Comparative study on a unique architecture of the brook lamprey liver and that of the hagfish and banded houndshark liver.

Although the liver of the lamprey, a group of cyclostomes that diverged the earliest among vertebrates, has abundant bile ducts in the larval stage, which degenerate during metamorphosis, there is no comparative study on its architecture with other early diverged vertebrates in terms of the morphological evolution of vertebrate livers. The present study was undertaken to compare the characteristics of the brook lamprey liver with those of the hagfish and banded houndshark, which have the portal triad type liver architecture, and to discuss its evolution. Although the liver of the brook lamprey had two-cell cords of hepatocytes lined by sinusoids in the ammocoetes larval stage, intrahepatic bile ducts around portal veins penetrated into the liver parenchyma with convolution and gradual reduction in diameter.

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.

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.

Changes of biliary cilia, smooth muscle tissue distribution, innervation and extracellular matrices during morphological evolution of hepatic architectures in vertebrates.

Background: The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having bile ducts independent of the course of portal veins). The former is typically detectable in livers of tetrapods and cartilaginous fish, and its ancestral state is found in the hagfish, an earliest diverged lineage among vertebrates. Teleosts other than osteoglossomorphs have the latter.

Comparative study on a novel lobule structure of the zebrafish liver and that of the mammalian liver.

The mammalian liver has a lobule structure with a portal triad consisting of the portal vein, hepatic artery, and bile duct, which exhibits zonal gene expression, whereas those of teleosts do not have a portal triad. It remains to be demonstrated what kind of the unit structures they have, including their gene expression patterns. The aims of the present study were to demonstrate the unit structure of the teleost liver and discuss it in terms of evolution and adaptation in vertebrates and the use of teleosts as an alternative model for human disease.

Liver progenitor cells may construct cysts having heterogeneous gene expression of liver-enriched transcription factors in mice with conditional knockout of the Hhex gene.

The deletion of the Hhex (Hematopoietically expressed homeobox) gene causes agenesis of the liver and polycystic liver disease depending on its timing. The present study was undertaken to determine the role of the Hhex gene in not only signaling cascades to cyst and abnormal bile duct formation but also the liver progenitor contribution to cystic development. Liver-specific Hhex knockout mice (Alb-Cre/Hhex) in adult stages were used.

Immunohistological analysis on distribution of smooth muscle tissues in livers of various vertebrates with attention to different liver architectures.

Background: The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having non-periportal bile ducts). The former is detectable from the hagfish, which is the most ancestral vertebrate, to tetrapod livers whereas many actinopterygian livers have the latter. The aim of the present study is to reveal the distribution of smooth muscle tissue in livers of various vertebrates with attention to their architectures.

The hepatic architecture of the coelacanth differs from that of the lungfish in portal triad formation.

The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having non-periportal bile ducts). The former is detectable in the tetrapod liver whereas the lungfish liver has the latter. It remains to be revealed which type of hepatic architecture the coelacanth, which together with the lungfish belongs to the Sarcopterygii, possesses.

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.

Identification of novel genetic markers for mouse yolk sac cells by using microarray analyses.

The mouse embryonic yolk sac consists of a visceral yolk sac (VYS) and parietal yolk sac (PYS), and may function as a materno-fetal exchange system for nutrients and wastes, and physical protector for the embryo/fetus. The present study was undertaken to characterize gene expression of the VYS and PYS endodermal cells, and to identify their novel genetic markers from microarray data. Apoa4, Lrp2, Fxyd2, Slc34a3 and Entpd2 were predominantly expressed in VYS epithelial cells.

Transdifferentiation of mouse visceral yolk sac cells into parietal yolk sac cells in vitro.

The mouse embryonic yolk sac is an extraembryonic membrane that consists of a visceral yolk sac (VYS) and parietal yolk sac (PYS), and functions in hematopoietic-circulation in the fetal stage. The present study was undertaken to examine the normal development of both murine VYS and PYS tissues using various molecular markers, and to establish a novel VYS cell culture system in vitro for analyzing differentiation potentials of VYS cells. RT-PCR and immunohistochemical analyses of gene expression in VYS and PYS tissues during development revealed several useful markers for their identification: HNF1β, HNF4α, Cdh1 (E-cadherin), Krt8 and Krt18 for VYS epithelial cells, and Stra6, Snail1, Thbd and vimentin for PYS cells.

Morphological, biochemical, transcriptional and epigenetic responses to fasting and refeeding in intestine of Xenopus laevis.

Background: Amphibians are able to survive for several months without food. However, it is unclear what molecular mechanisms underlie their survival. To characterize the intestinal responses to fasting and refeeding, we investigated morphological, biochemical, transcriptional and epigenetic changes in the intestine from adult male Xenopus laevis.

Immunohistochemical analyses of cell cycle progression and gene expression of biliary epithelial cells during liver regeneration after partial hepatectomy of the mouse.

The liver has a remarkable regeneration capacity, and, after surgical removal of its mass, the remaining tissue undergoes rapid regeneration through compensatory growth of its constituent cells. Although hepatocytes synchronously proliferate under the control of various signaling molecules from neighboring cells, there have been few detailed analyses on how biliary cells regenerate for their cell population after liver resection. The present study was undertaken to clarify how biliary cells regenerate after partial hepatectomy of mice through extensive analyses of their cell cycle progression and gene expression using immunohistochemical and RT-PCR techniques.

Molecular Cloning of cDNA Encoding an Aquaglyceroporin, AQP-h9, in the Japanese Tree Frog, Hyla japonica: Possible Roles of AQP-h9 in Freeze Tolerance.

