A causal gene and proteins related to rdw symptoms in the rdw rat with hereditary dwarfism/hypothyroidism

rdw大鼠最初是从Wistar-Imamichi大鼠的封闭群体中分离出来的遗传矮株。随后在rdw大鼠中发现明显的甲状腺功能减退。最近的几份报告显示，rdw甲状腺细胞中存在分子chapelone水平升高，其内质网明显扩张，提示细胞内蛋白质运输存在缺陷。在这里，我们进行了研究，以确定精确的分子缺陷和动物模型在rdw大鼠中的实用性。首先，遗传连锁分析表明，rdw位点位于大鼠第7染色体上，与甲状腺球蛋白（Tg）基因位点相同。此外，rdw甲状腺中的Tg蛋白水平降低，尽管其Tg基因转录物的水平与正常甲状腺相似，但其大小与正常甲状腺没有区别。接下来，对rdw和正常大鼠Tg cdna进行完整测序，发现G6958C单核苷酸变化，导致Tg分子高度保守区域的G2320R错义突变。最后，在COS-7细胞中瞬时表达含有rdw突变的完整Tg cDNA，在分泌培养基中没有检测到Tg，表明突变体Tg的输出存在严重缺陷。总之，我们的观察表明Tg基因中的错义突变G2320R是导致rdw大鼠rdw突变的原因。此外，许多关于rdw大鼠的研究表明了其作为动物模型的有效性。

The rdw rat was initially isolated as a hereditary dwarf strain from a closed colony of Wistar-Imamichi rat. Marked hypothyroidism was subsequently noted in the rdw rat. Several recent reports have shown the presence of elevated molecular chapelone levels in the rdw thyrocytes, the endoplasmic reticulum of which was markedly dilated, suggesting a defect in intracellular protein transport. Here the studies were undertaken to identify the precise molecular defect and the usefulness for animal models in the rdw rat. First, the genetic linkage analysis revealed that the rdw locus was on rat chromosome 7 and was identical to the thyroglobulin (Tg) gene locus. Moreover, the Tg protein level was reduced in the rdw thyroid despite a similar level of the Tg gene transcripts that were indistinguishable in their size from the normal. Next, the complete sequencing of the rdw and the normal rat Tg cDNAs revealed a single nucleotide change, G6958C, resulting in a G2320R missense mutation in a highly conserved region of the Tg molecule. Finally, transient expression of the intact Tg cDNA containing the rdw mutation in the COS-7 cells showed no detectable Tg in the secreted media, indicating a severe defect in the export of the mutant Tg. Together, our observations suggest that a missense mutation, G2320R, in the Tg gene is responsible for the rdw mutation in the rdw rat. Furthermore, the usefulness as animal models was indicated in many studies on the rdw rat.