vhnf1, the MODY5 and familial GCKD-associated gene, regulates regional specification of the zebrafish gut, pronephros, and hindbrain

Prenatal diagnosis of 17q12 copy number variants in fetuses via chromosomal microarray analysis - A retrospective cohort study and literature review

Purpose

17q12 copy number variants (CNVs) have variable presentations and incomplete penetrance, challenging prenatal counseling and management. This study aims to investigate the intrauterine phenotype.

Methods

We included 48 fetuses diagnosed with 17q12 microdeletion or microduplication by chromosomal microarray analysis.

Results

For 17q12 deletion, renal anomalies were found in 35 fetuses (35/37, 94.6 %), with hyperechogenic kidneys (HEK, 28/37, 75.7 %) and multicystic dysplastic kidneys (17/37, 45.9 %) being the most common findings. Duodenal obstruction (DO) was most frequently combined in 17q12 duplication fetuses. In addition, cardiac abnormalities were the first reported prenatal phenotype in 17q12 duplication fetuses.

Conclusion

Our study shows that HEK and DO are the most predominant presentations of 17q12 deletion and duplication, respectively, and cardiac structural abnormalities may be associated with the latter. Although 17q12 CNVs have incomplete penetrance and variable expressivity and may be mainly involved in neurodevelopmental disorders, their short-term prognosis appears positive.

Fibronectin and Hand2 influence tubulogenesis during pronephros development and mesonephros regeneration in zebrafish (Danio rerio)

Worldwide incidence of kidney diseases has been rising. Thus, recent research has focused on zebrafish, whose fast development and innate regeneration capacity allow identifying factors influencing renal processes. Among these poorly studied factors are extracellular matrix (ECM) proteins like Fibronectin (Fn) essential in various tissues but not yet evaluated in a renal context. We utilized early nat and han zebrafish mutant embryos and carrier adults to investigate Fn's role during kidney development and regeneration. The locus natter (nat) encodes Fn and the locus han encodes Hand2, which results in increased Fn deposition. Our results show that Fn impacts identity maintenance and morphogenesis during development and influences conditions for neonephrogenic cluster formation during regeneration. Histological analysis revealed disrupted pronephric structures and increased blood cell accumulation in Fn mutants. Despite normal expression of specification markers (pax2, ATPα1a.1), structural abnormalities were evident. Differences between wild-type and mutation-carriers suggest a haploinsufficiency scenario. These findings reveal a novel function for ECM in renal development and regeneration, with potential implications for understanding and treating kidney diseases.

Kidney transcriptome and cystic kidney disease genes in zebrafish

Introduction: Polycystic kidney disease (PKD) is a condition where fluid filled cysts form on the kidney which leads to overall renal failure. Zebrafish has been recently adapted to study polycystic kidney disease, because of its powerful embryology and genetics. However, there are concerns on the conservation of this lower vertebrate in modeling polycystic kidney disease. Methods: Here, we aim to assess the molecular conservation of zebrafish by searching homologues polycystic kidney disease genes and carrying transcriptome studies in this animal. Results and Discussion: We found that out of 82 human cystic kidney disease genes, 81 have corresponding zebrafish homologs. While 75 of the genes have a single homologue, only 6 of these genes have two homologs. Comparison of the expression level of the transcripts enabled us to identify one homolog over the other homolog with >70% predominance, which would be prioritized for future experimental studies. Prompted by sexual dimorphism in human and rodent kidneys, we studied transcriptome between different sexes and noted significant differences in male vs. female zebrafish, indicating that sex dimorphism also occurs in zebrafish. Comparison between zebrafish and mouse identified 10% shared genes and 38% shared signaling pathways. String analysis revealed a cluster of genes differentially expressed in male vs. female zebrafish kidneys. In summary, this report demonstrated remarkable molecular conservation, supporting zebrafish as a useful animal model for cystic kidney disease.

Review of neurodevelopmental disorders in patients with HNF1B gene variations

This review investigates the association between neurodevelopmental disorders (NDD) and variations of the gene HNF1B. Heterozygous intragenetic mutations or heterozygous gene deletions (17q12 microdeletion syndrome) of HNF1B are the cause of a multi-system developmental disorder, termed renal cysts and diabetes syndrome (RCAD). Several studies suggest that in general, patients with genetic variation of HNF1B have an elevated risk for additional neurodevelopmental disorders, especially autism spectrum disorder (ASD) but a comprehensive assessment is yet missing. This review provides an overview including all available studies of patients with HNF1B mutation or deletion with comorbid NDD with respect to the prevalence of NDDs and in how they differ between patients with an intragenic mutation or 17q12 microdeletion. A total of 31 studies was identified, comprising 695 patients with variations in HNF1B, (17q12 microdeletion N = 416, mutation N = 279). Main results include that NDDs are present in both groups (17q12 microdeletion 25.2% vs. mutation 6.8%, respectively) but that patients with 17q12 microdeletions presented more frequently with any NDDs and especially with learning difficulties compared to patients with a mutation of HNF1B. The observed prevalence of NDDs in patients with HNF1B variations seems to be higher than in the general population, but the validity of the estimated prevalence must be deemed insufficient. This review shows that systematical research of NDDs in patients with HNF1B mutations or deletions is lacking. Further studies regarding neuropsychological characteristics of both groups are needed. NDDs might be a concomitant of HFN1B-related disease and should be considered in clinical routine and scientific reports.

Research Progress on the Construction and Application of a Diabetic Zebrafish Model

Diabetes is a metabolic disease characterized by high blood glucose levels. With economic development and lifestyle changes, the prevalence of diabetes is increasing yearly. Thus, it has become an increasingly serious public health problem in countries around the world. The etiology of diabetes is complex, and its pathogenic mechanisms are not completely clear. The use of diabetic animal models is helpful in the study of the pathogenesis of diabetes and the development of drugs. The emerging vertebrate model of zebrafish has many advantages, such as its small size, large number of eggs, short growth cycle, simple cultivation of adult fish, and effective improvement of experimental efficiency. Thus, this model is highly suitable for research as an animal model of diabetes. This review not only summarizes the advantages of zebrafish as a diabetes model, but also summarizes the construction methods and challenges of zebrafish models of type 1 diabetes, type 2 diabetes, and diabetes complications. This study provides valuable reference information for further study of the pathological mechanisms of diabetes and the research and development of new related therapeutic drugs.

