Polytene chromosome maps in four species of tsetse flies Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans (Diptera: Glossinidae): a comparative analysis.

Photographic polytene chromosome maps from pupal trichogen cells of four tsetse species, Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans were constructed and compared. The homology of chromosomal elements between the species was achieved by comparing banding patterns. The telomeric and subtelomeric chromosome regions were found to be identical in all species. The pericentromeric regions were found to be similar in the X chromosome and the left arm of L1 chromosome (L1L) but different in L2 chromosome and the right arm of L1 chromosome (L1R). The L2 chromosome differs by a pericentric inversion that is fixed in the three species, G. pallidipes, G. morsitans morsitans and G. m. submorsitans. Moreover, the two morsitans subspecies appeared to be homosequential and differ only by two paracentric inversions on XL and L2L arm. Although a degree of similarity was observed across the homologous chromosomes in the four species, the relative position of specific chromosome regions was different due to chromosome inversions established during their phylogeny. However, there are regions that show no apparent homology between the species, an observation that may be attributed to the considerable intra--chromosomal rearrangements that have occurred following the species divergence. The results of this comparative analysis support the current phylogenetic relationships of the genus Glossina.

Photographic polytene chromosome maps for Glossina morsitans submorsitans (Diptera: Glossinidae): cytogenetic analysis of a colony with sex-ratio distortion.

Photographic polytene chromosome maps from trichogen cells of pharate adult Glossina morsitans submorsitans were constructed. Using the standard system employed to map polytene chromosomes of Drosophila, the characteristic landmarks were described for the X chromosome and the two autosomes (L1 and L2). Sex-ratio distortion, which is expressed in male G. m. submorsitans, was found to be associated with an X chromosome (X8) that contains three inversions in each arm. Preliminary data indicate no differences in the fecundity of X(A)X(A) and X(A)X(B) females, but there are indications that G. m. submorsitans in colonies originating from Burkina Faso and Nigeria have genes on the autosomes and (or) the Y chromosome that suppress expression of sex-ratio distortion.

Differential regulation of P and hobo mobile elements by two laboratory strains of Drosophila melanogaster.

Analysis of the transposition behaviour of the P and hobo elements borne by the 31.1/CyL4 MRF (P), 23.5 delta/CyL4 MRF (hobo) and 23.5*/Cy MRF (hobo) strains in the progeny of dysgenic crosses with two ME laboratory strains (Berlin-k and dp b cn bw) at 25 degrees C revealed that: (a) the two ME laboratory strains affect differently the transposition rates of P and hobo elements. More precisely, P element transposition is higher in heterozygotes with dp b cn bw than in those with Berlin-k. In contrast, the transposition rate of hobo elements is higher in Berlin-k than in dp b cn bw heterozygotes. (b) Like P, hobo has the potential to transpose at high frequencies and to nonhomologous chromosomes. (c) The dysgenically inactive hobo elements of the 31.1 MRF strain transpose more frequently than the dysgenically active hobo elements of the 23.5 MRF strains in certain crosses. (d) There are insertion hot spots for P and hobo elements. For the P elements there are enough data to suggest that the insertion hot spots are different in the two EM strains. The data are discussed on the basis of the involvement of putative host factors in transposition regulation of the P and hobo elements.

Distribution of P and hobo mobile elements in environmentally manipulated long-term Drosophila melanogaster cage populations.

The copy number and the chromosome positions of the P and hobo insertions were determined by means of in situ hybridization to polytene chromosomes, in five long-term Drosophila melanogaster cage populations kept for 18 years under different culture conditions (temperature and relative humidity). The analysis revealed that the copy number of both P and hobo elements were similar between the populations kept under the same culture conditions and significantly different among the populations maintained under different culture conditions. A tendency for similar distribution of these elements along the major chromosome arms was also observed in the populations of the same environmental manipulation. The distribution of the insertions along the chromosomes was not random for both the P and hobo elements; sites with high insertion frequencies were found (hot spots of occupation). Some of them were common in all cage populations while others were characteristic of the populations kept under the same conditions. Finally, fixed sites of occupation were also observed in all populations and refer mostly to hobo distribution. The data are discussed on the basis of the possible involvement of the P and hobo elements, in some way, to the adaptation process and speciation.

A three-season comparative analysis of the chromosomal distribution of P and hobo mobile elements in a natural population of Drosophila melanogaster.

An analysis on the chromosomal distribution of P and hobo elements in a Greek natural population extending over three seasons showed that the P elements were more abundant in the population than hobos. The copy number distribution per chromosome arm was in general random. The X chromosome had more P copies and the 3R arm more hobos in all three collections. Significant seasonal differences were not observed for these two elements in relation to the total number of insertions per haploid genome. There were, however, certain seasonal differences. They involved the copy number variability, the intra-arm distribution, the distribution along the chromosomes, and the spread and occupancy frequencies. There were no significant differences between the copy numbers of the two elements carried by the standard and the corresponding inverted regions for a number of inversions found in the population. Finally, three out of the five cosmopolitan inversions were found to have hobo insertions at or very near the one of the two breakpoints. Three out of the total had P insertions at or very near the one of the two breakpoints in some squashes and two of the three endemic inversions had a hobo insertion at or very near the one breakpoint, while the third had a P insertion.

