The eye migration and evolutionary origin of flatfish asymmetry

Abstract:

Asymmetry of flatfish has already caught people’s eye over one century. The research on eye migration is introducted as five sections in this review: diversity and distribution of Pleuronectiformes, the mechanical force driving eye migration, thyroid hormone dependent signalling pathway in regulating eye migration, the relationship between eye migration and the left/right asymmetry of visceral organs, and evolutionary origin of flatfish asymmetry. My lab’s findings on the genetic mechanism behind eye migration are introducted extensively, such as our important finding that eye migration is driven by proliferating cells in suborbital skin and the twist of frontal bone is dependent upon eye migration, which corrected some mistakes of previous hypothesis. Thyroid hormone dependent signalling pathway was investigated extensively as well. T₃ distribution and expressional location of type 2 deiodinase and thyroid hormone receptor(TRαA and TRβ1) in the skin around both eyes displayed left/right and dorsal/ventral asymmetry pattern, which is similar as observed pattern of proliferating cells in same area in previous study. The TH dependent signalling pathway in regulating eye migration might be T₄-Dio2-T₃-TRαA/TRβ1. Finally, we propose a hypothesis on evolutionary origin of flatfish asymmetry, and hope that this could arouse further discussion on the flatfish evolution.