Dynein motor regulation stabilizes interphase microtubule arrays and determines centrosome position.

Cytoplasmic dynein is a microtubule-based motor protein responsible for vesicle movement and spindle orientation in eukaryotic cells. We show here that dynein also supports microtubule architecture and determines centrosome position in interphase cells. Overexpression of the motor domain in Dictyostelium leads to a collapse of the interphase microtubule array, forming loose bundles that often enwrap the nucleus. Using green fluorescent protein (GFP)-alpha-tubulin to visualize microtubules in live cells, we show that the collapsed arrays remain associated with centrosomes and are highly motile, often circulating along the inner surface of the cell cortex. This is strikingly different from wild-type cells where centrosome movement is constrained by a balance of tension on the microtubule array. Centrosome motility involves force-generating microtubule interactions at the cortex, with the rate and direction consistent with a dynein-mediated mechanism. Mapping the overexpression effect to a C-terminal region of the heavy chain highlights a functional domain within the massive sequence important for regulating motor activity.