Study On The Fine Structure Of Liver And Bile Systerm In Zebrafish(Brachydanio Rerio)

Zebrafish (Brachydanio rerio) has many valuable features as an experimental model.Due to its prolific reproduction and the external development of the transparent embryo, the zebrafish is a prime model for genetic and developmental studies, as well as research in toxicology and molecular biology. The liver is the largest gland in the fish and it playes an important role in material metabolism, detoxification, blood coagulation and defense. Up to now, some scholars mainly from the genetic level to study the development of the liver in zebrafish, as well as the models of human diseases.The purpose of this study was undertaked to elucidate the liver structures from the morphological point, in order to provide morphological basis for further study the development and function of the liver in zebrafish. Lay the foundation for reconstructing the three-dimensional of liver.Experiment I Microstructure and ultrastructure of the liver in zebrafish (Brachydanio rerio) A morphological observation by light and electron microscopy was undertaken on the liver of the zebrafish, Brachydanio rerio.The results showed that, there was no typical portal area, bile ducts and venules were randomly distributed within the parenchyma.The polygonal hepatocytes are arranged in twisting, branching and anastomosing cords usually two cells thick.There was a single big and spherical nucleus in the hepatocyte,and the nucleoli displayed a separation into granulose component, fibrillar centers and dense fibrillar component.The cytoplasm are dominated by numerous stacks of non-fenestrated lamellae of rough endoplasmic reticulum (RER) of considerable length arranged in close parallel array. When the cytoplasm was rich in mitochondria, RER, ribosome and the number of nucleopore was massive, glycogen was found in small concentrations, and a few lysosome may be observed. When glycogen was found in large concentrations, the number of nucleopore was few, so other cytoplasmic organelles were. These suggested that the consumption of glycogen ensured normal metabolism of nucleic acids and proteins, and mitochondria provided energy in the process of protein synthesis. Erythrocytes, lymphocytes, fat-storing cells and endothelial cells were also described.A comparison between zebrafish liver and that of other teleosts was made.Experiment II Study on the bile system in zebrafish (Brachydanio rerio) A morphology observation by light microscopy, electron microscopy and immunohistochemistry was undertaken on the intrahepatic biliary system in the zebrafish, Brachydanio rerio.The results showed that the biliary system was arranged in arborization in the parenchyma. The biliary tree included sequentially by intracellular and intercellular canaliculi, preductules, ductules and ducts.The intercellular originated at the neighborhood of the nucleus to extend to the cell surface where it emptied into the intra parenchymal biliary passage running in the interhepatocytic space. In the preductules, the wall was formed by bile preductular epithelial cells and hepatocytes.The bile preductular epithelial cells were linked to hepatocytes by the tight junctions. The wall of the biliary ductule usually consisted integrally2to4biliary epithelial cells. These cells had no basal lamina and were contacted with hepatocytes directly. A ductule that was composed of a single cell and was embedded between two adjoining liver cells was found by TEM. The lumen of this ductule was very narrow and formed by the infolding of the plasma membrane of the ductule cell. The wall of bile ducts was composed of cuboidal epithelial cells, and the bile duct was encircled by the connective tissue. Whereas in ducts, apart from those cells, there were intraepithelial lymphocytes.This suggested that there exited mucosal immune response. The preducules and ductules formed a segment connecting canaliculi to ducts, thus, we considered that segment as being analogous to the mammalian canals of Hering.The reactions for Mg2+-dependent ATPase showed that bile tree was strained brownish-black color and interwove into a network. The bile system was revealed by immunstaining with a monoclonal antibody2F11that detected biliary epithelial cell bodies which are distributed scatteredly in interhepatocytic and the proximal regions of the ducts arising from these cells was stained.These results above showed that the bile systerm in zebtafish is not only different with the mammals and birds, but also with other bony fish.