Retrotransposon Dynamics: Control in the Germline and Functional Activation During Development

Abstract

This work explores retrotransposon activity throughout the life cycle of Drosophila melanogaster. We first investigate retrotransposon activity in the male germline and find that the LTR retrotransposon nomad abundantly produces ecDNA in the absence of the piRNA pathway. Despite efficient reverse transcription of nomad, there are minimal integration events in the germline. This suggests that sequestering the nomad DNA copies as ecDNA provides a way for the testes to tolerate transposon activity in the absence of the piRNA pathway. We next examined retrotransposon activity in the somatic cells of Drosophila. While somatic transposon activity is largely considered to be detrimental, we found a unique case where programmed activation of the mdg4 retrotransposon provides a benefit for the response to viral infection in adult flies. This phenotype is dependent on dSTING and Relish, indicating that mdg4 causes an immune response at the pupal stage that affords immune protection in the adult flies. Overall, this work explores the complicated relationship between retrotransposons and their host organisms.