Anna G. Brownell

Fibronectin: Its Relationship to Basement Membranes II. Ultrastructural Studies in Rat Kidney

Fibronectin, basement membrane and type I collagen antigens have been localized in normal rat kidney by electron immunohistochemical methods. Immunoreactive fibronectin was found in the interstitial connective tissue matrix and on collagen fibers, while tubular, endothelial and smooth muscle basement membranes throughout the kidney were consistently negative. In the glomerulus immunoreactive fibronectin was abundant in the mesangial matrix. The peripheral glomerular basement membrane was occasionally reactive in a spotty, irregular manner. These findings suggest that fibronectin antigens are probably not a constituent of basement membranes. It is proposed that some fibronectin antigen may be trapped in the glomerular filter, and that normal glomerular cleansing mechanisms would transport this trapped fibronectin toward the mesangial areas where it would be eventually processed.

Fibronectin: its relationship to basement membranes. I. Light microscopic studies.

Fibronectin is a large molecular weight glycoprotein which has been shown to be associated with cell surfaces, extracellular fluids, and connective tissues. Its possible relationship with basement membranes remains controversial. To define this relationship, the distribution of this antigen was evaluated by light microscopic immunoperoxidase techniques in kidney, skin, skeletal muscle, gastrointestinal tract and parietal yolk sac carcinoma. In addition, antibodies against basement membrane and interstitial collagen were used as controls of the specificity of this reaction. Any possible cross-reactivity between plasma fibronectin and basement membrane was examined by immunodiffusion, immunoelectrophoresis and ELISA techniques. The results indicate that antibodies to plasma fibronectin do not co-localize with antibodies to basement membrane constituents. Furthermore, by immunodiffusion or ELISA, there was no cross-reactivity between plasma fibronectin and anti-basement membrane antibody, nor between basement membrane and anti-plasma fibronectin antibody. We conclude that fibronectin is probably not part of the basement membranes studied.

Basal lamina degradation: The identification of mammalian-like collagenase activity in mesenchymal-derived matrix vesicles

Abstract Isolated matrix vesicles from 26-day embryonic New Zealand White rabbit incisor tooth organs were incubated on 14 C labeled reconstituted Type I collagen at 25°C for 18 hours. Under these conditions the matrix vesicles demonstrated the ability to degrade collagen as demonstrated by radio-activity solubilized. Analysis of the released radioactivity using SDS-PAGE demonstrated the presence of two molecular species with molecular weights of 67,000 and 32,000 daltons. These results are in accordance with the presence of a mammalian-like collagenase associated with the matrix vesicles, whose function may be the degradation of the basal lamina.

Role of Basal Lamina in Tissue Interactions

Basal lamina are extracellular structures found closely apposed to the plasma membrane on the basal surface of epithelial and endothelial cells and surround muscle and fat tissues. While the primary function of basal lamina in most adult tissues is probably supportive, significant evidence indicates that during embryonic development, basal lamina may be involved in regulating heterotypic tissue interactions. Changes in composition of the basal lamina of salivary and mammary gland epithelial tissues during development probably are important for branching morphogenesis which leads to the final form of the organ. During tooth organogenesis, selective basal lamina degradation and direct cell contact between developing epithelium and mesenchyme has been documented and suggested to be necessary for cytodifferentiation. Basal lamina turnover, as suggested by these morphological observations, no doubt involves both basal lamina synthesis and degradation. We have studied several factors evidently required for basal lamina reconstitution in vitro, and have discovered that fibronectin added to enamel organ epithelial cultures provided cues required for basal lamina formation in vitro. Both fetal calf serum and dental papilla mesenchyme-conditioned media also provided specific signals for basal lamina reconstitution. In addition, we have found that fibronectin is produced by the dental papilla mesenchyme, is released into the medium, and can be isolated from epithelial explants which have been cultured in mesenchyme-conditioned medium; the epithelial explants themselves do not make fibronectin in vitro.

Basic Biological Sciences DNA Synthesis of Enamel Organ Epithelium in vitro is Enhanced by Co-cultivation with Non-Viable Mesenchyme Cells

Developing enamel organ epithelium was cultured in the presence and absence of non-viable dental papilla mesenchyme cells. Epithelial cell proliferation was enhanced by 75% when cultivated on the mesenchyme cell substratum. The addition of epidermal growth factor (EGF) to enamel organ epithelium cultured on this substratum resulted in a synergistic enhancement of DNA synthesis.Developing enamel organ epithelium was cultured in the presence and absence of non-viable dental papilla mesenchyme cells. Epithelial cell proliferation was enhanced by 75% when cultivated on the mesenchyme cell substratum. The addition of epidermal growth factor (EGF) to enamel organ epithelium cultured on this substratum resulted in a synergistic enhancement of DNA synthesis.

Basic Biological Sciences

Developing enamel organ epithelium was cultured in the presence and absence of non-viable dental papilla mesenchyme cells. Epithelial cell proliferation was enhanced by 75% when cultivated on the mesenchyme cell substratum. The addition of epidermal growth factor (EGF) to enamel organ epithelium cultured on this substratum resulted in a synergistic enhancement of DNA synthesis.Developing enamel organ epithelium was cultured in the presence and absence of non-viable dental papilla mesenchyme cells. Epithelial cell proliferation was enhanced by 75% when cultivated on the mesenchyme cell substratum. The addition of epidermal growth factor (EGF) to enamel organ epithelium cultured on this substratum resulted in a synergistic enhancement of DNA synthesis.