Basement membranes laminins

Laminin [consisting of three polypeptide chains, A, Bl (possibly replaced in GBM by S) and B2] is the most important noncollagenous protein of the glomerular basement membrane. Laminin forms a second network, which is connected to the collagen IV network probably via another protein called entactin or nidogen. Laminin is probably very important for cellular differentiation and adhesion, but its mesh clearly also contributes to the structure of the glomerular basement membrane. The postnatally common embryonic laminin-10 isoform is... 

Tronchin G, Bouchara JP, Larcher G, Lissitzky JC, Chabasse D Interaction between Aspergillus fumigatus and basement membrane laminin Binding and substrate degradation. Biol Cell 1993 77 201-208. 

Martin, G.R. Timpl, R. (1987). Laminin and other basement membrane components. Ann. Rev. Cell. Biol. 3, 57-85. 

Certain proteoglycans (eg, heparan sulfate) are associated with the plasma membrane of cells, with their core proteins acmally spanning that membrane. In it they may act as receptors and may also participate in the mediation of cell growth and cell-cell communication. The attachment of cells to their substramm in cul-mre is mediated at least in part by heparan sulfate. This proteoglycan is also found in the basement membrane of the kidney along with type IV collagen and laminin... 

Jucker M, Tian M, Ingram DK. Laminins in the adult and aged brain. Mol Chem Neuropathol 1996 28 209-218. Bernstein JJ, Karps SM. Migrating fetal astrocytes do not intravasate since they are excluded from blood vessels by vital basement membrane. Int J Dev Neuroscience 1996 14 177-180. 

Another 3-D cornea model, comprising rabbit primary cultures of epithelial and stromal cells as well as mouse immortalized endothelial cells, was described in 1994 by Zieske and coworkers [70], They showed the influence of endothelial cells on the formation of a tightly packed, multilayered epithelium as well as the expression of laminin, type VII collagen, a6 integrin, keratin K3, and a-enolase. Furthermore, their findings suggested that the formation of an in vivo-like epithelium requires the cultivation of the 3-D corneal construct under AIC conditions. By contrast, LCC methods of cultivating corneal equivalents in the absence of endothelial cells failed to promote the expression of differentiation markers and basement membrane components. 

Speziale, P., Hook, M., Wadstrom, T., and Timpl, R. (1982). Binding of basement membrane protein laminin to Escherichia coli. FEBS Lett. 175, 55-58. 

Valkonen, K. H., Wadstrom, T., and Moran, A. P. (1994). Interaction of lipopolysaccharides of Helicobacter pylori with basement membrane protein laminin. Infect. Immun. 62,3640-3648. 

The transition from mesenchyme to epithelium involves biochemical changes in the cells and the extracellular matrix, N-CAM expression on cell surfaces disappears, replaced by L-CAM (uvomorulin). Vimentin, a characteristic cytoskeletal component of mesenchyme, disappears, and cytokeratin, characteristic of epithelia, appears. There is a decrease in collagen I extracellularly and an increase in the basement membrane components laminin and collagen IV. 

Helix bundles. A third peptide chain can be added to a coiled coil to form a triple-stranded bundle.180-183 An example is the glycoprotein laminin found in basement membranes. It consists of three peptide chains which, for -600 residues at their C-terminal ends, form a three-stranded coil with heptad repeats.182184 Numerous proteins are folded into four helical segments that associate as four-helix bundles (Fig. 2-22).185-188 These include electron carriers, hormones, and structural proteins. The four-helix bundle not only is a simple packing arrangement, but also allows interactions between the + and - ends of the macro-dipoles of the helices. 

Basement membranes (Fig. 1-6)663 function in part as an exoskeleton that helps keep cells positioned. However, the thick basement membranes of the capillary walls of the glomeruli of the kidney provide the ultrafilters that prevent most proteins from entering the urine. Basement membranes contain large amounts of collagen IV, which forms a polygonal network (Fig. 8-33A). A second macromolecular network is formed by the very large 950-kDa crossshaped multisubunit protein called laminin (Fig. 

Figure 1. The muscle dystrophin-glycoprotein complex. The dystrophin-glycoprotein complex normally spans the plasma membrane of the skeletal muscle cell and may stabilize the sarcolemma and cytoskeleton to allow force transduction between the intracellular cytoskeleton (F-actin filaments) and the extracellular matrix. The molecules indicated are core components of the dystrophin-glycoprotein complex. Laminin 2 is the predominant laminin isoform in skeletal muscle basement membranes. Modified from McNeil and Steinhardt (2003)...

The rest of the liver volume (about 15%) consists of intravascular space, the space of Disse, lymphatic vessels, and extracellular matrix molecules [8], These matrix proteins, located predominantly in the space of Disse and around blood vessels, consist mainly of basement membrane molecules (collagen type IV, laminin, and fibronectin) and fibronectin) and small amounts of collagen type I, III, VI, undulin, tenascin, and proteoglycans. The matrix proteins determine the specific phenotype and functions of many resident hepatic cells [9-11],... 

The glomerular basement membrane (GBM) forms the backbone of the glomerular tuft. It is composed of three layers lamina rara interna, lamina densa, and lamina rara externa. The glomerular basement membrane is composed of a network of collagen type IV molecules (H5) intertwined with nidogen to another network composed of molecules of laminin. Type IV collagen and laminin are responsible for the firmness of the glomerular basement membrane and enable adhesion of endothelial cells and podocytes as well. 

Cell attachment to the glomerular basement membrane is mediated by laminin, entactin, and fibronectin, at least partly through integrin receptors on the cell surface of both endothelial and visceral epithelial cells. 

The lamina densa is a well-delineated, highly stained zone whose presence is the sine qua non of a basement membrane. Many investigators use the term basement membrane to refer to this sheet-like structure, particularly where the presence of unique basement membrane components, such as collagen IV and laminin, can be established with specific antibodies. At higher magnification, the lamina densa can be seen to be a three-dimensional network of 3- to 8-nm cords (Fig. 2). In addition, in such preparations one can usually see tubule-like structures (basotubules) as well as small parallel rods known as double pegs (Inoue et al., 1983 Laurie et al., 1984). 

The network structure has been observed by electron microscopy in Reichert s membrane following treatment of tissue sections with plasmin (Inoue et al., 1983). This enzyme removes a major portion of the 3- to 8-nm-thick cords that constitute the major element in the basement membrane, leaving behind a network of fine filaments 1.5 to 2 nm in diameter. Presumably, the cords have a framework consisting of one or more collagen IV filaments that are coated with laminin and with other basement membrane components. 

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