Suppression of C/EBPalpha expression in periportal hepatoblasts may stimulate biliary cell differentiation through increased Hnf6 and Hnf1b expression

Pseudo-trajectory inference for identifying essential regulations and molecules in cell fate decisions

Cell fate decision is crucial in biological development and plays fundamental roles in normal development and functional maintenance of organisms. By identifying key regulatory interactions and molecules involved in these fate decisions, we can shed light on the intricate mechanisms underlying the cell fates. This understanding ultimately reveals the fundamental principles driving biological development and the origins of various diseases. In this study, we present an overarching framework which integrates pseudo-trajectory inference and differential analysis to determine critical regulatory interactions and molecules during cell fate transitions. To demonstrate feasibility and reliability of the approach, we employ the differentiation networks of hepatobiliary system and embryonic stem cells as representative model systems. By applying pseudo-trajectory inference to biological data, we aim to identify critical regulatory interactions and molecules during the cell fate transition processes. Consistent with experimental observations, the approach can allow us to infer dynamical cell fate decision processes and gain insights into the underlying mechanisms which govern cell state decisions.

The homeodomain regulates stable DNA binding of prostate cancer target ONECUT2

The CUT and homeodomain are ubiquitous DNA binding elements often tandemly arranged in multiple transcription factor families. However, how the CUT and homeodomain work concertedly to bind DNA remains unknown. Using ONECUT2, a driver and therapeutic target of advanced prostate cancer, we show that while the CUT initiates DNA binding, the homeodomain thermodynamically stabilizes the ONECUT2-DNA complex through allosteric modulation of CUT. We identify an arginine pair in the ONECUT family homeodomain that can adapt to DNA sequence variations. Base interactions by this ONECUT family-specific arginine pair as well as the evolutionarily conserved residues are critical for optimal DNA binding and ONECUT2 transcriptional activity in a prostate cancer model. The evolutionarily conserved base interactions additionally determine the ONECUT2-DNA binding energetics. These findings provide insights into the cooperative DNA binding by CUT-homeodomain proteins.

Generation of in vivo-like multicellular liver organoids by mimicking developmental processes: A review

Liver is involved in metabolic reactions, ammonia detoxification, and immunity. Multicellular liver tissue cultures are more desirable for drug screening, disease modeling, and researching transplantation therapy, than hepatocytes monocultures. Hepatocytes monocultures are not stable for long. Further, hepatocyte-like cells induced from pluripotent stem cells and in vivo hepatocytes are functionally dissimilar. Organoid technology circumvents these issues by generating functional ex vivo liver tissue from intrinsic liver progenitor cells and extrinsic stem cells, including pluripotent stem cells. To function as in vivo liver tissue, the liver organoid cells must be arranged precisely in the 3-dimensional space, closely mimicking in vivo liver tissue. Moreover, for long term functioning, liver organoids must be appropriately vascularized and in contact with neighboring epithelial tissues (e.g., bile canaliculi and intrahepatic bile duct, or intrahepatic and extrahepatic bile ducts). Recent discoveries in liver developmental biology allows one to successfully induce liver component cells and generate organoids. Thus, here, in this review, we summarize the current state of knowledge on liver development with a focus on its application in generating different liver organoids. We also cover the future prospects in creating (functionally and structurally) in vivo-like liver organoids using the current knowledge on liver development.

Inversin-deficient (inv) mice do not establish a polarized duct system in the liver and pancreas

Inversin-deficient (inv) mice have anomalies in liver and pancreatic development in addition to an inverted left-right axis of the body. The present study was undertaken to unveil mechanisms of bile and pancreatic duct development from immunohistochemical analyses of anomalies in inv mice. Intrahepatic bile ducts having proximodistal polarity in size and the height of their epithelia, and ductules were formed in livers of wild-type neonates. By contrast, in inv mice, ductal plates, precursor structures of intrahepatic bile ducts and ductules, persisted without the proximodistal polarity. Their epithelial cells did not acquire planar cell polarity (PCP) in terms of expression of tight junction proteins although they expressed bile duct markers, HNF1β and SOX9. They had an apicobasal polarity from expression of basal laminar components. Enlargement of the hepatic artery and poor connective tissue development, including the abnormal deposition of the extracellular matrices, were also noted in inv mice, suggesting that bile duct development was coupled to that of the hepatic artery and portal vein. In pancreata of inv neonates, neither the main pancreatic duct was formed, nor dilated duct-like structures had the morphological polarity from the connecting point with the common bile duct. Lumina of acini was dilated, and centroacinar cells changed their position in the acini to their neck region. Immunohistochemical analyses of tight junction proteins suggested that epithelial cells of the duct-like structures did not have a PCP. Thus, Invs may be required for the establishment of the PCP of the whole duct system in the liver and pancreas.

Gene expression in the liver of the hagfish (Eptatretus burgeri) belonging to the Cyclostomata is ancestral to that of mammals

Although the liver of the hagfish, an earliest diverged lineage among vertebrates, has a histological architecture similar to that of mammals, its gene expression has not been explored yet. The present study was undertaken to comparatively characterize gene expression in the liver of the hagfish with that of the mouse, using in situ hybridization technique. Expression of alb (albumin) was detectable in all hepatocytes of the hagfish liver, but was negative in intrahepatic bile ducts. Their expression in abundant periportal ductules was weak. The expression pattern basically resembled that in mammalian livers, indicating that the differential expression of hepatocyte markers in hepatocytes and biliary cells may have been acquired in ancestral vertebrates. alb expression was almost homogeneous in the hagfish liver, whereas that in the mouse liver lobule was zonal. The glul (glutamate-ammonia ligase) expression was also homogeneously detectable in hepatocytes without zonation, and weakly so in biliary cells of the hagfish, which contrasted with its restricted pericentral expression in mouse livers. These findings indicated that the hagfish liver did not have mammalian-type zonation. Whereas tetrapods had Hnf (hepatocyte nuclear factor) 1a and Hnf1b genes encoding the transcription factors, the hagfish had a single gene of their orthologue hnf1. Although HNF1α and HNF1β were immunohistochemically detected in hepatocytes and biliary cells of the mouse, respectively, hnf1 was expressed in both hepatocytes and biliary cells of the hagfish. These data indicate that gene expression of hnf1 in the hagfish liver may be ancestral with that of alb and glul during vertebrate evolution.

The homeodomain drives favorable DNA binding energetics of prostate cancer target ONECUT2

The ONECUT transcription factors feature a CUT and a homeodomain, evolutionarily conserved elements that bind DNA cooperatively, but the process remains mechanistically enigmatic. Using an integrative DNA binding analysis of ONECUT2, a driver of aggressive prostate cancer, we show that the homeodomain energetically stabilizes the ONECUT2-DNA complex through allosteric modulation of CUT. Further, evolutionarily conserved base-interactions in both the CUT and homeodomain are necessary for the favorable thermodynamics. We have identified a novel arginine pair unique to the ONECUT family homeodomain that can adapt to DNA sequence variations. Base interactions in general, including by this arginine pair, are critical for optimal DNA binding and transcription in a prostate cancer model. These findings provide fundamental insights into DNA binding by CUT-homeodomain proteins with potential therapeutic implications.

