The cellular origin of fibronectin in the basement membrane zone of developing tooth

The cellular source of fibronectin in the dental epitheliomesenchymal interface was studied in interspecies combinations of mouse and quail tissue. Species-specific fibronectin antibodies were produced by immunizing rabbits with purified mouse or chicken fibronectin and by absorbing both antisera with purified heterologous fibronectin and insoluble tissue extract. The absorbed antisera to mouse and chicken fibronectin showed fluorescent staining only in mouse and chicken tissue sections, respectively, but not vice versa. When the mouse mesenchymal dental papilla was combined and cultured either with the mouse enamel organ or with the quail pharyngeal epithelium, mesenchymal cell differentiation was initiated and typical alignment of mesenchymal cells along the basement membrane was seen. Examination with transmission electron microscope revealed a typical bilaminar basal lamina with adherent fibrillar matrix on its mesenchymal aspect. Immunofluorescent localization of fibronectin with the mouse-specific fibronectin antiserum showed a brilliant staining in the mesenchymal tissue and in the basement membrane zone. When the chicken-specific fibronectin antiserum was used, no staining was detected in either tissue recombinations. We have suggested earlier that fibronectin in the dental basement membrane plays an important role during the differentiation of mesenchymal cells into odontoblasts. The present study demonstrates that fibronectin in the basement membrane of the developing tooth is produced exclusively by the differentiating mesenchymal cells.