'Left-handed' and 'right-handed' shells of giant pond snails, Lymnaea stagnalis. (Kuroda Laboratory) Japanese researchers have created mirror-image snails whose shells coil in the opposite direction to what is written in their genes.

Scientists at the University of Tokyo coaxed the snails to grow their shells coiling in the opposite direction by physically manipulating their embryos.

Reiko Kuroda and her colleagues say this result is surprising because normally whether a snail's shell coils to the left or to the right is completely determined by genetics.

Giant pond snails, Lymnaea stagnalis, can have either a left-handed coiled shell or a right-handed coiled shell, and this difference is determined by its genes.

By manipulating the embryos at the eight-cell stage, the researchers were able to force genetically right-handed snails to grow shells that coil to the left, and vice-versa.

A snail embryo being manipulated using two thin glass rods to change the 'handedness' of the shell. (B. Endo) The researchers used two thin glass rods to change the "handedness" of the embryos.

Interestingly, the manipulation changed not only the direction of coiling in the shell, but also the reversed the expression of a gene called NODAL, which regulates asymmetrical characteristics in many species, including the proper placement of the heart.

The research appears this week in the journal Nature.