One-Sentence Summary

Base-specific interactions regulate homeodomain-mediated stabilization of DNA binding by the ONECUT2 transcription factor.

The Landscape of HNF1B Deficiency: A Syndrome Not Yet Fully Explored

The hepatocyte nuclear factor 1β (HNF1B) gene is involved in the development of specialized epithelia of several organs during the early and late phases of embryogenesis, performing its function mainly by regulating the cell cycle and apoptosis pathways. The first pathogenic variant of HNF1B (namely, R177X) was reported in 1997 and is associated with the maturity-onset diabetes of the young. Since then, more than 230 different HNF1B variants have been reported, revealing a multifaceted syndrome with complex and heterogenous genetic, pathologic, and clinical profiles, mainly affecting the pediatric population. The pancreas and kidneys are the most frequently affected organs, resulting in diabetes, renal cysts, and a decrease in renal function, leading, in 2001, to the definition of HNF1B deficiency syndrome, including renal cysts and diabetes. However, several other organs and systems have since emerged as being affected by HNF1B defect, while diabetes and renal cysts are not always present. Especially, liver involvement has generally been overlooked but recently emerged as particularly relevant (mostly showing chronically elevated liver enzymes) and with a putative relation with tumor development, thus requiring a more granular analysis. Nowadays, HNF1B-associated disease has been recognized as a clinical entity with a broader and more variable multisystem phenotype, but the reasons for the phenotypic heterogeneity are still poorly understood. In this review, we aimed to describe the multifaceted nature of HNF1B deficiency in the pediatric and adult populations: we analyzed the genetic, phenotypic, and clinical features of this complex and misdiagnosed syndrome, covering the most frequent, unusual, and recently identified traits.

Dynamics of hepatocyte-cholangiocyte cell-fate decisions during liver development and regeneration

The immense regenerative potential of the liver is attributed to the ability of its two key cell types – hepatocytes and cholangiocytes – to trans-differentiate to one another either directly or through intermediate progenitor states. However, the dynamic features of decision-making between these cell-fates during liver development and regeneration remains elusive. Here, we identify a core gene regulatory network comprising c/EBPα, TGFBR2, and SOX9 which is multistable in nature, enabling three distinct cell states – hepatocytes, cholangiocytes, and liver progenitor cells (hepatoblasts/oval cells) – and stochastic switching among them. Predicted expression signature for these three states are validated through multiple bulk and single-cell transcriptomic datasets collected across developmental stages and injury-induced liver repair. This network can also explain the experimentally observed spatial organization of phenotypes in liver parenchyma and predict strategies for efficient cellular reprogramming. Our analysis elucidates how the emergent dynamics of underlying regulatory networks drive diverse cell-fate decisions in liver development and regeneration.

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Identified minimal regulatory network to model liver development and regeneration

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Changes in phenotypic landscapes by in-silico perturbations of regulatory networks

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Ability to explain physiological spatial patterning of liver cell types

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Decoded strategies for efficient reprogramming among liver cell phenotypes

Genetics, pathobiology and therapeutic opportunities of polycystic liver disease

Polycystic liver diseases (PLDs) are inherited genetic disorders characterized by progressive development of intrahepatic, fluid-filled biliary cysts (more than ten), which constitute the main cause of morbidity and markedly affect the quality of life. Liver cysts arise in patients with autosomal dominant PLD (ADPLD) or in co-occurrence with renal cysts in patients with autosomal dominant or autosomal recessive polycystic kidney disease (ADPKD and ARPKD, respectively). Hepatic cystogenesis is a heterogeneous process, with several risk factors increasing the odds of developing larger cysts. Depending on the causative gene, PLDs can arise exclusively in the liver or in parallel with renal cysts. Current therapeutic strategies, mainly based on surgical procedures and/or chronic administration of somatostatin analogues, show modest benefits, with liver transplantation as the only potentially curative option. Increasing research has shed light on the genetic landscape of PLDs and consequent cholangiocyte abnormalities, which can pave the way for discovering new targets for therapy and the design of novel potential treatments for patients. Herein, we provide a critical and comprehensive overview of the latest advances in the field of PLDs, mainly focusing on genetics, pathobiology, risk factors and next-generation therapeutic strategies, highlighting future directions in basic, translational and clinical research.

Hepatobiliary Differentiation: Principles from Embryonic Liver Development

Hepatocytes and biliary epithelial cells (BECs), the two endodermal cell types of the liver, originate from progenitor cells called hepatoblasts. Based principally on in vitro data, hepatoblasts are thought to be bipotent stem cells with the potential to produce both hepatocytes and BECs. However, robust in vivo evidence for this model has only recently emerged. We examine the molecular mechanisms that stimulate hepatoblast differentiation into hepatocytes or BECs. In the absence of extrinsic cues, the default fate of hepatoblasts is hepatocyte differentiation. Inductive cues from the hepatic portal vein, however, initiate transcription factor expression in hepatoblasts, driving biliary specification. Defining the mechanisms of hepatobiliary differentiation provides important insights into congenital disorders, such as Alagille syndrome, and may help to better characterize the poorly understood hepatic lineage relationships observed during regeneration from liver injury.

Unraveling the Epigenetic Basis of Liver Development, Regeneration and Disease

A wealth of studies over several decades has revealed an epigenetic prepattern that determines the competence of cellular differentiation in the developing liver. More recently, studies focused on the impact of epigenetic factors during liver regeneration suggest that an epigenetic code in the quiescent liver may establish its regenerative potential. We review work on the pioneer factors and other chromatin remodelers that impact the gene expression patterns instructing hepatocyte and biliary cell specification and differentiation, along with the requirement of epigenetic regulatory factors for hepatic outgrowth. We then explore recent studies involving the role of epigenetic regulators, Arid1a and Uhrf1, in efficient activation of proregenerative genes during liver regeneration, thus highlighting the epigenetic mechanisms of liver disease and tumor development.

Development of the Intrahepatic and Extrahepatic Biliary Tract: A Framework for Understanding Congenital Diseases

The involvement of the biliary tract in the pathophysiology of liver diseases and the increased attention paid to bile ducts in the bioconstruction of liver tissue for regenerative therapy have fueled intense research into the fundamental mechanisms of biliary development. Here, I review the molecular, cellular and tissular mechanisms driving differentiation and morphogenesis of the intrahepatic and extrahepatic bile ducts. This review focuses on the dynamics of the transcriptional and signaling modules that promote biliary development in human and mouse liver and discusses studies in which the use of zebrafish uncovered unexplored processes in mammalian biliary development. The review concludes by providing a framework for interpreting the mechanisms that may help us understand the origin of congenital biliary diseases.

