pathway mediates these processes are largely unknown. Using a proteomic screen, we identify the kinesin superfamily protein Kif26b as a downstream target of the Wnt5a-Ror pathway. Wnt5a-Ror, through a process independent of the canonical Wnt/β-catenin-dependent pathway, regulates the cellular stability of Kif26b by inducing its degradation via the ubiquitin-proteasome system. Through this mechanism, Kif26b modulates the migratory behavior of cultured mesenchymal cells in a Wnt5a-dependent manner. Genetic perturbation of Kif26b function in vivo caused embryonic axis malformations and depletion of primordial germ cells in the developing gonad, two phenotypes characteristic of disrupted Wnt5a-Ror signaling. These findings indicate that Kif26b links Wnt5a-Ror signaling to the control of morphogenetic cell and tissue behaviors in vertebrates and reveal a new role for regulated proteolysis in noncanonical Wnt5a-Ror signal transduction.

PAX2 is dispensable for in vitro nephron formation from human induced pluripotent stem cells

The kidney is formed by reciprocal interactions between the nephron progenitor and the ureteric bud, the former of which gives rise to the epithelia of nephrons consisting of glomeruli and renal tubules. The transcription factor PAX2 is essential for this mesenchymal-to-epithelial transition of nephron progenitors, as well as ureteric bud lineage development, in mice. PAX2 mutations in humans cause renal coloboma syndrome. We previously reported the induction of nephron progenitors and three-dimensional nephron structures from human induced pluripotent stem (iPS) cells. Here we generate iPS cells lacking PAX2, and address the role of PAX2 in our in vitro induction protocol. While PAX2-null human nephron progenitors were properly formed, they unexpectedly became epithelialised to form glomeruli and renal tubules. However, the mutant glomerular parietal epithelial cells failed to transit to the squamous morphology, retaining the shape and markers of columnar epithelia. Therefore, PAX2 is dispensable for mesenchymal-to-epithelial transition of nephron progenitors, but is required for morphological development of glomerular parietal epithelial cells, during nephron formation from human iPS cells in vitro.

Human development, heredity and evolution

From March 27-29 2017, the RIKEN Center for Developmental Biology held a symposium entitled 'Towards Understanding Human Development, Heredity, and Evolution' in Kobe, Japan. Recent advances in technologies including stem cell culture, live imaging, single-cell approaches, next-generation sequencing and genome editing have led to an expansion in our knowledge of human development. Organized by Yoshiya Kawaguchi, Mitinori Saitou, Mototsugu Eiraku, Tomoya Kitajima, Fumio Matsuzaki, Takashi Tsuji and Edith Heard, the symposium covered a broad range of topics including human germline development, epigenetics, organogenesis and evolution. This Meeting Review provides a summary of this timely and exciting symposium, which has convinced us that we are moving into the era of science targeted on humans.

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

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

Generation of a Three-Dimensional Kidney Structure from Pluripotent Stem Cells

The kidney is a vital organ that has an important role in the maintenance of homeostasis by fluid volume regulation and waste product excretion. This role cannot be performed without the three-dimensional (3D) structure of the kidney. Therefore, it is important to generate the 3D structure of the kidney when inducing functional kidney tissue or the whole organ from pluripotent stem cells. In this chapter, we describe the detailed methods to induce kidney progenitor cells from pluripotent stem cells, which are based on embryological development. We also provide a method to generate 3D kidney tissue with vascularized glomeruli upon transplantation.

Cooperative Action between SALL4A and TET Proteins in Stepwise Oxidation of 5-Methylcytosine

TET family enzymes successively oxidize 5-methylcytosine to 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine, leading to eventual demethylation. 5hmC and TET enzymes occupy distinct chromatin regions, suggesting unknown mechanisms controlling the fate of 5hmC within diverse chromatin environments. Here, we report that SALL4A preferentially associates with 5hmC in vitro and occupies enhancers in mouse embryonic stem cells in a largely TET1-dependent manner. Although most 5hmC at SALL4A peaks undergoes further oxidation, this process is abrogated upon deletion of Sall4 gene, with a concomitant reduction of TET2 at these regions. Thus, SALL4A facilitates further oxidation of 5hmC at its binding sites, which requires its 5hmC-binding activity and TET2, supporting a collaborative action between SALL4A and TET proteins in regulating stepwise oxidation of 5mC at enhancers. Our study identifies SALL4A as a 5hmC binder, which facilitates 5hmC oxidation by stabilizing TET2 association, thereby fine-tuning expression profiles of developmental genes in mouse embryonic stem cells.

Sall4 controls differentiation of pluripotent cells independently of the Nucleosome Remodelling and Deacetylation (NuRD) complex

Sall4 is an essential transcription factor for early mammalian development and is frequently overexpressed in cancer. Although it is reported to play an important role in embryonic stem cell (ESC) self-renewal, whether it is an essential pluripotency factor has been disputed. Here, we show that Sall4 is dispensable for mouse ESC pluripotency. Sall4 is an enhancer-binding protein that prevents precocious activation of the neural gene expression programme in ESCs but is not required for maintenance of the pluripotency gene regulatory network. Although a proportion of Sall4 protein physically associates with the Nucleosome Remodelling and Deacetylase (NuRD) complex, Sall4 neither recruits NuRD to chromatin nor influences transcription via NuRD; rather, free Sall4 protein regulates transcription independently of NuRD. We propose a model whereby enhancer binding by Sall4 and other pluripotency-associated transcription factors is responsible for maintaining the balance between transcriptional programmes in pluripotent cells.

