Repeat-induced gene silencing in mammals
Repeat-induced gene silencing in mammals
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DOI：
10.1038/ng0198-56
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发表时间：
1998-01-01
期刊：
影响因子：
30.8
通讯作者：
Whitelaw, E
中科院分区：
文献类型：
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作者：
Garrick, D;Fiering, S;Whitelaw, E
在植物（1-3）和黑腹果蝇（4，5）中，当重复的转基因拷贝排列成多联体阵列时，转基因基因位点的表达可能会沉默。这种重复诱导的基因沉默通常表现为表达转基因的细胞比例的降低，导致多样化的表达模式。还有一些迹象表明，在转基因哺乳动物中，阵列内的转基因拷贝数可以对表达产生抑制性影响，几项小鼠研究报告随着拷贝数的增加，每个拷贝的表达水平降低（6-8）。然而，由于这些研究比较了不同的转基因整合位点以及具有不同拷贝数的阵列，因此观察到的表达水平可能受到不同位置效应以及多拷贝阵列的影响。在这里，我们描述了使用lox/Cre系统的位点特异性重组，以产生转基因小鼠品系，其中不同数量的转基因存在于相同的染色体位置，从而消除了位置效应的贡献，并允许分析拷贝数单独对转基因沉默的影响。拷贝数的减少导致转基因表达的显著增加，并且伴随着转基因基因位点处染色质致密化的降低和甲基化的降低。这些发现证实，在多联体阵列内存在转基因的多个同源拷贝可以对哺乳动物系统中的基因表达具有抑制作用。
In both plants(1-3) and Drosophila melanogaster(4,5), expression from a transgenic locus may be silenced when repeated transgene copies are arranged as a concatameric array. This repeat-induced gene silencing is frequently manifested as a decrease in the proportion of cells that express the transgene, resulting in a variegated pattern of expression. There is also some indication that, in transgenic mammals, the number of transgene copies within an array can exert a repressive influence on expression, with several mouse studies reporting a decrease in the level of expression per copy as copy number increases(6-8). However, because these studies compare different sites of transgene integration as well as arrays with different numbers of copies, the expression levels observed may be subject to varying position effects as well as the influence of the multicopy array. Here we describe use of the lox/Cre system of site-specific recombination to generate transgenic mouse lines in which different numbers of a transgene are present at the same chromosomal location, thereby eliminating the contribution of position effects and allowing analysis of the effect of copy number alone on transgene silencing. Reduction in copy number results in a marked increase in expression of the transgene and is accompanied by decreased chromatin compaction and decreased methylation at the transgene locus. These findings establish that the presence of multiple homologous copies of a transgene within a concatameric array can have a repressive effect upon gene expression in mammalian systems.