Collagen-fibronectin binding is required for ECM fibril organization.

<p>FN-null MEFs adherent to polymerized collagen were treated with fibronectin (25 or 100 nM) in the presence of either R1R2 or the control peptide III-11C. Following a 4-day incubation, cells were processed for immunofluorescence microscopy. Fibronectin (green) and collagen (blue) were visualized using an anti-FN pAb and second harmonic generation imaging, respectively. Images were collected at and above the collagen substrate and then projected onto the z-plane using ImageJ. Dashed red lines denote spheroid location. Arrowheads indicate colocalizing fibronectin and collagen fibrils. Arrows show fibronectin fibrils that do not colocalize with collagen fibrils. Scale bar, 50 μm.