Glycohistochemical characterization of sialoglycoconjugates in the allantoic duct epithelium of the horse umbilical cord

Introduction: The umbilical cord is the lifeline between the fetus and placenta. The glycoproteins are involved in many biological activities including cell proliferation and cell differentiation. Because of their negative charge and terminal location, sialic acids present a high potential in modulating epithelial permeability barrier and cytoprotective function in the urinary system. The aim of the present study was to examine and characterize sialoglycoproteins in the epithelium lining the allantoic duct by means of the lectin histochemistry. Methods: Fragments of the umbilical cord from fetuses were fixed in 4% (w/v) neutral formalin and embedded in paraffin wax. Sections (5 µm thick) were stained with SNA, MAL II, PNA, DBA, Con A, WGA before or after KOH-sialidase (Ks) treatment. Results: The luminal surface bound MAL II, SNA, Ks-PNA, SBA and Ks-WGA; MAL II did not reacted with the luminal surface of the proximal tract. The urothelium apical region bound MAL II, SBA,SNA, PNA and Ks-WGA in the proximal tract, whereas in the other tracts did not react with MAL II and SBA. Except for vacuolized cells, the entire cytoplasm of the urothelium throughout the ductus bound Con A, whereas some elongated cells reacted with Ks-PNA; the elongated cells of the distal region bound also SBA. Basal region of urothelium linked Ks-WGA. Conclusions: These results demonstrated the presence of sialoglycoconjugates mostly in the lumnal surface of the epithelium lining the horse allantoic duct as well as their regional difference. These glycoconjugates belong to N-linked type (Con A and Ks-WGA reactivity). Althought similar investigations on the allantoic duct lack, our findings agree with studies on the implication of N-linked sialoglycans in the protection and activity of urothelium. It is noteworthy that asialo- or sialylGalNAcα1,3(LFucα1,2)Galβ1,3/4GlcNAcβ1 terminating glycans (DBA and Ks-DBA reactivity) lack in the horse umbilical cord