Electron microscopic photographs of UT-7/GM cells cultured under various conditions. UT-7/GM cells were cultured with EPO (10 U/mL) or TPO (100 ng/mL). One month later, the cells were obtained for the analysis. (A) A representative UT-7/GM cell cultured with EPO. The cytoplasm of the cell is darker than the nucleus, implying the presence of hemoglobin. Insert shows higher magnification of atypical theta granules (arrow). Counterstaining was performed with lead citrate and uranyl acetate. Scale marker indicates 2 μm. (B) A representative UT-7/GM cell cultured with TPO. A multinucleated cell having developed demarcation membrane systems is shown. (C) Detection of PPO activity in a cell cultured with TPO. PPO activity is observed in nuclear envelope and rough endoplasmic reticulum of a large binuclear cell. Scale marker indicates 2 μm.