The (CGG)n repeat element within the 5′ untranslated region of the FMR1 message provides both positive and negative cis effects on in vivo translation of a downstream reporter
The (CGG)n repeat element within the 5′ untranslated region of the FMR1 message provides both positive and negative cis effects on in vivo translation of a downstream reporter
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DOI：
10.1093/hmg/ddg331
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发表时间：
2003-12-01
影响因子：
3.5
通讯作者：
Hagerman, PJ
中科院分区：
文献类型：
--
作者：
Chen, LS;Tassone, F;Hagerman, PJ
人类脆性X智力低下1(FMR1)基因在其5‘非翻译区含有一个多态(CGG)三核苷酸重复序列。(CGG)(N)元件超过200个重复(全突变范围)通常会导致转录沉默；随之而来的FMR1蛋白(FMRP)的丢失会导致脆性X综合征，这是最常见的遗传性智力障碍形式。对于较小扩增的携带者(55小于或等于200；前突变范围)，FMRP水平随着重复次数的增加而逐渐降低，尽管FMR1 mRNA水平升高，这表明翻译在前突变范围内受到阻碍。为了更详细地研究CGG重复对翻译的影响，将含有不同(CGG)(N)重复长度(0小于或等于99)重复长度的FMR1 5‘-UTR和下游(荧光素酶)报告基因的CMV即刻-早期启动子载体，导入两个人细胞系，神经细胞来源的细胞系(SK)和胎肾细胞来源的细胞系(293)。对于这两种细胞类型，CGG元件对报告基因的表达产生不同的影响，这取决于重复的长度。对于n大于或等于30，荧光素酶的表达随着重复长度的增加而减少，这与早期的观察结果一致，即在相同的重复范围内，外周血白细胞中FMRP的表达减少，尽管较大的重复略有增加。令人惊讶的是，对于较小的等位基因(0小于或等于30)，在没有任何mRNA水平变化的情况下，报告基因的表达实际上随着重复长度的增加而增加了近两倍。这些结果表明，CGG重复元件对翻译既有正向影响，也有正向影响。有趣的是，在一般人群中，最佳翻译似乎发生在模式重复数附近。
The human fragile X mental retardation 1 (FMR1) gene contains a polymorphic (CGG) trinucleotide repeat element in its 5' untranslated region. Expansion of the (CGG)(n) element beyond 200 repeats (full mutation range) generally leads to transcriptional silencing; consequent loss of the FMR1 protein (FMRP) results in fragile X syndrome, the most frequent form of inherited mental impairment. For carriers of smaller expansions (55less than or equal tonless than or equal to200; premutation range), FMRP levels are gradually reduced with increasing repeat number, despite elevated FMR1 mRNA levels, suggesting that translation is impeded within the premutation range. To examine in more detail the influence of the CGG repeat on translation, CMV immediate-early promoter constructs, containing the FMR1 5'-UTR with various (CGG)(n) repeat lengths (0less than or equal tonless than or equal to99) and a downstream (luciferase) reporter, were transfected into two human cell lines, a neural cell-derived line (SK) and a fetal kidney cell-derived line (293). For both cell types, the CGG element exerts distinct effects on reporter expression, depending on the length of the repeat. For ngreater than or equal to30, luciferase expression decreases with increasing repeat length, consistent with earlier observations of decreased FMRP expression in peripheral blood leucocytes over the same repeat range, despite a slight increase in mRNA level for the larger repeats. Surprisingly, for smaller alleles (0less than or equal tonless than or equal to30), reporter expression actually increases by nearly two-fold with increasing repeat length in the absence of any change in mRNA level. These results suggest that the CGG repeat element can exert both positive (n30) effects on translation. Interestingly, optimal translation appears to occur near the modal repeat number within the general human population.