Characterization of a hypermutable strain of Drosophila simulans

Can insect assemblages tell us something about the urban environment health?

If we consider Drosophilidae, the answer to the question above is yes. Many research groups in Brazil and abroad have been showing that assemblages of flies of this family can reflect environmental alteration levels caused by urbanization, and/or by other human disturbances. I will present here a summary of our findings in Drosophilidae assemblages reflecting different degrees of environmental perturbation. These studies were done by graduate students of two post graduate programs of UFRGS, under my supervision, along several decades. I will also present the results stemming from the effort of other Brazilian Drosophilid study groups while identifying the members of those assemblages in different Biomes. As a result of those field studies, several biological invasions were detected and many new important biological problems arose prone to be investigated by genetic, molecular biology and other related approaches.

Drosophila relics hobo and hobo-MITEs transposons as raw material for new regulatory networks

Hypermutable strains of Drosophila simulans have been studied for 20 years. Several mutants were isolated and characterized, some of which had phenotypes associated with alteration in development; for example, showing ectopic legs with eyes being expressed in place of antennae. The causal agent of this hypermutability is a non-autonomous hobo-related sequence (hoboVA). Around 100 mobilizable copies of this element are present in the D. simulans genome, and these are likely mobilized by the autonomous and canonical hobo element. We have shown that hoboVA has transcription factor binding sites for the developmental genes, hunchback and even-skipped, and that this transposon is expressed in embryos, following the patterns of these genes. We suggest that hobo and hobo-related elements can be material for the emergence of new regulatory networks.

The hobo transposon and hobo-related elements are expressed as developmental genes in Drosophila

Transposable elements comprise a significant part of genomes and are involved in their evolvability. The hobo element is found as an active class II transposable element in Drosophila melanogaster that is able to induce gonadal dysgenesis. Some hobo-related sequences (hRSs) are thought to be relics of old "hobo" invasions, and are therefore ancient genomic constituents. However, some of these hRSs are still mobile. The present study analyzed the expression pattern of hobo and a particular type of hRSs, hobo(VAHS). Both elements were shown to be expressed as sense and antisense mRNA transcripts. Expression analysis in whole mount embryos revealed a pattern similar to that of some developmental regulatory genes. Here we suggest that cis-regulatory sequences similar to those in developmental genes exist in hobo sequences. Therefore, hobo mobilization may contribute to the development of new regulatory networks during genomic evolution.

Mobilization of a hobo-related sequence in the genome of Drosophila simulans

The hobo transposable element can occur under three forms in the Drosophila genome: as a complete element (also called canonical), as internally deleted copies, or as hobo-related sequences (relics). Some evidence indicated that canonical elements and internally deleted copies are recent acquisitions of Drosophila genomes, while the "relics" are old components, normally degenerated and immobile. Here we present the characterization of a hobo-related sequence, found in the genome of a hypermutable strain of D. simulans, which insertion into the white locus raised a de novo white mutation. It is a shorter hobo related element presenting, overall, roughly 18% of divergence at the DNA level from the canonical hobo, with many indels that make clear this element is defective. However, its ITRs and flanking regions are extremely conserved. This is the first hobo "relic" showed to be mobilizable. We suggest, and point up some evidences, toward the idea that this sequence could have been mobilized by the canonical element. The presence of a similar "relic" element in D. sechellia allows us to suggest that these elements have been maintained mobilizable since the time of divergence between these species.

Analysis of phenotypes altered by temperature stress and hipermutability in Drosophila willistoni

Drosophila willistoni (Sturtevant, 1916) is a species of the willistoni group of Drosophila having wide distribution from the South of USA (Florida) and Mexico to the North of Argentina. It has been subject of many evolutionary studies within the group, due to its considerable ability to successfully occupy a wide range of environments and also because of its great genetic variability expressed by different markers. The D. willistoni 17A2 strain was collected in 1991 in the state of Rio Grande do Sul, Brazil (30°05'S, 51°39'W), and has been maintained since then at the Drosophila laboratory of UFRGS. Different to the other D. willistoni strains maintained in the laboratory, the 17A2 strain spontaneously produced mutant males white-like (white eyes) and sepia-like (brown eyes) in stocks held at 17°C. In order to discover if this strain is potentially hypermutable, we submitted it to temperature stress tests. Eighteen isofemale strains were used in our tests and, after the first generation, all the individuals produced in each strain were maintained at 29°C. Different phenotype alterations were observed in subsequent generations, similar to mutations already well characterized in D. melanogaster (white, sepia, blistered and curly). In addition, an uncommon phenotype alteration with an apparent fusion of the antennae was observed, but only in the isofemale line nº 31. This last alteration has not been previously described as a mutation in the D. melanogaster species. Our results indicate that the D. willistoni 17A2 strain is a candidate for hypermutability, which presents considerable cryptic genetic variability. Different factors may be operating for the formation of this effect, such as the mobilization of transposable elements, effect of inbreeding and alteration of the heat-shock proteins functions.