Unraveling the Genetic Landscape of Eye Migration and Visual Adaptation during Flatfish Metamorphosis

Flatfish have evolved their visual system to meet the demands of their environment through a fascinating process of metamorphosis. This morphological transformation involves a significant change in lifestyle from pelagic to benthic, accompanied by changes in body structure to achieve an asymmetrical flat shape. However, the fundamental change lies in the migration of one eye from its original position to the opposite location on the body. Although the role of thyroid hormone in triggering flatfish metamorphosis is well established, the specific gene regulatory network responsible for this extraordinary eye migration is still unknown. Here we show a global view through the creation of a general map of gene expression during the metamorphic process, encompassing both migrant and non-migrant eyes. Our research uncovers significant differences between migrant and non-migrant eyes of turbot in the pre-metamorphic and climax phases, emphasizing genetic disparities crucial for benthic adaptation. To investigate differences in gene expression during flatfish metamorphosis we selected three key stages in turbot development: pre-metamorphic stage (15 dpf); climax of metamorphosis (30dpf); and post-metamorphic stage (57dpf). These fish were reared under standard production conditions at 18ºC. The migrant and non-migrant eyes and their respective surrounding tissue were directed for each stage and RNA were extracted. Libraries were sequenced on a BGISEQ-500 platform and single-end reads of 50 base pairs length were generated per sample.