p21 expression in differentiating myeloid cells. Immunostained cytospins of CD34⁺ cells cultured for 2 days (top), 6 days (middle), or 11 days (bottom). Cells are stained for p21 expression (red, left) by using indirect Cy-3 conjugated antibody staining. Cell nuclei are counterstained with Hoechst (blue) shown as the same field on the left.