Expression of extracellular matrix proteins in the fetal rat gastric mucosa

At gestational day 16 the epithelium of the rat stomach consists of a strat ified layer of undifferentiated cells, and two days later glandular structu res appear. The present study was carried out to identify extracellular mat rix proteins that could be involved in the epithelial cell proliferation an d differentiation processes that occur in the fetal rat stomach during this period. For comparative purposes the expression of the same components in the adult gastric mucosa was examined. Pregnant Sprague-Dawley rats receive d an intraperitoneal injection of 5-bromo-2'-deoxyuridine to label prolifer ating cells. One. 3.5, or 6 h post-injection the stomachs were excised and immediately frozen. The specimens were sectioned and stained with hematoxyl in and eosin or for 5-bromo-2'-deoxyuridine. cytokeratin no. 8, H,K-ATPase, and the extracellular matrix proteins fibronectin, laminin, and collagens type I and IV. A stratified layer of proliferating cells was observed in th e epithelium of the fetal stomachs, while in adult stomachs proliferating c ells were detected in the isthmus/neck region of the glands. Cytokeratin, a n epithelial cell marker, was sparse at gestational day 16 but abundant bot h at gestational day 18 and in the isthmus/neck region of gastric glands of the adult stomach. The parietal cell marker H,K-ATPase could not be detect ed in the fetal stomachs during this period. Fibronectin was observed in th e stroma of both fetal and adult stomachs. Collagen type I could only be de tected in the stroma close to the oesophagus at gestational day 16. Two day s later, collagen type I was abundant in the lamina propria, the submucosa and in the serosa of the fetal stomachs. In adult tissue collagen type I wa s detected in the surface epithelium, the submucosa and in the serosa of th e stomach. Collagen type IV and laminin were expressed in the lamina propri a, the basement membranes around blood vessels, muscle cells, and nerve bun dles, as well as in the serosa of both 16- and 18-day-old fetal and adult r at stomachs. In conclusion, a high cell proliferation rate was observed in the epithelium at both gestational days 16 and 18. The increased expression of cytokeratin observed during this period indicates that the epithelial c haracter of the embryonic cells becomes more distinct, while the remarkable change in the expression of collagen type I might reflect an important rol e of collagen type I in the development of the gastric epithelium.