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Molecular regulation of mammalian hepatic architecture

The essential liver exocrine and endocrine functions require a precise spatial arrangement of the hepatic lobule consisting of the central vein, portal vein, hepatic artery, intrahepatic bile duct system, and hepatocyte zonation. This allows blood to be carried through the liver parenchyma sampled by all hepatocytes and bile produced by the hepatocytes to be carried out of the liver through the intrahepatic bile duct system composed of cholangiocytes. The molecular orchestration of multiple signaling pathways and epigenetic factors is required to set up lineage restriction of the bipotential hepatoblast progenitor into the hepatocyte and cholangiocyte cell lineages, and to further refine cell fate heterogeneity within each cell lineage reflected in the functional heterogeneity of hepatocytes and cholangiocytes. In addition to the complex molecular regulation, there is a complicated morphogenetic choreography observed in building the refined hepatic epithelial architecture. Given the multifaceted molecular and cellular regulation, it is not surprising that impairment of any of these processes can result in acute and chronic hepatobiliary diseases. To enlighten the development of potential molecular and cellular targets for therapeutic options, an understanding of how the intricate hepatic molecular and cellular interactions are regulated is imperative. Here, we review the signaling pathways and epigenetic factors regulating hepatic cell lineages, fates, and epithelial architecture.

Oct3/4 is potentially useful for the suppression of the proliferation and motility of hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) cells are immature compared with healthy mature hepatocytes. Transcription factors serve a role in hepatocyte differentiation. The expression levels of transcription factors in HCC cell lines have been investigated to determine potential therapeutic targets. In the present study, the HLE, HLF, PLC/PRF/5, Huh-7, Hep3B, Huh-6 and HepG2 HCC cell lines were subjected to reverse-transcription polymerase chain reaction (RT-PCR) of transcription factors, including NANOG, Oct3/4, GATA binding protein 4 (GATA4), GATA6 and hematopoietically expressed homeobox (HHEX). In addition, these cell lines were analyzed using RT-quantitative PCR (RT-qPCR) of NANOG and Oct3/4. The 201B7 human induced pluripotent stem cells were evaluated as a model of pluripotent cells. The HLF cells were transfected with Oct3/4 small interfering RNA (siRNA) and used in an MTS colorimetric assay and a scratch assay. NANOG was not expressed in any of the cell lines. However, GATA4, GATA6 and HHEX were expressed in the majority of the HCC cell lines. In addition, NANOG and Oct3/4 were expressed in 201B7 cells. Oct3/4 was expressed in HLE, HLF and Hep3B cells; however, its expression levels were significantly reduced compared with those in 201B7 cells. RT-qPCR demonstrated that the expression of Oct3/4 siRNA suppressed the proliferation and motility of HLF cells. Oct3/4 siRNA may be a potentially effective therapy for the suppression of the proliferation and motility of HCC cells.

Cell fate decisions of human iPSC-derived bipotential hepatoblasts depend on cell density

During embryonic development bipotential hepatoblasts differentiate into hepatocytes and cholangiocytes- the two main cell types within the liver. Cell fate decision depends on elaborate interactions between distinct signalling pathways, namely Notch, WNT, TGFβ, and Hedgehog. Several in vitro protocols have been established to differentiate human pluripotent stem cells into either hepatocyte or cholangiocyte like cells (HLC/CLC) to enable disease modelling or drug screening. During HLC differentiation we observed the occurrence of epithelial cells with a phenotype divergent from the typical hepatic polygonal shape- we refer to these as endoderm derived epithelial cells (EDECs). These cells do not express the mature hepatocyte marker ALB or the progenitor marker AFP. However they express the cholangiocyte markers SOX9, OPN, CFTR as well as HNF4α, CK18 and CK19. Interestingly, they express both E Cadherin and Vimentin, two markers that are mutually exclusive, except for cancer cells. EDECs grow spontaneously under low density cell culture conditions and their occurrence was unaffected by interfering with the above mentioned signalling pathways.

Fetal hepatocyte-derived culture medium elicits adipocyte differentiation to bile duct cell lineages in a mouse model

Fetal cells in the developmental stages function with a distinct mechanism in comparison to adult tissues, which may be a useful source for regenerative medicine in postnatal medicine; however, the precise molecular mechanism remains to be elucidated fully. The present study investigated murine fetal hepatocytes, which were cultured in vitro, and the supernatants were used for the culture with murine adipose tissue-derived cells. Notably, the results indicated that fetal hepatocyte-derived culture medium elicits the induction of differentiation of adipose tissue-derived cells to bile duct cell lineages, but not to hepatocyte lineages in mice. This indicates that fetal cells possess the multi potentials, which are already absent in adults, and may be useful for regenerative medicine in future.

MicroRNA-337-3p controls hepatobiliary gene expression and transcriptional dynamics during hepatic cell differentiation

Transcriptional networks control the differentiation of the hepatocyte and cholangiocyte lineages from embryonic liver progenitor cells and their subsequent maturation to the adult phenotype. However, how relative levels of hepatocyte and cholangiocyte gene expression are determined during differentiation remains poorly understood. Here, we identify microRNA (miR)-337-3p as a regulator of liver development. miR-337-3p stimulates expression of cholangiocyte genes and represses hepatocyte genes in undifferentiated progenitor cells in vitro and in embryonic mouse livers. Beyond the stage of lineage segregation, miR-337-3p controls the transcriptional network dynamics of developing hepatocytes and balances both cholangiocyte populations that constitute the ductal plate. miR-337-3p requires Notch and transforming growth factor-β signaling and exerts a biphasic control on the hepatocyte transcription factor hepatocyte nuclear factor 4α by modulating its activation and repression. With the help of an experimentally validated mathematical model, we show that this biphasic control results from an incoherent feedforward loop between miR-337-3p and hepatocyte nuclear factor 4α.

CONCLUSION

Our results identify miR-337-3p as a regulator of liver development and highlight how tight quantitative control of hepatic cell differentiation is exerted through specific gene regulatory network motifs. (Hepatology 2018;67:313-327).

Phylogenetic analyses of the hepatic architecture in vertebrates

The mammalian liver has a structural and functional unit called the liver lobule, in the periphery of which the portal triad consisting of the portal vein, bile duct and hepatic artery is developed. This type of hepatic architecture is detectable in many other vertebrates, including amphibians and birds, whereas intrahepatic bile ducts run independently of portal vein distribution in actinopterygians such as the salmon and tilapia. It remains to be clarified how the hepatic architectures are phylogenetically developed among vertebrates. The present study morphologically and immunohistochemically analyzed the hepatic structures of various vertebrates, including as many classes and subclasses as possible, with reference to intrahepatic bile duct distribution. The livers of vertebrates belonging to the Agnatha, Chondrichthyes, Amphibia, Aves, Mammalia, and Actinopterygii before Elopomorpha, had the portal triad-type architecture. The Anguilliformes livers developed both periportal bile ducts and non-periportal bile ducts. The Otocephala and Euteleostei livers had independent configuration of bile ducts and portal veins. Pancreatic tissues penetrated the liver parenchyma along portal veins in the Euteleostei. The liver of the lungfish, which shares the same origin with amphibians, did not have the portal triad-type architecture. Teleostei and lungfish livers had ductular development in the liver parenchyma similar to oval cell proliferation in injured mammalian livers. Euteleostei livers had penetration of significant numbers of independent portal veins from their intestines, suggesting that each liver lobe might receive a different blood supply. The hepatic architectures of the portal triad-type changed to non-portal triad-type architecture along the evolution of the Actinopterygii. The hepatic architecture of the lungfish resembles that of the Actinopterygii after Elopomorpha in intrahepatic biliary configuration, which may be an example of convergent evolution.

