Fig. 4. Differential tyrosine phosphorylation of podosomes during osteoclast polarization. RAW cells were induced to differentiate, and then fixed and double-stained for actin and phosphotyrosine (PY). Actin and PY are shown in an intensity spectrum scale. Ratio images (PY/act ratio) demonstrate tyrosine phosphorylation of the entire actin domain of clustered podosomes (b) whereas in the SZL structure (a) tyrosine phosphorylation is predominantly associated with the plaque domain. Bars, 10 µm.