Highlighted article: Sall4 and Sall1 inhibit neural differentiation in ESCs by acting at enhancer sequences independently of the NuRD complex, and are dispensable for the maintenance of pluripotency.

The pluripotency factor Nanog regulates pericentromeric heterochromatin organization in mouse embryonic stem cells

Here, Novo et al. identify a new critical role for the transcription factor Nanog in maintaining an open heterochromatin state in pluripotent mouse embryonic stem cells and demonstrate that forced expression of Nanog is sufficient to remodel and decondense chromatin in more developmentally advanced mammalian cell types. This study delineates a direct connection between the pluripotency network and chromatin organization and shows that maintainence of an open heterochromatin architecture is highly regulated in embryonic stem cells.

An open and decondensed chromatin organization is a defining property of pluripotency. Several epigenetic regulators have been implicated in maintaining an open chromatin organization, but how these processes are connected to the pluripotency network is unknown. Here, we identified a new role for the transcription factor NANOG as a key regulator connecting the pluripotency network with constitutive heterochromatin organization in mouse embryonic stem cells. Deletion of Nanog leads to chromatin compaction and the remodeling of heterochromatin domains. Forced expression of NANOG in epiblast stem cells is sufficient to decompact chromatin. NANOG associates with satellite repeats within heterochromatin domains, contributing to an architecture characterized by highly dispersed chromatin fibers, low levels of H3K9me3, and high major satellite transcription, and the strong transactivation domain of NANOG is required for this organization. The heterochromatin-associated protein SALL1 is a direct cofactor for NANOG, and loss of Sall1 recapitulates the Nanog-null phenotype, but the loss of Sall1 can be circumvented through direct recruitment of the NANOG transactivation domain to major satellites. These results establish a direct connection between the pluripotency network and chromatin organization and emphasize that maintaining an open heterochromatin architecture is a highly regulated process in embryonic stem cells.

Selective In Vitro Propagation of Nephron Progenitors Derived from Embryos and Pluripotent Stem Cells

Nephron progenitors in the embryonic kidney propagate while generating differentiated nephrons. However, in mice, the progenitors terminally differentiate shortly after birth. Here, we report a method for selectively expanding nephron progenitors in vitro in an undifferentiated state. Combinatorial and concentration-dependent stimulation with LIF, FGF2/9, BMP7, and a WNT agonist is critical for expansion. The purified progenitors proliferated beyond the physiological limits observed in vivo, both for cell numbers and lifespan. Neonatal progenitors were maintained for a week, while progenitors from embryonic day 11.5 expanded 1,800-fold for nearly 20 days and still reconstituted 3D nephrons containing glomeruli and renal tubules. Furthermore, progenitors generated from mouse embryonic stem cells and human induced pluripotent cells could be expanded with retained nephron-forming potential. Thus, we have established in vitro conditions for promoting the propagation of nephron progenitors, which will be essential for dissecting the mechanisms of kidney organogenesis and for regenerative medicine.

Sall1 transiently marks undifferentiated heart precursors and regulates their fate

Cardiac progenitor cells (CPCs) are a crucial source of cells in cardiac development and regeneration. However, reported CPCs are heterogeneous, and no gene has been identified to transiently mark undifferentiated CPCs throughout heart development. Here we show that Spalt-like gene 1 (Sall1), a zing-finger transcription factor, is expressed in undifferentiated CPCs giving rise to both left and right ventricles. Sall1 was transiently expressed in precardiac mesoderm contributing to the first heart field (left ventricle precursors) but not in the field itself. Similarly, Sall1 expression was maintained in the second heart field (outflow tract/right ventricle precursors) but not in cardiac cells. In vitro, high levels of Sall1 at mesodermal stages enhanced cardiomyogenesis, whereas its continued expression suppressed cardiac differentiation. Our study demonstrates that Sall1 marks CPCs in an undifferentiated state and regulates cardiac differentiation. These findings provide fundamental insights into CPC maintenance, which can be instrumental for CPC-based regenerative medicine.

Preformed Wolffian duct regulates Müllerian duct elongation independently of canonical Wnt signaling or Lhx1 expression

The Müllerian duct gives rise to female reproductive organs, such as the oviduct and uterus. During gestation, the Wolffian duct, which generates male reproductive organs and the kidney, is formed, and the Müllerian duct then elongates caudally along the preformed Wolffian duct. Anatomical separation of these two ducts in chick embryos demonstrated that the Wolffian duct is required for Müllerian duct formation. Likewise, a few reports supported this notion in mice, including studies on Wnt9b mutant mice and Wolffian duct-specific Lhx1 deletion. However, anatomical ablation of the Wolffian duct has not been established in mice. In this study, we addressed the importance of the interaction between these two reproductive ducts, by generating mice that specifically expressed a diphtheria toxin subunit in the Wolffian duct. While this genetic ablation of the Wolffian duct resulted in kidney hypoplasia/agenesis in both male and female mutant mice, the female mutant mice lacked the uterus, which is derived from the Müllerian duct. At mid-gestation, the Müllerian duct was truncated at the level where the mutant Wolffian duct was prematurely terminated, meaning that Müllerian duct elongation was dependent on the preformed Wolffian duct. However, Wnt9b expression in the Wolffian duct and the resultant canonical Wnt activity, as well as Lhx1 expression, were not affected in the mutant mice. These results suggest that the Wolffian duct regulates Müllerian duct elongation by currently unidentified mechanisms that are independent of canonical Wnt signaling or Lhx1 expression.