Murine MKs do not display podosome structures in the absence of WASp. (A) WASp-deficient MKs were grown in parallel with C57Bl/6- and 129Sv- derived MKs and processed for immunofluorescence for WASp and F-actin as described in “Materials and methods.” F-actin (red) and WASp (green) are colocalized in the core of podosomes, mainly at the cell periphery of 129Sv-derived MKs adherent to CI (i), CVX (ii), or GFOGER peptide (iii). Bar, 10 μm. (B) WASp-deficient MKs adherent to either CI (i), CVX (ii), or GFOGER peptide (iii) do not show podosome structures. Cells extend lamellipodia, but show “cracked-like” F-actin shape (i-iii). Note that spreading and stress fiber assembly were also reduced in WASp-deficient MKs adherent to CVX (ii). Bar, 10 μm. (C) Podosome assembly is drastically impaired in WASp-deficient MKs in comparison with 129Sv-derived MKs. Bars represent the mean ± standard deviation of 3 independent experiments.