Molecular control mechanism of left-right asymmetry of flounders

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Flounder larvae transform from symmetric to asymmetry shape by moving one eye at metamorphosis. Final shape is divided to sinistral species (e.g. Paralichthys olivaceus) and dextral species (e.g. Varasper veriegatus). We have elucidated the developmental control system of eye-sidedness of flounders. Eye migration proceeds in coordination with dynamic asymmetric formation of forebrain and cranium. Final L-R determinant gene, pitx2, of the Nodal pathway, known to control the laterality of internal organs, is expressed in the left side of dorsal diencephalon in flounders to lateralize the eye-sidedness. When pitx2 expression is suppressed, which eye migrates is randomized, resulting in reversal of eye-sidedness in part of larvae. The mechanism that divides flounders to sinistral and dextral species has close relation with the fact that the laterality of the optic chiasma is fixed in opposite direction between two species.