The gene that can lead to asymmetrical development in the shells of pond snails has been recently identified by scientists, according to a new study.
In the study – published Thursday (Feb. 25) in the journal Current Biology – the scientists were able to figure out which gene causes the asymmetrical twisting of snail shells.
Most creatures appear to be bilaterally symmetrical – meaning that their right side is an approximate mirror image of their left side. However that symmetry can only be seen on the surface, since in most animals, the organs are arranged asymmetrically inside the body – which seem to be a general rule on animal biology (radially symmetrical organisms are the exception – sea anemones, jelly fish, etc.).
Angus Davison, lead author of the study and an associate professor of evolutionary genetics at the University of Nottingham, said that outward symmetry helps with efficient movement, while inward asymmetry helps pack various organs (sometimes asymmetric) into a tight space.
Chirality, a property of asymmetry (objects that are chiral are distinguishable from their mirror image), happens in about ten percent of all snail species. Most snail species have clockwise-coiling shells, but there are some that have shells which twist in the opposite direction. That could have major biological implications, according to scientists.
Dr. Davison, said that the bodies of snails are mirror imaged, except for their shells. It is possible that in time, the gene variant that determines the different coiling styles might disappear, he added.
Ever since 2001, Dr. Davison has been trying to find the gene responsible for the mutation. To do that, he and his colleagues used DNA sequencing techniques and mapped the genome of pond snails. They found that there was just one base (or letter), in the one billion that make up the snail genome, that determined whether the shell coiled clockwise or counter-clockwise.
Pond snails (Lymnaeidae) are a family of gastropods that are can be found in rivers, lakes and ponds. Some species can reach a shell size of almost three inches (about seven centimetres) – which is a lot larger than the shell of the terrestrial Roman snail (Helix pomatia).
The mutation was discovered in a gene known as formin – the gene is active in pond snail embryos. The scientists were able to reverse the direction of the shell twisting in developing snails, by giving them an anti-formin treatment. However, none of the snails survived after the treatment ended.
Since the genes that lead to asymmetry are very important at a cellular level, any changes in them might be lethal, according to Dr. Davison. It is not an easy task to change asymmetry in a living organism, without also changing other functions of that organism, he explained.
When it comes to bilateral animals, formin may have been one of the earliest genes to turn symmetry into asymmetry, Dr. Davison and his colleagues said. Asymmetry could thus be an ancient trait, they noted.
Further research will be conducted on the genetics of pond snails by Davison and fellow researchers, to better understand what lead to the symmetry-breaking event.
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