Comparative Transcriptome Analysis Provides Novel Molecular Events for the Differentiation and Maturation of Hepatocytes during the Liver Development of Zebrafish

The liver plays an essential role in multiple biological functions including metabolism, detoxification, digestion, coagulation, and homeostasis in vertebrates. The specification and differentiation of embryonic hepatoblasts, the proliferation of hepatocytes, and the hepatic tissue architecture are well documented, but molecular events governing the maturation of hepatocytes during liver development remain largely unclear. In this study, we performed a comparative transcriptome analysis of hepatocytes that were sorted by flow cytometry from developing zebrafish embryos at 60, 72, and 96 hpf. We identified 667 up-regulated and 3640 down-regulated genes in hepatocytes between 60 and 72 hpf, 606 up-regulated and 3924 down-regulated genes between 60 and 96 hpf, and 1693 up-regulated genes and 1508 down-regulated genes between 72 and 96 hpf. GO enrichment analysis revealed that key biological processes, cellular components, and molecular functions in hepatocytes between 60 to 72 hpf, such as cell cycle, DNA replication, DNA repair, RNA processing, and transcription regulation, are mainly associated with the proliferation of hepatocytes. In addition to biological processes, cellular components, and molecular functions for cell proliferation, molecular functions for carbohydrate metabolism were enriched in hepatocytes during 72 to 96 hpf. KEGG enrichment analysis identified key signaling pathways, such as cell cycle, RNA degradation, ubiquitin-mediated proteolysis, ErbB and Hedgehog signaling, basal transcription factors, Wnt signaling, and glycan degradation, which are closely associated with cell proliferation or carbohydrate metabolism in hepatocytes between 60 to 72 hpf. Newly enriched signaling pathways in hepatocytes during 72 to 96 hpf include metabolisms of pyrimidine, purine, nicotinate and nicotinamide, caffeine, glycine, serine and threonine, ABC transporters, and p53 signaling that function in metabolisms of lipid, protein and energy, cellular secretion, or detoxification, indicating the functional maturation of hepatocytes between 72 to 96 hpf. These findings provide novel clues for further understanding the functional differentiation and maturation of hepatocytes during liver development.

Identification of downstream effectors of retinoic acid specifying the zebrafish pancreas by integrative genomics

Retinoic acid (RA) is a key signal for the specification of the pancreas. Still, the gene regulatory cascade triggered by RA in the endoderm remains poorly characterized. In this study, we investigated this regulatory network in zebrafish by combining RNA-seq, RAR ChIP-seq and ATAC-seq assays. By analysing the effect of RA and of the RA receptor (RAR) inverse-agonist BMS493 on the transcriptome and on the chromatin accessibility of endodermal cells, we identified a large set of genes and regulatory regions regulated by RA signalling. RAR ChIP-seq further defined the direct RAR target genes in zebrafish, including hox genes as well as several pancreatic regulators like mnx1, insm1b, hnf1ba and gata6. Comparison of zebrafish and murine RAR ChIP-seq data highlighted the conserved direct target genes and revealed that some RAR sites are under strong evolutionary constraints. Among them, a novel highly conserved RAR-induced enhancer was identified downstream of the HoxB locus and driving expression in the nervous system and in the gut in a RA-dependent manner. Finally, ATAC-seq data unveiled the role of the RAR-direct targets Hnf1ba and Gata6 in opening chromatin at many regulatory loci upon RA treatment.

Segmentation and patterning of the vertebrate hindbrain

During early development, the hindbrain is sub-divided into rhombomeres that underlie the organisation of neurons and adjacent craniofacial tissues. A gene regulatory network of signals and transcription factors establish and pattern segments with a distinct anteroposterior identity. Initially, the borders of segmental gene expression are imprecise, but then become sharply defined, and specialised boundary cells form. In this Review, we summarise key aspects of the conserved regulatory cascade that underlies the formation of hindbrain segments. We describe how the pattern is sharpened and stabilised through the dynamic regulation of cell identity, acting in parallel with cell segregation. Finally, we discuss evidence that boundary cells have roles in local patterning, and act as a site of neurogenesis within the hindbrain.

Overdosage of HNF1B Gene Associated With Annular Pancreas Detected in Neonate Patients With 17q12 Duplication

The annular pancreas (AP) is a congenital anomaly of the pancreas that can cause acute abdominal pain and vomiting after birth. However, the genetic cause of AP is still unknown, and no study has reported AP in patients with 17q12 duplication. This study retrospectively analyzed the next-generation sequencing (NGS) data of individuals from January 2016 to June 2020 for 17q12 duplication. To identify the function of the key gene of HNF1B in the 17q12 duplication region, human HNF1B mRNA was microinjected into LiPan zebrafish transgenic embryos. A total of 19 cases of 17q12 duplication were confirmed. AP was diagnosed during exploratory laparotomy in four patients (21.1%). The other common features of 17q12 duplication included intellectual disability (50%), gross motor delay (50%), and seizures/epilepsy (31.58%). The ratio of the abnormal pancreas in zebrafish was significantly higher in the HNF1B overexpression models. In conclusion, we first reported AP in patients with duplication of the 17q12 region, resulting in the phenotype of 17q12 duplication syndrome. Furthermore, our zebrafish studies verified the role of the HNF1B gene in pancreatic development.

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).

Autosomal dominant tubulointerstitial kidney disease

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a recently defined entity that includes rare kidney diseases characterized by tubular damage and interstitial fibrosis in the absence of glomerular lesions, with inescapable progression to end-stage renal disease. These diseases have long been neglected and under-recognized, in part due to confusing and inconsistent terminology. The introduction of a gene-based, unifying terminology led to the identification of an increasing number of cases, with recent data suggesting that ADTKD is one of the more common monogenic kidney diseases after autosomal dominant polycystic kidney disease, accounting for ~5% of monogenic disorders causing chronic kidney disease. ADTKD is caused by mutations in at least five different genes, including UMOD, MUC1, REN, HNF1B and, more rarely, SEC61A1. These genes encode various proteins with renal and extra-renal functions. The mundane clinical characteristics and lack of appreciation of family history often result in a failure to diagnose ADTKD. This Primer highlights the different types of ADTKD and discusses the distinct genetic and clinical features as well as the underlying mechanisms.

