[Molecular and genetic description of a new hypomorphic mutation of Trithorax-like gene and analysis of its effect on Drosophila melanogaster oogenesis].

The Trithorax-like (Trl) gene of Drosophila melanogaster encodes the multifunctional protein GAGA involved in many cellular processes. We have isolated and described a new hypomorphic mutation of the Trl gene--Trl(en82). The mutation is the insertion of a 1.4 kb P-element into the 5' untranslated region. Trl expression decreased in the ovaries of mutant flies by about 30%; however, it caused abnormalities. The Trl(en82) mutation combined with the null allele of Trl caused female sterility: the females laid a few small eggs with abnormal shape. Many egg chambers demonstrated abnormalities in the Trl(en82) mutants: the oocyte had a regular shape and intruded into the egg chamber region with nurse cells; the rapid transport of nurse cell cytoplasm into the oocyte was disturbed, which resulted in the "dumpless" phenotype of the chambers in mutants; follicular cells often did not completely cover the oocyte and concentrated on its posterior end; and the migration of centripetal cells was affected. We propose that the sterility of the Trl(en82) females is due to the abnormal functioning of follicular cells resulting from low Trl expression. This proposal is confirmed by normalizing the mutant phenotype of Trl(en82) females after the transfection of Trl cDNA. Note that even an insignificant decrease in Trl expression in such females seriously affected the somatic cell functioning, while a significant decrease in its expression in strong hypomorphic mutants affected both somatic and germline cells in the egg chambers.

[The effect of genetic environment on locus-specific instability of the yellow gene in Uman' population of Drosophila melanogaster].

The effects of genotype of the laboratory strains, C(1)DX, ywf/Y, 23.5 MRF/CyL4, and C(1)DX,yf; pi2, on locus-specific instability in the yellow gene of the strains y(2-717, y(2-715), and y(2-700 ) from Uman' population of Drosophila melanogaster was studied. Crosses of the males from Uman'-derived lines with the C(1)DX, ywf/Y females yielded a cascade of derivatives, mostly consisting of y+ and y2 alleles, while their crosses with the 23.5 MRF/CyL4 and C(1)DX,yf; pi2 females mostly resulted in the appearance of y+ and y(1) derivatives. The genomes of laboratory strains used in the study contained the full-sized hobo elements, which could differ from one another relative to the structure of variable region and affinity to different DNA sequences.

[Behavior of hobo and P transposons in yellow2-717 unstable line of Drosophila melanogaster and its derivatives after crossing with a laboratory strain].

Using fluorescent in situ hybridization technique (FISH), the frequency of hobo and P mobile elements transpositions on X chromosomes from the y2-717, isolated from the Uman' population of Drosophila melanogaster, as well as from its phenotypically normal and mutant derivatives, obtained as a result of crosses the males examined with the C(I)DX, ywf/Y females, was evaluated. It was demonstrated that the maximum frequency of hobo transpositions on X chromosomes of the males from derivative strains, subjected to repeated hobo-dysgenic crosses reached a value of 1.2 x 10(-2) per site per X chromosome per generation. The number of hobo copies in male X chromosomes from derivative strains was 3 times higher than in the original initial strain. Furthermore, the "old" hobo sites remained unchanged. In derivative strains, the frequency of hobo insertions was higher than that of excisions. One of the derivative strains, y1t-717alk3-2, was characterized by high intra-strain instability of hobo element localization. In the y2-717a1k3 and y1t-717alk3-2 strains a large inversion, In(1)1B; 13CD, was described. At the absence of the full-sized P element in the strains involved in crosses, maximum frequency of P element transpositions in the derivative strains reached a value of 1.2 x 10(-2) per site per X chromosome per generation.

[Cause for maintaining high instability at the yellow gene in Drosophila melanogaster lines, isolated during the "mode for mutation" period in Uman populations]. / Prichina sokhraneniia vysokoi nestabil'nosti po genu yellow v liniiakh Drosophila melanogaster, vydelennykh v period "mody na mutatsiiu" v populiatsii Umani.

