Fibronectin localization in the rat glomerulus.

Abstract

Fibronectin (FN) has been localized in the rat glomerulus using indirect immunolabeling . It was demonstrated in frozen sections by immunofluorescence, in sections of fixed kidneys by both peroxidase and ferritin-labeled antibodies, and in isolated glomerular basement membranes (GBM) with ferritin-labeled antibodies . Complementary and convergent results were obtained with these approaches . FN was most abundant in the mesangial matrix where it was especially concentrated at the interface between the endothelial and mesangial cells. In the peripheral capillary loop, FN was also detected in the laminae rarae (interna and externa) of the GBM -i.e ., between the endothelial and epithelial cells, respectively, and the GBM. These findings indicate that FN is an important constituent of the glomerulus, and they are compatible with the assumption that, in the glomerulus, as in cultured cells, FN is involved in cell-to-cell (mesangial-mesangial, mesangial-endothelial) and cell-to-substrate (mesangial cellmesangial matrix, epithelium-GBM, endothelium-GBM) attachment .Fibronectin (FN) (22) is a glycoprotein associated with fibrillar elements on the cell surface (11) and in the extracellular matrix (3,14, 33) which is involved in cell-to-cell and cell-to-substrate attachment (36). A similar, immunologically indistinguishable protein known as cold-insoluble globulin (CIG) (37), or plasma fibronectin, is found circulating in the blood .FN appears to be a major connective tissue protein, widely distributed in normal tissues (34). A close alignment or codistribution has been noted between extracellular fibronectin and intracellular actin (15, 33), and the possibility of a transmembrane linkage between the two has been proposed (15). Thus, a complex network' involving actin, FN, and probably other components (e.g., proteoglycans [7, 301) has been envisaged which connects adjacent cells, mediates cell anchorage to the extracellular matrix, and transmits deformation generated by the contractile cells. Because the glomerulus is under a high and variable hydrostatic pressure, it seemed possible that such a network may operate to maintain glomerular integrity and to regulate its blood flow (28). By immunofluorescence, FN has already been localized in the mesangium of newborn (24), adult (5,29, 31, 32,34,38), or diseased glomeruli (25, 31, 32) . By electron microscopy, a prominent fibrillar material is observed in the mesangial matrix (MM) (9), the nature of which is unknown. Some investigators described immunoreactivity for fibronectin (5,29, 31, 32) in the peripheral regions of the capillary loops, whereas others reported that it was absent (25,34,38) . In these regions, an extensive fibrillar network is also ' This network has been referred to as a "fibronexus" (33) .THE JOURNAL OF CELL BIOLOGY " VOLUME 87 DECEMBER 1980 691-696 ©The Rockefeller University Press " 0021-9525/80/12/0691/06 $1 .00 observed in the laminae rarae of the glomerular basement membrane (GBM), which appears to anchor the epithelial and endothelial...

Topographical arrangement of basement membrane proteins in lactating rat mammary gland: comparison of the distribution of type IV collagen, laminin, fibronectin, and Thy-1 at the ultrastructural level.

“…Fibronectin also has been located in the lamina densa of muscle fibers (5) and embryonic neural tube (19). In the epidermal/dermal and glomerular basement membranes, laminin and fibronectin are restricted to the lamina-lucida (7,10,12). In the lactating rat mammary gland, both type IV collagen and laminin are located predominantly in the lamina densa.…”

“…Several protein components of basement membranes have been identified (4). Type IV collagen appears to be restricted to the lamina densa (5-7), whereas laminin, fibronectin, and heparan sulfate proteoglycan are present in either the lamina lucida or lamina densa (5,(7)(8)(9)(10)(11)(12). We have shown that antibodies to type IV collagen, laminin, and the thymocyte differentiation antigen Thy-1 stain the basement membrane in the mammary glands of both virgin and lactating rats at the light microscope level, whereas antibodies to fibronectin only stain the basement membrane in the mammary gland of lactating rats (1,13,14).…”

Association of fibronectin and vinculin with focal contacts and stress fibers in stationary hamster fibroblasts.

“…Fibronectin-negative focal contacts may be the least stable type of adhesion site characteristic of motile cells, whereas G l-arrested stationary cells probably possess fibronectin beneath their focal contacts and stress fibers to augment their substrate attachment. It is important to mention that many cell types that are not usually exposed to high serum levels are attached to fibronectin-containing basement membranes in vivo (15,47) ; they might use fibronectin-and vinculin-containing adhesion complexes similar to those described in our stationary cultures to maintain a stable tissue organization .…”

Cell-mediated extracellular acidification and bone resorption: evidence for a low pH in resorbing lacunae and localization of a 100-kD lysosomal membrane protein at the osteoclast ruffled border.

“…The basic procedures used for the localization of the 100-kD protein by indirect immunoperoxidase were as previously described (8,9), with the modifications suggested by Brown and Farquhar (6). The nature of the tissue imposed further modifications, described below.…”