Transcriptional profiling of the zebrafish proximal tubule

The hepatocyte nuclear factor-1β (Hnf1b) transcription factor is a key regulator of kidney tubule formation and is associated with a syndrome of renal cysts and early onset diabetes. To further our understanding of Hnf1b in the developing zebrafish kidney, we performed RNA sequencing analysis of proximal tubules from hnf1b-deficient larvae. This analysis revealed an enrichment of gene transcripts encoding transporters of the solute carrier (SLC) superfamily, including multiple members of slc2 and slc5 glucose transporters. An investigation of expression of slc2a1a, slc2a2, and slc5a2 as well as a poorly studied glucose/mannose transporter encoded by slc5a9 revealed that these genes undergo dynamic spatiotemporal changes during tubule formation and maturation. A comparative analysis of zebrafish SLC genes with those expressed in mouse proximal tubules showed a substantial overlap at the level of gene families, indicating a high degree of functional conservation between zebrafish and mammalian proximal tubules. Taken together, our findings are consistent with a role for Hnf1b as a critical determinant of proximal tubule transport function by acting upstream of a large number of SLC genes and validate the zebrafish as a physiologically relevant model of the mammalian proximal tubule.

In vivo analysis of renal epithelial cells in zebrafish

The zebrafish kidney has been used effectively for studying kidney development, repair and disease. New gene editing capability makes it a more versatile in vivo vertebrate model system to investigate renal epithelial cells in their native environment. In this chapter we focus on dissecting gene function in basic cellular biology of renal epithelial cells, including lumen formation and cell polarity, in intact zebrafish embryos.

Hindbrain induction and patterning during early vertebrate development

The hindbrain is a key relay hub of the central nervous system (CNS), linking the bilaterally symmetric half-sides of lower and upper CNS centers via an extensive network of neural pathways. Dedicated neural assemblies within the hindbrain control many physiological processes, including respiration, blood pressure, motor coordination and different sensations. During early development, the hindbrain forms metameric segmented units known as rhombomeres along the antero-posterior (AP) axis of the nervous system. These compartmentalized units are highly conserved during vertebrate evolution and act as the template for adult brainstem structure and function. TALE and HOX homeodomain family transcription factors play a key role in the initial induction of the hindbrain and its specification into rhombomeric cell fate identities along the AP axis. Signaling pathways, such as canonical-Wnt, FGF and retinoic acid, play multiple roles to initially induce the hindbrain and regulate Hox gene-family expression to control rhombomeric identity. Additional transcription factors including Krox20, Kreisler and others act both upstream and downstream to Hox genes, modulating their expression and protein activity. In this review, we will examine the earliest embryonic signaling pathways that induce the hindbrain and subsequent rhombomeric segmentation via Hox and other gene expression. We will examine how these signaling pathways and transcription factors interact to activate downstream targets that organize the segmented AP pattern of the embryonic vertebrate hindbrain.

Sweet fish: Fish models for the study of hyperglycemia and diabetes

Fish are good for your health in more ways than you may expect. For one, eating fish is a common dietary recommendation for a healthy diet. However, fish have much more to provide than omega-3 fatty acids to your circulatory system. Some fish species now serve as important and innovative model systems for diabetes research, providing novel and unique advantages compared with classical research models. Not surprisingly, the largest share of diabetes research in fish occurs in the laboratory workhorse among fish, the zebrafish (Danio rerio). Established as a genetic model system to study development, these small cyprinid fish have eventually conquered almost every scientific discipline and, over the past decade, have emerged as an important model system for metabolic diseases, including diabetes mellitus. In this review we highlight the practicability of using zebrafish to study diabetes and hyperglycemia, and summarize some of the recent research and breakthroughs made using this model. Equally exciting is the appearance of another emerging discipline, one that is taking advantage of evolution by studying cases of naturally occurring insulin resistance in fish species. We briefly discuss two such models in this review, namely the rainbow trout (Oncorhynchus mykiss) and the cavefish (Astyanax mexicanus).

In Vivo Rodent Models of Type 2 Diabetes and Their Usefulness for Evaluating Flavonoid Bioactivity

About 40% of the world’s population is overweight or obese and exist at risk of developing type 2 diabetes mellitus (T2D). Obesity is a leading pathogenic factor for developing insulin resistance (IR). It is well established that IR and a progressive decline in functional β-cell mass are hallmarks of developing T2D. In order to mitigate the global prevalence of T2D, we must carefully select the appropriate animal models to explore the cellular and molecular mechanisms of T2D, and to optimize novel therapeutics for their safe use in humans. Flavonoids, a group of polyphenols, have drawn great interest for their various health benefits, and have been identified in naturally occurring anti-diabetic compounds. Results from many clinical and animal studies demonstrate that dietary intake of flavonoids might prove helpful in preventing T2D. In this review, we discuss the currently available rodent animal models of T2D and analyze the advantages, the limitations of each T2D model, and highlight the potential anti-diabetic effects of flavonoids as well as the mechanisms of their actions.

Discovering human diabetes-risk gene function with genetics and physiological assays

Developing systems to identify the cell type-specific functions regulated by genes linked to type 2 diabetes (T2D) risk could transform our understanding of the genetic basis of this disease. However, in vivo systems for efficiently discovering T2D risk gene functions relevant to human cells are currently lacking. Here we describe powerful interdisciplinary approaches combining Drosophila genetics and physiology with human islet biology to address this fundamental gap in diabetes research. We identify Drosophila orthologs of T2D-risk genes that regulate insulin output. With human islets, we perform genetic studies and identify cognate human T2D-risk genes that regulate human beta cell function. Loss of BCL11A, a transcriptional regulator, in primary human islet cells leads to enhanced insulin secretion. Gene expression profiling reveals BCL11A-dependent regulation of multiple genes involved in insulin exocytosis. Thus, genetic and physiological systems described here advance the capacity to identify cell-specific T2D risk gene functions.

Regenerative medicine in kidney disease: where we stand and where to go

The kidney is a complex organ with more than 20 types of specialized cells that play an important role in maintaining the body's homeostasis. The epithelial tubular cell is formed during embryonic development and has little proliferative capacity under physiological conditions, but after acute injury the kidney does have regenerative capacity. However, after repetitive or severe lesions, it may undergo a maladaptation process that predisposes it to chronic kidney injury. Regenerative medicine includes various repair and regeneration techniques, and these have gained increasing attention in the scientific literature. In the future, not only will these techniques contribute to the repair and regeneration of the human kidney, but probably also to the construction of an entire organ. New mechanisms studied for kidney regeneration and repair include circulating stem cells as mesenchymal stromal/stem cells and their paracrine mechanisms of action; renal progenitor stem cells; the leading role of tubular epithelial cells in the tubular repair process; the study of zebrafish larvae to understand the process of nephron development, kidney scaffold and its repopulation; and, finally, the development of organoids. This review elucidates where we are in terms of current scientific knowledge regarding these mechanisms and the promises of future scientific perspectives.

