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I F Zhimulev

Publications and source records attributed to I F Zhimulev.

At least 37 records · Page 2Linked to original sources
PubMed2001

Polytene chromosome interband DNA is organized into nucleosomes.

The molecular basis that underlies the maintenance of polytene chromosome banding pattern remains unclear. To test the possibility that the decondensed state of interbands is provoked by the absence of nucleosomes, we have subjected chromatin from the previously defined 61C7/C8 interband to digestion with micrococcal nuclease. We have demonstrated that interband DNA forms nucleosomes both in salivary glands and in the bulk of larval tissues. This finding strongly suggests that the difference in compaction between DNA in polytene chromosome bands and interbands results from differences that appear at the higher levels of chromatin organization.

Animals↗
PubMed2001

Formation and morphology of dark puffs in Drosophila melanogaster polytene chromosomes.

The formation of unusual dark puffs in Drosophila melanogaster polytene chromosomes has been studied by electron microscopic (EM) analysis. Fly stocks transformed by the P[ry; Prat:bw] and P[hs-BRC-z1] constructs were used. In the former the bw gene is under the promoter of a housekeeping gene, Prat; in the latter the Br-C locus, mapping to the dark puff 2B, is under the promoter of a heat-shock gene, hsp70. Inserted into region 65A of the 3L chromosome, the Prat:bw copies give rise to structures which are morphologically reminiscent of the so-called "dark" puffs. In contrast, insertion of P[hs-BRC-z1] into region 99B of the 3R chromosome causes a regular "light" puff of form. Comparative analysis of the dark puffs--both transgenic and natural--suggests that there might be at least two mechanisms underlying their formation. One is a local incomplete decondensation of activated bands, characteristic of the so-called small puffs. The other is the formation of ectopic-looking contacts between the bands adjacent to the puffing zone. Transposition of the DNA, from which such a puff develops, causes a regular light puff to form at the new location. Heterochromatic regions do not appear to be directly involved in puffing.

Animals↗
PubMed2001

[Modeling dark puffs using P-transposons in Drosophila melanogaster polytene chromosomes].

Modeling of morphologically unusual "dark" puffs was conducted using Drosophila melanogaster strains transformed by construct P[ry; Prat:bw], in which gene brown is controlled by the promoter of the housekeeping gene Prat. In polytene chromosomes, insertions of this type were shown to form structures that are morphologically similar to small puffs. By contrast, the Broad-Complex (Br-C) locus, which normally produce a dark puff in the 2B region of the X chromosome, forms a typical light-colored puffs when transferred to the 99B region of chromosome 3R using P[hs-BRC-z1]. A comparison of transposon-induced puffs with those appearing during normal development indicates that these puff types are formed via two different mechanisms. One mechanism involves decompaction of weakly transcribed bands and is characteristic of small puffs. The other mechanism is associated with contacts between bands adjacent to the puffing zone, which leads to mixing of inactive condensed and actively transcribed decondensed material and forming of large dark puffs.

Animals↗
PubMed2001

[Analysis of DNA interband regions 3A5/A6, 3C5-6/c7 and 60E8-9/E10 of Drosophila melanogaster polytene chromosomes].

Using electron microscopic (EM) data on the formation of a novel band from the P-element material after its insertion in the interband and the procedure of P-target rescue, DNA interband regions 3A5/A6, and 60E8-9/E10 of Drosophila melanogaster polytene chromosomes were cloned and sequenced. EM analysis of the 3C region have shown that the formation of the full-size 3C5-6/C7 interband requires a 880-bp DNA sequences removed by deletion Df(1)faswb. A comparison of DNA sequences of six bands, two of which were obtained in the present work and four were described earlier, demonstrated the uniqueness of each of them in the Drosophila genome and heterogeneity of their molecular organization. Interband 60E8-9/E10 contains gene rpl19 transcribed throughout the development, in particular in salivary glands. In the other interbands examined 5' and 3' nontranslated gene regions are located. These results suggest that Drosophila interbands may contain both housekeeping genes and regulatory sequences of currently inactive genes from adjacent bands.

Animals↗
PubMed2001

[Interline differences in morphology of the precentromeric region of polytene X-chromosome in Drosophila melanogaster salivary glands].

