Positive correlation between the occurrence of chromosome breakage and the induction of point mutations associated with male recombination 31.1 MRF system of hybrid dysgenesis in Drosophila melanogaster

One of the weak singed (snw) mutations, induced by the 31.1 MRF in the X-chromosome of a laboratory strain, is highly unstable, often changing to either a strong expression (snst) or reverting to wild type (sn+). The present study shows that the X-chromosome carrying the (snw) mutation and the X-chromosome carrying one of the snst alleles derived from the snw mutation generate different frequencies of deletions associated with the w locus. Moreover, they produce different frequencies of mutations associated with the w locus in males after the reintroduction of the 31.1 MRF second chromosome. The occurrence of the deletions and the induction of the mutations are positively correlated and increase when flies are raised at a higher temperature. These data indicate that the induction of the w mutations follows the generation of chromosome breaks in the w locus. The break-points of the recovered deletions occurred in specific sites in the 3C subdivision. Furthermore both snw and snst X-chromosomes induce different frequencies of non-disjunction in females depending on the culture temperature and the genetic background. The present data also show that the 23.5 MRF second chromosome which exhibits specific differences in its activities from the 31.1 MRF is unable to induce w mutations. This fact supports our previous indications that the 31.1 MRF and the 23.5 MRF are not identical.     

Ability of the male recombination factor 31.1 MRF to be transposed to another chromosome in Drosophila melanogaster.

Summary By classical genetic experiments, evidence is provided that the male recombination factor, 31.1 MRF, has the ability to be transposed to another chromosome. The procedure by which the transposition occurs must be different from that of classical crossing over. It appears that transposition occurs only when the factor is active in male germ cells. Moreover, the factor appears to be able to undergo successive transpositions. Furthermore, the integration sites of the factor, when transposed into another chromosome, may not be completely random. Finally, the third chromosome of the 31.1/Cy L ⁴ strain can also induce male recombination.     

Mobilization of hobo elements residing within the decapentaplegic gene complex: suggestion of a new hybrid dysgenesis system in Drosophila melanogaster

We present results demonstrating that the hobo family of transposable elements can promote high rates of chromosomal instability. Using strains with a hobo element inserted within the decapentaplegic gene complex (DPP-C), we have recovered numerous DPP-C mutations involving chromosomal rearrangements and deletions with one endpoint in the vicinity of the pre-existing hobo element. This hypermutability occurred in the germ lines of hybrid progeny from crosses involving strains containing hobo elements to strains lacking them. In some crosses, the offspring had rudimentary gonads, reminiscent of GD sterility. The germline hypermutability and infertility are similar to those produced by P-element-mediated hybrid dysgenesis. Given the many genetic and molecular similarities of the P and hobo systems, we propose that a system analogous to P-M hybrid dysgenesis has been activated in the hobo+ X hobo- crosses.     

Sequences homologous to the hobo transposable element in E strains of Drosophila melanogaster

Hobo is one of the three Drosophila melanogaster transposable elements, together with the P and I elements, that seem to have recently invaded the genome of this species. Surveys of the presence of hobo in strains from different geographical and temporal origins have shown that recently collected strains contain complete and deleted elements with high sequence similarity (H strains), but old strains lack hobo elements (E strains). Besides the canonical hobo sequences, both H and E strains show other poorly known hobo-related sequences. In the present work, we analyze the presence, cytogenetic location, and structure of some of these sequences in E strains of D. melanogaster. By in situ hybridization, we found that euchromatic hobo-related sequences were in fixed positions in all six E strains analyzed: 38C in the 2L arm; 42B and 55A in the 2R arm; 79E and 80B in the 3L arm; and 82C, 84C, and 84D in the 3R arm. Sequence comparison shows that some of the hobo-related sequences from Oregon-R and iso-1 strains are similar to the canonical hobo element, but their analysis reveals that they are substantially diverged and rearranged and cannot code for a functional transposase. Our results suggest that these ubiquitous hobo-homologous sequences are immobile and are distantly related to the modern hobo elements from D. melanogaster.     

Induction of male recombination in Drosophila melanogaster by chemical treatment

Acridine orange (AO), ethidium bromide (EB), ethyl methanesulfonate (EMS) and 8- ethoxycaffeine ( EOC ) were fed to larvae of Drosophila melanogaster in order to test their capacity for the induction of meiotic recombination in males. Our results show that AO and EB increase significantly the male recombination frequencies. No relationship between chromosome breakage ability and male recombination induction was found since EMS and EOC , two effective chromosome-breaking agents, were unable to increase the male recombination.     

