Dispersion of transposable elements and multigene families: Microstructural variation in Characidium (Characiformes: Crenuchidae) genomes

Abstract Eukaryotic genomes consist of several repetitive DNAs, including dispersed DNA sequences that move between chromosome sites, tandem repeats of DNA sequences, and multigene families. In this study, repeated sequences isolated from the genome of Characidium gomesi were analyzed and mapped to chromosomes in Characidium zebra and specimens from two populations of C. gomesi. The sequences were transposable elements (TEs) named retroelement of Xiphophorus (Rex); multigene families of U2 small nuclear RNA (U2 snRNA); and histones H1, H3, and H4. Sequence analyses revealed that U2 snRNA contains a major portion corresponding to the Tx1-type non-LTR retrotransposon Keno, the preferential insertion sites of which are U2 snRNA sequences. All histone sequences were found to be associated with TEs. In situ localization revealed that these DNA sequences are dispersed throughout the autosomes of the species, but they are not involved in differentiation of the specific region of the W sex chromosome in C. gomesi. We discuss mechanisms of TE invasion into multigene families that lead to microstructural variation in Characidium genomes.

摘要 真核生物基因组包含多种重复DNA序列，涵盖可在染色体位点间移动的分散DNA序列、DNA串联重复序列与多基因家族。本研究从格氏溪脂鲤（Characidium gomesi）基因组中分离得到重复序列，对其展开分析，并将这些序列定位至斑马溪脂鲤（Characidium zebra）以及两个格氏溪脂鲤（C. gomesi）种群的染色体上。所分析的序列包括命名为剑尾鱼属逆转座子（retroelement of Xiphophorus, Rex）的转座因子（transposable elements, TEs）、U2小核RNA（U2 small nuclear RNA, U2 snRNA）多基因家族，以及组蛋白H1、H3与H4。序列分析结果显示，U2 snRNA包含一段与Tx1型非长末端重复序列逆转座子Keno（Tx1-type non-LTR retrotransposon Keno）相对应的主要区段，该逆转座子的优先插入位点即为U2 snRNA序列。所有组蛋白序列均与转座因子相关联。原位定位结果表明，这些DNA序列分散于该物种的常染色体中，但未参与格氏溪脂鲤W性染色体的特定区域分化。本研究讨论了转座因子入侵多基因家族的机制，该机制可导致溪脂鲤属（Characidium）基因组出现微观结构变异。