Morphology of the Drosophila melanogaster polytene X chromosome section 20 in normal flies, in strains carrying inversions that break pericentric heterochromatin at different points, and at the background of the Su(UR)ES mutation has been examined. In all of the strains carrying the Su(UR)ES mutation section 20 displayed a distinct banding pattern till to the section 20F, while in the wild-type strains this region was represented by beta-heterochromatin. The strains carrying different inversions substantially differed in the number and morphology of bands forming section 20. In the Su(UR)ES mutants the most proximal X chromosome euchromatin gene, su(f), is mapped to the boundary between sections 20E and F, while rDNA forming the middle part of the X chromosome mitotic heterochromatin is located in the proximal part of section 20F. All large bands observed in section 20 of the w; Su(UR)ES strain were also present in In(1)sc4; Su(UR)ES, which breaks heterochromatin in the distal part. Hence, the bands of polytene chromosome section 20 are virtually devoid of mitotic heterochromatin.

Animals↗
PubMed2000

The transposon A(R)4-24P[white, rosy] in Drosophila melanogaster is subject to position-effect variegation at a non-centromeric insertion site.

The white gene within the transposon A(R)4-24P[white,rosy] inserted at cytological location 24D1-2 in the euchromatic portion of the Drosophila melanogaster genome exhibits a mosaic pattern of expression which is modified by temperature and Y-chromosome number, as in cases of classical position-effect variegation (PEV). The eye colour of the flies in this variegated stock remains mosaic in the presence of the PEV modifier Su(var)3-6, slightly less so with Su(var)3-9 and Su(var)2-5, and full suppression of variegation occurs in the presence of Su(var)3-7. We have induced further transposition of A(R)4-24 and isolated two mosaic stocks with this transgene at new cytological locations. In these stocks, the A(R)4-24 transposon was flanked by the same genomic DNA fragments as in the original location. Spontaneous loss of these fragments leads to reversion of the variegated eye colour to wild-type. We suggest that the flanking DNA fragments from 24D1-2 are capable of inducing position-effect variegation without any association with centromeric heterochromatin. In situ hybridisation and Southern analysis demonstrate that the 5' flanking genomic fragment contains repeated sequences which are abundantly present in heterochromatin.

ATP-Binding Cassette Transporters↗
PubMed2000

[Position effect variegation of the mosaic type, arising as a result of transposition AR4-24P[white, rosy] in the Drosophila melanogaster genome].

A line with the mosaic expression of the white+ transgene was obtained by inducing transposition of the AR4-24P[white, rosy] transposon and was used for the second round of induction. As a result, 57 lines with the mosaic eye pigmentation were obtained. In situ hybridization and Southern blotting showed that genomic DNA fragments flanking AR4-24 were, in some cases, transposed together with the transposon. A spontaneous loss of these fragments resulted in reversion to the wild-type phenotype. The mosaic eye pigmentation in a line that carried the AR4-24 transposon flanked with the same fragments in region 24D1-2 was not affected by the Su(var)3-6 gene modifying position effect variegation (PEV). Other PEV modifiers, Su(var)3-9 and Su(var)2-5, had only a slight effect on PEV; Su(var)3-7 restored the wild-type phenotype. The genomic fragments captured by the transposon may contain DNA sequences that autonomously induce mosaic PEV of the white gene.

Animals↗
PubMed2000

[Effect of four doses of the Su(UR)ES gene on intercalary heterochromatin in Drosophila melanogaster].

Polytene chromosomes of salivary glands of various Drosophila melanogaster strains containing two doses of the normal Su(UR)ES allele have a constant set of intercalary heterochromatin (IHC) sites. Their DNA is underreplicated, which leads to breaks and ectopic contacts emerging at a certain rate. Almost no underreplication, breaks, or ectopic conjugation are present in mutants lacking the normal Su(UR)ES gene product. It could be expected that an increase in the number of the Su(UR)ES+ gene doses would, in turn, drastically increase ectopic conjugation and breakage. To test this hypothesis, a strain of D. melanogaster was obtained with two additional doses of Su(UR)ES+ introduced into its genome. The flies with four gene doses exhibited a considerable increase in ectopic conjugation: both the proportion of regions participating in conjugation and the number of chromosomes with numerous contact nodes were increased. As a result, chromosomes that were straight and well-stretched in homozygotes for the mutation in Su(UR)ES became twisted and wound and contained many loops or nodes. Many chromosomes were wound too tightly for cytological analysis. Four doses of Su(UR)ES+ considerably increased the number of weak "points." For example, the 2R chromosome has only 3 weak points in strains with two doses of Su(UR)ES+ and as many as 22 weak points in the strain with four doses. In the transgenic strain, the frequency of breaks in previously known weak points increased, and new breaks appeared in 19 additional sites. All new break points appeared in the regions that were earlier described as regions of late replication in the S phase.