Analysis of novel caudal hindbrain genes reveals different regulatory logic for gene expression in rhombomere 4 versus 5/6 in embryonic zebrafish

BACKGROUND

Previous work aimed at understanding the gene regulatory networks (GRNs) governing caudal hindbrain formation identified morphogens such as Retinoic Acid (RA) and Fibroblast growth factors (FGFs), as well as transcription factors like hoxb1b, hoxb1a, hnf1ba, and valentino as being required for rhombomere (r) r4-r6 formation in zebrafish. Considering that the caudal hindbrain is relatively complex - for instance, unique sets of neurons are formed in each rhombomere segment - it is likely that additional essential genes remain to be identified and integrated into the caudal hindbrain GRN.

METHODS

By taking advantage of gene expression data available in the Zebrafish Information Network (ZFIN), we identified 84 uncharacterized genes that are expressed in r4-r6. We selected a representative set of 22 genes and assayed their expression patterns in hoxb1b, hoxb1a, hnf1b, and valentino mutants with the goal of positioning them in the caudal hindbrain GRN. We also investigated the effects of RA and FGF on the expression of this gene set. To examine whether these genes are necessary for r4-r6 development, we analyzed germline mutants for six of the genes (gas6, gbx1, sall4, eglf6, celf2, and greb1l) for defects in hindbrain development.

RESULTS

Our results reveal that r4 gene expression is unaffected by the individual loss of hoxb1b, hoxb1a or RA, but is under the combinatorial regulation of RA together with hoxb1b. In contrast, r5/r6 gene expression is dependent on RA, FGF, hnf1ba and valentino - as individual loss of these factors abolishes r5/r6 gene expression. Our analysis of six mutant lines did not reveal rhombomere or neuronal defects, but transcriptome analysis of one line (gas6 mutant) identified expression changes for genes involved in several developmental processes - suggesting that these genes may have subtle roles in hindbrain development.

CONCLUSION

We conclude that r4-r6 formation is relatively robust, such that very few genes are absolutely required for this process. However, there are mechanistic differences in r4 versus r5/r6, such that no single factor is required for r4 development while several genes are individually required for r5/r6 formation.

Function and Regulation of the Wilms' Tumor Suppressor 1 (WT1) Gene in Fish

The Wilms' tumor suppressor gene Wt1 is highly conserved among vertebrates. In contrast to mammals, most fish species possess two wt1 paralogs that have been named wt1a and wt1b. Concerning wt1 in fish, most work so far has been done using zebrafish, focusing on the embryonic kidney, the pronephros. In this chapter we will describe the structure and development of the pronephros as well as the role that the wt1 genes play in the embryonic zebrafish kidney. We also discuss Wt1 target genes and describe the potential function of the Wt1 proteins in the adult kidney. Finally we will summarize data on the role of Wt1 outside of the kidney.

Gut-like ectodermal tissue in a sea anemone challenges germ layer homology

Cnidarians (for example, sea anemones and jellyfish) develop from an outer ectodermal and inner endodermal germ layer, whereas bilaterians (for example, vertebrates and flies) additionally have a mesodermal layer as intermediate germ layer. Currently, cnidarian endoderm (that is, 'mesendoderm') is considered homologous to both bilaterian endoderm and mesoderm. Here we test this hypothesis by studying the fate of germ layers, the localization of gut cell types, and the expression of numerous 'endodermal' and 'mesodermal' transcription factor orthologues in the anthozoan sea anemone Nematostella vectensis. Surprisingly, we find that the developing pharyngeal ectoderm and its derivatives display a transcription-factor expression profile (foxA, hhex, islet, soxB1, hlxB9, tbx2/3, nkx6 and nkx2.2) and cell-type combination (exocrine and insulinergic) reminiscent of the developing bilaterian midgut, and, in particular, vertebrate pancreatic tissue. Endodermal derivatives, instead, display cell functions and transcription-factor profiles similar to bilaterian mesoderm derivatives (for example, somatic gonad and heart). Thus, our data supports an alternative model of germ layer homologies, where cnidarian pharyngeal ectoderm corresponds to bilaterian endoderm, and the cnidarian endoderm is homologous to bilaterian mesoderm.

LITTLE FISH, BIG DATA: ZEBRAFISH AS A MODEL FOR CARDIOVASCULAR AND METABOLIC DISEASE

The burden of cardiovascular and metabolic diseases worldwide is staggering. The emergence of systems approaches in biology promises new therapies, faster and cheaper diagnostics, and personalized medicine. However, a profound understanding of pathogenic mechanisms at the cellular and molecular levels remains a fundamental requirement for discovery and therapeutics. Animal models of human disease are cornerstones of drug discovery as they allow identification of novel pharmacological targets by linking gene function with pathogenesis. The zebrafish model has been used for decades to study development and pathophysiology. More than ever, the specific strengths of the zebrafish model make it a prime partner in an age of discovery transformed by big-data approaches to genomics and disease. Zebrafish share a largely conserved physiology and anatomy with mammals. They allow a wide range of genetic manipulations, including the latest genome engineering approaches. They can be bred and studied with remarkable speed, enabling a range of large-scale phenotypic screens. Finally, zebrafish demonstrate an impressive regenerative capacity scientists hope to unlock in humans. Here, we provide a comprehensive guide on applications of zebrafish to investigate cardiovascular and metabolic diseases. We delineate advantages and limitations of zebrafish models of human disease and summarize their most significant contributions to understanding disease progression to date.

