I. K. Zakharov

The endosymbiont Wolbachia in Eurasian populations of Drosophila melanogaster

The endosymbiotic α-proteobacteria Wolbachia is widely spread among arthropods and Filariidae nematodes. This bacterium is transmitted vertically via a transovarian route. Wolbachia is a cause of several reproductive abnormalities in the host species. We analyzed the isofemale lines created using flies collected from Drosophila melanogaster natural populations for infection with the endosymbiont Wolbachia. Wolbachia were genotyped according to five variable markers: the presence of insertion sequence IS5 in two loci, the copy number of two minisatellite repeats, and an inversion. Overall, 665 isofemale lines isolated from the populations of D. melanogaster from Ukraine, Belarus, Moldova, Caucasus, Central Asia, Ural, Udmurtia, Altai, West and East Siberia, and Far East in 1974 through 2005 were used in the work. The samples from Ukrainian, Altaian, and Middle Asian populations were largest. The infection rate of D. melanogaster populations from Middle Asia, Altaian, and Eastern Europe (Ukraine, Moldavia, and Belarus) with Wolbachia amounted to 64, 56, and 39%, respectively. The D. melanogaster population from the Caucasus displayed heterogeneity in the genotypes of this cytoplasmic infection. The Wolbachia genotype wMel, detected in all the populations studied, was the most abundant. The genotype wMelCS2 was always present in the populations from Middle Asia and Altai and was among the rare variants in the D. melanogaster populations from the Eastern Europe. Single instances of the Wolbachia genotype wMelCS occurred in a few flies from the Central Asian and Altai populations, but was not found this genotype in the other regions.

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 y2-717 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 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%.

REARRANGEMENTS AT A HOBO ELEMENT INSERTED INTO THE FIRST INTRON OF THE SINGED GENE IN THE UNSTABLE SN49 SYSTEM OF DROSOPHILA MELANOGASTER

Abstract The cytological structure of the X chromosome and the DNA organisation of the singed locus were examined in five singed bristle mutants of Drosophila melanogaster. These mutants are all derived from the unstable mutant singed-49, isolated from a wild population in the Russian Far East in 1975. Rearrangements were found at a site within the first intron of the singed gene, where a hobo element is inserted in these mutants. One rearrangement, which is associated with a strong bristle phenotype, has an inversion between 2D and the location of singed at 7D, which separates the singed promoter from the singed coding region. Two phenotypically wild-type derivatives have smaller rearrangements within the first intron which do not appear to interfere with singed expression. Two derivatives with bristle phenotypes have more complex rearrangements, and one of them shows a dominant or antimorphic phenotype. DNA blotting and in situ hybridisation experiments show that, in addition to these rearrangements at a hobo element inserted at singed, other hobo elements in these strains have been mobilised. This system is therefore similar to others in which functional hobo elements continue to transpose, resulting in elevated rates of mutation and chromosome rearrangement.

Temporal dynamics and variation of multilocus ISSR-PCR DNA markers in the Uman’ population of Drosophila melanogaster over two decades (1984–2004)

The temporal dynamics of genomic variation in the Uman’ (Ukraine) population of Drosophila melanogaster over the period 1984–2004 was studied using multilocus ISSR markers. Considerable polymorphism of the genomic DNA fragments corresponding to ISSR markers was found in the D. melanogaster population studied: the values of average heterozygosity varied from 0.085 to 0.127 depending on the year. Significant differences in the frequencies of dominant alleles between the samples of different years were recorded for 12 of the 30 DNA fractions detected. These changes are nondirectional and random. The pattern of detected variation suggests the determining influence of gene drift and migration process on the variation of noncoding DNA sequences in the Uman’ population of D. melanogaster.

Polymorphism and differentiation of multilocus DNA markers in natural populations of Drosophila melanogaster

Using multilocus (RAPD) markers, variation and divergence of genomic DNA was examined in two Drosophila melanogaster populations from Russia and three populations from Ukraine. The populations were found to exhibit high polymorphism at RAPD markers. Estimation of genetic distances between the populations showed low differentiation of geographically distant populations of D. melanogaster. Significant gene flow between the D. melanogaster populations was found, which depended on the geographical distance between them.

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.

Transposable elements: Instability of genes and genomes

The role of transposable elements as controlling and destabilizing factors of the genome of germ and somatic cells is considered. The ability of various stress factors, both intragenomic (hybrid dysgenesis, inbreeding, and outbreeding) and environmental (heat and ionizing radiation), to induce transposable element transposition is analyzed.

Cytoplasmic incompatibility in Drosophila melanogaster is caused by different Wolbachia genotypes

The Wolbachia endosymbiont is found among different species of arthropods and some nematodes. Bacteria induce reproductive abnormalities (cytoplasmic incompatibility (CI), parthenogenesis, male-killing and feminization) that promote Wolbachia spread within the host populations. We have managed to estimate the level of CI in Drosophila melanogaster that is caused by three Wolbachia genotypes (wMel, wMelCS and wMelCS2). wMel and wMelCS genotypes are shown to cause a weak CI, whereas wMelCS2 does not demonstrate CI validity. Possible mechanisms involved in Wolbachia prevalence in Drosophila melanogaster populations are discussed.

Comparative Molecular Genetic Study of the Asian Population of Drosophila mercatorum (Diptera; Drosophilidae) at the COI Gene Fragment and the ITS1-ITS2 Region of the rRNA Genes

Drosophila mercatorum is a species of neotropical origin. It is represented by two subspecies, marcatorum and pararepleta. Synanthropic subspecies D. mercatorum mercatorum spread into Eurasia in the mid-20th century, and to date, it is widespread over the territory of Europe and the former Soviet Union. The experiments were performed using the specimens of D. m. mercatorum from natural Asian populations, laboratory stock 2328 of D. mercatorum (displaying some morphological differences from Asian wild-type flies), the specimens of D. busckii and D. virilis, and the COI gene sequence of D. mercatorum from NCBI database, accession number, DQ471607. The specimens were investigated for the variability of the standard DNA sequences used for species identification (the cytochrome oxidase subunit I (COI) gene fragment and the ITS1–ITS2 region of rRNA genes). Sequences of the COI gene fragment from Asian D. m. mercatorum were identical between the specimens, but differed from the sequences of stock 2328, as well as from the NCBI sequence. Asian populations of D. mercatorum and stock 2328 were identical in the ITS1–ITS2 sequences. Low sequence divergence between the COI gene fragments, along with the absence of differences at the ITS1–ITS2 region of the rRNA genes indicate that the difference between the Asian populations of D. m. mercatorum and morphologically different stock 2328 are within the frames of intraspecies divergence.

Effect of high temperature on survival of Drosophila melanogaster infected with pathogenic strain of Wolbachia bacteria

The pathogenic Wolbachia strain wMelPop is detected in the central nervous system, muscles, and retina of Drosophila melanogaster. It reduces the host lifespan by a factor of two. This fact makes it promising for the control of insect pests and vectors of human diseases. Any symbiotic association is exposed to various stress factors: starvation, heat, cold and etc., which affect the symbiont interaction significantly. This study considers the influence of low (16°C) and high (29°C) temperature on the survival and lifespan of D. melanogaster females infected with the Wolbachia strain wMelPop. The ultrastructure of brain cells and distribution of the bacteria in this cells were studied. On day 7 of exposure to high temperature, electron-dense bodies occur in brain cells of the flies, resembling degrading bacteria. The amount of these bodies increases dramatically by day 13 of incubation at 29°C. On the basis of population and EM analysis, we identified the critical period (7–13 days) of high temperature influence, which dramatically decreases the survival of D. melanogaster.