Goldberg Y P, Kalchman M A, Metzler M, Nasir J, Zeisler J, Graham R, Koide H B, O'Kusky J, Sharp A H, Ross C A, Jirik F, Hayden M R
Department of Medical Genetics, University of British Columbia, Vancouver, Canada.
Hum Mol Genet. 1996 Feb;5(2):177-85. doi: 10.1093/hmg/5.2.177.
The mutation underlying Huntington disease (HD) is CAG expansion in the first exon of the HD gene. In order to investigate the role of CAG expansion in the pathogenesis of HD, we have produced transgenic mice containing the full length human HD cDNA with 44 CAG repeats. By 1 year, these mice have no behavioral abnormalities and morphometric analysis at 6 (one animal) and 9 (two animals) months age revealed no changes. Despite high levels of mRNA expression, there was no evidence of the HD gene product in any of these transgenic mice. In vitro transfection studies indicated that the inclusion of 120 bp of the 5' UTR in the cDNA construct and the presence of a frameshift mutation at nucleotide 2349 prevented expression of the HD cDNA. These findings suggest that the pathogenesis of HD is not mediated through DNA-protein interaction and that presence of the RNA transcript with an expanded CAG repeat is insufficient to cause the disease. Rather, translation of the CAG is crucial for the pathogenesis of HD. In contrast to that seen in humans, the CAG repeat in these mice was remarkably stable in 97 meioses. This suggests that genomic sequences may play a critical role in influencing repeat instability.
亨廷顿舞蹈病（HD）的潜在突变是HD基因第一外显子中的CAG重复序列扩增。为了研究CAG重复序列扩增在HD发病机制中的作用，我们制备了含有44个CAG重复序列的全长人类HD cDNA的转基因小鼠。到1岁时，这些小鼠没有行为异常，在6个月龄（1只动物）和9个月龄（2只动物）时的形态计量学分析也未发现变化。尽管mRNA表达水平很高，但在任何一只转基因小鼠中均未发现HD基因产物的证据。体外转染研究表明，cDNA构建体中包含5'UTR的120 bp以及核苷酸2349处的移码突变阻止了HD cDNA的表达。这些发现表明，HD的发病机制不是通过DNA-蛋白质相互作用介导的，并且具有扩增的CAG重复序列的RNA转录本的存在不足以引发该疾病。相反，CAG的翻译对于HD的发病机制至关重要。与人类情况相反，这些小鼠中的CAG重复序列在97次减数分裂中非常稳定。这表明基因组序列可能在影响重复序列不稳定性方面起关键作用。