MiR-145 mediates zebrafish hepatic outgrowth through progranulin A signaling

MicroRNAs (miRs) are mRNA-regulatory molecules that fine-tune gene expression and modulate both processes of development and tumorigenesis. Our previous studies identified progranulin A (GrnA) as a growth factor which induces zebrafish hepatic outgrowth through MET signaling. We also found that miR-145 is one of potential fine-tuning regulators of GrnA involved in embryonic hepatic outgrowth. The low level of miR-145 seen in hepatocarinogenesis has been shown to promote pathological liver growth. However, little is known about the regulatory mechanism of miR-145 in embryonic liver development. In this study, we demonstrate a significant decrease in miR-145 expression during hepatogenesis. We modulate miR-145 expression in zebrafish embryos by injection with a miR-145 mimic or a miR-145 hairpin inhibitor. Altered embryonic liver outgrowth is observed in response to miR-145 expression modulation. We also confirm a critical role of miR-145 in hepatic outgrowth by using whole-mount in situ hybridization. Loss of miR-145 expression in embryos results in hepatic cell proliferation, and vice versa. Furthermore, we demonstrate that GrnA is a target of miR-145 and GrnA-induced MET signaling is also regulated by miR-145 as determined by luciferase reporter assay and gene expression analysis, respectively. In addition, co-injection of GrnA mRNA with miR-145 mimic or MO-GrnA with miR-145 inhibitor restores the liver defects caused by dysregulation of miR-145 expression. In conclusion, our findings suggest an important role of miR-145 in regulating GrnA-dependent hepatic outgrowth in zebrafish embryonic development.

Wnt8a expands the pool of embryonic kidney progenitors in zebrafish

During zebrafish embryogenesis the pronephric kidney arises from a small population of posterior mesoderm cells that then undergo expansion during early stages of renal organogenesis. While wnt8 is required for posterior mesoderm formation during gastrulation, it is also transiently expressed in the post-gastrula embryo in the intermediate mesoderm, the precursor to the pronephros and some blood/vascular lineages. Here, we show that knockdown of wnt8a, using a low dose of morpholino that does not disrupt early mesoderm patterning, reduces the number of kidney and blood cells. For the kidney, wnt8a deficiency decreases renal progenitor growth during early somitogenesis, as detected by EdU incorporation, but has no effect on apoptosis. The depletion of the renal progenitor pool in wnt8a knockdown embryos leads to cellular deficits in the pronephros at 24 hpf that are characterised by a shortened distal-most segment and stretched proximal tubule cells. A pulse of the canonical Wnt pathway agonist BIO during early somitogenesis is sufficient to rescue the size of the renal progenitor pool while longer treatment expands the number of kidney cells. Taken together, these observations indicate that Wnt8, in addition to its well-established role in posterior mesoderm patterning, also plays a later role as a factor that expands the renal progenitor pool prior to kidney morphogenesis.

On the development of the hepatopancreatic ductal system

The hepatopancreatic ductal system is the collection of ducts that connect the liver and pancreas to the digestive tract. The formation of this system is necessary for the transport of exocrine secretions, for the correct assembly of the pancreatobiliary ductal system, and for the overall function of the digestive system. Studies on endoderm organ formation have significantly advanced our understanding of the molecular mechanisms that govern organ induction, organ specification and morphogenesis of the major foregut-derived organs. However, little is known about the mechanisms that control the development of the hepatopancreatic ductal system. Here, we provide a description of the different components of the system, summarize its development from the endoderm to a complex system of tubes, list the pathologies produced by anomalies in its development, as well as the molecules and signaling pathways that are known to be involved in its formation. Finally, we discuss its proposed potential as a multipotent cell reservoir and the unresolved questions in the field.

Zebrafish Pronephros Development

The pronephros is the first kidney type to form in vertebrate embryos. The first step of pronephrogenesis in the zebrafish is the formation of the intermediate mesoderm during gastrulation, which occurs in response to secreted morphogens such as BMPs and Nodals. Patterning of the intermediate mesoderm into proximal and distal cell fates is induced by retinoic acid signaling with downstream transcription factors including wt1a, pax2a, pax8, hnf1b, sim1a, mecom, and irx3b. In the anterior intermediate mesoderm, progenitors of the glomerular blood filter migrate and fuse at the midline and recruit a blood supply. More posteriorly localized tubule progenitors undergo epithelialization and fuse with the cloaca. The Notch signaling pathway regulates the formation of multi-ciliated cells in the tubules and these cells help propel the filtrate to the cloaca. The lumenal sheer stress caused by flow down the tubule activates anterior collective migration of the proximal tubules and induces stretching and proliferation of the more distal segments. Ultimately these processes create a simple two-nephron kidney that is capable of reabsorbing and secreting solutes and expelling excess water-processes that are critical to the homeostasis of the body fluids. The zebrafish pronephric kidney provides a simple, yet powerful, model system to better understand the conserved molecular and cellular progresses that drive nephron formation, structure, and function.

Zebrafish Pancreas Development and Regeneration: Fishing for Diabetes Therapies

The zebrafish pancreas shares its basic organization and cell types with the mammalian pancreas. In addition, the developmental pathways that lead to the establishment of the pancreatic islets of Langherhans are generally conserved from fish to mammals. Zebrafish provides a powerful tool to probe the mechanisms controlling establishment of the pancreatic endocrine cell types from early embryonic progenitor cells, as well as the regeneration of endocrine cells after damage. This knowledge is, in turn, applicable to refining protocols to generate renewable sources of human pancreatic islet cells that are critical for regulation of blood sugar levels. Here, we review how previous and ongoing studies in zebrafish and beyond are influencing the understanding of molecular mechanisms underlying various forms of diabetes and efforts to develop cell-based approaches to cure this increasingly widespread disease.

Targeted resequencing of regulatory regions at schizophrenia risk loci: Role of rare functional variants at chromatin repressive states

There is mounting evidence that regulatory variation plays an important role in genetic risk for schizophrenia. Here, we specifically search for regulatory variants at risk by sequencing promoter regions of twenty-three genes implied in schizophrenia by copy number variant or genome-wide association studies. After strict quality control, a total of 55,206bp per sample were analyzed in 526 schizophrenia cases and 516 controls from Galicia, NW Spain, using the Applied Biosystems SOLiD System. Variants were filtered based on frequency from public databases, chromatin states from the RoadMap Epigenomics Consortium at tissues relevant for schizophrenia, such as fetal brain, mid-frontal lobe, and angular gyrus, and prediction of functionality from RegulomeDB. The proportion of rare variants at polycomb repressive chromatin state at relevant tissues was higher in cases than in controls. The proportion of rare variants with predicted regulatory role was significantly higher in cases than in controls (P=0.0028, OR=1.93, 95% C.I.=1.23-3.04). Combination of information from both sources led to the identification of an excess of carriers of rare variants with predicted regulatory role located at polycomb repressive chromatin state at relevant tissues in cases versus controls (P=0.0016, OR=19.34, 95% C.I.=2.45-2495.26). The variants are located at two genes affected by the 17q12 copy number variant, LHX1 and HNF1B. These data strongly suggest that a specific epigenetic mechanism, chromatin remodeling by histone modification during early development, may be impaired in a subset of schizophrenia patients, in agreement with previous data.

