2-Aminopurine induces spindle cell morphology in MM14 myoblasts in the absence of differentiation signals

MM14 murine myoblast cells remain in an undifferentiated and proliferative state if they are maintained in the continuous presence of basic fibroblast growth factor (FGF-2) and serum factors, but terminally differentiate into myocytes and myotubes if deprived of FGF-2 during G1 of the cell cycle. We find that 2-aminopurine (2-AP) induces a reversible, rapid, and profound alteration in the morphology of proliferating MM14 cells to a polarized shape which is similar to that observed during normally induced differentiation. This change requires neither a differentiation signal nor de novo protein synthesis. In contrast, we do not observe a morphological change in response to 2-AP in nonmyogenic cell lines. The morphological alteration of MM14 cells in response to 2-AP requires reorganization of the microtubule and actin cytoskeletons, in common with changes during normal differentiation. Additionally, we show that cytoskeletal rearrangements that occur during both normal differentiation and in response to 2-AP require the activity of the small GTPase Rho. Differentiation defective MM14 cells (DD-1 cells), which lack MyoD, also undergo a profound morphological alteration in the presence of 2-AP. These results indicate that morphological changes consistent with myoblast differentiation are regulated by a pathway independent of MyoD transcriptional control.