Animals↗
PubMed1999

Interbands of Drosophila melanogaster polytene chromosomes contain matrix association regions.

The DNA of three previously cloned interband regions (85D9/D10, 86B4/B6, and 61C7/C8) of Drosophila melanogaster polytene chromosomes has been tested for the presence of matrix association regions (MAR), using the in vitro matrix-binding assay of Cockerill and Garrard. MARs were found in all three interband regions under study. These results are discussed in frames of a model postulating that interband regions of polytene chromosomes correspond to the chromosomal DNA loop borders, which can be identified in interphase nuclei using biochemical approaches.

Animals↗
PubMed1999

Dynamic organization of the beta-heterochromatin in the Drosophila melanogaster polytene X chromosome.

Region 20 of the polytene X chromosome of Drosophila melanogaster was studied in salivary glands (SG) and pseudonurse cells (PNC) of otu mutants. In SG chromosomes the morphology of the region strongly depends on two modifiers of position effect variegation: temperature and amount of heterochromatin. It is banded in XYY males at 25 degrees C and beta-heterochromatic in X0 males at 14 degrees C, i.e. it shows dynamic transitions. In PNC chromosomes region 20 is not heterochromatic, but demonstrates a clear banding pattern. Some molecular markers of mitotic heterochromatin were localized by means of in situ hybridization on PNC chromosomes: DNA of the gene su(f) in section 20C, the nucleolar organizer and 359-bp satellite in 20F. The 359-bp satellite, which has been considered to be specific for heterochromatin of the mitotic X chromosome, was found at two additional sites on chromosome 3L, proximally to 80C. The right arm of the X chromosome in SG chromosomes was localized in the inversion In(ILR)pn2b: the telomeric HeT-A DNA and AAGAG satellite from the right arm are polytenized, having been relocated from heterochromatin to euchromatin.

Animals↗
PubMed1999

A novel simple satellite DNA is colocalized with the Stalker retrotransposon in Drosophila melanogaster heterochromatin.

In the T(1:2)dor(var7) multibreak rearrangement the distal 1A-2B segment of the X chromosome of Drosophila melanogaster is juxtaposed to an inverted portion of the heterochromatin of chromosome 2. Analysis of mitotic chromosomes by a series of banding techniques has permitted us precisely to locate the heterochromatic breakpoint of this translocation in the h42 region of 2R. Cloning and sequencing of the eu-heterochromatic junction revealed that the translocated 1A-2B fragment is joined to (AACAC)n repeats, which represent a previously undescribed satellite DNA in D. melanogaster. These repeated sequences have been estimated to account for about 1 Mb of the D. melanogaster genome. The repeats are located mainly in the Y chromosome and in the heterochromatin of the right arm of chromosome 2 (2Rh), where they are colocalized with the Stalker retrotransposon.

Animals↗
PubMed1999

[Microcloning and characteristics of DNA from regions of the centromeric heterochromatin of Drosophila melanogaster polytene chromosomes].

A method of microcloning, which involves microsurgical excision of chromosome fragments, DNA amplification by means of a polymerase chain reaction (PCR), and ligation of amplified products with plasmids, was employed in studying Drosophila polytene chromosomes for the first time. Clones of the DNA library thus obtained contained inserts varying in size from 0.1 to 0.5 kb. DNA sequencing of five clones of the library showed that pericentromeric heterochromatin contained the 17.6 and 297 retrotransposons, the ninja retrotransposon characteristic of D. simulans, and two Drosophila repetitive elements, a8 and a12, the function of which remains unknown.

Amino Acid Sequence↗
PubMed1998

Su(UR)ES: a gene suppressing DNA underreplication in intercalary and pericentric heterochromatin of Drosophila melanogaster polytene chromosomes.

