Biedler J K, Chen X, Tu Z
Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
Insect Mol Biol. 2015 Jun;24(3):331-7. doi: 10.1111/imb.12160. Epub 2015 Jan 23.
AaegR4_1 and AgamR4_1 are the sole R4 clade non-long terminal repeat (non-LTR) retrotransposons in Aedes aegypti and Anopheles gambiae, two species that diverged approximately 145-200 million years ago. Twelve full-length copies were found in Ae. aegypti and have less than 1% nucleotide (nt) divergence, suggesting recent activity on an evolutionary time scale. Five of these copies have intact open reading frames and the 3.6 kb open reading frame of AaegR4_1.1 has 78% nt identity to AgamR4_1.1. No intact copies were found in An. gambiae. Searches of 25 genomic databases for 22 mosquito species from three genera revealed R4 clade representatives in Aedes and Anopheles genera but not in Culex. Interestingly, these elements are present in all six species of the An. gambiae species complex that were searched but not in 13 other anopheline species. These results combined with divergence vs. age analysis suggest that horizontal transfer is the most likely explanation for the low divergence between R4 clade retrotransposon sequences of the divergent mosquito species from the Aedes and Anopheles genera. This is the first report of the horizontal transfer of an R4 clade non-LTR retrotransposon and the first report of the horizontal transfer of a non-LTR retrotransposon in mosquitoes.
AaegR4_1和AgamR4_1是埃及伊蚊和冈比亚按蚊中仅有的R4分支非长末端重复（non-LTR）逆转座子，这两个物种大约在1.45 - 2亿年前分化。在埃及伊蚊中发现了12个全长拷贝，其核苷酸（nt）差异小于1%，这表明在进化时间尺度上其近期有活性。其中5个拷贝具有完整的开放阅读框，AaegR4_1.1的3.6 kb开放阅读框与AgamR4_1.1有78%的核苷酸同一性。在冈比亚按蚊中未发现完整拷贝。对来自三个属的22种蚊子的25个基因组数据库进行搜索，结果显示在伊蚊属和按蚊属中有R4分支代表，但在库蚊属中没有。有趣的是，在所搜索的冈比亚按蚊物种复合体的所有六个物种中都存在这些元件，但在其他13种按蚊中不存在。这些结果与差异与年龄分析相结合表明，水平转移最有可能解释来自伊蚊属和按蚊属的不同蚊子物种的R4分支逆转座子序列之间的低差异。这是R4分支非LTR逆转座子水平转移的首次报道，也是蚊子中非LTR逆转座子水平转移的首次报道。