In vivo and ex vivo methods of growing a liver bud through tissue connection

Cell-based therapy has been proposed as an alternative to orthotopic liver transplantation. The novel transplantation of an in vitro-generated liver bud might have therapeutic potential. In vivo and ex vivo methods for growing a liver bud are essential for paving the way for the clinical translation of liver bud transplantation. We herein report a novel transplantation method for liver buds that are grown in vivo involving orthotopic transplantation on the transected parenchyma of the liver, which showed long engraftment and marked growth in comparison to heterotopic transplantation. Furthermore, this study demonstrates a method for rapidly fabricating scalable liver-like tissue by fusing hundreds of liver bud-like spheroids using a 3D bioprinter. Its system to fix the shape of the 3D tissue with the needle-array system enabled the fabrication of elaborate geometry and the immediate execution of culture circulation after 3D printing—thereby avoiding an ischemic environment ex vivo. The ex vivo-fabricated human liver-like tissue exhibited self-tissue organization ex vivo and engraftment on the liver of nude rats. These achievements conclusively show both in vivo and ex vivo methods for growing in vitro-generated liver buds. These methods provide a new approach for in vitro-generated liver organoids transplantation.

Epithelial Morphogenesis during Liver Development

Tissue stem/progenitor cells supply multiple types of epithelial cells that eventually acquire specialized functions during organ development. In addition, three-dimensional (3D) tissue structures need to be established for organs to perform their physiological functions. The liver contains two types of epithelial cells, namely, hepatocytes and cholangiocytes, which are derived from hepatoblasts, fetal liver stem/progenitor cells (LPCs), in mid-gestation. Hepatocytes performing many metabolic reactions form cord-like structures, whereas cholangiocytes, biliary epithelial cells, form tubular structures called intrahepatic bile ducts. Analyses for human genetic diseases and mutant mice have identified crucial molecules for liver organogenesis. Functions of those molecules can be examined in in vitro culture systems where LPCs are induced to differentiate into hepatocytes or cholangiocytes. Recent technical advances have revealed 3D epithelial morphogenesis during liver organogenesis. Therefore, the liver is a good model to understand how tissue stem/progenitor cells differentiate and establish 3D tissue architectures during organ development.

CCAAT/enhancer-binding protein α decreases the viability of gastric cancer cells

CCAAT/enhancer-binding protein (C/EBP) α, C/EBPβ and C/EBPδ are involved in inflammation and cell differentiation. In the present study, their roles in human gastric cancer cells were investigated. The human gastric cancer cell lines MKN45 and MKN74 were subjected to the reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to analyze the expression levels of C/EBPα, C/EBPβ and C/EBPδ. The cells were transfected with expression plasmids for either C/EBPα or C/EBPδ, and subjected to a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay and RT-qPCR for analysis of cyclin D1 expression. Expression levels of C/EBPα and C/EBPδ were decreased in MKN45 and MKN74 cells compared with in normal gastric tissue. Expression levels of C/EBPβ were decreased in MKN45 cells and increased in MKN74 cells. Viability of MKN45 cells was decreased by C/EBPα and C/EBPδ. Viability of MKN74 cells was decreased by C/EBPα, but increased by C/EBPδ. Expression levels of cyclin D1 were decreased in association with C/EBPα and C/EBPδ overexpression in MKN45 cells. Expression levels of cyclin D1 were decreased in association with C/EBPα overexpression, but increased in association with C/EBPδ overexpression, in MKN74 cells. The results of the present study indicate that C/EBPα is potentially useful for the treatment of gastric cancer.

Gene regulatory networks in differentiation and direct reprogramming of hepatic cells

Liver development proceeds by sequential steps during which gene regulatory networks (GRNs) determine differentiation and maturation of hepatic cells. Characterizing the architecture and dynamics of these networks is essential for understanding how cell fate decisions are made during development, and for recapitulating these processes during in vitro production of liver cells for toxicology studies, disease modelling and regenerative therapy. Here we review the GRNs that control key steps of liver development and lead to differentiation of hepatocytes and cholangiocytes in mammals. We focus on GRNs determining cell fate decisions and analyse subcircuitry motifs that may confer specific dynamic properties to the networks. Finally, we put our analysis in the perspective of recent attempts to directly reprogram cells to hepatocytes by forced expression of transcription factors.

Morphogenesis of liver epithelial cells

The mammalian liver is a physiologically important organ performing various types of metabolism, producing serum proteins, detoxifying bilirubin and ammonia, and protecting the body from infection. Those physiological functions are achieved with the 3D tissue architecture of liver epithelial cells. The liver contains two types of epithelial cells, namely, hepatocytes and cholangiocytes. They split from hepatoblasts (embryonic liver stem cells) in mid-gestation and differentiate into structurally and functionally mature cells. Analyses of mutant mice showing abnormal liver organogenesis have identified genes involved in liver development. In vitro culture systems have been used to examine the mechanism in which each molecule or signaling pathway regulates the morphogenesis and functional differentiation of hepatocytes and cholangiocytes. In addition, liver epithelial cells as well as mesenchymal, sinusoidal endothelial and hematopoietic cells can be purified from developing livers, which enables us to perform genome-wide screening to identify novel genes regulating epithelial morphogenesis in the liver. By combining these in vivo and in vitro systems, the liver could be a unique and suitable model for revealing a principle, governing epithelial morphogenesis. In this review, we summarize recent progress in the understanding of the development of liver epithelial tissue structures.

Transcription Factors and Medium Suitable for Initiating the Differentiation of Human-Induced Pluripotent Stem Cells to the Hepatocyte Lineage

Transcription factors and culture media were investigated to determine the condition to initiate the differentiation of human-induced pluripotent stem (iPS) cells most efficiently. The expression of genes in human adult liver was compared with that in 201B7 cells (iPS cells) using cDNA microarray analysis. Episomal plasmids expressing transcription factors were constructed. 201B7 cells were transfected with the episomal plasmids and cultured in ReproFF (feeder-free media maintaining pluripotency), Leibovitz-15 (L15), William's E (WE), or Dulbecco's modified Eagle medium/Nutrient F-12 Ham (DF12) for 7 days. RNA was isolated and subjected to real-time quantitative PCR to analyze the expression of alpha-feto protein (AFP) and albumin. cDNA microarray analysis revealed 16 transcription factors that were upregulated in human adult liver relative to that in 201B7 cells. Episomal plasmids expressing these 16 genes were transfected into 201B7 cells. CCAAT/enhancer-binding protein alpha (CEBPA), CCAAT/enhancer-binding protein beta (CEBPB), forkhead box A1 (FOXA1), and forkhead box A3 (FOXA3) up-regulated AFP and down-regulated Nanog. These four genes were further analyzed. The expression of AFP and albumin was the highest in 201B7 cells transfected with the combination of CEBPA, CEBPB, FOXA1, and FOXA3 and cultured in WE. The combination of CEBPA, CEBPB, FOXA1, and FOXA3 was suitable for 201B7 cells to initiate differentiation to the hepatocyte lineage and WE was the most suitable medium for culture after transfection. J. Cell. Biochem. 117: 2001-2009, 2016. © 2016 Wiley Periodicals, Inc.

