Study On The Fine Structure Of Intestine And Intestinal Mucosal Barrier In Zebrfish (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 intestine is the major place where zebrafish absorbs nutrition and defends itself against the harmful materials. Up to now, some scholars mainly have made a bunch of exploration at the genetic level to study the development and endocrine situation of the intestine in zebrafish, as well as the models of human diseases. While this study was undertaked to elucidate the intestine structures and intestinal mucosal barrier from the morphological point, in order to provide morphological basis for further study on absorption and immunity of the intestine in zebrafish.ExperimentⅠMicro-and ultra-structure of the intestine in zebrafish(Brachydanio rerio) A morphological observation by light and electron microscopy was undertaken on the intestine of the zebrafish, Brachydanio rerio. We found that zebrafish intestine could be divided into three segments:anterior segment, middle segment, posterior segment and its wall was made up of three layers:mucosa, muscularis, and serosa. The mucosa comprised an epithelial lining with distinct basement membrane and a lamina propria which was a thin connective tissue. While no muscularis mucosa and intestinal glands existed. Columnar epithelium cells had tall columnar cell bodis with very developed junctional complexs. The goblet cells were interspersed between the columnar epithelium cells. And the intraepithelial lymphocytes(IELs) usually appeared near the basement membrane as well as mastocytes, few of the formers were found approaching the apical surface of epithelium. The whole epithelial lining projected into the lumen of the intestine to form intestinal villis which were branching or finger-like shape. The muscularis had two layers of smooth muscle cells called circular muscle layer in the internal and longitudinal muscle layer in the external. While serosa was thin. We had four items measured:the longitudinal section area of intestinal villi which was 12384.00±1923.95μm2 in anterior gut,6839.59±853.02μm2 in middle gut and 7018.86±1148.40μm2 in posterior gut; the height of intestinal villi whose data was individually 157.72±12.62μm,79.24±12.49μm and 82.69±16.25μm in sequence; the height of columnar epithelium cell which were 38.39±3.53μm of anterior gut, 33.71±1.95μm of middle gut and 33.62±3.99μm of posterior gut; and the thickness of muscularis, the results of which were 11.29±1.31μm,8.67±0.84μm and 9.50±1.69μm from anterior to posterior gut. Based on these results we could discovered that all anterior intestine data was extremely significant with that of middle and posterior intestine. However there were no significant differences between middle and posterior intestine data. The variation tendency declined from the anterior to the posterior which indicated that the anterior intestine was the main place of zebrafish digestive tract for absorption. And the locations of IELs and mastocytes suggested that zebrafish intensified its immunity function by improving the distribution of immunocytes.ExperimentⅡIntestinal mucosal barrier of zebrafish(Brachydanio rerio) A morphological observation by electron microscopy, immunohistochemistry and histochemistry was undertaken on the intestinal mucosal barrier of the zebrafish, Brachydanio rerio. We found that zebrafish intestine had an intact structure of mechanical barrier, chemical barrier and immune barrier. Developed junctional complexes existed between the absorptive cells, which confirmed the mechanical barrier. The goblet cells secreted neutral mucoitin and mucin to the mucus layer which was also composed with cell factors and immunoglobulins in order to lubricate and protect the mucosa. The main immunocytes in zebrafish intestine mucosa such as IELs and mastocytes found in the epithelium built the immune barrier by way of the cellular immunity and the humoral immunity.