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I F Zhimulev

Publications and source records attributed to I F Zhimulev.

At least 73 records · Page 4Linked to original sources
PubMed1992

Localization of genes ecs, dor and swi in eight Drosophila species.

A cluster of genes corresponding to the early ecdysone stimulated puff 2B of the Drosophila melanogaster X chromosome has been localized using in situ hybridization in eight Drosophila species. Genes ecs, dor and swi from this cluster have been mapped in D. funebris, D. virilis, D. hydei, D. repleta, D. mercatorum and D. paranaensis to the telomeric region of the X chromosome, in D. kanekoi to the distal region, and in D. pseudoobscura, to the proximal region of the X chromosome. It is assumed that organization of this cluster in these species is conserved. In D. hydei, multiple hybridization sites of certain DNA probes from this region were found.

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PubMed1991

Chromomeric organization of polytene chromosomes.

This is a review summarizing work carried out at the Laboratory of Molecular Cytogenetics in recent years. Problems of genetic organization of bands, interbands and puffs as well as intercalary heterochromatin and position effect variegation are discussed from the point of view of the dynamic model of polytene chromosome organization.

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PubMed1991

Constitutive heterochromatin in early embryogenesis of Drosophila melanogaster.

The formation of constitutive heterochromatin was studied during the embryonic development of Drosophila melanogaster, using the C-banding technique. During embryonic cleavage, C-banded material is not seen in mitotic chromosomes; the differentiation between euchromatin and heterochromatin only occurs at blastoderm. This event correlates with the establishment of position-effect variegation.

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PubMed1991

Cytogenetical analysis of the 2B3-4-2B11 region of the X chromosome of Drosophila melanogaster. VII. Influence of the ecs locus on female fertility.

Of 13 ecs mutations, which affect female fertility, as revealed by complementation analysis, 7 are chromosome rearrangements involving the br complementation group. The other six show no cytologically detectable rearrangements and behave as completely or partially noncomplementing ecs alleles. All viable combinations of these 13 mutations were characterized by partial or complete female sterility. Viable heterozygotes carrying any of these mutations and the rearrangements Df(1)sta, T(1;3)sta, Df(1)St490, previously localized distal to the ecs locus, were also sterile. Using deletions and an electrophoretic mobility variant from the Staket strain, a minor chorion gene S70 has been mapped. It had been thought this gene was located in the 2B3-5 region, and corresponded to the ecs locus. However, in the present study, this gene was shown to map in the region removed by Df(1)sta (1E1-2-2B3-4) but outside that removed by Df(1)At127 (1E1-2-2A1-2), i.e. within the 2A1-2-2B3-4 region which is distal to the ecs locus. Rearrangements and point mutations at the ecs locus that result in female sterility had no effect on synthesis of the chorion protein s70. It may therefore be suggested that the chorion protein gene is not functionally associated with the ecs locus and that sterility is caused not by disruptions of the chorion protein gene but by lesions in the ecs gene itself. Thus, an ecs product, which controls cell sensitivity to ecdysterone is also necessary for female fertility.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1991

Cytogenetic and molecular aspects of position effect variegation in Drosophila melanogaster. IV. Underreplication of chromosomal material as a result of gene inactivation.

A chromosomal region subjected to position effect variegation was analysed for possible DNA under-replication. DNA clones from the vicinity of the euheterochromatin junction and from a distance of hundreds of kilobase pairs were used as probes. Formation of compact blocks of chromatin is regarded as a characteristic feature of position effect variegation. It was shown that in T (1;2) dorvar7 males undergoing position effect variegation clones representing the DNA nearest to the breakpoint in 2B7 hybridized normally in situ to the compact blocks, providing evidence against DNA underreplication. In females the same clones did not hybridize to the compact blocks. These variations in hybridization may be related to different degrees of compaction of chromosome regions in males and females. A correlation between the degree of underreplication and the level of cell polyteny was shown by Southern-blot hybridization of a DNA probe from the 2B region to DNA from an X/O strain carrying Dp (1;1)pn2b displaying position effect variegation and compaction in 94% of salivary gland cells. Almost complete underreplication of the DNA of this region was found in salivary gland cells (with a maximal degree of polyteny), intermediate underreplication was found in fat body cells (with an intermediate degree of polyteny), and replication was not disturbed in diploid cells of the larval cephalic complex.

