Inhibition of PLC or MLCK causes loss of phosphorylated myosin regulatory light chain from the contractile ring. Phase-contrast and immunofluorescence images of dividing Drosophila spermatocytes stained for phospho-Sqh (green), F-actin (red) and DNA (blue). (A) Untreated control cell. Note colocalization of phospho-Sqh and F-actin in the contractile ring. (B) Cell treated with U73122. (C) Cell treated with ET-18-OCH3. (D) Cell treated with ML-7. (B-C) In cells treated with these inhibitors, phospho-Sqh and F-actin were no longer evident at the equator, whereas F-actin was relocalized to the poles. Bar, 10 μm.