Abstract: Spinocerebellar ataxia type 3 (SCA3) is a type of polyglutamine (polyQ) disease with expansion mutant ATXN3 gene as its causative gene which contains cytosine-adenine-guanine (CAG) repeat sequence at the coding region of 3-terminal. The polyQ expansion mutant ATXN3 gene encoded polyQ expansion mutant ataxin-3 protein with a polyQ peptide chain at its carboxyl-terminal. The polyQ expansion mutant ataxin-3 protein selectively accumulates in specific areas of the central nervous system, such as cerebellum, brainstem, spinal cord, etc, and forms neuronal intranuclear inclusions (NIIs). Researches about micro RNA (miRNA) and small interference RNA (siRNA) are dramatically rapidly increasing. miRNAs are a class of small non-coding RNAs that widely exist in higher eukaryotes, with approximately 21-23 bp. They inhibit target gene expression by combining with the 3' untranslated region (3'UTR) of the target gene mRNA. siRNAs are the effect molecules in RNA interference (RNAi) technology, with a length of about 21-23 bp. They induce mRNA degradation and silence on the basis of completely complementary combination with mRNA coding sequence (CDS). miRNA and siRNA have many similarities in both structure and mechanism, and both of them can be used to analyze gene function and to investigate pathogenesis of diseases.

Key words: MicroRNAs, RNA, small interfering, Machado-Joseph disease, Trinucleotide repeats, Review

摘要： 脊髓小脑共济失调3 型（SCA3）为多聚谷氨酰胺（PolyQ）病，其致病基因为编码区内含胞嘧啶-腺嘌呤-鸟嘌呤（CAG）重复序列的ATXN3 基因，编码蛋白ataxin-3 羧基末端含PolyQ 肽链，PolyQ 扩展突变型ataxin-3 蛋白可选择性地在中枢神经系统特定区域（小脑、脑干、脊髓等）聚积形成神经元核内包涵体。微小RNA 是广泛存在于高等真核细胞中、长度为21 ~ 23 bp 的小分子非编码RNA，与靶基因mRNA 的3’端非编码区特异性结合后抑制靶基因的表达。小干扰RNA 是RNA 干扰技术中的效应分子，其长度为21 ~ 23 bp，特异性与mRNA 的编码序列完全互补结合后，导致mRNA 降解和沉默。二者在结构和作用机制存在许多类似之处，可用来进行基因功能分析和疾病发病机制的研究。

关键词: 微RNAs, RNA, 小分子干扰, Machado-Joseph病, 三核苷酸重复, 综述