Laboratory of Comparative Endocrinology, Animal Physiology and Neurobiology Section, Department of Biology, KU Leuven, B-3000 Leuven, Belgium.
Gen Comp Endocrinol. 2013 Sep 1;190:96-104. doi: 10.1016/j.ygcen.2013.05.003. Epub 2013 May 21.
Thyroid hormones (THs) are crucial elements in vertebrate brain development. They exert their action mainly through binding of 3,5,3'-triiodothyronine (T3) to nuclear receptors that directly influence the expression of TH-regulated genes. Intracellular TH action is therefore dependent on both the availability of T3 and its receptors. TH uptake in cells is regulated by specific TH transporters and local activation and inactivation is regulated by deiodinases. This review provides an overview of the general expression pattern of TH transporters, deiodinases and receptors during embryonic chicken brain development and compares it to the situation in mammals. It is clear that THs and their regulators are present in the embryonic brain from the early stages of development, long before the onset of embryonic thyroid gland functioning. The mechanism of TH uptake across the brain barriers during development is only partly understood. At the developing blood-brain-barrier expression of the TH-activating type 2 deiodinase is closely associated with the blood vessels, but contrary to the situation in (adult) mammals no expression of MCT8 or OATP1C1 TH transporters is found at that level in the developing chicken. At the blood-cerebrospinal fluid-barrier co-expression of the TH-inactivating type 3 deiodinase and MCT8 and OATP1C1 is found in birds and mammals. These comparative data show overlapping patterns, pointing to general mechanisms, but also indicate specific interspecies differences that may help to understand species-specific responses to regulator gene knockout/mutation.
甲状腺激素（THs）是脊椎动物大脑发育的关键因素。它们主要通过与核受体结合 3,5,3'-三碘甲状腺原氨酸（T3）发挥作用，直接影响 TH 调节基因的表达。因此，细胞内 TH 的作用取决于 T3 的可用性及其受体。细胞内 TH 的摄取受特定的 TH 转运蛋白调节，局部激活和失活受脱碘酶调节。 本文综述了胚胎鸡大脑发育过程中 TH 转运蛋白、脱碘酶和受体的一般表达模式，并将其与哺乳动物的情况进行了比较。很明显，TH 及其调节剂在胚胎发育的早期阶段就存在于胚胎大脑中，远早于胚胎甲状腺功能的开始。TH 穿过脑屏障在发育过程中的摄取机制尚未完全了解。在发育中的血脑屏障上，TH 激活型 2 脱碘酶的表达与血管密切相关，但与哺乳动物（成年）的情况相反，在该水平上未发现发育中的鸡的 MCT8 或 OATP1C1 TH 转运蛋白的表达。在血脑脊液屏障上，TH 失活型 3 脱碘酶和 MCT8 和 OATP1C1 的共表达在鸟类和哺乳动物中均有发现。这些比较数据显示出重叠的模式，指向一般的机制，但也表明了特定的种间差异，这可能有助于理解对调节剂基因敲除/突变的物种特异性反应。
