Transposition of mobile genetic elements in interspecific hybrids of Drosophila

Abstract

In situ hybridization of labeled DNA of four mobile dispersed genetic elements (mdg), isolated from D. melanogaster and C. virilis genomes, with polytene chromosomes of the larvae of several Drosophila species has been carried out. The data show that the mdg elements exhibit a high degree of species specificity. The same conclusions are derived from filter hybridization using 32P-labeled D. melanogaster and D. virilis DNA and cloned mdg sequences immobilized on nitrocellulose filters. We attempted to induce transpositions ("jumping") of mdg elements specific for D. virilis chromosomes to the chromosomes of related species (e.g. D. littoralis Meigen) originally lacking the representatives of this family of repeats. For this purpose we produced hybrid stocks with "synthetic" karyotoypes characterized by different combinations of D. virilis homologous chromosomes and "hybrid" chromosomes. In one of such stocks we did find by in situ hybridization the insertion of a D. virilis mdg element into the fifth chromosome of D. littoralis Meigen. The transposition ("jumping") took place in the only region where somatic pairing between the fifth chromosomes of D. virilis and D. littoralis occurs more or less regularly in the hybrids. Since crossing-over in hybrid chromosomes of males is excluded in such "synthetic" stocks, gene conversion may be responsible for this transposition. The possible bearing of the phenomenon observed on the problem of hybrid dysgenesis is discussed.

Behaviour of the transposable elements copia and mdg1 in hybrids between the sibling species Drosophila melanogaster and D. simulans

“…In Drosophila, gonadal atrophy, mutations and elevated rates of chromosomal breakage have also been observed in interspecific crosses between sibling species (Sturtevant, 1939;Naveira & Fontdevila, 1985). In some of these Drosophila hybrids, germline transposition seems to occur (Evgen'ev et al, 1982;Labrador & Fontdevila, 1994) at a rate similar to those reported previously in dysgenic lines of D. melanogaster (Fontdevila, 1993). The causes of transposition induction in interspecific hybrids are not known but the observation that syndromes characteristic of hybrid dysgenesis are common to both intraspecific and interspecific crosses suggests analogies with this phenomenon.…”

“…These data concern the repleta and virilis Drosophila groups in which hybrids were checked only for germinal transpositions and the analyses have been carried out many generations after the hybridization event, sometimes 200 generations after (Evgen'ev et a!., 1982).…”

Evolution of thermotolerance and the heat-shock response: evidence from inter/intraspecific comparison and interspecific hybridization in the virilis species group of Drosophila. I. Thermal phenotype

“…Drosophila thermotolerance and heat-shock proteins in essence, an independent but related phylad (the montana phylad) replicates the patterns of latitudinal and geographic replacement seen in the virilis phylad. Species within each phylad can be crossed with one another to produce partially fertile progeny; moreover, some species belonging to different phylads can also be crossed (Evgenev et al, 1982;Patterson and Stone, 1952). Second, markers present on each chromosome make possible the introgression of a single chromosome or even a portion of a chromosome bearing, for example, the hsp70 gene cluster, whose location is known (Evgenev et al, 1978).…”

What makes transposable elements move in the Drosophila genome?

“…Although experiments on transcription rates of some TEs seem to demonstrate a response to thermal gradients (Strand and McDonald, 1985), there is not a consensus relative to variations in transposition rates under thermal stresses (Junakovic et al, 1986;Ratner et al, 1992;Arnault et al, 1997). Although spontaneous mobilizations of TEs in laboratory lines may occur 'spontaneously' without any evident explanation (Gerasimova et al, 1985;Biémont et al, 1987), dysgenic crosses (Picard, 1976;Kidwell et al, 1977;Petrov et al, 1995), hybrid crosses (Evgen'ev et al, 1982;Labrador and Fontdevila, 1994;Labrador et al, 1999) and colonization events (Wisotzkey et al, 1997;Labrador et al, 1998;Vieira, 1999;García Guerreiro and Fontdevila, 2001;García Guerreiro et al, 2008) can greatly increase transposition rates of some TEs.…”