Tilt back to turn left

Tilt back to turn left perating an eggbeater vertically creates a vortex, but a slight tilt makes fluid move across a bowl. now claim that a similar backward tilting of mouse cilia may create a flow that defines the left side of the embryo. Flow had already been established as a determinant of left–right asymmetry, at least in mice. Leftwards flow is created by a group of ‫ف‬ 30 cilia in the mouse node, a fluid-filled region on the surface of the embryo. Interference with this flow creates a mirror image (situs inversus) of the normal left–right asymmetry of internal organs. Situs inversus happens in either half the cases (if mutation results in no Pulling the spindle into shape utants, RNAi, and extracts were unanimous: myosin II is not needed in mitosis before cytokinesis. But now 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 treatments: myosin M flow and a random breaking of symmetry) or most cases (if an artificial rightward flow is imposed). Biologists came up with this model but lacked the fluid physics to explain how a bunch of spinning cilia could create a directional flow. The Spanish team took known data on the size, speed, and viscosity of the system and realized that viscosity would dominate over inertia, so varying the angular velocity in different parts of the cilia's rotation cycle would not give a directional effect. A set of cilia yields a set of vortices unless, and this was the group's insight, the cilia are tilted relative to the substrate. " Given that the cilia are cylindrical, " says Cartwright, " there's no other way to produce this flow. " If cilia rotating clockwise are tilted toward the back of the embryo, the cilia sweep toward the …