Mobile genetic elements are responsible for most spontaneous mutations in Drosophila melenogaster. The discovered in the 1980s phenomenon of frequent change of the wild-type yellow phenotype for a mutant one, and vice-versa, in strains of Drosophila melanogaster isolated from the Uman' natural population can be, according to our data, explained by repeated inversions and reinversions of the gene regulatory region located between the two copies of the hobo transport. However, most molecular genetic events accompanying the process can occur without the phenotype change. After several generations, the strains, remaining phenotypically unchanged, can possess different molecular genetic properties with respect to yellow. Using genetically homogenous or isogenic strains for the genetic analysis or for production of the new plant cultivars or animal breeds, geneticists and breeders often face the problem of stability of the strains. In the present study, the mechanism underlying the generation of instability at the yellow locus of D. melanogaster determined by the hobo-induced genome instability is described.

["Mode for mutation" in the natural population of Drosophila melanogaster from Umani is caused by distribution of a hobo-induced inversion in the regulatory region of the yellow gene]. / "Moda na mutatsiiu" v prirodnoi populiatsii Drosophila melanogaster Umani vyzvana rasprostraneniem indutsirovannoi homo-élementom nestabil'noi inversii reguliatornoi chasti gena yellow.

A mutation outburst of the yellow gene occurred in a Drosophila melanogaster population from the town of Uman' from 1982 to 1991 and was associated with the instability of several alleles. Molecular genetic analysis revealed a deletion variant of the hobo transposable element in the same site of the regulatory region of yellow in the mutant alleles and their derivatives. The outburst of the yellow-2 mutations was attributed to the spreading of the X chromosome, which contained an inversion of the yellow regulatory region, through the population. Reinversion resulted in the wild-type phenotype. Crossing lines carrying the inversion with laboratory line C(1)DX, ywf induced instability of the yellow alleles, which was associated with duplication or multiplication of a fragment of the yellow gene. Most derivative lines eventually became stable. The loss of instability was not associated with phenotypic changes; molecular genetic changes included a loss of the duplicated sequences or a deletion of the inverted regulatory region of the yellow gene.

hobo-induced rearrangements are responsible for mutation bursts at the yellow locus in a natural population of Drosophila melanogaster.

In 1981 recurrent local bursts of mutability of the yellow gene were observed in a natural population of Drosophila melanogaster from Uman' (Ukraine). A series of y2-like mutations in the yellow gene were recovered during the period 1982 to 1991. Most of the mutants display the y2-phenotype, i.e. mutant yellow color of wings and body cuticle. Ninety-nine y2 mutants were shown to be generated by an inversion that occurred between two hobo elements, one located 129 bp from the start site of yellow transcription, and the other in the distal telomere region. The y2 phenotype was caused by the separation of the body and wing enhancers from the transcription unit. Many of the y2-like alleles were highly unstable and reverted to y+, which again, gave rise to y2-like mutants. We found that the y2-->y+-->y2 transitions were generated by repeated inversions between the two hobo elements mentioned. The y2 and y+ alleles lost their instability after deletion of the hobo element present at the tip of the X chromosome.

[Mutation bursts of the yellow gene in a natural Drosophila melanogaster population is connected with insertion of the hobo transposon]. / Vspyshki mutatsii gena yellow v prirodnoi populiatsii Drosophila melanogaster sviazany s insertsiei transpozona hobo.

In 1981, a recurrent local burst of high mutability and high allele frequency of the yellow gene was recorded in the natural population of Drosophila melanogaster from Uman', Ukraine. A detailed genetic analysis showed that hypomorphic alleles y2 prevailed during the mutation burst. Mutations were strictly allele-specific and occurred only in two directions: from y2 to y+ and from y+ to y2. Alleles y2 isolated from the natural population differed in the degree of instability of mutant and wild-type derivatives, expression of the mutant phenotype, and complementation properties. In this work, the insertion nature of all unstable alleles derived from the natural population is confirmed by direct molecular methods. The mutation burst at the yellow locus is shown to result from insertion of a defective hobo copy. Six mutations y2 independently isolated from the natural population were caused by an insertion of hobo in the same site of the yellow regulatory region. The hobo copies were identical according to the restriction map. In three y2 alleles, the mutant phenotype was associated with inversion between hobo copies, one of which was located in the yellow locus and the other, in another unidentified region of the X chromosome. The remaining y2 alleles were associated with deletions that were located in the vicinity of the hobo insertion site and in the region of yellow enhancers.

