Flexible substrates can induce podosome belt formation.

<p>Osteoclasts were incubated for 5 hours in MEM/BSA with M-CSF (50 ng/ml), RANKL (30 ng/ml) and IL-1α (10 ng/ml) on PDMS sheets or silicone films coated with vitronectin or fibronectin (50 µg/ml). A,B: Osteoclasts adhered to fibronectin-coated PDMS sheets in large numbers, but podosome belts were very rare. In contrast, a similar proportion of osteoclasts formed podosome belts on vitronectin-coated PDMS sheets to our previous experience using rigid substrates. *p<0.05 <i>versus</i> control (ANOVA + Dunnett's); n = 10 per group. C–F: Representative views of osteoclasts on fibronectin-coated silicone film (C) or PDMS sheet (E)0; and vitronectin-coated silicone film (D) or PDMS sheet (F). Note that osteoclasts on fibronectin-coated substrates are well-spread but lack podosome belts. Phalloidin/DAPI staining. Scale bars: C,D: 50 µm; E,F: 100 µm.