鱼类甲状腺轴对胚胎发育、仔鱼变态及性别分化的调控作用研究进展

鱼类甲状腺轴由下丘脑、垂体、甲状腺组成,下丘脑通过分泌促甲状腺激素释放激素、促肾上腺皮质激素释放激素调节垂体促甲状腺激素的合成和分泌,促甲状腺激素促进甲状腺滤泡合成并释放甲状腺激素(主要为甲状腺素—T4),T4运输至肝脏等外周组织中,经过脱碘转化形成生物活性更强的三碘甲腺原氨酸(T3),T3主要通过同核受体结合发挥生物学功能。甲状腺激素对鱼类胚胎发育、仔鱼变态及性别分化等早期生长发育过程具有重要调控作用:甲状腺激素为鱼类胚胎发育期所必须,外加适量甲状腺激素能够提高胚胎或仔鱼存活率;仔鱼变态过程中,某些外部形态变化及相关组织分化依赖甲状腺激素的调控,牙鲆等仔鱼变态期体内甲状腺激素水平及其受体表达量会显著升高;性腺发育期,甲状腺激素对调控鱼类性别分化方向可能具有一定作用。

Advances in Piscine Thyroidal Axis and Its Regulatory Effects on Embryogenesis,Metamorphosis and Sex Differentiation

In fish,the thyroidal axis is composed of hypothalamus,pituitary and thyroid.Thyroid L-thyroxine(T4) secretion is mainly controlled by the hypothalamus pituitary thyroid axis.The thyroid is stimulated by thyroid stimulating hormone,a glycoprotein secreted by the pituitary thyrotrope cells,hypothalamic control of thyrotropes mainly refers to thyrotropin-releasing hormone and corticotropin-releasing hormone.3,3′,5-triiodo-Lthyronine(T3)-the most active thyoid hormone,is formed by extrathyroidal T4 deiodination after T4 is transported into liver and some other peripheral tissues by binding to transporter proteins in the plasma and acts mainly by binding to specific nuclear thyroid hormone receptors.THs play important roles in the embryogenesis,metamorphosis and sex differentiation in the early stages of the fish life cycle.For instance,thyroid hormones are required during the embryogenesis stage and moderated exogenous THs treatment may have positive effect on survival and development of fish larvae;in addition to the clear change in external morphology induced by THs,a range of other tissues differentiation during metamorphosis of fish have also been shown to mediated by THs,and there is a concomitant rise in both THs and TRs during flounder metamorphosis;at last THs may also be involved and play an important role in the process of gonadal sex differentiation of fish.