Characterization of MR (P) strains of Drosophila melanogaster: the number of intact P elements and their genetic effect.

To study the effect of mutagenic/carcinogenic agents on P-element transposition, the P strains used should be defined, especially with respect to the number of intact and functional P elements present. In this investigation, the relation between the number of complete P elements present in dysgenic males and P-insertion mutagenesis was studied in several MR (P) strains. The main conclusions from this investigation are: (1) Complete P elements can be present in the genome without genetic activity (even in a 'dysgenic' cross). As a consequence, the number of complete P elements present in particular dysgenic flies, is not necessarily an indication of their dysgenic genetic activity. (2) The MR-h12/Cy strain carries two complete P elements, one on the X chromosome without and one on the MR chromosome with genetic activity (making this strain most suitable for studies on P-transposition mechanisms).

Seasonal analysis of 23.5 MRF (hobo) and P-M hybrid dysgenesis determinants in a Greek natural population of Drosophila melanogaster.

Genetic analysis of 23.5 MRF (hobo) and P-M hybrid dysgenesis determinants in a Greek natural population in six collections over 24 months, showed the existence of hobo activity in the population at rates higher than P activity. Moreover, seasonal differentiation in hobo GD-sterility potential and hobo repressor abilities were observed. The P activity was low in the population but some tendency for seasonal differentiation of the cytotype was detected. The two systems operate independently in nature. Analysis of isofemale lines, established from inseminated wild-caught females, showed rapid differentiation of their hybrid dysgenesis determinants in the laboratory. This shows that results obtained from isofemale lines do not necessarily reflect the original population structure. The seasonal differentiation may be correlated with seasonal environmental factors, and may be attributed to differences in structure and function of the elements that consequently affect their regulation and transposition.

The P-M and the 23.5 MRF (hobo) systems of hybrid dysgenesis in Drosophila melanogaster are independent of each other.

Strains of Drosophila melanogaster bearing the male recombination factor 23.5 MRF induce hybrid dysgenesis in a way which is highly reminiscent of the P-M system, and, most probably, causally related to the activity of the transposable element hobo. We have investigated potential interactions between the two systems of hybrid dysgenesis by studying mixed lines derived from bidirectional crosses between 23.5 MRF and P strains, and analyzed their potentials to induce or suppress the occurrence of dysgenesis. All new lines possess the P induction abilities, as determined by two different procedures, and have also acquired a P cytotype. In contrast, some of them lost their ability to induce the non-P-M dysgenesis, as well as to suppress the action of 23.5 MRF. This loss of the 23.5 MRF induction abilities parallels the selective loss of full-length hobo elements from the genome of these lines, providing further substantiation to the notion that the 23.5 MRF activity is directly linked to this transposable element.

Cohabitation of KP and full-length P elements in the genome of MR strains inducing P-M-like hybrid dysgenesis in Drosophila melanogaster.

P strains of Drosophila melanogaster are characterized by the presence of both full-length and deletion derivatives of the transposable element P in their genome, and by their ability to induce the syndrome of hybrid dysgenesis among the progeny of certain intra-strain crosses, when introduced through the male parents. In contrast, strains belonging to the M' class, and which were also found to bear P element-homologous sequences, lack this ability and this has been attributed to the presence in the genome of most of these strains of a distinct class of deletion derivatives termed KP, which can suppress the action of functional P factors. Here we demonstrate that KP elements are present, next to full-length ones, in the genome of at least three strains which induce P-M-like dysgenic symptoms, including GD sterility. KP elements form the majority of the P-homologous sequences in the strains MR-h12, 23.5/CyL4 and the latter's derivative 23.5*/Cy. While the first one is a genuine P strain and the second one depicts a strong P cytotype, the third is a genuine M' strain. The hybrid dysgenesis induced by the two 23.5 MRF strains seems to be due, not primarily to the P elements, but to the action of hobo elements.

The instability of the TE-like mutation Dp(2:2)GYL of Drosophila melanogaster is intimately associated with the hobo element.

We have characterized molecularly several derivatives of the TE-like element Dp(2:2)GYL of Drosophila melanogaster. This highly unstable mutation occurred in a dysgenic cross involving the 23.5 MRF chromosome, and represents an inverted insertional duplication of approximately 130 polytene bands of the paternal 2L, at 50AB of the right arm of the maternal 2R. The instability of this mutation is characterized by deletion of some of duplicated material, by the induction of rearrangements in its vicinity and by the transposition of parts of the original element. We have found that the mobile element hobo is present at , or very near, the breakpoints of all GYL derivatives analysed, demonstrating that hobo is not only active in dysgenic crosses, but also that it can promote genetic instability reminiscent of transposable elements (TE).

hobo is responsible for the induction of hybrid dysgenesis by strains of Drosophila melanogaster bearing the male recombination factor 23.5MRF.