The effect of gamma-radiation on induction of the hobo element transposition in Drosophila melanogaster

The transposition frequency of the hobo mobile element in four successive generations of Drosophila melanogaster strain y2-717 after an acute gamma-irradiation with a dose of 30 Gr amounted to 7.5 x 10(-4) per site per genome per generation. Under the same conditions, PCR analysis of the genomic DNA of y2-717 flies detected new variants of defective hobo sequence. No changes in the hobo localization and PCR products compared with the control were detected in the case of single irradiation with doses of 3 and 30 Gr. The localizations of hobo element on polytene chromosomes of y2-717 strain did not change during 11 generations after five exposures of flies to 30 Gr. Irradiation of a highly unstable D. melanogaster strain y+743 did not increase the number of families with mutant progeny, yet increased the total number of mutant descendants almost twofold, from 5 to 9%.     

Asymmetric exchange is associated with P element induced male recombination in Drosophila melanogaster

Spontaneous meiotic recombination events do not normally occur in the male germ line of Drosophila melanogaster. However, such events are induced in males when a P transposable element or a source of P element encoded transposase protein is present in its genome. This report concerns a molecular analysis of the meiotic exchanges that were induced in the male Drosophila by P elements within a genetically marked region of the third chromosome. The marked region also harbors a single P-element called P(lArB). Fifty-six percent of the P(lArB) region crossovers indicated some alterations in the P element 5' fragment. Such alterations appear to be related to asymmetric or unequal genetic exchanges. Finally, P(lArB) excision was found to be independent of P(lArB) region crossover events.     

Alteration of chromosome structure in ovarian nurse cells of Drosophila melanogaster by hybrid dysgenesis

The impact of hybrid dysgenesis on the chromosome structure of Drosophila melanogaster ovarian nurse cells was studied. In the examined lines and interlinear hybrids (including those yielded by dysgenic crosses in the P-M and I-R systems of hybrid dysgenesis), disturbed chromosome synapsis was revealed. The disturbance was somewhat similar to that observed in interspecific hybrids. Quantitative analysis showed that the mean frequency of nuclei with defective chromosome pairing ranged from 60.4 to 76%. FISH analysis of ovarian nurse chromosomes of Canton S x Berlin hybrids showed differences in the label localization in asynaptic homologs of arm 2L, which probably results in disrupted homolog pairing and reveal interlinear differences in localization of mobile genetic elements. Our results conform to Sved's model stating that hybrid dysgenesis is based on disorganization of the germline nuclear space.     

The effect of γ-radiation on induction of the hobo element transposition in Drosophila melanogaster

The transposition frequency of the hobo mobile element in four successive generations of Drosophila melanogaster strain y ^2-717 after an acute γ-irradiation with a dose of 30 Gr amounted to 7.5 × 10^?4 per site per genome per generation. Under the same conditions, PCR analysis of the genomic DNA of y ^2-717 flies detected new variants of defective hobo sequence. No changes in the hobo localization and PCR products compared with the control were detected in the case of single irradiation with doses of 3 and 30 Gr. The localizations of hobo element on polytene chromosomes of y ^2-717 strain did not change during 11 generations after five exposures of flies to 30 Gr. Irradiation of a highly unstable D. melanogaster strain y ⁺⁷⁴³ did not increase the number of families with mutant progeny, yet increased the total number of mutant descendants almost twofold, from 5 to 9%.     

Transposition of the hobo element in Drosophila melanogaster somatic cells

Somatic mutation and recombination test on wing cells of Drosophila melanogaster showed that the recombination frequency in the somatic tissues of strains studied correlated with the presence of a full-length copy of the hobo transposable element in the genome. Transposition of hobo in somatic tissue cells at a frequency 3.5 x 10-2 per site per X chromosome was shown by fluorescence in situ hybridization with salivary gland polytene chromosomes of larvae of one of the D. melanogaster strains having a full-length hobo copy.     

Transposition of the hobo element in Drosophila melanogaster somatic cells

Somatic mutation and recombination test on wing cells of Drosophila melanogaster showed that the recombination frequency in the somatic tissues of strains studied correlated with the presence of a full-length copy of the hobo transposable element in the genome. Transposition of hobo in somatic tissue cells at a frequency 3.5 × 10^?2 per site per X chromosome was shown by fluorescence in situ hybridization with salivary gland polytene chromosomes of larvae of one of the D. melanogaster strains having a full-length hobo copy.     

Characteristic features of induced mutagenesis in hybrid dysgenesis systems of Drosophila melanogaster

The mutagenic effect of low-dose gamma-irradiation was studied in Drosophila melanogaster systems of hybrid dysgenesis by estimating polytene chromosome rearrangements, recombination frequency, and viability at the embryonic and postembryonic developmental stages. A dose of gamma-irradiation which had no effect detectable by routine line crossing proved to significantly reduce the number of recombinants in the H-E and P-M systems and mortality at postembryonic stages. However, this combined effect was obtained if irradiation followed transposition, i.e., it depended on the application sequence of the mutagenic factors. The reverse order of the mutagenic treatment led to summation of the effects: as compared to either control, the frequencies of the dominant allele mutations as well as the larval and pupal mortality in F2 increased significantly (at the level of 99.9%). This allowed us to estimate the contribution of extremely low-dose gamma-irradiation into the mutagenic effect, which was impossible under routine conditions.