[Effect of genetic background on mutation frequency of insertional alleles of the lozenge in Drosophila melanogaster]. / Vliianie geneticheskogo fona na chastotu mutirovaniia insertsionnykh alleli gena lozenge u Drosophila melanogaster.

We studied the effect of genetic background on mutation frequency of an unstable lz75V allele of the lozenge gene (lz; 1-27.7) isolated from natural populations of Drosophila melanogaster and its mutant derivatives lzB abd lzsl. Genetic composition of the X chromosome containing unstable alleles (X75V chromosome) was shown to affect their mutability. The region of the chromosome proximal to lozenge contains factors required for high mutability of lz75V and lzB. Substitution of a distal part of the X chromosome from a laboratory strain for a homologous part of the X75V chromosome also resulted in stabilizing lz75V, but caused an increase in mutation frequency of lzB. Association between instability of lz75V and the presence of P element with the locus was revealed by in situ hybridization. Studying effects of regulatory elements from a pi 2 P strain showed that the P cytotype is associated with a twofold to threefold decrease in mutation frequency of lzB and lzsl, but P-M hybrid dysgenesis is associated with its slight increase. Regulation of instability of the lozenge gene within the X75V chromosome was assumed to involve three levels: (1) character and topography of a mobile element inserted into the locus, (2) regulatory factors of other X-chromosomal regions, and (3) cytoplasmic factors. The results obtained are discussed in terms of regulation of transposition of mobile genetic elements.

[Genetic instability in the Drosophila melanogaster lozenge locus: characteristics of the lz75V locus]. / Geneticheskaia nestabil'nost' v lokuse lozenge u Drosophila melanogaster: kharakteristika allelia lz75V.

Genetic properties of lz75V, an unstable allele of the lozenge locus, are described. The lz75V allele appeared in progeny of a male from a Far East natural population of Drosophila melanogaster. Mutation of this allele produces a broad spectrum of mutant derivatives with phenotypes varying from normal to extreme. The arising alleles can be stable or unstable. Some lz75V derivatives continuously preserve their spontaneous mutability in laboratory conditions, whereas other alleles of the same family show progressive stabilization at the intralocus or intrachromosome level. Instability of the lz75V-bearing X chromosome is locus-specific: only the lozenge gene mutates with high frequency, while visible mutations at other loci rarely occur. As shown previously, the lz75V allele appears to be caused by a P-element insertion. The appearance of spontaneous instability is discussed with regard to the general problem of transposition regulation in mobile elements. Different systems of hybrid dysgenesis, and, in particular, P elements are assumed to play an important role in induction of unstable mutations in nature.

[Preparation and primary genetic analysis of Drosophila melanogaster transformants line w'lz(b)/XXywf, containing mini-white genes, integrated in the genome during P-element-dependent transformation]. / Poluchenie i pervichnyi geneticheskii analiz transformantov Drosophila melanogaster linii w'lz(b)/XXywf, soderzhashchikh gen mini-white, integrirovannyi v genom pri P-élementzavisimoi transformatsii.

Transformation of Drosophila melanogaster using P-element-based vectors yielded 129 sublines, which carried mini-white gene copies in the different genome regions. Dependence of mini-white gene expression on the location, gene dosage, and sex of the transformed individuals was analyzed. The mutation lzb was shown to suppress mini-white gene expression, the degree of suppression depending on the location and dosage of the mini-white gene.

[Interaction of mobile elements P and mdg3 in Drosophila melanogaster: genetic aspects]. / Vzaimootnoshenie mobil'nykh élementov P i mdg3 u Drosophila melanogaster: geneticheskii aspekt.

It was found earlier that two unstable sn mutants isolated from natural populations are connected with insertion of mobile element mdg3 into the 7D1-2 region where singed gene (1-21.0) is localised. From two original sn mutants, a series of unstable sn alleles, both mutant and normal for phenotype, was extracted. Then we studied, how they change the mutation rate in germinal and somatic cells of different hybrids with pi 2 stock having P cytotype and active P elements in the chromosomes. Addition of P chromosomes, independently of the background of cytoplasm, proved to reduce the sn instability. The level of sn mutability was decreased with increasing the dose of P chromosomes. It is suggested that mutation events are caused by transposition of mdg3 and that both mdg3 and P elements compete for the same cellular factor, capable of activation of transposition process.