Evolutionary history and classification of Micropia retroelements in Drosophilidae species

Abstract

Current knowledge indicates TEs have been shaping the evolution of genomes and host species, contributing to the creation of new genes and promoting rearrangements frequently associated with new regulatory networks. Support for these hypothesis frequently result from studies with model species, and Drosophila detaches as a great model organism to the study of TEs. Micropia belongs to the Ty3/Gypsy group of LTR retroelements, and comprises one of the least studied Drosophila transposable elements. In this study, we assessed the evolutionary history of Micropia within Drosophilidae, while trying to assist in the classification of this TE. At first, we analyzed its presence in the genome of several species from natural populations and then, based on searches within genomic databases, we retrieved Micropia-like sequences from distinct Drosophilidae species genomes. We expanded the knowledge of Micropia distribution within Drosophila, and detected an array of divergent sequences, which allowed subdividing this retroelement in 20 subfamilies. Even so, a patchy distribution of Micropia sequences within the Drosophilidae phylogeny could be identified combined with incongruences of the species and the Micropia phylogenies. Comparing dS values between Micropia and host nuclear sequences, we found several cases of unexpected high levels of similarity between Micropia sequences found in divergent species. All these findings propose a hypothesis to the evolution of Micropia within Drosophilidae, including several VTTs and HTTs events, associated to ancestral polymorphisms and recurrent Micropia sequences diversification.