Intrahepatic bile ducts are developed through formation of homogeneous continuous luminal network and its dynamic rearrangement in mice

The intrahepatic bile duct (IHBD) is a highly organized tubular structure consisting of cholangiocytes, biliary epithelial cells, which drains bile produced by hepatocytes into the duodenum. Although several models have been proposed, it remains unclear how the three-dimensional (3D) IHBD network develops during liver organogenesis. Using 3D imaging techniques, we demonstrate that the continuous luminal network of IHBDs is established by 1 week after birth. Beyond this stage, the IHBD network consists of large ducts running along portal veins (PVs) and small ductules forming a mesh-like network around PVs. By analyzing embryonic and neonatal livers, we found that newly differentiated cholangiocytes progressively form a continuous and homogeneous luminal network. Elongation of this continuous network toward the liver periphery was attenuated by a potent Notch-signaling inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester. Subsequent to this first step, the fine homogenous network is reorganized into the mature hierarchical network consisting of large ducts and small ductules. Between E17 and E18, when the homogenous network is radically reorganized into the mature hierarchical network, bile canaliculi rapidly extend and bile flow into IHBDs may increase. When formation of bile canaliculi was blocked between E16 and E18 by a multidrug resistance protein 2 inhibitor (benzbromarone), the structural rearrangement of IHBDs was significantly suppressed.

CONCLUSION

Establishment of the mature IHBD network consists of two sequential events: (1) formation of the continuous luminal network regulated by the Notch-signaling pathway and (2) dynamic rearrangement of the homogeneous network into the hierarchical network induced by increased bile flow resulting from the establishment of hepatobiliary connections. (Hepatology 2016;64:175-188).

The basic helix-loop-helix transcription factor, Mist1, induces maturation of mouse fetal hepatoblasts

Hepatic stem/progenitor cells, hepatoblasts, have a high proliferative ability and can differentiate into mature hepatocytes and cholangiocytes. Therefore, these cells are considered to be useful for regenerative medicine and drug screening for liver diseases. However, it is problem that in vitro maturation of hepatoblasts is insufficient in the present culture system. In this study, a novel regulator to induce hepatic differentiation was identified and the molecular function of this factor was examined in embryonic day 13 hepatoblast culture with maturation factor, oncostatin M and extracellular matrices. Overexpression of the basic helix-loop-helix type transcription factor, Mist1, induced expression of mature hepatocytic markers such as carbamoyl-phosphate synthetase1 and several cytochrome P450 (CYP) genes in this culture system. In contrast, Mist1 suppressed expression of cholangiocytic markers such as Sox9, Sox17, Ck19, and Grhl2. CYP3A metabolic activity was significantly induced by Mist1 in this hepatoblast culture. In addition, Mist1 induced liver-enriched transcription factors, CCAAT/enhancer-binding protein α and Hepatocyte nuclear factor 1α, which are known to be involved in liver functions. These results suggest that Mist1 partially induces mature hepatocytic expression and function accompanied by the down-regulation of cholangiocytic markers.

Regulation of hepatocyte identity and quiescence

The liver is a highly differentiated organ with a central role in metabolism, detoxification and systemic homeostasis. To perform its multiple tasks, liver parenchymal cells, the hepatocytes, express a large complement of enabling genes defining their complex phenotype. This phenotype is progressively acquired during fetal development and needs to be maintained in adulthood to guarantee the individual's survival. Upon injury or loss of functional mass, the liver displays an extraordinary regenerative response, mainly based on the proliferation of hepatocytes which otherwise are long-lived quiescent cells. Increasing observations suggest that loss of hepatocellular differentiation and quiescence underlie liver malfunction in chronic liver disease and pave the way for hepatocellular carcinoma development. Here, we briefly review the essential mechanisms leading to the acquisition of liver maturity. We also identify the key molecular factors involved in the preservation of hepatocellular homeostasis and finally discuss potential strategies to preserve liver identity and function.

Liver maturation deficiency in p57(Kip2)-/- mice occurs in a hepatocytic p57(Kip2) expression-independent manner

Fetal hepatic stem/progenitor cells, hepatoblasts, are highly proliferative cells and the source of both hepatocytes and cholangiocytes. In contrast, mature hepatocytes have a low proliferative potency and high metabolic functions. Cell proliferation is regulated by cell cycle-related molecules. However, the correlation between cell cycle regulation and hepatic maturation are still unknown. To address this issue, we revealed that the cell cycle inhibitor p57(Kip2) was expressed in the hepatoblasts and mesenchymal cells of fetal liver in a spatiotemporal manner. In addition, we found that hepatoblasts in p57(Kip2)-/- mice were highly proliferative and had deficient maturation compared with those in wild-type (WT) mice. However, there were no remarkable differences in the expression levels of cell cycle- and bipotency-related genes except for Ccnd2. Furthermore, p57(Kip2)-/- hepatoblasts could differentiate into mature hepatocytes in p57(Kip2)-/- and WT chimeric mice, suggesting that the intrinsic activity of p57(Kip2) does not simply regulate hepatoblast maturation.

Human pluripotent stem cell-derived cholangiocytes: current status and future applications

PURPOSE OF REVIEW

Pluripotent stem cells, such as embryonic stem cells and inducible pluripotent stem (iPS) cells, have high proliferative multipotency for differentiation into mature functional cells that are useful for treatment and basic research on several diseases. Cholangiocytes are differentiated from fetal hepatic progenitor cells (hepatoblasts) and are important for transport of bile acids that are synthesized by mature hepatocytes in the liver. However, the molecular mechanisms of development and function of human cholangiocytes remain unknown. This review mentions the potential of human cholangiocytic culture from pluripotent stem cells to contribute to the analyses of the human bile duct system and diseases.

RECENT FINDINGS

Recent studies found that human hepatic cholangiocytic cells can be differentiated from human embryonic stem and iPS cells in a suitable culture condition. Cholangiocytic cysts have epithelial cell polarity formed in a three-dimensional cell culture system using extracellular matrices.

