Hhex regulates the specification and growth of the hepatopancreatic ductal system

Fenoxycarb induces cardiovascular, hepatic, and pancreatic toxicity in zebrafish larvae via ROS production, excessive inflammation, and apoptosis

Fenoxycarb, a carbamate insecticide, functions as a juvenile hormone agonist to inhibit pests, and its detection in aquatic environments is concerning because of its widespread application. These concerns have led to ecotoxicological studies on aquatic crustaceans; however, research on the effects of fenoxycarb on the developmental processes of organisms is limited. In the present study, the deleterious effects of fenoxycarb on zebrafish development and the related cellular mechanisms mediating this toxicity were addressed. Exposure to sublethal concentrations of fenoxycarb (0, 0.5, 1, and 2 mg/L) resulted in morphological defects in zebrafish larvae, particularly in the heart region, eyes, and body length. These defects were accompanied by an increase in the number of apoptotic cells and the upregulation of related gene expression. Moreover, fenoxycarb increased ROS production and the number of macrophages, and altered the expression of immune-related genes, thereby inducing inflammation. These results revealed various abnormalities in the heart, vasculature, liver, and pancreas, as confirmed by transgenic models, such as cmlc2:DsRed, fli1a:EGFP, and fabp10a:DsRed;elastase:GFP. These developmental impairments were associated with the altered expression levels of genes involved in the development and function of each organ. These results suggest that fenoxycarb can affect multiple organs through excessive inflammation during development and highlight its potent toxic effects on other non-target organisms.

An animal model recapitulates human hepatic diseases associated with GATA6 mutations

Heterozygotic GATA6 mutations are responsible for various congenital diseases in the heart, pancreas, liver, and other organs in humans. However, there is lack of an animal that can comprehensively model these diseases since GATA6 is essential for early embryogenesis. Here, we report the establishment of a gata6 knockout zebrafish which recapitulates most of the symptoms in patients with GATA6 mutations, including cardiac outflow tract defects, pancreatic hypoplasia/agenesis, gallbladder agenesis, and various liver diseases. Particularly in the liver, the zebrafish gata6 model exhibits the paucity of intrahepatic bile ducts, disrupted bile canaliculi, cholestasis, resembling the liver diseases associated with GATA6 mutations. Moreover, an unreported phenotype, hepatic cysts, has been also revealed in the model. Mechanistically, Gata6 interacts with Hhex and binds lrh-1 promoter to synergistically activate its expression, thereby enhancing the Lrh-1-mediated β-catenin signaling which is essential for liver development. This transcriptional activation of lrh-1 is tightly controlled by the negative feedback, in which Lrh1 interacts with Gata6 to weaken its transactivation ability. Moreover, Gata6 level is regulated by Hhex-mediated proteasomal degradation. The orchestration by these three transcription factors precisely modulates Gata6 activity, ensuring β-catenin signaling output and proper liver development in zebrafish. Importantly, the molecular mechanism identified in zebrafish is conserved in human cells. GATA6 mutant variants associated with hepatobiliary malformations in humans interact aberrantly with HHEX, resulting in subsequent impairments of LRH-1 activation. Conclusively, the disease model established here provides both phenotypic and mechanism insights into the human hepatic diseases associated with GATA6 mutations.

Prox1a promotes liver growth and differentiation by repressing cdx1b expression and intestinal fate transition in zebrafish

The liver is a key endoderm-derived multifunctional organ within the digestive system. Prospero homeobox 1 (Prox1) is an essential transcription factor for liver development, but its specific function is not well understood. Here, we show that hepatic development, including the formation of intrahepatic biliary and vascular networks, is severely disrupted in prox1a mutant zebrafish. We find that Prox1a is essential for liver growth and proper differentiation but not required for early hepatic cell fate specification. Intriguingly, prox1a depletion leads to ectopic initiation of a Cdx1b-mediated intestinal program and the formation of intestinal lumen-like structures within the liver. Morpholino knockdown of cdx1b alleviates liver defects in the prox1a mutant zebrafish. Finally, chromatin immunoprecipitation analysis reveals that Prox1a binds directly to the promoter region of cdx1b, thereby repressing its expression. Overall, our findings indicate that Prox1a is required to promote and protect hepatic development by repression of Cdx1b-mediated intestinal cell fate in zebrafish.

