While a small percentage of people have their insides flipped, their overall internal arrangement is a mirror image of the norm. Anyone with a random arrangement of internal organs would be dead, Patel said, because his or her organs wouldn't fit together properly.
Other vertebrates are the same. In fact, scientists have identified a gene called "nodal" that - in all vertebrates checked to date - is expressed on the left side of the body and necessary to set up left-right asymmetry. If nodal doesn't work or is knocked out, internal organs are jumbled and the organism dies.
"In vertebrates, a set of genes tells the body it has to form a heart toward one side, and nodal is one of those genes," said Grande, who recently took a position at the Centro de Biologa Molecular "Severo Ochoa" in Madrid, Spain.
"There are a lot of asymmetric molecules in the body, that is, molecules that are active on only one side of the body, but nodal is always expressed on the left side in all vertebrates, which is evidence of a conserved pathway," Patel said.
Genes similar to nodal have been found throughout the so-called deuterostomes, one of the three subgroups of bilateral animals that includes not only vertebrates, but also sea urchins and sea squirts.
But the most common lab animals, fruit flies and nematodes, apparently do not have a gene like nodal, despite their asymmetry. As a result, biologists have assumed that fruit flies and all other non-deuterostomes - snails included - use some other mechanism to establish right and left. Fruit flies and nematodes are in the clade Ecdysozoa, while snails and worms are members of the clade Lophotrochozoa.
Grande approached Patel four years ago to collaborate in a test of this assumption in snails, which have an obvious and easy-to-check handedness: Their shell
|Contact: Robert Sanders|
University of California - Berkeley