Characterization of natural populations of Drosophila melanogaster with regard to the hobo system: a new hypothesis on the invasion

Paternal Induction of Hybrid Dysgenesis in Drosophila melanogaster Is Weakly Correlated with Both P-Element and hobo Element Dosage

Transposable elements (TEs) are virtually ubiquitous components of genomes, yet they often impose significant fitness consequences on their hosts. In addition to producing specific deleterious mutations by insertional inactivation, TEs also impose general fitness costs by inducing DNA damage and participating in ectopic recombination. These latter fitness costs are often assumed to be dosage-dependent, with stronger effects occurring in the presence of higher TE copy numbers. We test this assumption in Drosophila melanogaster by considering the relationship between the copy number of two active DNA transposons, P-element and hobo element, and the incidence of hybrid dysgenesis, a sterility syndrome associated with transposon activity in the germline. By harnessing a subset of the Drosophila Genetic Reference Panel (DGRP), a group of fully-sequenced D. melanogaster strains, we describe quantitative and structural variation in P-elements and hobo elements among wild-derived genomes and associate these factors with hybrid dysgenesis. We find that the incidence of hybrid dysgenesis is associated with both P-element and hobo element copy number in a dosage-dependent manner. However, the relationship is weak for both TEs, suggesting that dosage alone explains only a small part of TE-associated fitness costs.

Hermes transposon distribution and structure in Musca domestica

Hermes are hAT transposons from Musca domestica that are very closely related to the hobo transposons from Drosophila melanogaster and are useful as gene vectors in a wide variety of organisms including insects, planaria, and yeast. hobo elements show distinct length variations in a rapidly evolving region of the transposase-coding region as a result of expansions and contractions of a simple repeat sequence encoding 3 amino acids threonine, proline, and glutamic acid (TPE). These variations in length may influence the function of the protein and the movement of hobo transposons in natural populations. Here, we determine the distribution of Hermes in populations of M. domestica as well as whether Hermes transposase has undergone similar sequence expansions and contractions during its evolution in this species. Hermes transposons were found in all M. domestica individuals sampled from 14 populations collected from 4 continents. All individuals with Hermes transposons had evidence for the presence of intact transposase open reading frames, and little sequence variation was observed among Hermes elements. A systematic analysis of the TPE-homologous region of the Hermes transposase-coding region revealed no evidence for length variation. The simple sequence repeat found in hobo elements is a feature of this transposon that evolved since the divergence of hobo and Hermes.

Genomic environment influences the dynamics of the tirant LTR retrotransposon in Drosophila

Combining genome sequence analysis and functional analysis, we show that some full-length copies of tirant are present in heterochromatic regions in Drosophila simulans and that when tested in vitro, these copies have a functional promoter. However, when inserted in heterochromatic regions, tirant copies are inactive in vivo, and only transcription of euchromatic copies can be detected. Thus, our data indicate that the localization of the element is a hallmark of its activity in vivo and raise the question of genomic invasions by transposable elements and the importance of their genomic integration sites.

High polymorphism of TPE repeats within natural populations of Drosophila melanogaster: a gradient of the 5TPE hobo element in Western Europe

To find out whether the polymorphism of TPE repeats of the hobo transposable element observed in some populations results from polymorphism within flies or from variability between flies, or both, we carried out isofemale line analyses of 25 populations. We found that polymorphic populations result from the presence of polymorphic flies combined with interfly variability within these populations. The fact that populations display different levels of polymorphism, i.e., different types of element and different frequencies of polymorphic flies, can be used to differentiate between qualitatively identical populations. This showed that the geographical structuring previously observed is reinforced and, in particular, that the western European populations, which have 3TPE and 5TPE elements, display a centrifugal decrease in the frequency of 5TPE hobo elements which start in western France. This gradient supports the hypothesis of a dynamic invasion by this type of elements: a total invasion by 3TPE elements, followed by further invasions involving other types of hobo elements. Moreover, the analysis of numerous sequences in current populations revealed the existence of seven types of never-previously described hobo elements with regard to TPE repeats. This diversity, which contrasts with the conservation of other parts of the element, highlights the high mutation rate of the S region.