In order to study the freeze-tolerance mechanism in the Japanese tree frog, Hyla japonica, wecloned a eDNA encoding aquaporin (AQP) 9 from its liver. The predicted amino acid sequence ofH. japonica AQP9 (AQP-h9) contained six putative transmembrane domains and two conservedAsn-Pro-Aia motifs, which are characteristic of AQPs.

Histochemical Analyses of Biliary Development During Metamorphosis of Xenopus laevis Tadpoles.

In mammalian liver development, intrahepatic biliary morphogenesis takes place in periportal, but not in pericentral, regions. Liver progenitor cells transiently form epithelial plate structures and then intrahepatic bile ducts around the portal veins under the influence of the mesenchyme. The present study was undertaken to histochemically examine normal biliary development and its dependence on the action of the thyroid hormone triiodothyronine (T3) in Xenopus laevis tadpoles.

Immunomagnetic exclusion of PECAM-1-positive endothelial cells in fetal mouse liver cell cultures causes impaired growth and gene expression of hepatoblasts and stellate cells.

Previous studies using mice having defective VEGF signaling have demonstrated that vascular development is indispensable for early hepatic organogenesis. However, not only whether its action lasts during later hepatic development, but also what molecules are involved in that action remains to be determined. The present study was undertaken to examine the effects of primitive sinusoidal endothelial cells on hepatic growth and maturation in primary culture of fetal mouse liver cells, and to determine their molecular mechanisms.

Impaired hepatocyte maturation, abnormal expression of biliary transcription factors and liver fibrosis in C/EBPα(Cebpa)-knockout mice.

Inactivation of the C/EBPα gene (Cebpa) in the mouse not only causes impaired hepatocyte maturation, but also induces pseudoglandular structures in the liver parenchyma. The present study was undertaken to determine how the expression of other transcription factors controlling differentiation into hepatocytes and biliary epithelial cells is affected, and how the hepatic architecture, including the bile and vascular systems, is disordered in the fetal knockout liver. Histochemical analyses demonstrated that the expression of HNF1α and HNF4α was heterogeneous in the knockout liver, and that not all parenchymal cells (pseudoglandular) expressed these transcription factors, whereas parenchymal cells in the wild-type liver homogeneously expressed these transcription factors.

Histochemical analyses of hepatic architecture of the hagfish with special attention to periportal biliary structures.

The hagfish liver was histochemically examined with special attention to biliary structures around the portal veins. Hepatocytes were organized into tubular structures surrounded by sinusoids. Biliary ductule structures, which resemble the ductal plates transiently appearing in mammalian liver development, were observed around the portal veins, but they did not appear around central veins.

Immunomagnetic exclusion of E-cadherin-positive hepatoblasts in fetal mouse liver cell cultures impairs morphogenesis and gene expression of sinusoidal endothelial cells.

Previous studies have shown that various cell-cell interactions between hepatoblasts and nonparenchymal cells, including sinusoidal endothelial cells and stellate cells, are indispensable for the development of fetal murine hepatic architecture. The present study was undertaken to determine the effects of hepatoblasts on the sinusoidal structural formation using a culture system of fetal mouse livers. Primitive sinusoidal structures extensively developed in fetal livers, and were composed of LYVE-1- and PECAM-1-positive endothelial cells, desmin-positive stellate cells and F4/80-positive macrophages.

Purification and culture of fetal mouse hepatoblasts that are precursors of mature hepatocytes and biliary epithelial cells.

To investigate cell-cell interactions during mammalian liver development, it is essential to separate hepatoblasts (fetal liver progenitor cells) from nonparenchymal cells, including stellate cells, endothelial cells, and hemopoietic cells. Various factors, which may be produced by nonparenchymal cells, could be assayed for their effects on the growth and maturation of separated hepatoblasts. The protocol using immunomagnetic beads coated with anti-mouse E-cadherin antibody is described for efficient isolation of hepatoblasts from cell suspensions of fetal mouse livers.

Developmental changes of cell adhesion molecule expression in the fetal mouse liver.

Developmental changes of cell adhesion molecule expression, especially in nonparenchymal cells, have hardly ever been analyzed in the murine liver. The present study was undertaken to immunohistochemically examine the expression of NCAM, ICAM, VCAM, and N-cadherin during mouse liver development and in fetal liver cell cultures. NCAM was transiently expressed in mesenchymal cells of the septum transversum and sinusoidal cells in liver development.

Sinusoid development and morphogenesis may be stimulated by VEGF-Flk-1 signaling during fetal mouse liver development.

Early morphogenesis of hepatic sinusoids was histochemically and experimentally analyzed, and the importance of VEGF-Flk-1 signaling in the vascular development was examined during murine liver organogenesis. FITC-gelatin injection experiments into young murine fetuses demonstrated that all primitive sinusoidal structures were confluent with portal and central veins, suggesting that hepatic vessel development may occur via angiogenesis. At 12.

Immunohistochemical analyses of cell-cell interactions during hepatic organoid formation from fetal mouse liver cells cultured in vitro.

Cell-cell interactions among cell types constituting the fetal liver such as hepatoblasts, stellate cells and endothelial cells lead to functional lobule development. The present study was undertaken to investigate hepatic histogenesis in the primary culture of E12.5 mouse livers, including cell-cell and cell-matrix interactions.

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

The expression of C/EBPalpha, which may govern transcription of mature hepatocyte marker genes, was suppressed in periportal hepatoblasts in mouse liver development, leading to biliary cell differentiation. This study was undertaken to analyze how inactivation of the Cebpa gene affects biliary cell differentiation and gene expression of the regulatory genes for that differentiation, including Hnf1b and Hnf6. In the knockout mouse liver at midgestation stages, pseudoglandular structures were abundantly induced in the parenchyma with elevated expression of Hnf6 and Hnf1b mRNAs.