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PubMed1991

Cytogenetic and molecular aspects of position effect variegation in Drosophila. III. Continuous and discontinuous compaction of chromosomal material as a result of position effect variegation.

Variations in compaction of chromosomal material of the rearrangements Dp(1;f) 1337, Dp(1;f) R, Dp(1;1)pn2b, and T(1;4)wm258-21, which display an extended position effect, were characterized. Morphological changes found in these rearangements were assigned to two major types: (i) continuous compaction, in which bands and interbands located distal to the eu/heterochromatin junction fuse into one compacted block of chromatin. The extent of compaction is increased by enhancers of position effect (low temperature, removal of the Y or 2R chromosome heterochromatin). In extreme cases compaction extends over dozens of bands. (ii) Discontinuous compaction, in which at least two zones of compaction separated by morphologically normal zones can readily be identified. As a result, some regions located at a greater distance from heterochromatin may be compacted more frequently than others that map nearer to it. A few regions (1D, 2B1-12, 2D) were shown to be most frequently compacted in all rearrangements investigated. The 2B13-18, 2C1-2, 2E, and 2F regions exhibited the lowest frequencies of compaction. Compaction of the zone containing the 2B1-12 bands is always accompanied by inactivation of the ecs locus, which maps in the 2B3-5 puff. At the same time the 2C1-2 and 2E bands located nearer to the breakpoint can retain normal morphology and puffing in response to ecdysterone. The results are interpreted as morphological manifestations of the discontinuity of the spreading effect.

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PubMed1991

[Hidden polyteny in giant embryonic nuclei of Drosophila melanogaster gnu mutants].

Drosophila melanogaster embryos, whose mothers are homozygous for the gnu (a recessive lethal mutation with maternal effect) undergo DNA synthesis but are defective in nuclear division. This leads to formation of giant nuclei in the syncytial blastoderm. The interior spatial chromatin organization and possibility of obtaining polytene chromosomes in these nuclei was analysed. Partial conjugation of homologous chromatids, which is an evidence for cryptic polyteny in the gnu embryos nuclei, was shown.

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PubMed1990

[Changes in the duration of replication of the polytene chromosome region during position effect in Drosophila melanogaster].

Replication pattern of the X chromosome 2B region translocated to the pericentric heterochromatin in the 2L chromosome within the T(1; 2) dorvar7 rearrangement which causes position effect was studied. It was found that this pattern is affected by the 2B region morphology. When normal, i.e. with decondensed bands in this region, it completes replication early. But after compaction, i.e. fusion of bands in the 2B region into dense block, due to position effect, its late replication was observed, together with the most late replicating intercalary heterochromatin regions in the X chromosome and the 75C-80A-C segment of the 3L chromosome. Possible mechanisms of replication delay and their role in promoting the position effect are discussed.

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PubMed1990

[The effect of locus ecs in Drosophila melanogaster on fertility of females].

A total of 13 ecs mutations affecting female fertility were isolated by complementation analysis. Seven of them were rearrangements with the br complementation group phenotype. Six other mutations had no cytologically detectable rearrangements and behaved as completely or partially non-complementing alleles of the ecs locus. All viable combinations of the above 13 mutations disturbed female fertility. Sterile were all fully viable compounds carrying any of these mutations and rearrangements Df (1) sta, T(1; 3)sta, Df(1)St490, previously localized on the molecular map distally to the ecs locus. According to data on location on molecular map of lesions affecting fertility, at least two elements at the ecs locus seem essential for this function: the most distal (left) cis-acting zone with no effect on viability and a sequence within the limits of the essential part of the ecs locus. Disturbance of any of these zones or their separation in the rearranged chromosomes lead to female sterility.

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PubMed1990

[Molecular-genetic analysis of of the band 10A1-2 in the Drosophila melanogaster chromosome X].

With the help of in situ hybridization respective location of 33 microclones from the genomic library of the Drosophila melanogaster large band 10A1-2, 4 clones obtained by chromosomal walking and 18 chromosomal rearrangements with breakpoints in the limits of this band was determined. A DNA fragment homologous to poly(A)+ RNA from the 3rd instar larvae has been revealed. Summarizing the obtained and published data, at least 3 genes and 6 transcriptionally active fragments appear to be located in the 10A1-2 band. Using DNA clones from different regions of Drosophila melanogaster 10A1-2 as probes in some Diptera species, the 10A1-2 distal clone, carrying vermilion gene, in D. virilis was shown to be located in a very thin band of the 5A region, while the proximal clones of the 10A1-2 band were mapped in a large band of the 2B region. In D. paranaensis a sequence homologous to the vermilion gene DNA was mapped in a large band, whereas the proximal clones of the 10A1-2 band were localized in a different region. These results evidence for the fact that DNA sequences are not evolutionary fixed, i. e. in different species they may belong to different chromomeres.

