The Spatio‐temporal Expression Pattern Of Three Iodothyronine Deiodinases During Metamorphosis Of Paralichthys Olivaceus

Flatfish（Pleuronetiform）metamorphosis is the most evident considering itstransition from symmetrical pelagic larvae to unsymmetrical benthic juvenile, withone eye migration from one side to another, pigment occurence on the ocular side, thechange of digestive tract, bone remodeling, and the nsynchronous development ofpaired fins. Thyroid hormone is necessary for most vertebrates, and themetamorphosis of flatfish is also regulated by thyroid hormone. T4is the mainproduct of thyroid with little biological activity. In order to produce T3, which hasconsiderable biological activity, T4molecule deiodination should happen at the outerring, which was catalyzed by type1iodothyronine deiodinase(Dio1) and type2iodothyronine deiodinase(Dio2).If the deiodination happens at the inner ring of T4,the rT3will be produced, which has no biological activity. The inner ring deiodinationof T4was catalyzed by type3iodothyronine deiodinase(Dio3), which can alsodeiodinate T3and thereby terminate thyroid hormone action. Three deiodinases playroles in maintaining thyroid hormone homeostasis, at the same time, they alsoparticipate in local thyroid hormone controlling. Although it is almost clear that thethyroid hormone is necessary for the metamorphosis of flounder, the investigation ofdeiodinase is still only conducted to the research of whole body expression level andactivity. In this research, we designed Dio1,Dio2and Dio3antisense RNA proberespectively, and conducted the whole-mount in situ hybridization of threedeiodinases to detect the sptio-temporal expression of these three deiodinases. Theresults show that Dio1,Dio2and Dio3are all widely expressed before metamorphosis.Dio1and Dio3are still widely expressed during metamorphosis, while Dio2expression is limited to a few tissues like gill and epithelial around the eyes. Aleft-right unsymmetry expression in epithelial around the eyes is found in all threedeiodinases, which of Dio3is the most evident, then of the Dio2, which of Dio1is themost weak. The left-right unsymmetry expression in epithelial around the eyes of onedeiodinase gene becomes stronger as the development of flounder larvae, then weakeragain. In9DAH(day after hatch) larvae a new moon shape of three deiodinase signalis found in the dorsal fin membrane bottom near the head. The signal becomes largerand move forward towards head as the larvae becomes larger. Finally the crown-likelarval fin appears in the position where the deiodinase signal existed. The signals ofboth Dio1and Dio3in lateral line are found in Japanese flounder duringmetamorphosis. Dot-shaped Dio3signals are found in the outer primary cuticula ofintestine, heart, body muscle and eyes etc, while the signals of Dio1and Dio2don’tshow this phenomenon.