High Evolutionary Dynamism in 5S rDNA of Fish: State of the Art
High Evolutionary Dynamism in 5S rDNA of Fish: State of the Art
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DOI：
10.1159/000354871
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发表时间：
2013-09
影响因子：
1.7
通讯作者：
L. Rebordinos;I. Cross;Alejandro Merlo
中科院分区：
文献类型：
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作者：
L. Rebordinos;I. Cross;Alejandro Merlo
5S核糖体DNA（rDNA）由约120个碱基对的一个转录单位组成，其通过非转录间隔区（NTS）与下一个单位分开。编码序列和NTS一起形成重复单元，其可以在基因组中以串联重复的数百至数千个拷贝存在。NTS区域似乎受到快速进化的影响。这些多基因家族进化的第一个一般模型被称为趋异进化，基于使用血红蛋白和肌红蛋白作为模型系统的研究。后来的研究表明，不同的多基因家族成员的核苷酸序列在物种内比在物种之间更密切相关。这一发现导致了一种新的多基因家族进化模型，称为协同进化。另一种进化模型，称为出生和死亡模型，已被发现更适合于解释这些多基因家族的长期进化。根据这一模型，新的基因是通过连续的复制产生的，这些新的基因要么保持很长一段时间，要么丢失，要么退化为假基因。在这篇综述中，我们描述了不同来源的变异在几个不同的鱼类中观察到的5S rDNA基因。这种变异性主要涉及NTS，包括其他多基因家族（主要是LINE、西内斯、非LTR反转录转座子和U snRNA家族）的存在。还发现不同类型的微型卫星有助于增加该区域的变异性。我们最近的研究结果表明，水平转移有助于增加的多样性，在NTS的一些物种。在5S rDNA编码区的可变性影响的结构的稳定性，但不影响的5S rRNA的功能，也被描述。反转录转座子似乎是负责高动力的5S rDNA，而微卫星作为重组热点可以稳定各种各样的不寻常的DNA结构，影响DNA复制和增强或降低基因表达的启动子活性。分子水平的高变异性和染色体水平的低变异性之间的关系也进行了讨论。
The 5S ribosomal DNA (rDNA) consists of one transcriptional unit of about 120 base pairs, which is separated from the next unit by a non-transcribed spacer (NTS). The coding sequence and the NTS together form a repeat unit which can be found in hundreds to thousands of copies tandemly repeated in the genomes. The NTS regions seem to be subject to rapid evolution. The first general model of evolution of these multigene families was referred to as divergent evolution, based on studies using hemoglobin and myoglobin as model systems. Later studies showed that nucleotide sequences of different multigene family members are more closely related within species than between species. This observation led to a new model of multigene family evolution, termed concerted evolution. Another model of evolution, named the birth-and-death model, has been found to be more suitable to explain the long-term evolution of these multigene families. According to this model, new genes originate by successive duplications, and these new genes are either maintained for a long time or are lost, or else degenerate into pseudogenes. In this review we describe different sources of variability in the 5S rDNA genes observed in several distinct fish species. This variability is mainly referred to NTSs and includes the presence of other multigene families (mainly LINEs, SINEs, non-LTR retrotransposons, and U snRNA families). Different types of microsatellites have also been found to contribute to the increase of variability in this region. Our recent results suggest that horizontal transfer contributes to the increase of diversity in the NTSs of some species. Variability in the 5S rDNA coding region affecting the stability of the structure, but without effects on the function of the 5S rRNA, is also described. Retrotransposons seem to be responsible for the high dynamism of 5S rDNA, while microsatellites acting as recombination hot spots could stabilize a wide variety of unusual DNA structures, affecting DNA replication and enhancing or decreasing promoter activity in gene expression. The relationship between the high variability found at molecular level and the low variability found at chromosomal level is also discussed.