Transposable Element Bm1645 is a Source of BmAGO2-associated Small RNAs that affect its expression in Bombyx mori

Abstract

BackgroundA transposable element (TE) is a DNA fragment that can change its position within a genome. Transposable elements play important roles in maintaining the stability and diversity of organisms by transposition. Recent studies have shown that approximately half of the genes in Bombyx mori are TEs.ResultsWe systematically identified and analyzed the BmAGO2-associated TEs, which exceed 100 in the B. mori genome. Additionally, we also mapped the small RNAs associated with BmAGO2 in B.mori. The transposon Bm1645 is the most abundant TE associated with BmAGO2, and Bm1645-derived small RNAs represent a small RNA pool. We determined the expression patterns of several Bm1645-derived small RNAs by northern blotting, and the results showed there was differential expression of multiple small RNAs in normal and BmNPV-infected BmN cells and silkworms from various developmental stages. We confirmed that four TE-siRNAs could bind to BmAGO2 using EMSA and also validated the recognition sites of these four TE-siRNAs in Bm1645 by dual-luciferase reporter assays. Furthermore, qRT-PCR analysis revealed the overexpression of the four TE-siRNAs could downregulate the expression of Bm1645 in BmN cells, and the transcription of Bm1645 was upregulated by the downregulation of BmAGO2.ConclusionsOur results suggest Bm1645 functions as a source of small RNAs pool and this pool can produce many BmAGO2-associated small RNAs that regulate TE’s expression.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3598-5) contains supplementary material, which is available to authorized users.

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“…In addition, small RNAs with antisense orientation corresponding to sequences of transposons, e.g., the non-LTR retrotransposon Bm1645 , were found to associate with Ago2 protein, indicating that the endo-siRNA pathway can contribute to the control of transposable elements [ 181 ]. In Hi5 cells and T. ni thorax, ovaries, and testes, 21–52% of endogenous siRNAs also map to transposons, indicating a role in transposon suppression in both somatic tissues and germlines [ 167 ].…”