Chiral shells to chiral cells

New paper published in Current Biology.

We are all asymmetrical – not just left or right handed in how we write, but fundamentally, inside our bodies. So are frogs, fish and snails – being left/right asymmetric appears to be the rule in animals. However, it is not at all clear how the left/right axis is consistently set up, such that while animals are always asymmetric, they are asymmetric in the same direction (e.g. heart on the left), except in very rare circumstances. In comparison, while the majority of snails are invariable like ourselves, inherited variation in shell coiling and body asymmetry, or chirality, occurs in 1-10% of all species.

While components of the pathway that establishes left-right asymmetry have been identified in diverse animals, from vertebrates to flies, it is striking that the genes involved in the first symmetry-breaking step have long remained wholly unknown in these most obviously chiral animals. In a breakthrough piece of work , with myself leading an international collaboration involving researchers from Universities in Scotland, Germany and the USA, we have shown that variation in a cytoskeletal protein (the cell scaffold) is perfectly associated with symmetry-breaking in the pond snail, creating either right (dextral) or left (sinistral) coiling snails. Furthermore, contrary to expectations, we discovered asymmetric gene expression in very early (2 cell) snail embryos, preceding morphological asymmetry, and that the same gene has a similar function in vertebrates. Taken together these results overturn the thinking that diverse species initiate left-right patterning differently, and are instead consistent with the view that animals, from invertebrate snails to vertebrate frogs, may derive their asymmetries from the same intracellular chiral elements.