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DIRECTIONSThe same species of snail coils either left or right depending on the positioning of cells when the first four divide into eight. Repositioning those cells with a pair of tiny glass rods (inset) reverses the snail's fate.Kuroda lab (inset: B. Endo)

This is a long way from working in politics. But for a snail, researchers report that just a little nudge of some early-dividing cells can push a youngster from left-leaning to right, or vice versa.

That nudge has to come when the Lymnaea stagnalis’ embryo’s first four cells split into eight, says Reiko Kuroda of the University of Tokyo, who studies chirality, or handedness. In nature, a single gene (not yet identified) acts in the mother snail to control which way offspring coil. Kuroda and her colleagues intervened in the usual development, using tiny glass rods to push four of the newly forming cells in the direction opposite to their usual shift. The repositioning reversed the direction of the snail’s spiral from its otherwise genetically determined left or right twist, the researchers report online November 25 in Nature.

The researchers’ little push reversed the patterns of expression for the embryo’s important nodal gene later in development. After the early rearrangement, embryos that would have been right-spiraling showed nodal activity normal for lefties and vice versa. The altered snails grew up backward but otherwise normal, healthy and fertile.

That a single gene and cell-position shift in the embryonic stage can determine such a big switch in animal form has implications for evolutionary mechanisms, says Stuart Newman of New York Medical College in Valhalla. "Evolution can take big jumps and does not have to proceed by increments."

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