Directed differentiation of pancreatic δ cells from human pluripotent stem cells

Dysfunction of pancreatic δ cells contributes to the etiology of diabetes. Despite their important role, human δ cells are scarce, limiting physiological studies and drug discovery targeting δ cells. To date, no directed δ-cell differentiation method has been established. Here, we demonstrate that fibroblast growth factor (FGF) 7 promotes pancreatic endoderm/progenitor differentiation, whereas FGF2 biases cells towards the pancreatic δ-cell lineage via FGF receptor 1. We develop a differentiation method to generate δ cells from human stem cells by combining FGF2 with FGF7, which synergistically directs pancreatic lineage differentiation and modulates the expression of transcription factors and SST activators during endoderm/endocrine precursor induction. These δ cells display mature RNA profiles and fine secretory granules, secrete somatostatin in response to various stimuli, and suppress insulin secretion from in vitro co-cultured β cells and mouse β cells upon transplantation. The generation of human pancreatic δ cells from stem cells in vitro would provide an unprecedented cell source for drug discovery and cell transplantation studies in diabetes.

Chimeric Livers: Interspecies Blastocyst Complementation and Xenotransplantation for End-Stage Liver Disease

Orthotopic liver transplantation (OLT) currently serves as the sole definitive treatment for thousands of patients suffering from end-stage liver disease; and the existing supply of donor livers for OLT is drastically outpaced by the increasing demand. To alleviate this significant gap in treatment, several experimental approaches have been devised with the aim of either offering interim support to patients waiting on the transplant list or bioengineering complete livers for OLT by infusing them with fresh hepatic cells. Recently, interspecies blastocyst complementation has emerged as a promising method for generating complete organs in utero over a short timeframe. When coupled with gene editing technology, it has brought about a potentially revolutionary transformation in regenerative medicine. Blastocyst complementation harbors notable potential for generating complete human livers in large animals, which could be used for xenotransplantation in humans, addressing the scarcity of livers for OLT. Nevertheless, substantial experimental and ethical challenges still need to be overcome to produce human livers in larger domestic animals like pigs. This review compiles the current understanding of interspecies blastocyst complementation and outlines future possibilities for liver xenotransplantation in humans.

Hhex and Prox1a synergistically dictate the hepatoblast to hepatocyte differentiation in zebrafish

The specification of endoderm cells to prospective hepatoblasts is the starting point for hepatogenesis. However, how a prospective hepatoblast gains the hepatic fate remains elusive. Previous studies have shown that loss-of-function of either hhex or prox1a alone causes a small liver phenotype but without abolishing the hepatocyte differentiation, suggesting that absence of either Hhex or Prox1a alone is not sufficient to block the hepatoblast differentiation. Here, via genetic studies of the zebrafish two single (hhex-/- and prox1a-/-) and one double (hhex-/-prox1a-/-) mutants, we show that simultaneous loss-of-function of the hhex and prox1a two genes does not block the endoderm cells to gain the hepatoblast potency but abolishes the hepatic differentiation from the prospective hepatoblast. Consequently, the hhex-/-prox1a-/- double mutant displays a liverless phenotype that cannot be rescued by the injection of bmp2a mRNA. Taken together, we provide strong evidences showing that Hhex teams with Prox1a to act as a master control of the differentiation of the prospective hepatoblasts towards hepatocytes.

