A polarized morphology correlates with the amount of phosphoMLC in different cells. (A) Representative morphologies of DiI-stained CHO.K1, MEF, B16, and Rat2 cells plated on fibronectin for 30 min. F, front; B, back. Representative axes are used to calculate the polarity index (PI) as shown in B. Solid line is the migration axis; dashed line is the transverse axis. Bar, 10 μm. (B) Polarity indices (long migratory axis divided by short transversal axis) of the cell lines shown in A under the same experimental conditions. Data represent the average ± SD of >200 cells in two independent experiments. (C) Phosphorylation of MLC and expression of myosin II heavy chain isoforms in the cell lines shown in A. The cells were plated under the same conditions. Arrow points to the P-MLC band. Representative immunoblots from four individual experiments are shown. (D) Densitometric analysis of the phosphorylation of MLC as shown in C. Values are normalized with respect to the amount of actin in control blots, and normalized values referred to the amount of P-MLC present in MEFs. Data represent the mean ± SD of four independent experiments.