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PubMed1990

[Formation of interdisks from the P-element DNA material in Drosophila polytene chromosomes].

Electron microscopical (EM) analysis of regions of Drosophila melanogaster polytene chromosomes containing a matrial of the P element was carried out. In one of the stocks analysed the DNA fragment of 54 kb in length was inserted in the genome by the P element-mediated transformation. This fragment consists of four tandemly repeated copies of the rosy gene and each of them has P-DNAs at the terminal sites. In polytene chromosomes the fragment forms a complex of loose chromatin, where, nevertheless, it is possible to distinguish four bands. EM analysis of two regions with the P element in other stock reveals lengthening of interbands, as compared with the same interbands in the initial stock without the P element. In the third of the stocks analysed the P element was inserted in the region of vermilion gene which is situated in the large single band, 10A1-2 of the X-chromosome. In this case, the splitting of the band into two unequal parts and formation of a new interband was observed. Data obtained show the possibility of interband formation from DNA material of the P element, which is probably connected with its transcriptional activity.

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PubMed1989

Position-effect variegation and intercalary heterochromatin: a comparative study.

The behaviour of IH (intercalary heterochromatin) regions of Drosophila melanogaster polytene chromosomes was compared with that of euchromatin condensed as a result of position-effect variegation. Normally replicating regions, when subject to such an effect, were found to become among the last regions in the genome to replicate. It is shown that the factors which enhance position effect (low temperature, the removal of the Y chromosome, genetic enhancers of position effect) increase the weak point frequency in the IH, i.e. enhance DNA underreplication in these regions. We suggest that the similarity in the properties of IH, CH (centromeric heterochromatin) and the dense blocks induced by position effect is due to strong genetic inactivation and supercondensation caused by specific proteins in early development. The primary DNA structure is not likely to play a key role in this process.

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PubMed1989

Electron microscopical analysis of Drosophila polytene chromosomes. V. Characteristics of structures formed by transposed DNA segments of mobile elements.

An electron microscopical (EM) analysis was performed on regions of polytene chromosomes which contained DNA segments of different genetic composition, inserted by P element-mediated transformation into the Drosophila melanogaster genome. In seven of ten regions examined, containing insertions of the hsp28-ry, hsp70-Adh, ryhsp 70-beta-gal genes and of the ry gene tetramer, new bands appeared. Lack of new bands in three other strains is apparently connected with the fusion of the inserted material to preexisting bands. The new bands do not differ morphologically from the usual bands of polytene chromosomes, and their formation is likely due to predominant insertion of DNA segments into interbands. Among the constructs examined, the minimal length of a DNA segment which appears as a new band is about 5 kb; the DNA packing ratio in the new bands varies from 30 to 50. Activation of the inserted genes by heat shock has enabled us to observe the puffing characteristics of new bands. A sequence of some one kb forms a large interband, or micropuff; the puff size is correlated with the length of the genes being activated. If a DNA segment contains a single gene, then its activation causes the decompaction of the whole band; however, when a DNA segment consists of two genes and the promoter element of the activated gene is positioned in the middle of the sequence, the band splits and only part is decompacted and puffed. The DNA packing ratio in the puffs is 1.4-3.5. The subsequent deletion of the hsp70 promoter but retention of 23, 59, and 73 by from the transcription start points leads to failure of puff formation. In all the transformed sites an increase in the total length of the interbands adjacent to the insert as compared with the initial interband was observed. This increase appears to be due to decompaction of the P element DAN flanking the inserted segments. It is shown that a DNA segment, consisting of four tandemly repeated ry gene copies and interspersed by material which includes P DNA, forms a complex of loose chromatin in which, however, four bands can be resolved. We also observed a lengthening of interband regions containing only the P element sequence itself. Insertion of the complete 2.9 kb P element into the large single 10A1-2 bound of the X chromosome (an insertion in the region approximately 10 kb to the right of the v gene) causes splitting of the band into two parts and formation of a new interband.(ABSTRACT TRUNCATED AT 400 WORDS)

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