Permanyer Jon, Albalat Ricard, Gonzàlez-Duarte Roser
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain.
Int J Biol Sci. 2006;2(2):48-53. doi: 10.7150/ijbs.2.48. Epub 2006 Apr 10.
Non-LTR retrotransposons are common in vertebrate genomes and although present in invertebrates they appear at a much lower frequency. The cephalochordate amphioxus is the closest living relative to vertebrates and has been considered a good model for comparative analyses of genome expansions during vertebrate evolution. With the aim to assess the involvement of transposable elements in these events, we have analysed the non-LTR retrotransposons of Branchiostoma floridae. In silico searches have allowed to reconstruct non-LTR elements of six different clades (CR1, I, L1, L2, NeSL and RTE) and assess their structural features. According to the estimated copy number of these elements they account for less than 1% of the haploid genome, which reminds of the low abundance also encountered in the urochordate Ciona intestinalis. Amphioxus (B. floridae) and Ciona share a pre-vertebrate-like organization for the non-LTR retrotransposons (<150 copies, < 1% of the genome) versus the complexity associated to higher vertebrates (Homo sapiens >1.3.10(6) copies, > 20% of the genome).
非长末端重复反转录转座子在脊椎动物基因组中很常见，尽管在无脊椎动物中也存在，但出现频率要低得多。头索动物文昌鱼是现存与脊椎动物亲缘关系最近的物种，被认为是比较分析脊椎动物进化过程中基因组扩张的良好模型。为了评估转座元件在这些事件中的作用，我们分析了佛罗里达文昌鱼的非长末端重复反转录转座子。通过计算机搜索，我们重建了六个不同分支（CR1、I、L1、L2、NeSL和RTE）的非长末端重复元件，并评估了它们的结构特征。根据这些元件的估计拷贝数，它们在单倍体基因组中所占比例不到1%，这与在尾索动物海鞘中发现的低丰度情况相似。文昌鱼（佛罗里达文昌鱼）和海鞘的非长末端重复反转录转座子具有类似脊椎动物之前的组织形式（<150个拷贝，占基因组的<1%），而与高等脊椎动物（智人>1.3×10⁶个拷贝，占基因组的>20%）相关的复杂性不同。
