The house musk shrew, Suncus murinus as unique laboratory animal model for estimation of thyroid hormone function

1)麝香鼩属于最原始的哺乳动物食虫目。该物种广泛分布于东非至东亚的炎热气候地区2)我们发现，鼩鼱肝脏中1型碘甲状腺原氨酸脱碘酶（D1）的活性是大鼠肝脏的三分之一。另一方面，D2活性较高。为了阐明这些活性的机制，我们从鼩鼱肝脏中克隆了D1和D2 cDNA。采用不同引物进行RT-PCR，引物是根据不同物种中D1、D2和D3的保守氨基酸序列设计的。克隆的cdna包含整个开放阅读框。鉴定出一种假定的硒代半胱氨酸（Sec），它在哺乳动物物种中保守。从鼩鼱克隆的D1和D2 cDNA与其他哺乳动物相同。3)在空腹状态下，鼩鼱血液T3水平稳定，而小鼠和大鼠血液T3水平下降。肝脏中D1 mRNA和棕色脂肪组织中D2 mRNA活性降低，脑组织中D2 mRNA活性升高。脑D2活动可能支持正常血T3水平。4)空腹状态下鼩鼱血T3水平不变，基本代谢不降低。因此，鼩鼱很快就在禁食状态下死亡。鼩鼱是研究甲状腺激素代谢机制的独特动物，可与大鼠和小鼠相媲美

1) The house musk shrew Suncus murinus belongs to the most primitive mammalian oder Insectivora. This species is widely distributed in hot climate area from East Africa to East Asia2) We found that the type-1 iodothyronine deiodinase (D1) activity in shrew liver was one third of that in the rat liver. The other hand, D2 activity was higher level. To elucidate the mechanism for those activities, we cloned the D1 and D2 cDNA from the shrew liver. RT-PCR was performed using different sets of primers, which were designed based on conserved amino acid sequences of the D1, D2 and D3 among different species. The cloned cDNAs contain the entire open reading frame. A putative selenocystein (Sec) was identified, which is conserved among mammalian species. Cloned the D1 and D2 cDNA from the shrew were comparable same to other mammal species3) Blood T3 level in the shrew was stable at the fasting status, but T3 level in the mouse and rat was decreased. D1 mRNA in the liver and D2 mRNA in the brown adipose tissue were reduced but D2 activities in the brain were incresed. Brain D2 activities may support normal blood T3 level in the shrew4) Blood T3 level in the shrew was constant in fasting status and basic metabolism was not reduced in fasting status. So, the shrew is soon died in fasting status. The shrew is so unique animal to study the mechanism of thyroid hormone metabolism comparable to the rats and mice