Developmental toxicity of flufenacet including vascular, liver, and pancreas defects is mediated by apoptosis and alters the Mapk and PI3K/Akt signal transduction in zebrafish

Release of agrochemicals from agricultural fields could unintentionally harm organisms that not targeted by pesticides. Flufenacet is one of the oxyacetamide herbicide applied in cultivation fields of crops and this has a possibility of unintentional exposure to diverse ecosystems including streams and surface water. Despite these environmental risks, limited information regarding toxicity of flufenacet on vertebrates is available. This study is aimed to assess environmental hazards and underlying toxic mechanisms of flufenacet by using a zebrafish model. Mortality measurements and morphological observations after the treatment of flufenacet suggested developmental toxicity of flufenacet in zebrafish. In addition, its toxicity on specific organs was evaluated using transgenic fluorescent zebrafish embryo. Adverse effects of flufenacet on vascular and hepatopancreatic development were demonstrated using Tg(flk1:EGFP) and Tg(fabp10a:DsRed; ela3l:EGFP) respectively. To address intracellular actions of flufenacet in zebrafish, cellular responses including apoptosis, cell cycle modulation, and Mapk and Akt signaling pathway were verified in transcriptional and protein levels. These results demonstrated developmental toxicity of flufenacet using the zebrafish model, providing essential information for assessing its potential hazards on vertebrates that are not directly targeted by the pesticide and for elucidating molecular mechanisms.

Single-cell epigenome analysis identifies molecular events controlling direct conversion of human fibroblasts to pancreatic ductal-like cells

Cell fate can be reprogrammed by ectopic expression of lineage-specific transcription factors (TFs). However, the exact cell state transitions during transdifferentiation are still poorly understood. Here, we have generated pancreatic exocrine cells of ductal epithelial identity from human fibroblasts using a set of six TFs. We mapped the molecular determinants of lineage dynamics using a factor-indexing method based on single-nuclei multiome sequencing (FI-snMultiome-seq) that enables dissecting the role of each individual TF and pool of TFs in cell fate conversion. We show that transition from mesenchymal fibroblast identity to epithelial pancreatic exocrine fate involves two deterministic steps: an endodermal progenitor state defined by activation of HHEX with FOXA2 and SOX17 and a temporal GATA4 activation essential for the maintenance of pancreatic cell fate program. Collectively, our data suggest that transdifferentiation-although being considered a direct cell fate conversion method-occurs through transient progenitor states orchestrated by stepwise activation of distinct TFs.

The Haematopoietically-expressed homeobox transcription factor: roles in development, physiology and disease

The Haematopoietically expressed homeobox transcription factor (Hhex) is a transcriptional repressor that is of fundamental importance across species, as evident by its evolutionary conservation spanning fish, amphibians, birds, mice and humans. Indeed, Hhex maintains its vital functions throughout the lifespan of the organism, beginning in the oocyte, through fundamental stages of embryogenesis in the foregut endoderm. The endodermal development driven by Hhex gives rise to endocrine organs such as the pancreas in a process which is likely linked to its role as a risk factor in diabetes and pancreatic disorders. Hhex is also required for the normal development of the bile duct and liver, the latter also importantly being the initial site of haematopoiesis. These haematopoietic origins are governed by Hhex, leading to its crucial later roles in definitive haematopoietic stem cell (HSC) self-renewal, lymphopoiesis and haematological malignancy. Hhex is also necessary for the developing forebrain and thyroid gland, with this reliance on Hhex evident in its role in endocrine disorders later in life including a potential role in Alzheimer's disease. Thus, the roles of Hhex in embryological development throughout evolution appear to be linked to its later roles in a variety of disease processes.

Differential Occupancy and Regulatory Interactions of KDM6A in Bladder Cell Lines

Epigenetic deregulation is a critical theme which needs further investigation in bladder cancer research. One of the most highly mutated genes in bladder cancer is KDM6A, which functions as an H3K27 demethylase and is one of the MLL3/4 complexes. To decipher the role of KDM6A in normal versus tumor settings, we identified the genomic landscape of KDM6A in normal, immortalized, and cancerous bladder cells. Our results showed differential KDM6A occupancy in the genes involved in cell differentiation, chromatin organization, and Notch signaling depending on the cell type and the mutation status of KDM6A. Transcription factor motif analysis revealed HES1 to be enriched at KDM6A peaks identified in the T24 bladder cancer cell line; moreover, it has a truncating mutation in KDM6A and lacks a demethylase domain. Our co-immunoprecipitation experiments revealed TLE co-repressors and HES1 as potential truncated and wild-type KDM6A interactors. With the aid of structural modeling, we explored how truncated KDM6A could interact with TLE and HES1, as well as RUNX and HHEX transcription factors. These structures provide a solid means of studying the functions of KDM6A independently of its demethylase activity. Collectively, our work provides important contributions to the understanding of KDM6A malfunction in bladder cancer.

