疯牛病是一种朊病毒疾病，朊病毒蛋白表达量与疾病的易感性正相关。申请人的前期研究发现：在中枢神经系统和淋巴系统的几个组织中，黄牛朊蛋白表达量显著高于水牛，这个结果与"黄牛易感疯牛病而水牛不易感"的现象相吻合，但机制尚不清楚。近来我们发现朊蛋白表达的差异并不是由朊病毒基因（PRNP）转录水平的差异引起，而是由两个物种中该基因在转录后水平调控的差异引起。因此，本项目拟从对基因转录后调控起重要作用的miRNA入手，研究两个物种3′UTR序列的差异及其结合miRNA类群的异同，鉴定引起种间和组织间朊病毒表达差异的miRNA类群，通过双荧光素酶报告技术验证PRNP与miRNA的靶标关系，用定量RT-PCR技术确认miRNA的表达情况，并分析牛科物种PRNP和miRNA基因的进化特征，最终阐明黄牛和水牛PRNP基因转录后调控机制的差异。本研究结果将为朊病毒疾病易感性的研究和疾病的治疗提供新思路和新靶点。

Bovine spongiform encephalopathy (BSE) is one of prion diseases caused by prion protein (PrP). PrP levels play a crucial role in susceptibility and development of clinical BSE. Since no case of BSE has ever been reported in buffalo, compared to more than 190,000 cattle infected by BSE, we hypothesized that differences in expression of PrP may relate to these species-specific susceptibility. Recently, our findings revealed that buffaloes have significantly lower relative expressions of PrP in several tissues belonging to the central nervous system and the lymphoreticular system. Although the results support our primary assumption, PrP expressions did not synchronize with the corresponding mRNA expression levels. It was suggested that the biological modulations of PrP are at a post-transcriptional level. The mechanism remains to be clarified. More and more studies report microRNAs (miRNAs) are kind of non-coding small RNAs that function as regulators of post-transcriptional gene expression. In this study, we will screen differentiated miRNA cascade relate to differentiated 3′UTR of PRNP between cattle and buffalo. Luciferase reporter assays will be performed to confirm the relationship between target and predicted miRNA.The different expressions of miRNAs in various tissues between cattle and buffaoes will be analyzed by real-time PCR. Moreover, the evolutionary analysis of PRNP and miRNA genes will be performed in Bovidae. Finally, the different mechanisms of post-transcriptional regulation of PRNP between cattle and buffalo by miRNAs will be revealed. These findings may prove insight into better understanding the mechanism of susceptibility to prion diseases, and prove drug discoveries/development.