Pulling the spindle into shape

Mutants, RNAi, and extracts were unanimous: myosin II is not needed in mitosis before cytokinesis. But now Jody Rosenblatt, Karen McGee (University College London, England), and colleagues report that myosin II does, indeed, function in mitosis to pull apart and position centrosomes.

Rosenblatt did not set out to contradict the myosin II dogma. She was working on her primary interest of cell extrusion, checking the effect of blocking myosin, when “one day I was staining for tubulin and noticed spindle defects.” One colleague told her, “you really need to focus,” but she continued to see the unexpected phenotype. “Basically it was really crazy but it was happening,” she says. “It took me a long time to convince myself.”

That convincing involved getting the same phenotype—defective spindles and displaced or misaligned chromosomes—after any one of four...