Tel2 regulates redifferentiation of bipotential progenitor cells via Hhex during zebrafish liver regeneration

Upon extensive hepatocyte loss or impaired hepatocyte proliferation, liver regeneration occurs via biliary epithelial cell (BEC) transdifferentiation, which includes dedifferentiation of BECs into bipotential progenitor cells (BP-PCs) and then redifferentiation of BP-PCs to nascent hepatocytes and BECs. This BEC-driven liver regeneration involves reactivation of hepatoblast markers, but the underpinning mechanisms and their effects on liver regeneration remain largely unknown. Using a zebrafish extensive hepatocyte ablation model, we perform an N-ethyl-N-nitrosourea (ENU) forward genetic screen and identify a liver regeneration mutant, liver logan (lvl), in which the telomere maintenance 2 (tel2) gene is mutated. During liver regeneration, the tel2 mutation specifically inhibits transcriptional activation of a hepatoblast marker, hematopoietically expressed homeobox (hhex), in BEC-derived cells, which blocks BP-PC redifferentiation. Mechanistic studies show that Tel2 associates with the hhex promoter region and promotes hhex transcription. Our results reveal roles of Tel2 in the BP-PC redifferentiation process of liver regeneration by activating hhex.

Role of YAP1 Signaling in Biliary Development, Repair, and Disease

Yes-associated protein 1 (YAP1) is a transcriptional coactivator that activates transcriptional enhanced associate domain transcription factors upon inactivation of the Hippo signaling pathway, to regulate biological processes like proliferation, survival, and differentiation. YAP1 is most prominently expressed in biliary epithelial cells (BECs) in normal adult livers and during development. In the current review, we will discuss the multiple roles of YAP1 in the development and morphogenesis of bile ducts inside and outside the liver, as well as in orchestrating the cholangiocyte repair response to biliary injury. We will review how biliary repair can occur through the process of hepatocyte-to-BEC transdifferentiation and how YAP1 is pertinent to this process. We will also discuss the liver's capacity for metabolic reprogramming as an adaptive mechanism in extreme cholestasis, such as when intrahepatic bile ducts are absent due to YAP1 loss from hepatic progenitors. Finally, we will discuss the roles of YAP1 in the context of pediatric pathologies afflicting bile ducts, such as Alagille syndrome and biliary atresia. In conclusion, we will comprehensively discuss the spatiotemporal roles of YAP1 in biliary development and repair after biliary injury while describing key interactions with other well-known developmental pathways.

NCK-associated protein 1 like (nckap1l) minor splice variant regulates intrahepatic biliary network morphogenesis

Impaired formation of the intrahepatic biliary network leads to cholestatic liver diseases, which are frequently associated with autoimmune disorders. Using a chemical mutagenesis strategy in zebrafish combined with computational network analysis, we screened for novel genes involved in intrahepatic biliary network formation. We positionally cloned a mutation in the nckap1l gene, which encodes a cytoplasmic adaptor protein for the WAVE regulatory complex. The mutation is located in the last exon after the stop codon of the primary splice isoform, only disrupting a previously unannotated minor splice isoform, which indicates that the minor splice isoform is responsible for the intrahepatic biliary network phenotype. CRISPR/Cas9-mediated nckap1l deletion, which disrupts both the primary and minor isoforms, showed the same defects. In the liver of nckap1l mutant larvae, WAVE regulatory complex component proteins are degraded specifically in biliary epithelial cells, which line the intrahepatic biliary network, thus disrupting the actin organization of these cells. We further show that nckap1l genetically interacts with the Cdk5 pathway in biliary epithelial cells. These data together indicate that although nckap1l was previously considered to be a hematopoietic cell lineage-specific protein, its minor splice isoform acts in biliary epithelial cells to regulate intrahepatic biliary network formation.

