Ribosomes are large, multi-subunit ribonucleoprotein complexes, essential for protein synthesis. To meet the high cellular demand for ribosomes, all eukaryotes have numerous copies of ribosomal DNA (rDNA) genes that encode ribosomal RNA (rRNA), usually far in excess of the requirement for ribosome biogenesis. In all eukaryotes studied, rDNA genes are arranged in one or more clusters of tandem repeats localized to nucleoli. The tandem arrangement of repeats, combined with the high rates of transcription at the rDNA loci, and the difficulty of replicating repetitive sequences make the rDNA inherently unstable and particularly susceptible to large variations in repeat copy number. Despite mounting evidence suggesting extra-ribosomal functions of the rDNA, its repetitive nature has excluded it from traditional sequencing-based studies. However, more recently, several studies have revealed the unique potential of the rDNA to act as a "canary in the coalmine," being particularly sensitive to genomic stresses and acting as a source of adaptive response. Here, we review evidence uncovering mechanisms of regulation of instability and copy number variation at the rDNA and their role in adaptation to the environment, which could serve to understand the basic principles governing the behavior of other tandem repeats and their role in shaping the genome.

中文翻译：

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核糖体DNA不稳定性和基因组适应性。

核糖体是蛋白质合成必不可少的大型多亚基核糖核蛋白复合物。为了满足细胞对核糖体的高需求，所有真核生物均具有许多拷贝的编码核糖体RNA（rRNA）的核糖体DNA（rDNA）基因，通常远远超出了核糖体生物发生的要求。在所有研究的真核生物中，rDNA基因排列在一个或多个位于核仁的串联重复序列簇中。重复的串联排列，再加上在rDNA位点的高转录率，以及难以复制重复序列，使得rDNA固有地不稳定，特别容易受到重复拷贝数变化的影响。尽管越来越多的证据表明rDNA具有核糖体外功能，但其重复性已将其排除在基于传统测序的研究之外。然而，最近，几项研究揭示了rDNA发挥“煤矿中的金丝雀”的独特潜力，它对基因组压力特别敏感，并且可以作为适应性反应的来源。在这里，我们审查了证据揭示了rDNA的不稳定性和拷贝数变异的调控机制，以及它们在适应环境中的作用，这可能有助于理解指导其他串联重复序列行为的基本原理及其在塑造基因组中的作用。