The genomic basis of chiral variation and speciation in mirror-image snails

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While our bodies are bilaterally symmetric on the outside, the internal organs exhibit consistent, directional asymmetries in their position or anatomy, such that left/right positional errors are an important class of human birth defect, and in later life, numerous diseases affect seemingly symmetric organs in a lateralised fashion. However, while invariant left/right asymmetry appears to be the rule in nearly all animals, until recently it has not been clear if the path to asymmetry is conserved, or how/why the left/right axis is consistently set up in the same direction (e.g. heart to the left). In recent BBSRC funded research (Current Biology 26: 654-660), we identified the one in a billion base pair change in a formin gene that determines mirror image development ("chirality") in the pond snail, finally identifying the first described locus that reverses the whole body structure of an animal. As we also showed that the same gene is similarly involved in setting up asymmetry in the frog, then our work that began in snails ultimately revealed one of the earliest common symmetry-breaking steps across the whole of the Bilateria. A key problem with respect to understanding natural chiral variation is that the pond snail is one of the few snail species in which the causative mutation is pathological - only about a half of the offspring survive. In other species of snail, such as Japanese Euhadra, we have shown that formin is not involved in determining variation in chirality, but we have no idea what the genes are, nor the (almost) inconceivable means by which they are able to cause a switch in chirality without associated pathology. It is the ambitious aim of this project to identify the chirality locus in Euhadra, and to understand how it contributes to possible speciation. The project will most likely involve a range of techniques, from fieldwork in Japan to genomics and bioinformatics - with the balance determined by the interests of the student.