Cloning of Transcriptional Regulatory Factors for the Prolactin Gene Using a TRH Knockout Mice.

我们最近报道了TRH缺陷小鼠表现出特征性的三级甲状腺功能减退。在目前的研究中，我们调查了这种三级性甲状腺功能减退症是如何发生的，特别是在出生前和出生后阶段。免疫组织化学分析显示，胚胎17.5天和出生时，TRH-/-垂体腺内有大量TSH免疫阳性细胞。从TRH缺乏的母鼠出生的幼鼠出生时，突变的垂体腺也没有明显的形态变化，表明母体或胚胎的TRH对垂体腺激素的发育没有要求。反之，TSH阳性细胞的数量和染色水平在出生后第10天后明显减少。在8周大的突变型垂体中也观察到了类似的下降，而在其他垂体激素产生细胞中没有观察到明显的变化，长期给予TRH完全逆转了这一效应。与这些形态学结果一致的是，TRH-/-小鼠出生时甲状腺激素水平正常，但随后出生后的增加受到抑制，导致甲状腺功能减退。正如预期的那样，TRH-/-垂体中的TSH含量显著下降，仅为野生型的40%。尽管突变小鼠出现了甲状腺功能减退，但其脑下垂体促甲状腺激素β和阿尔法基因水平均低于野生型。这些表型变化是针对促甲状腺激素的脑垂体区的。这些结果表明：1)TRH仅对出生后维持正常的垂体促甲状腺激素功能是必要的，包括甲状腺激素对TSH基因的正常反馈调节；2)胎儿垂体促甲状腺激素的正常发育不需要母体或胚胎TRH；以及3)TRH缺陷小鼠出生时不表现出甲状腺功能低下。此外，与它的名字一样，TRH对垂体促甲状腺激素细胞的影响比对其他垂体激素产生细胞的影响更关键。

We recently reported that TRH-deficient mice showed characteristic tertiary hypothyroidism. In the present study, we investigated how this tertiary hypothyroidism occurred particularly in pre- and postnatal stages. Immunohistochemical analysis revealed that a number of TSH-immunopositive cells in the TRH-/- pituitary on embryonic day 17.5 and at birth. The mutant pituitary at birth in pups born from TRH-deficient dams also showed no apparent morphological changes, indicating no requirement of either maternal or embryonic TRH for the development of pituitary thyrotrophs. In contrast, apparent decrease in number and level of staining of TSH-positive cells were observed after postnatal day 10 in mutant pituitary. Similar decreases were observed in the 8-week-old mutant pituitary, while no apparent changes were observed in other pituitary hormone-producing cells, and prolonged TRH administration completely reversed this effect. Consistent with these morphological results, TRH-/- mice showed normal thyroid hormone levels at birth, but the subsequent postnatal increase was depressed, resulting in hypothyroidism. As expected, TSH content in the TRH-/- pituitary showed a marked reduction to only 40% of that in the wild-type. Despite hypothyroidism in the mutant mice, both the pituitary TSH β and alpha mRNA levels were lower than those of the wild-type pituitary. These phenotypic changes were specific to the pituitary of thyrotrophs. These findings indicated that 1) TRH is essential only for the postnatal maintenance of the normal function of pituitary thyrotrophs, including the normal feedback regulation of the TSH gene by thyroid hormone ; 2) neither maternal nor embryonic TRH is required for normal development of the fetal pituitary thyrotrophs ; and 3) TRH-deficient mice do not exhibit hypothyroidism at birth. Moreover, reflecting its name, TRH has more critical effects on the pituitary thyrotrophs than on other pituitary hormone-producing cells.