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

1)家栖麝鼠属于食虫目最原始的哺乳动物。该物种广泛分布于从东非到东亚的炎热气候地区。2)我们发现，在大鼠肝脏中，甲状旁腺原氨酸脱碘酶(D_1)的活性是大鼠肝脏的1/3。另一方面，D2活性水平较高。为了阐明这些活性的机制，我们从大鼠肝脏中克隆了d1和d2基因。根据不同物种间D1D2和D3的保守氨基酸序列设计了不同的引物进行RT-PCR扩增。克隆的cDNA包含完整的开放阅读框架。发现了一种可能的硒半胱氨酸(SEC)，它在哺乳动物中是保守的。3)禁食状态下，大鼠血T_3水平稳定，而小鼠和大鼠的T_3水平降低。肝脏D1m RNA和棕色脂肪组织D2m RNA减少，脑D2活性增加。4)禁食状态下树鼠血T_3水平不变，禁食状态下基本代谢未见降低。因此，这只泼妇很快就会在禁食状态下死去。在研究甲状腺激素代谢机制方面，地鼠是唯一可与大鼠和小鼠相媲美的动物

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