Abstract
BackgroundNon-long terminal repeat (non-LTR) retrotransposons are mobile genetic elements that propagate themselves by reverse transcription of an RNA intermediate. Non-LTR retrotransposons are known to evolve mainly via vertical transmission and random loss. Horizontal transmission is believed to be a very rare event in non-LTR retrotransposons. Our knowledge of distribution and diversity of insect non-LTR retrotransposons is limited to a few species – mainly model organisms such as dipteran genera Drosophila, Anopheles, and Aedes. However, diversity of non-LTR retroelements in arthropods seems to be much richer. The present study extends the analysis of non-LTR retroelements to CR1 clade from four butterfly species of genus Maculinea (Lepidoptera: Lycaenidae).The lycaenid genus Maculinea, the object of interest for evolutionary biologists and also a model group for European biodiversity studies, possesses a unique, specialized myrmecophilous lifestyle at larval stage. Their caterpillars, after three weeks of phytophagous life on specific food plants drop to the ground where they are adopted to the ant nest by Myrmica foraging workers.ResultsWe found that the genome of Maculinea butterflies contains multiple CR1 lineages of non-LTR retrotransposons, including those from MacCR1A, MacCR1B and T1Q families. A comparative analysis of RT nucleotide sequences demonstrated an extremely high similarity among elements both in interspecific and intraspecific comparisons. CR1A-like elements were found only in family Lycaenidae. In contrast, MacCR1B lineage clones were extremely similar to CR1B non-LTR retrotransposons from Bombycidae moths: silkworm Bombyx mori and Oberthueria caeca.ConclusionThe degree of coding sequence similarity of the studied elements, their discontinuous distribution, and results of divergence-versus-age analysis make it highly unlikely that these sequences diverged at the same time as their host taxa. The only reasonable alternative explanation is horizontal transfer. In addition, phylogenetic markers for population analysis of Maculinea could be developed based on the described non-LTR retrotransposons.
Highlights
Non-long terminal repeat retrotransposons are mobile genetic elements that propagate themselves by reverse transcription of an RNA intermediate
We examined the diversity of CR1 clade of non-long terminal repeat (LTR) retrotransposons in lycaenid butterflies of the genus Maculinea
After preliminary identification of reverse transcriptase (RT) fragments by comparison with sequences in the GenBank database, we found that 49 clones showed clear similarity with RT domain of non-LTR retrotransposons, while three sequences revealed no presence of RT
Summary
Non-long terminal repeat (non-LTR) retrotransposons are mobile genetic elements that propagate themselves by reverse transcription of an RNA intermediate. Non-long terminal repeat (non-LTR) retrotransposons are mobile genetic elements that propagate by reverse transcription of an RNA intermediate. These elements lack terminal repeats and utilize a simplified target-primed reverse transcription (TPRT) mechanism for their retrotransposition. Resulting cDNA copy is integrated into the target site [1,2] Based on their structure, non-LTR retrotransposons can be classified into two groups. The second group of non-LTR retrotransposons has two ORFs: ORF1 and ORF2; the latter encodes two domains responsible for retrotransposition: apurinic/ apyrimidinic endonuclease (APE)-like endonuclease domain at the N-terminus and RT domain in the middle
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