Transcription factors β-catenin and Hex in postnatal development of the rat adrenal cortex: implication in proliferation control

Transcriptional regulation of growth, maturation, and cell turnover in adrenal cortex during postnatal development has been significantly less studied than in embryonic period, while elucidation of factors mediating its normal postnatal morphogenesis could clarify mechanisms of tumorigenesis in adrenal cortex. Expression of transcription factors Hex, β-catenin, and Wnt signaling in the adrenal cortex of male pubertal and postpubertal Wistar rats were examined. Adrenal cortex morphology and hormone production during postnatal development were also studied. Adrenocortical zones demonstrated similar reduction of Ki-67-expressing cells, but different patterns of morphological and functional changes. Age-dependent decrease in percentage of cells with membrane localization of β-catenin and stable rate of cells with nuclear β-catenin, indicative of Wnt signaling activation, were revealed in each cortical zone. Nuclear β-catenin was not observed in immature areas of zona fasciculata. No association between Wnt signaling activation and rates of proliferation as well as changes in secretion of adrenocortical hormones was observed in postnatal development of rat adrenal cortex. Hex, known as antiproliferative factor, showed up-regulation of expression after puberty. Strong inverse correlations between ratio of Hex-positive cells and proliferating cells were found in zona glomerulosa and zona fasciculata. Zona reticularis demonstrated moderate correlation. Thus, these findings suggest a role for Hex in proliferation control during postnatal development of the rat adrenal cortex and possible implication of Hex down-regulation in adrenocortical dysplasia and neoplasia, which requires further study. Evaluation of Hex expression may also be considered a potent tool in assessment of cell proliferation in rat adrenal cortex.

Generating liver using blastocyst complementation: Opportunities and challenges

Orthotopic liver transplantation (OLT) is the only definitive treatment option for many patients with end-stage liver disease. Current supply of donor livers for OLT is not keeping up with the growing demand. To overcome this problem, a number of experimental strategies have been developed either to provide a bridge to transplant for patients on the waiting list or to bioengineer whole livers for OLT by replenishing them with fresh supplies of hepatic cells. In recent years, blastocyst complementation has emerged as the most promising approach for generating whole organs and, in combination with gene editing technology, it has revolutionized regenerative medicine. This methodology was successful in producing xenogeneic organs in animal hosts. Blastocyst complementation has the potential to produce whole livers in large animals that could be xenotransplanted in humans, thereby reducing the shortage of livers for OLT. However, significant experimental and ethical barriers remain for the production of human livers in domestic animals, such as the pig. This review summarizes the current knowledge and provides future perspectives for liver xenotransplantation in humans.

Core Hippo pathway components act as a brake on Yap and Taz in the development and maintenance of the biliary network

The development of the biliary system is a complex yet poorly understood process, with relevance to multiple diseases, including biliary atresia, choledochal cysts and gallbladder agenesis. We present here a crucial role for Hippo-Yap/Taz signaling in this context. Analysis of sav1 mutant zebrafish revealed dysplastic morphology and expansion of both intrahepatic and extrahepatic biliary cells, and ultimately larval lethality. Biliary dysgenesis, but not larval lethality, is driven primarily by Yap signaling. Re-expression of Sav1 protein in sav1-/- hepatocytes is able to overcome these initial deficits and allows sav1-/- fish to survive, suggesting cell non-autonomous signaling from hepatocytes. Examination of sav1-/- rescued adults reveals loss of gallbladder and formation of dysplastic cell masses expressing biliary markers, suggesting roles for Hippo signaling in extrahepatic biliary carcinomas. Deletion of stk3 revealed that the phenotypes observed in sav1 mutant fish function primarily through canonical Hippo signaling and supports a role for phosphatase PP2A, but also suggests Sav1 has functions in addition to facilitating Stk3 activity. Overall, this study defines a role for Hippo-Yap signaling in the maintenance of both intra- and extrahepatic biliary ducts.