Fig. 1: This is a co-culture of osteoclasts (purple multinucleated cells - red arrow) and mesenchymal stromal cells (mononuclear cells - blue arrow). The cells have been treated for 150 minutes with a chemical inhibitor of the enzyme PI3Kinase prior to fixation. Nuclei are stained with Hoechst 33258 to reveal chromatin morphology. Large, normal nuclei are seen in the stromal cells whereas osteoclast nuclei are condensed, exhibiting chromatin condensation that is indicative of apoptosis. These data suggest that osteoclasts are highly sensitive to PI3Kinase inhibition compared to stromal cells.