Visualization of cellular focal contacts using a monoclonal antibody to 80 kD serum protein adsorbed on the substratum.

We have obtained a monoclonal antibody to 80 kD protein of calf serum; this protein easily and uniformly adsorbs on glass from serum-containing media. Indirect immunofluorescence staining of chick and mouse embryo fibroblasts cultured in the presence of calf serum, fixed with formaldehyde and permeabilized with Triton X-100, revealed black non-fluorescent strips and dots under the ventral cell surface, whereas all other parts of the substratum under and between cells were highly fluorescent. The distribution of non-fluorescent regions coincided with the distributed of focal contacts of cells with the substratum, revealed by interference reflection microscopy, as well as with the distribution of vinculin-containing plaques. The dark regions were also associated with the ends of microfilament bundles revealed by immunofluorescence with an anti-actin antibody. Thus, non-fluorescent regions seen after anti-80 kD staining are parts of the substratum under the focal contacts. Visualization of focal contacts with anti-80 kD provides very contrasting and high resolution pictures. Evidence is presented that 80 kD protein is adsorbed to glass in the areas of focal contacts, but the antibodies used for staining cannot penetrate these contacts.