Type IV collagen lateral associations in the EHS tumor matrix. Comparison with amniotic and in vitro networks

The macromolecular structural organization of the type IV collagen network in the extracellular matrix of the EHS tumor has been investigated using a stereoscopic freeze-dry Pt/C replication technique. This network, which can be specifically decorated with type IV collagen antibody, is formed in great part by the lateral joining of narrow filaments (2.7 nm average metal coated diameter) to form a complex three-dimensional irregular polygonal array of variable diameter branching strands. Globular domains, similar to the C-terminal globular domains of purified type IV dimers, can be identified in the network. In many regions of the network the filaments appear to twist around each other along the strand axis. The network is similar to that visualized in the human amnion as well as to a reconstituted network formed in vitro. These data strongly suggest that the laterally and end-domain-associated network is a widespread supramolecular architecture of type IV collagen in basement membranes.