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The make-up of many animals — be it internal or external — is asymmetrical. In vertebrates such as mice and chickens, two genes, nodal and Pitx, are known to control this left–right body asymmetry. It wasn't clear how far back in time these genes originated, although it was thought that nodal was restricted to deuterostomes, which include all vertebrates; sea urchins, starfish and their kin; and some worms. Nipam Patel (pictured) and his postdoctoral fellow Cristina Grande at the University of California, Berkeley, have found that a version of nodal also controls the directional spiral of snail shells (see page 1007). The duo's findings suggest that nodal's forerunner might have been present in the common ancestor of all bilateral organisms — those with a two-sided body plan. This would make it much more ancient than was originally believed, possibly dating back as far as 650 million years. Patel, an evolutionary developmental biologist, tells Nature about exploring new territory with snails.

Why are some organisms asymmetrical?

They need to be to fit all of their organs into the body cavity. In addition, organs are not always symmetrical. The human heart, for example, is larger on one side because that side is pumping blood around the entire body. The liver turns in one direction and our guts coil in another.

How did you learn that nodal controls asymmetry in snails' shells?

In examining the genomes of the marine limpet Lottia gigantea and the freshwater snail Biomphalaria glabrata, the snails we worked with, Cristina found a gene similar to nodal. In L. gigantea, which coils counterclockwise, the gene is expressed on the right side. In B. glabrata, which coils clockwise, it's expressed on the left. The next question was whether the gene was linked to asymmetry in the snails, so we blocked the nodal pathway. Although most of the embryos died early on, a few got past that stage. They didn't live long, but they survived long enough to develop straight, unspiralled shells.

Are snails challenging research subjects?

We had to develop experimental procedures as we went along. We had to work largely from scratch because no one had worked on the molecular biology of snails before.

Where did your snails come from?

We got stocks of B. glabrata from the National Institutes of Health, but the L. gigantea came from the wild. Cristina had to apply for a state permit and travel down to southern California, where they live on rocks on the beach.