A gene defines left and right during embryonic development in snails and frogs.

Credit: Esther de Roij/Gary McDowell/Jeremy Guay, Peregrine Creative

Animals generally look symmetrical, but internal organs are often positioned asymmetrically. To find out how embryos first define left and right at the molecular level, Angus Davison at the University of Nottingham, UK, and his colleagues compared the DNA of pond snails (Lymnaea stagnalis; pictured) that had shells with clockwise or anti-clockwise spirals. They found that formin, a cell-structure protein, was consistently linked to spiral direction and is expressed early in snail development, showing asymmetry even in two-cell embryos.

The team treated frog embryos (Xenopus laevis) with anti-formin drugs, and found that 13% developed an organ on the opposite side to its normal position, suggesting that formin also coordinates this process in frogs.

Curr. Biol. http://dx.doi.org/10.1016/j.cub.2015.12.071 (2016)