Search PubMed⌕ Search

Biomedical subjects

T B Nesterova

Publications and source records attributed to T B Nesterova.

At least 19 recordsLinked to original sources
PubMed2002

Reorganization of the X chromosome in voles of the genus Microtus.

Comparative chromosomal analysis is a powerful tool in the investigation of the mechanisms of chromosomal evolution. The accuracy of the analysis depends on the availability of region-specific markers to follow the fate of the particular chromosomal region through the evolution of species. We have assigned 12 unique sequences to the euchromatic part of the vole X chromosome, which serve as reliable markers of chromosomal segments. Together with region-specific libraries and GTG banding, these markers allow us to delineate the homologous regions of the X chromosomes in five species of the genus Microtus. We found that X chromosomes of these species differ by numerous rearrangements and all rearrangements are clustered at specific breakpoints. Moreover, these breakpoints were found to colocalise with repetitive and/or duplicated DNA sequences. We suggest that clusters of repeated and/or duplicated DNA sequences have played a crucial role in the formation of rearrangement hot spots during evolution of the X chromosome in the subgenus Microtus.

Animals↗
PubMed2001

Loss of Xist imprinting in diploid parthenogenetic preimplantation embryos.

We have analysed Xist expression patterns in parthenogenetic and control fertilised preimplantation embryos by using RNA FISH. In normal XX embryos, maternally derived Xist alleles are repressed throughout preimplantation development. Paternal alleles are expressed as early as the 2-cell stage. In parthenogenetic embryos, we observed Xist RNA expression and accumulation from the morula stage onwards, indicating loss of maternal imprinting. In the majority of cells, expression was from a single allele, indicating that X chromosome counting occurs to establish appropriate monoallelic Xist expression. We discuss these data in the context of models for regulation of imprinted and random X inactivation.

Alleles↗
PubMed2001

Comparative chromosome and mitochondrial DNA analyses and phylogenetic relationships within common voles (Microtus, Arvicolidae).

The four species of common voles within the genus Microtus--M. kirgisorum, M. transcaspicus, M. arvalis, and M. rossiaemeridionalis--are so closely related that neither morphological features nor paleontological evidence allow clarification of their phylogeny. Analysis of vole karyotypes and mitochondrial DNA sequences, therefore, is essential for determining their phylogenetic relationships. A comparison of high resolution GTG-banding patterns allows us to ascertain the similarity between the karyotypes of these species, revealing that they are composed of rearrangements of the same chromosomal elements. Based on this analysis, we propose possible routes of chromosomal divergence involved in speciation within this group of voles and construct a phylogenetic tree of their karyotypes. We suggest that two different karyotypic variants existed during the course of vole evolution--one resulting in M. rossiaemeridionalis and M. transcaspicus, the other, M. kirgisorum and M. arvalis. As an alternative approach FITCH and KITSCH computer programs were used to construct a phylogenetic tree of vole molecular evolution based on a pairwise comparison of mitochondrial cytochrome b sequences and the divergence time of the species was determined. The correlation between the trees constructed using karyologic and molecular approaches is discussed in the context of other available data.

Algorithms↗
PubMed2001

Characterization of the genomic Xist locus in rodents reveals conservation of overall gene structure and tandem repeats but rapid evolution of unique sequence.

The Xist locus plays a central role in the regulation of X chromosome inactivation in mammals, although its exact mode of action remains to be elucidated. Evolutionary studies are important in identifying conserved genomic regions and defining their possible function. Here we report cloning, sequence analysis, and detailed characterization of the Xist gene from four closely related species of common vole (field mouse), Microtus arvalis. Our analysis reveals that there is overall conservation of Xist gene structure both between different vole species and relative to mouse and human Xist/XIST. Within transcribed sequence, there is significant conservation over five short regions of unique sequence and also over Xist-specific tandem repeats. The majority of unique sequences, however, are evolving at an unexpectedly high rate. This is also evident from analysis of flanking sequences, which reveals a very high rate of rearrangement and invasion of dispersed repeats. We discuss these results in the context of Xist gene function and evolution.

3' Untranslated Regions↗
PubMed1999

Xist RNA exhibits a banded localization on the inactive X chromosome and is excluded from autosomal material in cis.

The propagation of X chromosome inactivation is thought to be mediated by the cis- limited spreading of the non-protein coding Xist transcript. In this report we have investigated the localization of Xist RNA on rodent metaphase chromosomes. We show that Xist RNA exhibits a banded pattern on the inactive X and is excluded from regions of constitutive heterochromatin. The banding pattern suggests a preferential association with gene-rich, G-light regions. Analysis of X:autosome rearrangements revealed that restricted propagation of X inactivation into cis -linked autosomal material is reflected by a corresponding limited spread of Xist RNA. We discuss these results in the context of models for the function of Xist RNA in the propagation of X inactivation.

