Evolution of sea urchin retroviral-like (SURL) elements: Evidence from 40 echinoid species
Evolution of sea urchin retroviral-like (SURL) elements: Evidence from 40 echinoid species
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DOI：
10.1093/oxfordjournals.molbev.a026183
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发表时间：
1999-07-01
影响因子：
10.7
通讯作者：
Lessios, HA
中科院分区：
文献类型：
--
作者：
Gonzalez, P;Lessios, HA
我们对海胆纲 33 个物种（海胆、沙钱和心海胆）的海胆逆转录病毒样 (SURL) 逆转录转座元件进行了系统发育调查。逆转录酶 (RT) 基因编码区的 263 bp 片段被扩增、克隆并测序。从独立克隆中分离出的元素的系统发育关系，以及 Springer 等人早期获得的另外 7 个海胆物种的系统发育关系，与宿主系统发育进行了比较：垂直传播和在宿主物种形成之前分歧的旁系同源序列的存在：可以解释 SURL 元素之间的大部分系统发育关系。进化速率是根据 SURL 和宿主系统发育一致的情况估计的。与 Springer 等人先前得出的结论一致，同义替换的平均率与单拷贝海胆 DNA 的平均替换率相当。高比例的同义与非同义取代表明元素的 RT 处于强纯化选择之下。然而，具有有害移码和终止密码子的元素的高比例（大约15%）以及同义与非同义取代的比率随分歧时间的增加表明，在短期内这种选择是宽松的。尽管垂直传播占主导地位，但来自分离 240 Myr 的宿主的 SURL 元件的序列相似性为 83%-94%，这表明现有海胆物种的祖先之间存在明显的水平转移的四个案例。在另外三个案例中，在海胆物种中发现了具有相同 RT 序列的元件，分离距离至少为 3 Myr。因此，水平转移在该反转录转座子家族的进化中发挥着作用。
We conducted a phylogenetic survey of sea urchin retroviral-like (SURL) retrotransposable elements in 33 species of the class Echinoidea (sea urchins, sand dollars, and heart urchins). A 263-bp fragment from the coding region of the reverse transcriptase (RT) gene was amplified, cloned, and sequenced. Phylogenetic relationships of the elements isolated from independent clones, along with those from seven additional echinoid species obtained earlier by Springer et al.,, were compared with host phylogeny: Vertical transmission and the presence of paralogous sequences that diverged prior to host speciation:can explain most of the phylogenetic relationships among SURL elements. Rates of evolution were estimated from cases in which SURL and host phylogenies were concordant. In agreement with conclusions reached previously be Springer et al., average rates of synonymous substitution were comparable with those of single-copy sea urchin DNA. High ratios of synonymous to nonsynonymous substitution suggest that the RT of the elements is under strong purifying selection. However, a high proportion (similar to 15%) of elements with deleterious frameshifts and stop codons and an increase of the ratio of synonymous to nonsynonymous substitutions with divergence time show that in the short term this selection is relaxed. Despite, the predominance of vertical transmission, sequence similarity of 83%-94% for SURL elements from hosts that have been separated for 240 Myr suggests four cases of apparent horizontal transfer between the ancestors of the extant echinoid species. In three additional cases, elements with identical RT sequences were found in sea urchin species separated for a minimum of 3 Myr. Thus, horizontal transfer plays a role in the evolution of this retrotransposon family.