β-Amyloid precursor protein-b is essential for Mauthner cell development in the zebrafish in a Notch-dependent manner

Amyloid precursor protein (APP) is a transmembrane glycoprotein that has been the subject of intense research because of its implication in Alzheimer's disease. However, the physiological function of APP in the development and maintenance of the central nervous system remains largely unknown. We have previously shown that the APP homologue in zebrafish (Danio rerio), Appb, is required for motor neuron patterning and formation. Here we study the function of Appb during neurogenesis in the zebrafish hindbrain. Partial knockdown of Appb using antisense morpholino oligonucleotides blocked the formation of the Mauthner neurons, uni- or bilaterally, with an aberrant behavior as a consequence of this cellular change. The Appb morphants had decreased neurogenesis, increased notch signaling and notch1a expression at the expense of deltaA/D expression. The Mauthner cell development could be restored either by a general decrease in Notch signaling through γ-secretase inhibition or by a partial knock down of Notch1a. Together, this demonstrates the importance of Appb in neurogenesis and for the first time shows the essential requirement of Appb in the formation of a specific cell type, the Mauthner cell, in the hindbrain during development. Our results suggest that Appb-regulated neurogenesis is mediated through balancing the Notch1a signaling pathway and provide new insights into the development of the Mauthner cell.

Focusing the Spotlight on the Zebrafish Intestine to Illuminate Mechanisms of Colorectal Cancer

Colorectal cancer, encompassing colon and rectal cancer, arises from the epithelial lining of the large bowel. It is most prevalent in Westernised societies and is increasing in frequency as the world becomes more industrialised. Unfortunately, metastatic colorectal cancer is not cured by chemotherapy and the annual number of deaths caused by colorectal cancer, currently 700,000, is expected to rise. Our understanding of the contribution that genetic mutations make to colorectal cancer, although incomplete, is reasonably well advanced. However, it has only recently become widely appreciated that in addition to the ongoing accumulation of genetic mutations, chronic inflammation also plays a critical role in the initiation and progression of this disease. While a robust and tractable genetic model of colorectal cancer in zebrafish, suitable for pre-clinical studies, is not yet available, the identification of genes required for the rapid proliferation of zebrafish intestinal epithelial cells during development has highlighted a number of essential genes that could be targeted to disable colorectal cancer cells. Moreover, appreciation of the utility of zebrafish to study intestinal inflammation is on the rise. In particular, zebrafish provide unique opportunities to investigate the impact of genetic and environmental factors on the integrity of intestinal epithelial barrier function. With currently available tools, the interplay between epigenetic regulators, intestinal injury, microbiota composition and innate immune cell mobilisation can be analysed in exquisite detail. This provides excellent opportunities to define critical events that could potentially be targeted therapeutically. Further into the future, the use of zebrafish larvae as hosts for xenografts of human colorectal cancer tissue, while still in its infancy, holds great promise that zebrafish could one day provide a practical, preclinical personalized medicine platform for the rapid assessment of the metastatic potential and drug-sensitivity of patient-derived cancers.

Fishing for Nature's Hits: Establishment of the Zebrafish as a Model for Screening Antidiabetic Natural Products

Diabetes mellitus affects millions of people worldwide and significantly impacts their quality of life. Moreover, life threatening diseases, such as myocardial infarction, blindness, and renal disorders, increase the morbidity rate associated with diabetes. Various natural products from medicinal plants have shown potential as antidiabetes agents in cell-based screening systems. However, many of these potential "hits" fail in mammalian tests, due to issues such as poor pharmacokinetics and/or toxic side effects. To address this problem, the zebrafish (Danio rerio) model has been developed as a "bridge" to provide an experimentally convenient animal-based screening system to identify drug candidates that are active in vivo. In this review, we discuss the application of zebrafish to drug screening technologies for diabetes research. Specifically, the discovery of natural product-based antidiabetes compounds using zebrafish will be described. For example, it has recently been demonstrated that antidiabetic natural compounds can be identified in zebrafish using activity guided fractionation of crude plant extracts. Moreover, the development of fluorescent-tagged glucose bioprobes has allowed the screening of natural product-based modulators of glucose homeostasis in zebrafish. We hope that the discussion of these advances will illustrate the value and simplicity of establishing zebrafish-based assays for antidiabetic compounds in natural products-based laboratories.

Transcription Factor Hepatocyte Nuclear Factor-1β (HNF-1β) Regulates MicroRNA-200 Expression through a Long Noncoding RNA

The transcription factor hepatocyte nuclear factor-1β (HNF-1β) regulates tissue-specific gene expression in the kidney and other epithelial organs. Mutations of HNF-1β produce kidney cysts, and previous studies have shown that HNF-1β regulates the transcription of cystic disease genes, including Pkd2 and Pkhd1. Here, we combined chromatin immunoprecipitation and next-generation sequencing (ChIP-Seq) with microarray analysis to identify microRNAs (miRNAs) that are directly regulated by HNF-1β in renal epithelial cells. These studies identified members of the epithelial-specific miR-200 family (miR-200b/200a/429) as novel transcriptional targets of HNF-1β. HNF-1β binds to two evolutionarily conserved sites located 28 kb upstream to miR-200b. Luciferase reporter assays showed that the HNF-1β binding sites were located within a promoter that was active in renal epithelial cells. Mutations of the HNF-1β binding sites abolished promoter activity. RT-PCR analysis revealed that a long noncoding RNA (lncRNA) is transcribed from the promoter and encodes the miR-200 cluster. Inhibition of the lncRNA with siRNAs decreased the levels of miR-200 but did not affect expression of the Ttll10 host gene. The expression of the lncRNA and miR-200 was decreased in kidneys from HNF-1β knock-out mice and renal epithelial cells expressing dominant-negative mutant HNF-1β. The expression of miR-200 targets, Zeb2 and Pkd1, was increased in HNF-1β knock-out kidneys and in cells expressing mutant HNF-1β. Overexpression of miR-200 decreased the expression of Zeb2 and Pkd1 in HNF-1β mutant cells. These studies reveal a novel pathway whereby HNF-1β directly contributes to the control of miRNAs that are involved in epithelial-mesenchymal transition and cystic kidney disease.