SUMMARY

Disease pathogenesis was elucidated in vitro using differentiated cells from disease-related iPS cells. Using genome-editing enzymes, iPS cells with disease-specific gene mutations can be easily and rapidly established. These disease-related iPS cells and cholangiocytic culture system may be useful for analyses and drug screening of human bile duct diseases.

Polycystic liver diseases: advanced insights into the molecular mechanisms

Polycystic liver diseases are genetic disorders characterized by progressive bile duct dilatation and/or cyst development. The large volume of hepatic cysts causes different symptoms and complications such as abdominal distension, local pressure with back pain, hypertension, gastro-oesophageal reflux and dyspnea as well as bleeding, infection and rupture of the cysts. Current therapeutic strategies are based on surgical procedures and pharmacological management, which partially prevent or ameliorate the disease. However, as these treatments only show short-term and/or modest beneficial effects, liver transplantation is the only definitive therapy. Therefore, interest in understanding the molecular mechanisms involved in disease pathogenesis is increasing so that new targets for therapy can be identified. In this Review, the genetic mechanisms underlying polycystic liver diseases and the most relevant molecular pathways of hepatic cystogenesis are discussed. Moreover, the main clinical and preclinical studies are highlighted and future directions in basic as well as clinical research are indicated.

The biliary epithelium gives rise to liver progenitor cells

Severe liver diseases are characterized by expansion of liver progenitor cells (LPC), which correlates with disease severity. However, the origin and role of LPC in liver physiology and in hepatic injury remains a contentious topic. We found that ductular reaction cells in human cirrhotic livers express hepatocyte nuclear factor 1 homeobox B (HNF1β). However, HNF1β expression was not present in newly generated epithelial cell adhesion molecule (EpCAM)-positive hepatocytes. In order to investigate the role of HNF1β-expressing cells we used a tamoxifen-inducible Hnf1βCreER/R26R(Yfp/LacZ) mouse to lineage-trace Hnf1β(+) biliary duct cells and to assess their contribution to LPC expansion and hepatocyte generation. Lineage tracing demonstrated no contribution of HNF1β(+) cells to hepatocytes during liver homeostasis in healthy mice or after loss of liver mass. After acute acetaminophen or carbon tetrachloride injury no contribution of HNF1β(+) cells to hepatocyte was detected. We next assessed the contribution of Hnf1β(+) -derived cells following two liver injury models with LPC expansion, a diethoxycarbonyl-1,4-dihydro-collidin (DDC)-diet and a choline-deficient ethionine-supplemented (CDE)-diet. The contribution of Hnf1β(+) cells to liver regeneration was dependent on the liver injury model. While no contribution was observed after DDC-diet treatment, mice fed with a CDE-diet showed a small population of hepatocytes derived from Hnf1β(+) cells that were expanded to 1.86% of total hepatocytes after injury recovery. Genome-wide expression profile of Hnf1β(+) -derived cells from the DDC and CDE models indicated that no contribution of LPC to hepatocytes was associated with LPC expression of genes related to telomere maintenance, inflammation, and chemokine signaling pathways.

CONCLUSION

HNF1β(+) biliary duct cells are the origin of LPC. HNF1β(+) cells do not contribute to hepatocyte turnover in the healthy liver, but after certain liver injury, they can differentiate to hepatocytes contributing to liver regeneration.

Hepatocyte-ductal transdifferentiation is mediated by reciprocal repression of SOX9 and C/EBPα

Primary hepatocytes rapidly dedifferentiate when cultured in vitro. We have studied the mechanism of hepatocyte dedifferentiation by using two culture media: one that maintains hepatocytes in a differentiated state and another that allows dedifferentiation. We show that dedifferentiation involves partial transformation of hepatocytes into cells that resemble biliary epithelial cells. Lineage labeling and time-lapse filming confirm that the dedifferentiated cells are derived from hepatocytes and not from contaminating ductal or fibroblastic cells in the original culture. Furthermore, we establish that the conversion of hepatocytes to biliary-like cells is regulated by mutual antagonism of CCAAT/enhancer binding protein alpha (C/EBPα) and SOX9, which have opposing effects on the expression of hepatocyte and ductal genes. Thus, hepatocyte dedifferentiation induces the biliary gene expression program by alleviating C/EBPα-mediated repression of Sox9. We propose that reciprocal antagonism of C/EBPα and SOX9 also operates in the formation of hepatocytes and biliary ducts from hepatoblasts during normal embryonic development. These data demonstrate that reprogramming of differentiated cells can be used to model the acquisition and maintenance of cell fate in vivo.

Prox1 ablation in hepatic progenitors causes defective hepatocyte specification and increases biliary cell commitment

The liver has multiple functions that preserve homeostasis. Liver diseases are debilitating, costly and often result in death. Elucidating the developmental mechanisms that establish the liver's architecture or generate the cellular diversity of this organ should help advance the prevention, diagnosis and treatment of hepatic diseases. We previously reported that migration of early hepatic precursors away from the gut epithelium requires the activity of the homeobox gene Prox1. Here, we show that Prox1 is a novel regulator of cell differentiation and morphogenesis during hepatogenesis. Prox1 ablation in bipotent hepatoblasts dramatically reduced the expression of multiple hepatocyte genes and led to very defective hepatocyte morphogenesis. As a result, abnormal epithelial structures expressing hepatocyte and cholangiocyte markers or resembling ectopic bile ducts developed in the Prox1-deficient liver parenchyma. By contrast, excessive commitment of hepatoblasts into cholangiocytes, premature intrahepatic bile duct morphogenesis, and biliary hyperplasia occurred in periportal areas of Prox1-deficient livers. Together, these abnormalities indicate that Prox1 activity is necessary to correctly allocate cell fates in liver precursors. These results increase our understanding of differentiation anomalies in pathological conditions and will contribute to improving stem cell protocols in which differentiation is directed towards hepatocytes and cholangiocytes.

Polycystic liver disease: ductal plate malformation and the primary cilium

Polycystic livers are found in autosomal dominant polycystic kidney disease (ADPKD), caused by polycystic kidney disease (PKD)1 and PKD2 mutations in virtually all cases, and in isolated polycystic liver disease (PCLD), where 20% of cases are caused by mutations in Protein kinase C substrate 80K-H (PRKCSH) or SEC63. Loss of heterozygosity in single hepatoblasts leads to underlying cystogenic ductal plate malformations. Crucially, actual components driving this development remain elusive. Recent advances have unraveled the roles of transforming growth factor (TGF)-β, Notch and Wnt signaling, transcriptional regulators such as hepatocyte nuclear factor (HNF)6 and HNF1β, as well as cilium function in hepatobiliary organogenesis. In polycystic liver disease, mutation or defective co-translational processing of key elements required for primary cilium formation have been implicated. This review recapitulates liver patterning factors in hepatobiliary development and extracts molecular players in hepatic cystogenesis.