The male recombination factor 23.5MRF, isolated ten years ago from a natural Greek population of Drosophila melanogaster, has been shown to induce hybrid dysgenesis when crossed to some M strains, in a fashion slightly different from that of most P strains. Furthermore, it was recently shown that 23.5MRF can also induce GD sterility when crossed to specific P strain females (e.g., Harwich, pi 2 and T-007). In these experiments, the P strains mentioned behaved like M strains in that they did not induce sterility in the reciprocal crosses involving 23.5MRF. We extended the analysis to show that 23.5MRF does not destabilize snW(M) and that a derivative with fewer full-length P elements behaves like an M strain toward the same P strains and still retains its dysgenic properties in the reciprocal crosses. We show that there is a strong correlation between the site of dysgenic chromosomal breakpoints induced by 23.5MRF and the localization of hobo elements on the second chromosome, and also that hobo elements are found associated with several 23.5MRF induced mutations. These results suggest that hobo elements are responsible for the aberrant dysgenic properties of this strain, and that they may express their dysgenic properties independent of the presence of P elements.

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.

Site-specific breaks induced by the male recombination factor 23.5 MRF in Drosophila melanogaster.

The male recombination second chromosome 23.5 MRF was isolated from the same Greek population (Southern Greece) in which some years ago 31.1 MRF was discovered. A cytological analysis was carried out on the salivary gland chromosomes of the third-instar larvae deriving from crosses of males heterozygous for the 23.5 MRF chromosome II with various laboratory strains, with the following findings. (a) 23.5 MRF caused all types of chromosome rearrangements most of which involved chromosome II. (b) Discernible aberrations were not detected on the X-chromosome or the left arm of chromosome II. (c) The distribution of the break-points involving the second chromosome showed that 23.5 MRF induced breaks at specific sites on this chromosome. (d) The rearrangements induced were not stable; some were lost during the study, and new arrangements were generated. (e) Evidence was provided that 23.5 MRF was able to induce chromosome breakage in mitotic cells of salivary-gland chromosomes as well. (f) A comparison of the present results with data from the same natural population was made, and hypotheses explaining the present results are discussed.

Unstable chromosome rearrangements associated with male recombination in Drosophila melanogaster.

The male recombination second chromosome 23.5 MRF isolated from the same Greek natural population with the second chromosome 31.1 MRF induced high frequencies of chromosome rearrangements, including specific deletions and duplications. A number of the duplications recovered were found to be highly unstable. The duplicated chromosome segments of the unstable duplications had been either completely or partially lost. The loss occurred most probably by excision of the corresponding segments and not by unequal crossing-over involving sister chromatids. As regards the unstable deletions, they became either shorter or longer or they showed complete restoration. Hypotheses explaining the high frequencies of the unstable chromosome mutations detected are discussed.

Differences in the induction of specific deletions and duplications by two male recombination factors isolated from the same Drosophila natural population.

2 male recombination factors, the 31.1 and 23.5 MRF isolated from the same natural population, were tested for the induction of specific deletions and duplications in the regions b and cn of the second chromosome. Genetic and cytological analysis of the double recombinants derived from appropriate crosses of the 23.5/CyL4 and 31.1/CyL4 strains with the dp b cn bw; ve revealed the following differences between the 2 MRFs. (1) The 23.5 MRF induced (a) higher frequencies of double "putative' recombinants, which often appeared in large clusters, (b) large clusters of single recombinants and (c) cases were the wild-type and sometimes the dp b cn bw phenotype were not produced among the F2-F10 progeny. Such cases were never found with 31.1 MRF. (2) The b and cn recombinants carried deletions whereas the reciprocal dp cn bw and dp b bw had duplications of the corresponding regions. Each cluster carried an identical deletion or duplication. (3) The breakpoints of the 22 cn deletions detected were distributed in the polytene region 42E-44C. On the basis of the cn deletions, we mapped the cn and so loci to polytene intervals 43E6-16 and 42E3.4--43C5.6, respectively. Hypotheses explaining the different results obtained by the 2 factors are discussed.

Induction of somatic and male crossing-over by bleomycin in Drosophila melanogaster.

Bleomycin (BLM) is well known as an antibiotic as well as for its antineoplastic activity. A clinical preparation of BLM was tested for its recombinogenicity in a higher eukaryotic organism, Drosophila melanogaster. Feeding of the F1 larvae on a medium with BLM increased somatic crossing-over spots on female tergites and induced recombination in male germ cells. However, nonlinear dose-response curves were obtained. Malformed tergites were also observed in females treated with BLM.

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

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/CyL4 strain can also induce male recombination.