The lure of zebrafish in liver research: regulation of hepatic growth in development and regeneration

The liver is an essential organ that plays a pivotal role in metabolism, digestion and nutrient storage. Major efforts have been made to develop zebrafish (Danio rerio) as a model system to study the pathways regulating hepatic growth during liver development and regeneration. Zebrafish offer unique advantages over other vertebrates including in vivo imaging at cellular resolution and the capacity for large-scale chemical and genetic screens. Here, we review the cellular and molecular mechanisms that regulate hepatic growth during liver development in zebrafish. We also highlight emerging evidence that developmental pathways are reactivated following liver injury to facilitate regeneration. Finally, we discuss how zebrafish have transformed drug discovery efforts and enabled the identification of drugs that stimulate hepatic growth and provide hepatoprotection in pre-clinical models of liver injury, with the ultimate goal of identifying novel therapeutic approaches to treat liver disease.

The gene regulatory networks underlying formation of the auditory hindbrain

Development and evolution of auditory hindbrain nuclei are two major unsolved issues in hearing research. Recent characterization of transgenic mice identified the rhombomeric origins of mammalian auditory nuclei and unraveled genes involved in their formation. Here, we provide an overview on these data by assembling them into rhombomere-specific gene regulatory networks (GRNs), as they underlie developmental and evolutionary processes. To explore evolutionary mechanisms, we compare the GRNs operating in the mammalian auditory hindbrain with data available from the inner ear and other vertebrate groups. Finally, we propose that the availability of genomic sequences from all major vertebrate taxa and novel genetic techniques for non-model organisms provide an unprecedented opportunity to investigate development and evolution of the auditory hindbrain by comparative molecular approaches. The dissection of the molecular mechanisms leading to auditory structures will also provide an important framework for auditory processing disorders, a clinical problem difficult to tackle so far. These data will, therefore, foster basic and clinical hearing research alike.

A novel function for Egr4 in posterior hindbrain development

Segmentation of the vertebrate hindbrain is an evolutionarily conserved process. Here, we identify the transcription factor early growth response 4 (egr4) as a novel regulator of posterior hindbrain development in Xenopus. egr4 is specifically and transiently expressed in rhombomeres 5 and 6 (r5/r6), and Egr4 knockdown causes a loss of mafb/kreisler and krox20/egr2 expression in r5/r6 and r5, respectively. This phenotype can be fully rescued by injection of frog or mouse Egr4 mRNA. Moreover Egr4-depleted embryos exhibit a specific loss of the neural crest stream adjacent to r5, and have inner ear defects. While the homeodomain protein vHnf1/Hnf1b directly activates Mafb and Krox20 expression in the mouse hindbrain to specify r5, we show that in Xenopus this process is indirect through the activation of Egr4. We provide evidence that rearrangements in the regulatory sequences around egr4 and mafb genes may account for this difference.

Retinoic acid regulates size, pattern and alignment of tissues at the head-trunk transition

At the head-trunk transition, hindbrain and spinal cord alignment to occipital and vertebral bones is crucial for coherent neural and skeletal system organization. Changes in neural or mesodermal tissue configuration arising from defects in the specification, patterning or relative axial placement of territories can severely compromise their integration and function. Here, we show that coordination of neural and mesodermal tissue at the zebrafish head-trunk transition crucially depends on two novel activities of the signaling factor retinoic acid (RA): one specifying the size and the other specifying the axial position relative to mesodermal structures of the hindbrain territory. These activities are each independent but coordinated with the well-established function of RA in hindbrain patterning. Using neural and mesodermal landmarks we demonstrate that the functions of RA in aligning neural and mesodermal tissues temporally precede the specification of hindbrain and spinal cord territories and the activation of hox transcription. Using cell transplantation assays we show that RA activity in the neuroepithelium regulates hindbrain patterning directly and territory size specification indirectly. This indirect function is partially dependent on Wnts but independent of FGFs. Importantly, RA specifies and patterns the hindbrain territory by antagonizing the activity of the spinal cord specification gene cdx4; loss of Cdx4 rescues the defects associated with the loss of RA, including the reduction in hindbrain size and the loss of posterior rhombomeres. We propose that at the head-trunk transition, RA coordinates specification, patterning and alignment of neural and mesodermal tissues that are essential for the organization and function of the neural and skeletal systems.

The small molecule probe PT-Yellow labels the renal proximal tubules in zebrafish

We report the development of a small fluorescent molecule, BDNCA3-D2, herein referred to as PT-Yellow. Soaking zebrafish embryos in PT-Yellow or intraperitoneal injection into adults results in non-toxic in vivo fluorescent labeling of the renal proximal tubules, the major site of blood filtrate reabsorption and a common target of injury in acute kidney injury. We demonstrate the applicability of this new compound as a rapid and simple readout for zebrafish kidney filtration and proximal tubule reabsorption function.

Grouper tshβ promoter-driven transgenic zebrafish marks proximal kidney tubule development

Kidney tubule plays a critical role in recovering or secreting solutes, but the detailed morphogenesis remains unclear. Our previous studies have found that grouper tshβ (gtshβ) is also expressed in kidney, however, the distribution significance is still unknown. To understand the gtshβ role and kidney tubule morphogenesis, here, we have generated a transgenic zebrafish line Tg(gtshβ:GFP) with green fluorescent protein driven by the gtshβ promoter. Similar to the endogenous tshβ in zebrafish or in grouper, the gtshβ promoter-driven GFP is expressed in pituitary and kidney, and the developing details of proximal kidney tubule are marked in the transgenic zebrafish line. The gfp initially transcribes at 16 hours post fertilization (hpf) above the dorsal mesentery, and partially co-localizes with pronephric tubular markers slc20a1a and cdh17. Significantly, the GFP specifically localizes in proximal pronephric segments during embryogenesis and resides at kidney duct epithelium in adult fish. To test whether the gtshβ promoter-driven GFP may serve as a readout signal of the tubular development, we have treated the embryos with retinoic acid signaing (RA) reagents, in which exogenous RA addition results in a distal extension of the proximal segments, while RA inhibition induces a weakness and shortness of the proximal segments. Therefore, this transgenic line provides a useful tool for genetic or chemical analysis of kidney tubule.

