Fig. 7. (a) Electron microscopy. Schwann cells were incubated with and without 10 µg/ml of laminin-1 for 18 hours. In addition, cells incubated with laminin were treated with E3 fragment or blocking antibodies. Three types of cell membrane-associated ECM were detected: continuous electron-dense cell surface associated structure (lamina densa, frame A, >2 µm); or short stretches of electron-dense matrix (frame B, <2 µm); cells cultured without laminin revealed a matrix-free plasma membrane surface (frame C), with infrequent small amorphous deposits such as that in the middle of frame C. By contrast, cells incubated with laminin showed the presence of a lamina densa. Inhibition of laminin-ß1-integrin interaction by antibody Ha2/5 (50 µg/ml) did not abolish the appearance of a membrane-associated electron dense structure. Fragment E3 (100 µg/ml), in contrast to ß1-integrin blocking antibody, prevented formation of an electron dense structure. Bar, 500 nm.

(b) Quantitation of morphology. The distribution of non-polymerizable laminin and its ability to induce a membrane-associated electron dense structure was analyzed after 8 hours of incubation with 10 µg/ml of polymerizing or AEBSF-laminin-1. Non-polymerizing laminin generated little continuous matrix. The graph shows the relative number of events according to analysis of three random cross-sections, as described in Materials and Methods.