Endodermal and mesenchymal cross talk: a crossroad for the maturation of foregut organs

The developmental stages of each foregut organ are intimately linked to the development of the other foregut organs such that the ultimate function of any one foregut organ, such as the metabolic function of the liver, depends on organizational changes associated with the maturation of multiple foregut organs. These changes include: (i) proliferation of the intrahepatic bile ducts and hepatoblasts within the liver coinciding with parenchymal expansion, (ii) elongation of extrahepatic bile ducts, which allows for proper gallbladder (GB) formation, and (iii) duodenal elongation and rotation, which coincides with all of the above to connect the intrahepatic, extrahepatic, and pancreatic ductal systems with the intestine. It is well established that cross talk between endodermal and mesenchymal components of the foregut occurs, particularly regarding the vascularization of developing organs. Furthermore, genetic mutations in mesenchymal and hepatic compartments of the developing foregut result in similar foregut pathologies: hypoplastic liver, absence of GB, biliary atresia (intrahepatic and/or extrahepatic), and failure of gut elongation and rotation. Finally, these shared pathologies can be linked to deficiencies in genes specific to the septum transversum mesenchyme (Hes1, Hlx, and Foxf1) or liver (Hhex and Hnf6), illustrating the complexity of such cross talk.

CCAAT/enhancer binding protein-mediated regulation of TGFβ receptor 2 expression determines the hepatoblast fate decision

Human embryonic stem cells (hESCs) and their derivatives are expected to be used in drug discovery, regenerative medicine and the study of human embryogenesis. Because hepatocyte differentiation from hESCs has the potential to recapitulate human liver development in vivo, we employed this differentiation method to investigate the molecular mechanisms underlying human hepatocyte differentiation. A previous study has shown that a gradient of transforming growth factor beta (TGFβ) signaling is required to segregate hepatocyte and cholangiocyte lineages from hepatoblasts. Although CCAAT/enhancer binding proteins (c/EBPs) are known to be important transcription factors in liver development, the relationship between TGFβ signaling and c/EBP-mediated transcriptional regulation in the hepatoblast fate decision is not well known. To clarify this relationship, we examined whether c/EBPs could determine the hepatoblast fate decision via regulation of TGFβ receptor 2 (TGFBR2) expression in the hepatoblast-like cells differentiated from hESCs. We found that TGFBR2 promoter activity was negatively regulated by c/EBPα and positively regulated by c/EBPβ. Moreover, c/EBPα overexpression could promote hepatocyte differentiation by suppressing TGFBR2 expression, whereas c/EBPβ overexpression could promote cholangiocyte differentiation by enhancing TGFBR2 expression. Our findings demonstrated that c/EBPα and c/EBPβ determine the lineage commitment of hepatoblasts by negatively and positively regulating the expression of a common target gene, TGFBR2, respectively.

Hepatic biliary epithelial cells acquire epithelial integrity but lose plasticity to differentiate into hepatocytes in vitro during development

In developing organs, epithelial tissue structures are mostly developed by the perinatal period. However, it is unknown whether epithelial cells are already functionally mature and whether they are fixed in their lineage. Here we show that epithelial cells alter their plasticity during postnatal development by examining the differentiation potential of epithelial cell adhesion molecule (EpCAM)(+) cholangiocytes (biliary epithelial cells) isolated from neonatal and adult mouse livers. We found that neonatal cholangiocytes isolated from 1-week-old liver converted into functional hepatocytes in the presence of oncostatin M and Matrigel®. In contrast, neither morphological changes nor expression of hepatocyte markers were induced in adult cholangiocytes. The transcription factors hepatocyte nuclear factor 4α and CCAAT/enhancer binding protein α (C/EBPα), which are necessary for hepatocytic differentiation, were induced in neonatal cholangiocytes but not in adult cells, whereas grainyhead-like 2 (Grhl2) and hairy-enhance of slit 1 (Hes1), which are implicated in cholangiocyte differentiation, were continuously expressed in adult cells. Overexpression of C/EBPα and Grhl2 promoted and inhibited hepatocytic differentiation, respectively. Furthermore, adult cholangiocytes formed a monolayer with higher barrier function than neonatal ones did, suggesting that cholangiocytes are still in the process of epithelial maturation even after forming tubular structures during the neonatal period. Taken together, these results suggest that cholangiocytes lose plasticity to convert into hepatocytes during epithelial maturation. They lose competency to upregulate hepatocytic transcription factors and downregulate cholagiocytic ones under conditions inducing hepatocytic differentiation. Our results suggest that a molecular machinery augmenting epithelial integrity limits lineage plasticity of epithelial cells.

Cellular and molecular basis of liver development

Liver is a prime organ responsible for synthesis, metabolism, and detoxification. The organ is endodermal in origin and its development is regulated by temporal, complex, and finely balanced cellular and molecular interactions that dictate its origin, growth, and maturation. We discuss the relevance of endoderm patterning, which truly is the first step toward mapping of domains that will give rise to specific organs. Once foregut patterning is completed, certain cells within the foregut endoderm gain competence in the form of expression of certain transcription factors that allow them to respond to certain inductive signals. Hepatic specification is then a result of such inductive signals, which often emanate from the surrounding mesenchyme. During hepatic specification bipotential hepatic stem cells or hepatoblasts become apparent and undergo expansion, which results in a visible liver primordium during the stage of hepatic morphogenesis. Hepatoblasts next differentiate into either hepatocytes or cholangiocytes. The expansion and differentiation is regulated by cellular and molecular interactions between hepatoblasts and mesenchymal cells including sinusoidal endothelial cells, stellate cells, and also innate hematopoietic elements. Further maturation of hepatocytes and cholangiocytes continues during late hepatic development as a function of various growth factors. At this time, liver gains architectural novelty in the form of zonality and at cellular level acquires polarity. A comprehensive elucidation of such finely tuned developmental cues have been the basis of transdifferentiation of various types of stem cells to hepatocyte-like cells for purposes of understanding health and disease and for therapeutic applications.

Preexisting epithelial diversity in normal human livers: a tissue-tethered cytometric analysis in portal/periportal epithelial cells

Routine light microscopy identifies two distinct epithelial cell populations in normal human livers: hepatocytes and biliary epithelial cells (BECs). Considerable epithelial diversity, however, arises during disease states when a variety of hepatocyte-BEC hybrid cells appear. This has been attributed to activation and differentiation of putative hepatic progenitor cells (HPC) residing in the canals of Hering and/or metaplasia of preexisting mature epithelial cells. A novel analytic approach consisting of multiplex labeling, high-resolution whole-slide imaging (WSI), and automated image analysis was used to determine if more complex epithelial cell phenotypes preexist in normal adult human livers, which might provide an alternative explanation for disease-induced epithelial diversity. "Virtually digested" WSI enabled quantitative cytometric analyses of individual cells displayed in a variety of formats (e.g., scatterplots) while still tethered to the WSI and tissue structure. We employed biomarkers specifically associated with mature epithelial forms (HNF4α for hepatocytes, CK19 and HNF1β for BEC) and explored for the presence of cells with hybrid biomarker phenotypes. The results showed abundant hybrid cells in portal bile duct BEC, canals of Hering, and immediate periportal hepatocytes. These bipotential cells likely serve as a reservoir for the epithelial diversity of ductular reactions, appearance of hepatocytes in bile ducts, and the rapid and fluid transition of BEC to hepatocytes, and vice versa.