The emerging use of zebrafish to model metabolic disease

The zebrafish research community is celebrating! The zebrafish genome has recently been sequenced, the Zebrafish Mutation Project (launched by the Wellcome Trust Sanger Institute) has published the results of its first large-scale ethylnitrosourea (ENU) mutagenesis screen, and a host of new techniques, such as the genome editing technologies TALEN and CRISPR-Cas, are enabling specific mutations to be created in model organisms and investigated in vivo. The zebrafish truly seems to be coming of age. These powerful resources invoke the question of whether zebrafish can be increasingly used to model human disease, particularly common, chronic diseases of metabolism such as obesity and type 2 diabetes. In recent years, there has been considerable success, mainly from genomic approaches, in identifying genetic variants that are associated with these conditions in humans; however, mechanistic insights into the role of implicated disease loci are lacking. In this Review, we highlight some of the advantages and disadvantages of zebrafish to address the organism’s utility as a model system for human metabolic diseases.

Hnf1beta and nephron segmentation

The nephron is the functional unit that executes the homeostatic roles of the kidney in vertebrates. Critical to this function is the physical arrangement of the glomerular blood filter attached to a tubular epithelium that is subdivided into specialized proximal and distal segments. During embryogenesis, nephron progenitors undergo a mesenchymal-epithelial transition (MET) and adopt different segment-specific cell fates along the proximo-distal axis of the nephron. The molecular basis of how these segments arise remains largely unknown. Recent studies using the zebrafish have identified the Hnf1beta transcription factor (Hnf1b) as a major regulator of tubular segmentation. In Hnf1b-deficient zebrafish embryos, nephron progenitors fail to adopt the proximo-distal segmentation pattern of the nephron, yet still undergo MET. This observation suggests that the functional segmentation of renal tubular epithelial cells is independent of pathways that induce their epithelialization. Here we review this new role of Hnf1b for nephron segmentation during zebrafish and mouse kidney development.

Zebrafish models of human liver development and disease

The liver performs a large number of essential synthetic and regulatory functions that are acquired during fetal development and persist throughout life. Their disruption underlies a diverse group of heritable and acquired diseases that affect both pediatric and adult patients. Although experimental analyses used to study liver development and disease are typically performed in cell culture models or rodents, the zebrafish is increasingly used to complement discoveries made in these systems. Forward and reverse genetic analyses over the past two decades have shown that the molecular program for liver development is largely conserved between zebrafish and mammals, and that the zebrafish can be used to model heritable human liver disorders. Recent work has demonstrated that zebrafish can also be used to study the mechanistic basis of acquired liver diseases. Here, we provide a comprehensive summary of how the zebrafish has contributed to our understanding of human liver development and disease.

Expanding horizons: ciliary proteins reach beyond cilia

Once obscure, the cilium has come into the spotlight during the past decade. It is now clear that aside from generating locomotion by motile cilia, both motile and immotile cilia serve as signaling platforms for the cell. Through both motility and sensory functions, cilia play critical roles in development, homeostasis, and disease. To date, the cilium proteome contains more than 1,000 different proteins, and human genetics is identifying new ciliopathy genes at an increasing pace. Although assigning a function to immotile cilia was a challenge not so long ago, the myriad of signaling pathways, proteins, and biological processes associated with the cilium have now created a new obstacle: how to distill all these interactions into specific themes and mechanisms that may explain how the organelle serves to maintain organism homeostasis. Here, we review the basics of cilia biology, novel functions associated with cilia, and recent advances in cilia genetics, and on the basis of this framework, we further discuss the meaning and significance of ciliary connections.

Distinct enhancers of ptf1a mediate specification and expansion of ventral pancreas in zebrafish

Development of the pancreas and cerebellum require Pancreas-specific transcription factor-1a (Ptf1a), which encodes a subunit of the transcription factor complex PTF1. Ptf1a is required in succession for specification of the pancreas, proper allocation of pancreatic progenitors to endocrine and exocrine fates, and the production of digestive enzymes from the exocrine acini. In several neuronal structures, including the cerebellum, hindbrain, retina and spinal cord, Ptf1a is transiently expressed and promotes inhibitory neuron fates at the expense of excitatory fates. Transcription of Ptf1a in mouse is maintained in part by PTF1 acting on an upstream autoregulatory enhancer. However, the transcription factors and enhancers that initially activate Ptf1a expression in the pancreas and in certain structures of the nervous system have not yet been identified. Here we describe a zebrafish autoregulatory element, conserved among teleosts, with activity similar to that described in mouse. In addition, we performed a comprehensive survey of all non-coding sequences in a 67kb interval encompassing zebrafish ptf1a, and identified several neuronal enhancers, and an enhancer active in the ventral pancreas prior to activation of the autoregulatory enhancer. To test the requirement for autoregulatory control during pancreatic development, we restored ptf1a function through BAC transgenesis in ptf1a morphants, either with an intact BAC or one lacking the autoregulatory enhancer. We find that ptf1a autoregulation is required for development of the exocrine pancreas and full rescue of the ptf1a morphant phenotype. Similarly, we demonstrate that a ptf1a locus lacking the early enhancer region is also capable of rescue, but only supports formation of a hypoplastic exocrine pancreas. Through our dissection of the complex regulatory control of ptf1a, we identified separate cis-regulatory elements that underlie different aspects of its expression and function, and further demonstrated the requirement of maintained ptf1a expression for normal pancreatic morphogenesis. We also identified a novel enhancer that mediates initiation of ptf1a expression in the pancreas, through which the signals that specify the ventral pancreas are expected to exert their action.

Specification of hepatopancreas progenitors in zebrafish by hnf1ba and wnt2bb

Although the liver and ventral pancreas are thought to arise from a common multipotent progenitor pool, it is unclear whether these progenitors of the hepatopancreas system are specified by a common genetic mechanism. Efforts to determine the role of Hnf1b and Wnt signaling in this crucial process have been confounded by a combination of factors, including a narrow time frame for hepatopancreas specification, functional redundancy among Wnt ligands, and pleiotropic defects caused by either severe loss of Wnt signaling or Hnf1b function. Using a novel hypomorphic hnf1ba zebrafish mutant that exhibits pancreas hypoplasia, as observed in HNF1B monogenic diabetes, we show that hnf1ba plays essential roles in regulating β-cell number and pancreas specification, distinct from its function in regulating pancreas size and liver specification, respectively. By combining Hnf1ba partial loss of function with conditional loss of Wnt signaling, we uncover a crucial developmental window when these pathways synergize to specify the entire ventrally derived hepatopancreas progenitor population. Furthermore, our in vivo genetic studies demonstrate that hnf1ba generates a permissive domain for Wnt signaling activity in the foregut endoderm. Collectively, our findings provide a new model for HNF1B function, yield insight into pancreas and β-cell development, and suggest a new mechanism for hepatopancreatic specification.