Myosin II inhibition in oligodendrocyte-DRG cocultures enhances myelin formation. (A) Purified OL progenitors (OPC) were seeded onto 3-wk-old DRG neuronal cultures. After 2 wk in media containing 1 μg/ml TrkA-Fc, cultures were stained for Olig2, MBP, and neurofilament. Treatment with blebbistatin resulted in a prominent dose-dependant increase in the amount of myelin segments formed in cultures. (B) Quantitation of myelin segments (left), OL cell number (middle), and MBP expression (right) in control and blebbistatin-treated cultures. A significant dose-dependent increase in the amount of MBP⁺ segments was observed in cultures treated with blebbistatin (P < 0.001, ANOVA). The percentage of MBP⁺ cells is comparable in all conditions, and at the highest blebbistatin concentration (25 μM), a significant reduction in the number of Olig2⁺ cells was observed. Data represent mean ± SEM from two independent experiments (two cultures per condition per experiment). (C, left) Quantitation of the number of myelin segments formed per single OL in cultures. Low-density 16-d-old myelinating cocultures were stained for Olig2, MBP, and neurofilament to identify individual OL nuclei, OL expressing MBP, and OL actively myelinating axons. A significant increase in the mean number of myelin segments made by a single OL in treated cultures was observed (P < 0.001, ANOVA). Data represent mean ± SEM from two independent experiments (two cultures per condition per experiment). (right) Representative examples of myelinating OL in control and treated cultures are shown. Bars: (A) 50 μm; (C) 20 μm.