Jansen A, Gemayel R, Verstrepen K J
Laboratory for Systems Biology, Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.
Genome Dyn. 2012;7:108-25. doi: 10.1159/000337121. Epub 2012 Jun 25.
Tandem repeats are intrinsically highly variable sequences since repeat units are often lost or gained during replication or following unequal recombination events. Because of their low complexity and their instability, these repeats, which are also called satellite repeats, are often considered to be useless 'junk' DNA. However, recent findings show that tandem repeats are frequently found within promoters of stress-induced genes and within the coding regions of genes encoding cell-surface and regulatory proteins. Interestingly, frequent changes in these repeats often confer phenotypic variability. Examples include variation in the microbial cell surface, rapid tuning of internal molecular clocks in flies, and enhanced morphological plasticity in mammals. This suggests that instead of being useless junk DNA, some variable tandem repeats are useful functional elements that confer 'evolvability', facilitating swift evolution and rapid adaptation to changing environments. Since changes in repeats are frequent and reversible, repeats provide a unique type of mutation that bridges the gap between rare genetic mutations, such as single nucleotide polymorphisms, and highly unstable but reversible epigenetic inheritance.
串联重复序列本质上是高度可变的序列，因为重复单元在复制过程中或在不等位重组事件之后常常会丢失或增加。由于其低复杂性和不稳定性，这些重复序列，也被称为卫星重复序列，常常被认为是无用的“垃圾”DNA。然而，最近的研究结果表明，串联重复序列经常出现在应激诱导基因的启动子内以及编码细胞表面和调节蛋白的基因的编码区域内。有趣的是，这些重复序列的频繁变化常常导致表型变异。例子包括微生物细胞表面的变异、果蝇内部分子时钟的快速调整以及哺乳动物形态可塑性的增强。这表明，一些可变串联重复序列并非无用的垃圾DNA，而是有用的功能元件，赋予“进化能力”，促进快速进化和对不断变化的环境的快速适应。由于重复序列的变化频繁且可逆，重复序列提供了一种独特的突变类型，弥合了罕见基因突变（如单核苷酸多态性）与高度不稳定但可逆的表观遗传遗传之间的差距。
