Hepatic parenchyma, biliary ducts and gall bladder forming potency in the hepatic primordium in the quail embryo

Developmental and posthatch effects of in ovo exposure to 2,3,7,8-TCDD, 2,3,4,7,8-PECDF, and 2,3,7,8-TCDF in Japanese quail (Coturnix japonica), common pheasant (Phasianus colchicus), and white leghorn chicken (Gallus gallus domesticus) embryos

An egg injection study was conducted to confirm a proposed model of relative sensitivity of three avian species to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like chemicals. It was previously reported that the order of species sensitivity to in ovo exposure to TCDD, 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) at doses ranging from 0.044 to 37 picomoles (pmol)/g egg was the chicken (Gallus gallus domesticus), common pheasant (Phasianus colchicus), and Japanese quail (Coturnix japonica) based on embryo mortality and hepatic enzyme induction. In the present study, the incidence of developmental deformities, changes in body and relative organ masses, and organ pathology of hatchlings as additional indicators of species sensitivity were assessed; in addition, embryo mortality in the three species was categorized by stage of development. Embryo mortality varied temporally with significant increases generally occurring after organogenesis and just prior to hatching. A significant increase in the percentage of developmental deformities was observed only in Japanese quail exposed to TCDF. Body and relative organ masses of quail, pheasants, and chickens dosed in ovo with TCDD, PeCDF, or TCDF were not consistently affected. Chemical-related pathology occurred only in livers of quail at the greatest doses of each compound. These results indicated that the incidence of developmental deformities, changes in body and relative organ masses and organ pathology could not be used as indicators of species sensitivity or chemical potency.

Sox17 regulates organ lineage segregation of ventral foregut progenitor cells

The ventral pancreas, biliary system, and liver arise from the posterior ventral foregut, but the cell-intrinsic pathway by which these organ lineages are separated is not known. Here we show that the extrahepatobiliary system shares a common origin with the ventral pancreas and not the liver, as previously thought. These pancreatobiliary progenitor cells coexpress the transcription factors PDX1 and SOX17 at E8.5 and their segregation into a PDX1+ ventral pancreas and a SOX17+ biliary primordium is Sox17-dependent. Deletion of Sox17 at E8.5 results in the loss of biliary structures and ectopic pancreatic tissue in the liver bud and common duct, while Sox17 overexpression suppresses pancreas development and promotes ectopic biliary-like tissue throughout the PDX1+ domain. Restricting SOX17+ biliary progenitor cells to the ventral region of the gut requires the notch effector Hes1. Our results highlight the role of Sox17 and Hes1 in patterning and morphogenetic segregation of ventral foregut lineages.

Development of Dolichos biflorus agglutinin (DBA) binding sites in the bile duct of the embryonic mouse liver

The distribution of binding sites for Dolichos biflorus agglutinin (DBA) was studied by histochemical staining in the embryonic mouse liver. The liver primordium consists of cranial and caudal diverticula. DBA bound to the pseudostratified endodermal cells of the caudal hepatic diverticulum, and also to some endodermal cells of the cranial one. Most extrahepatic bile duct cells and all epithelial cells of the gall bladder were consistently DBA-positive. In intrahepatic bile ducts and their precursors, the DBA binding sites showed a patchy distribution. Most hepatocytes were DBA-negative, though some young hepatocytes were DBA-positive. The results suggest that DBA binding sites are useful markers of epithelial cells of the gall bladder and the bile ducts, especially the extrahepatic bile duct. Differentiation of bile duct cells was also discussed with special reference to the developmental change of the distribution of the DBA binding sites.

Secondary joining of the bile ducts during the hepatogenesis of the mouse embryo

Development of the bile duct system of the mouse embryo was studied histologically and by an immunofluorescent technique. The hepatic primordium consisted of cranial and caudal portions. In the liver of young embryos, the hepatic cords were present in the presumptive cystic duct epithelium, and the histology of the presumptive cystic duct epithelium near the hilus was similar to that of the hilus epithelium. The results suggest that at least a part of the cystic duct epithelium develops from the cranial diverticulum of the hepatic primordium. Lumen structures were precursors of intrahepatic bile ducts and originated from type I (immature) hepatocytes. The lumina of the lumen structures appeared near the hilus area first, but most were discontinuous with those of the hepatic ducts. With the progress of development, the discontinuous lumen structures became distributed around the portal vein branches in the central part of the liver parenchyma, and gradually connected with each other and also with hepatic ducts. The discontinuous laminin immunofluorescence also appeared in the endodermal cells around the portal vein branches at the younger stages. Therefore, it is conceivable that the intrahepatic bile ducts originate from discrete cell populations of type I hepatocytes around the portal vein branches and subsequently become confluent, but not from the cells of hepatic ducts.

Changes in intercellular junctions. I. Embryonic chick liver development

Quantitation of junctional changes during development may clarify the relation between intercellular junctions and processes such as cell proliferation, morphogenesis, and cytodifferentiation. Chick embryo hepatocytes at 3 days (stage 21) 6 days (stage 28), 14 days (stage 39) of incubation, and 5 days posthatching showed thymidine-labeling indices of 41 +/- 1, 33 +/- 0.8, 13 +/- 0.04, and 7 +/- 1%, respectively. This decline in mitotic activity was correlated with a gradual increase in amount of cell surface occupied by tight junctions. In early embryonic stages these junctions were characteristically linear or macular in form. At embryonic stages 28 and 39 the anastomosing strands of the tight-junction networks characteristically had many free ends while in liver from hatched chicks, tight junction strands frequently ran almost parallel to one another. The area covered by gap junctions increased at embryonic stage 28, then declined with further development. Scanning electron microscopy of developing chick liver showed that the elongated cells of hepatic buds are reorganized into hepatic cords between embryonic stages 21 and 28. Cytochemical demonstration of ATPase at the bile canalicular surface is first apparent at embryonic stage 28 and the cell surface occupied by gap junctions is highest near this time. These findings suggest that modification of proliferative rate or of synthetic activity associated with the maturation of hepatocytes could be correlated with predictable changes in junctional patterns.