Role of dynactin in proplatelet elongation. (A-J) Effects of p50 dynamitin expression on proplatelet elongation. (A,C) Differential-interference-contrast and (B,D-G) fluorescence images of p50-GFP–expressing cells exhibiting a range of elongation distortions, compared with the unperturbed elongation of representative megakaryocytes (H) retrovirally directed to express GFP–β1-tubulin and (I-J) uninfected, nonexpressing cells. All images were acquired by fluorescence and DIC microscopy. Scale bars all represent 10 μm.