Mechanisms of asymmetrical body formation during flatfish metamorphosis and prevention of malformed juveniles in seed production process

对于比目鱼发育过程中不对称体形成的机制，我们提出了一个工作假说“时间假说”。从多个方面的证据来看，甲状腺激素诱导盲侧特征（白色体色和对侧眼的移位），并且对甲状腺激素的组织反应性在身体的左右侧之间存在差异。为了发育成正常的青少年，甲状腺激素必须在一个有限的时间窗口内分泌，当反应只出现在一侧时。本研究的目的是更详细地证实这一假说的有效性和普遍性。对牙鲆发育过程中所有色素细胞的活体外观进行了研究，发现存在以下三种类型的外观庄园：1）对称性幼虫型（幼虫型黑色素细胞、黄色素细胞和白色素细胞），2）不对称成虫型（3）对称性成虫型（虹膜细胞）。为进一步研究，我们尝试了体外培养色素细胞的方法。在本项目期末，我们已经建立了所有色素细胞（除幼虫黄色素细胞外）出现的培养条件。在日本的比目鱼中，黏比目鱼（Microstomus achne）具有非常长的浮游生活阶段，而星比目鱼（Platichthys stellatus）具有相对较短的浮游生活阶段。对于这两个物种，甲状腺激素（T4，甲状腺素）被添加到饲养罐在不同的时间，和正常的，pseudoalbino，和ambicolorate的组成，完成变态后进行了检查。定时T4除了显着改变的比例，与庄园，可以解释的时间假说。此外，正常的青少年的比例最高，观察到在一个类似的时间，以海洋的幼虫变态的坦克。这些结果表明，这两个物种的假设的一般性。

For the mechanisms of asymmetrical body formation of flatfish development, we proposed a working hypothesis "timing hypothesis". From several lines of evidences, thyroid hormone induces blind side characteristics (white body color and migration of eye of the own side), and the tissue responsiveness to thyroid hormone exists differentially between right and left side of the body. Thyroid hormone has to be secreted during a limited time window when the responsiveness only presents on one side, in order to develop into normal juveniles. This project aimed to confirm the validity and generality of the hypothesis more in detail and for more species.In vivo appearance of all pigment cells during Japanese flounder development revealed the presence of three types of appearance manor as follows, 1) symmetrical larval type (larval type melanophore and xanthophore, and leucophore), 2) asymmetrical adult type (adult type melanophore and xanthophore), 3) symmetrical adult type (iridophore). For detailed study in future, in vitro culture for pigment cell ontogeny was attempted. At the end of this project term, we have established the culture condition in which all pigment cells (except for larval xanthophore) appear.Slime flounder (Microstomus achne) has extremely long, and starry flounder (Platichthys stellatus) has relatively short, pelagic life stages among flatfishes in Japan. For both species, thyroid hormone (T4, thyroxine) was added to the rearing tanks at various timings, and composition of normal, pseudoalbino, and ambicolorate, was examined after the completion of metamorphosis. Timing of T4 addition significantly altered the ratio, with a manor that can be explained by the timing hypothesis. In addition, the highest ratio of normal juveniles was observed in the tanks where the larvae metamorphosed at a similar timing to the sea. These results indicate the generality of the hypothesis to both species.