A genetic locus suppressing DNA underreplication in intercalary heterochromatin (IH) and pericentric heterochromatin (PH) of the polytene chromosomes of Drosophila melanogaster salivary glands, has been described. Found in the In(1)scV2 strain, the mutation, designated as Su(UR)ES, was located on chromosome 3L at position 34. 8 and cytologically mapped to region 68A3-B4. A cytological phenotype was observed in the salivary gland chromosomes of larvae homozygous and hemizygous for Su(UR)ES: (i) in the IH regions, that normally are incompletely polytenized and so they often break to form "weak points," underreplication is suppressed, breaks and ectopic contacts disappear; (ii) the degree of polytenization in PH grows higher. That is why the regions in chromosome arm basements, normally beta-heterochromatic, acquire a distinct banding pattern, i. e., become euchromatic by morphological criteria; (iii) an additional bulk of polytenized material arises between the arms of chromosome 3 to form a fragment with a typical banding pattern. Chromosome 2 PH reveals additional alpha-heterochromatin. Su(UR)ES does not affect the viability, fertility, or morphological characters of the imago, and has semidominant expression in the heterozygote and distinct maternal effect. The results obtained provide evidence that the processes leading to DNA underreplication in IH and PH are affected by the same genetic mechanism.

Animals↗
PubMed1998

Drosophila hormone receptor 38 functions in metamorphosis: a role in adult cuticle formation.

DHR38 is a member of the steroid receptor superfamily in Drosophila homologous to the vertebrate NGFI-B-type orphan receptors. In addition to binding to specific response elements as a monomer, DHR38 interacts with the USP component of the ecdysone receptor complex in vitro, in yeast and in a cell line, suggesting that DHR38 might modulate ecdysone-triggered signals in the fly. We characterized the molecular structure and expression of the Dhr38 gene and initiated an in vivo analysis of its function(s) in development. The Dhr38 transcription unit spans more than 40 kb in length, includes four introns, and produces at least four mRNA isoforms differentially expressed in development; two of these are greatly enriched in the pupal stage and encode nested polypeptides. We characterized four alleles of Dhr38: a P-element enchancer trap line, l(2)02306, which shows exclusively epidermal staining in the late larval, pre-pupal and pupal stages, and three EMS-induced alleles. Dhr38 alleles cause localized fragility and rupturing of the adult cuticle, demonstrating that Dhr38 plays an important role in late stages of epidermal metamorphosis.

Alleles↗
PubMed1998

[Somatic pairing of homologs of the fourth chromosome as a reason for suppression of the Dubinin effect in Drosophila melanogaster].

The position effect of the cubitus interruptus (ci) gene occurs when this gene, which is normally located in the vicinity of the pericentric heterochromatin of chromosome 4, is transferred by chromosome rearrangements to euchromatin regions. Cytological aspects of this phenomenon were investigated. For six reciprocal translocations causing the position effect (Dubinin effect) of ci, the frequencies of the ectopic contacts of the translocated chromosome 4 homologue with pericentric heterochromatin were compared to the conjugation frequencies of this chromosome's homologues. The frequencies were significantly higher when the gene was transferred to proximal chromosome regions. This suggested that the suppression of the Dubinin effect in the case of translocations with euchromatin breaks in proximal chromosome regions is caused by the higher conjugation frequency of translocated and normal chromosome 4 homologues in proximal than in distal regions. The effect of genes modulo and Su(var)2-05, which are known as modifiers of the position effect variegation, on the conjugation frequency of chromosome 4 homologues was studied for three translocations. It was shown that modulo did not affect this frequency, whereas Su(var)205 significantly decreased it. Cytogenetic data confirmed the association of the ci position effect with damage in the somatic pairing of chromosome 4 homologues. These data indicate that pericentric heterochromatin participates in determination of the localization of chromosome regions in the interphase nucleus.

Animals↗
PubMed1998

[A genetic factor, suppressing DNA underreplication in Drosophila melanogaster polytene chromosomes].

The Drosophila melanogaster line carrying the In(I)scv2 was found to exhibit unique cytological phenotype distinguished by the lack of "weak" points in the intercalary heterochromatin of the salivary gland polytene chromosomes, the absence of ectopic contacts between the chromosome regions, and the occurrence of additional intercalary heterochromatin in the centromeric regions. Southern blot hybridization revealed the absence of DNA underreplication in the intercalary heterochromatin region 39E carrying the histone gene cluster. This phenotype may have arisen under the influence of a genetic factor, Su(UR), which suppressed DNA underreplication in polytene chromosomes. Genetic analysis of the inheritance of the "suppression of DNA underreplication" phenotype showed that this factor was located in the third chromosome and was expressed in a semidominant manner. Discovery of Su(UR) suggested existence of common mechanisms regulating DNA underreplication in the centromeric and intercalary heterochromatin regions containing genes that were completely inactivated during ontogeny. These results confirm the assumption of common mechanisms of epigenetic repression of highly repetitive, somewhat repetitive, and unique sequences of the Drosophila genome.

Animals↗