CONCLUSION

Novel imaging and computational tools enable increased information extraction from tissue samples and quantify the considerable preexistent hybrid epithelial diversity in normal human liver. This computationally enabled tissue analysis approach offers much broader potential beyond the results presented here.

Single-step protocol for the differentiation of human-induced pluripotent stem cells into hepatic progenitor-like cells

Induced pluripotent stem (iPS) cells are ideal sources of hepatocyte for transplantation into patients experiencing hepatic failure. Growth and transcription factors were analyzed to design a single-step protocol for the differentiation of iPS cells into hepatocytes. The expression of transcription factors was analyzed using reverse transcription-polymerase chain reaction (RT-PCR) and compared among iPS cells, as well as fetal and adult liver cells. iPS cells were cultured with growth factors and RT-PCR was performed to analyze the expression of transcription factors. iPS cells were introduced with transcription factors, cultured with growth factors and subjected to real-time quantitative PCR. Indocyanine green (ICG) was added to the medium as a hepatocyte marker. Sox17, GATA4, GATA6, FoxA2, HEX, HNF4α and C/EBPα were expressed in fetal and adult liver cells, but not in iPS cells. Sox17, GATA6 and HNF4α were expressed after exposure a combination of oncostatin M, epidermal growth factor, retinoic acid, dexamethasone and ITS (OERDITS). When iPS cells were introduced with FoxA2, GATA4, HEX and C/EBPα and cultured with OERDITS for 8 days, the cells expressed α-fetoprotein, δ-like (Dlk)-1 and γ-glutamyl transpeptidase (GTP), and ICG uptake was observed. Exposure to FoxA2, GATA4, HEX and C/EBPα and culturing with OERDITS supplementation potentially serves as a single-step inducer for the differentiation of iPS cells into hepatic progenitor-like cells within 8 days.

Macrophage-derived Wnt opposes Notch signaling to specify hepatic progenitor cell fate in chronic liver disease

During chronic injury a population of bipotent hepatic progenitor cells (HPCs) become activated to regenerate both cholangiocytes and hepatocytes. Here we show in human diseased liver and mouse models of the ductular reaction that Notch and Wnt signaling direct specification of HPCs via their interactions with activated myofibroblasts or macrophages. In particular, we found that during biliary regeneration, expression of Jagged 1 (a Notch ligand) by myofibroblasts promoted Notch signaling in HPCs and thus their biliary specification to cholangiocytes. Alternatively, during hepatocyte regeneration, macrophage engulfment of hepatocyte debris induced Wnt3a expression. This resulted in canonical Wnt signaling in nearby HPCs, thus maintaining expression of Numb (a cell fate determinant) within these cells and the promotion of their specification to hepatocytes. By these two pathways adult parenchymal regeneration during chronic liver injury is promoted.

Progress in research of molecular markers for hepatic oval cells You-Lin Yu, Bao-Ming Shi

Hepatic stem cells have the capacity of self-renewal, proliferation and differentiation and can produce progeny cells that have the same phenotypes and genotype as parental cells. The cells originate from the foregut endoderm and exist in the form of hepatic cells in embryonic liver, and small oval cells (OCs) with a large nuclear/cytoplasmic ratio and special cell markers in the adult liver. Hepatic stem cells are normally in the dormant state and divide at a very slow rate. The cells begin to be activated to proliferate quickly and transit from quiescent phase to proliferative phase when the liver is resected by operation or injured by drugs. In recent years, numerous studies have confirmed that hepatic OCs are hepatic stem cells that have the bipotential capability of differentiation into mature hepatocytes and biliary epithelial cells when hepatocyte proliferation is inhibited and liver regeneration compromised. The research of the role of hepatic OCs in the management of acute and chronic liver dysfunction, advanced cirrhosis, other liver diseases, and diabetes caused by pancreatic lesions has attracted wide attention. Great efforts have been made to find and isolate hepatic OCs. This review discusses the progress in research of molecular markers for hepatic OCs.

Transcriptional control of hepatocyte differentiation

The liver is the largest glandular organ in the body and plays a central role in controlling metabolism. During hepatogenesis, complex developmental processes must generate an array of cell types that are spatially arranged to generate a hepatic architecture that is essential to support liver function. The processes that control the ultimate formation of the liver are diverse and complex and in many cases poorly defined. Much of the focus of research during the past three decades has been on understanding how hepatocytes, which are the predominant liver parenchymal cells, differentiate during embryogenesis. Through a combination of mouse molecular genetics, embryology, and molecular biochemistry, investigators have defined a myriad of transcription factors that combine to control formation and function of hepatocytes. Here, we will review the major discoveries that underlie our current understanding of transcriptional regulation of hepatocyte differentiation.

White adipose tissue development in zebrafish is regulated by both developmental time and fish size

Adipocytes are heterogeneous. Whether their differences are attributed to anatomical location or to different developmental origins is unknown. We investigated whether development of different white adipose tissue (WAT) depots in zebrafish occurs simultaneously or whether adipogenesis is influenced by the metabolic demands of growing fish. Like mammals, zebrafish adipocyte morphology is distinctive and adipocytes express cell-specific markers. All adults contain WAT in pancreatic, subcutaneous, visceral, esophageal, mandibular, cranial, and tail-fin depots. Unlike most zebrafish organs that form during embryogenesis, WAT was not found in embryos or young larvae. Instead, WAT was first identified in the pancreas on 12 days postfertilization (dpf), and then in visceral, subcutaneous, and cranial stores in older fish. All 30 dpf fish exceeding 10.6 mm standard length contained the adult repertoire of WAT depots. Pancreatic, esophageal, and subcutaneous WAT appearance correlated with size, not age, as found for other features appearing during postembryonic zebrafish development.

Beta-catenin signaling in hepatic development and progenitors: which way does the WNT blow?

The Wnt/β-catenin pathway is an evolutionarily conserved signaling cascade that plays key roles in development and adult tissue homeostasis and is aberrantly activated in many tumors. Over a decade of work in mouse, chick, xenopus, and zebrafish models has uncovered multiple functions of this pathway in hepatic pathophysiology. Specifically, beta-catenin, the central component of the canonical Wnt pathway, is implicated in the regulation of liver regeneration, development, and carcinogenesis. Wnt-independent activation of beta-catenin by receptor tyrosine kinases has also been observed in the liver. In liver development across various species, through regulation of cell proliferation, differentiation, and maturation, beta-catenin directs foregut endoderm specification, hepatic specification of the foregut, and hepatic morphogenesis. Its role has also been defined in adult hepatic progenitors or oval cells especially in their expansion and differentiation. Thus, beta-catenin undergoes tight temporal regulation to exhibit pleiotropic effects during hepatic development and in hepatic progenitor biology.