Walpita Chaminda N, Van der Geyten Serge, Rurangwa Eugene, Darras Veerle M
Laboratory of Comparative Endocrinology, Zoological Institute, K.U. Leuven, Naamsestraat 61, B-3000 Leuven, Belgium.
Gen Comp Endocrinol. 2007 Jun-Jul;152(2-3):206-14. doi: 10.1016/j.ygcen.2007.02.020. Epub 2007 Feb 27.
The importance of thyroid hormones (TH) for embryonic development has long been shown in many vertebrates, but is not yet established in pre-hatch teleost models despite the presence of TH, TH receptors and iodothyronine deiodinases. Lack of data about the dynamics of TH metabolism in embryonic stages of fish does not allow to speculate about the involvement and/or role of TH in fish embryonic development. We therefore set up an experiment to examine the effect of 3,5,3'-triiodothyronine (T(3)) on zebrafish (Danio rerio) embryonic development and on the expression of some thyroid hormone-regulated genes as measured by real-time PCR. Maternally derived thyroxine (T(4)) and T(3) were detected throughout embryonic development and total levels remained stable. Thyroid hormone receptor (TR) alpha and beta mRNA were found to be present in early embryos. After an initial fall, TRalpha mRNA levels in the control group increased gradually from 12h post fertilization (HPF) onwards. TRbeta mRNA levels of control embryos were relatively stable during embryonic development, but increased around the hatching period. We also quantified type I (D1) and type II (D2) deiodinase mRNA expression in zebrafish embryos. D1 mRNA levels in the control group gradually increased during development while D2 levels were kept at a low and stable level until hatching. At 75 HPF, a fivefold increase of D2 expression was observed compared to embryonic levels. Exogenous T(3) added to the water (5nM) was taken up by the embryos, causing increased pigmentation and accelerated hatching. T(3) treatment significantly up regulated TRalpha mRNA levels at 48 HPF, while D2 mRNA was significantly down regulated at 75 HPF. Neither TRbeta nor D1 mRNA levels seemed responsive to the treatment. Taken together, these data show that during embryonic development zebrafish already have the necessary regulatory machinery for TH activation and signaling, and that T(3) treatment at that stage indeed influence embryonic development.
甲状腺激素（TH）对许多脊椎动物胚胎发育的重要性早已得到证实，但在孵化前的硬骨鱼模型中，尽管存在TH、TH受体和碘甲状腺原氨酸脱碘酶，这一点尚未得到证实。缺乏关于鱼类胚胎阶段TH代谢动态的数据，使得我们无法推测TH在鱼类胚胎发育中的参与情况和/或作用。因此，我们开展了一项实验，以研究3,5,3'-三碘甲状腺原氨酸（T(3)）对斑马鱼（Danio rerio）胚胎发育以及通过实时PCR检测的一些甲状腺激素调节基因表达的影响。在整个胚胎发育过程中均检测到母体来源的甲状腺素（T(4)）和T(3)，且总水平保持稳定。发现甲状腺激素受体（TR）α和β mRNA在早期胚胎中存在。在对照组中，TRα mRNA水平在受精后12小时（HPF）开始最初下降后逐渐升高。对照胚胎的TRβ mRNA水平在胚胎发育过程中相对稳定，但在孵化期前后有所增加。我们还对斑马鱼胚胎中I型（D1）和II型（D2）脱碘酶mRNA表达进行了定量。对照组中D1 mRNA水平在发育过程中逐渐升高，而D2水平在孵化前一直保持在低且稳定的水平。在75 HPF时，观察到D2表达相比胚胎期增加了五倍。添加到水中的外源性T(3)（5nM）被胚胎吸收，导致色素沉着增加和孵化加速。T(3)处理在48 HPF时显著上调TRα mRNA水平，而在75 HPF时D2 mRNA显著下调。TRβ和D1 mRNA水平似乎均对该处理无反应。综上所述，这些数据表明在胚胎发育过程中斑马鱼已经具备TH激活和信号传导所需的调节机制，并且该阶段的T(3)处理确实会影响胚胎发育。
