Process formation results from the imbalance between motor-mediated forces.

Several reports have suggested that neurite outgrowth is mediated by opposing forces generated on microtubules and microfilaments but the molecular basis underlying these forces have not been determined. Here, we show that in non-neuronal cell lines, the inhibition of actomyosin activity by acidic calponin promotes the formation of processes. This effect is blocked by inhibition of the motor activity of cytoplasmic dynein. Therefore, neurite formation is due to an imbalance between tensile and compressive forces mediated by myosins and dyneins, respectively. We propose a mechanism that involves the motor-mediated forces in a tight regulation of the process formation.