Animals↗
PubMed1998

Developmentally regulated Xist promoter switch mediates initiation of X inactivation.

Developmental regulation of the mouse Xist gene at the onset of X chromosome inactivation is mediated by RNA stabilization. Here, we show that alternate promoter usage gives rise to distinct stable and unstable RNA isoforms. Unstable Xist transcript initiates at a novel upstream promoter, whereas stable Xist RNA is transcribed from the previously identified promoter and from a novel downstream promoter. Analysis of cells undergoing X inactivation indicates that a developmentally regulated promoter switch mediates stabilization and accumulation of Xist RNA on the inactive X chromosome.

Animals↗
PubMed1998

Comparative mapping of X chromosomes in vole species of the genus Microtus.

Comparative mapping of X-linked genes has progressed rapidly since Ohno's prediction that genes on the X chromosome should be conserved as a syntenic group in all mammals. Although several conserved blocks of homology between human and mouse have been discovered, rearrangements within the X chromosome have also been characterized. More recently, some exceptions to Ohno's law have been reported. We have used fluorescence in situ hybridization (FISH) to map five genes, Gla, G6pd, Hprt, Pgk1 and Xist, to two of the largest conserved segments of X material in five members of the genus Microtus (grey vole) and show that vole X chromosomes demonstrate greater homology to human than to mouse. Cytogenetic analysis indicates a relatively high frequency of rearrangement during vole evolution, although certain blocks of homology appear to be highly conserved in all species studied to date. On this basis we were able to predict the probable location of the rat X inactivation centre (Xic) based solely on high-resolution G-banding. Our prediction was then confirmed by mapping the rat Xist gene by FISH. The possible significance of conserving long-range chromosome structure in the vicinity of the Xic is discussed with respect to the mechanism of X inactivation.

Animals↗
PubMed1998

Repetitive DNA sequences in the common vole: cloning, characterization and chromosome localization of two novel complex repeats MS3 and MS4 from the genome of the East European vole Microtus rossiaemeridionalis.

We have characterized two novel, complex, heterochromatic repeat sequences, MS3 and MS4, isolated from Microtus rossiaemeridionalis genomic DNA. Sequence analysis indicates that both repeats consist of unique sequences interrupted by repeat elements of different origin and can be classified as long complex repeat units (LCRUs). A unique feature of both repeat units is the presence of short interspersed repeat elements (SINEs), which are usually characteristic of the euchromatic part of the genome. Comparative analysis revealed no significant stretches of homology in the nucleotide sequences between the two repeats, suggesting that the repeats originated independently during the course of vole genome evolution. Fluorescence in situ hybridization analysis demonstrates that MS3 and MS4 occupy distinct domains in the heterochromatic regions of the sex chromosomes in M. transcaspicus and M. arvalis but collocalize in M. rossiaemeridionalis and M. kirgisorum heterochromatic blocks. The localization pattern of the repeats on the vole chromosomes confirms the independent origin of the two repeats and suggests that expansion of the heterochromatic blocks has occurred subsequent to speciation.

Animals↗
PubMed1998

[High-resolution GTG-banding and nucleolar organizer regions of chromosomes of two vole species: Microtus rossiaemeridonionalis and M. transcaspicus (Rodentia, Arvicolidae)].

With the use of the GTG-banding of prometaphase chromosomes, 503 and 402 segments were revealed in haploid chromosome sets of voles Microtus rossiaemeridionalis and M. transcaspicus, respectively. Based on a detailed study of chromosomes at different condensation levels, idiograms of M. rossiaemeridionalis and M. transcaspicus chromosomes were constructed. Sequential Ag-staining and GTG-banding allowed nucleolar organizer regions (NORs) to be localized in 16 and 11 chromosome pairs of M. rossiaemeridionalis and M. transcaspicus, respectively.

Animals↗
PubMed1997

Stabilization of Xist RNA mediates initiation of X chromosome inactivation.

The onset of X inactivation is preceded by a marked increase in the level of Xist RNA. Here we demonstrate that increased stability of Xist RNA is the primary determinant of developmental up-regulation. Unstable transcript is produced by both alleles in XX ES cells and in XX embryos prior to the onset of random X inactivation. Following differentiation, transcription of unstable RNA from the active X chromosome allele continues for a period following stabilization and accumulation of transcript on the inactive X allele. We discuss the implications of these findings in terms of models for the initiation of random and imprinted X inactivation.

Alleles↗
PubMed1997

Novel strategies for eutherian x marsupial somatic cell hybrids: mapping the genome of Monodelphis domestica.

Two hundred thirty-seven independent somatic cell hybrids have been obtained between opossum (Monodelphis domestica) splenocytes, bone marrow cells, or primary fibroblasts, and HPRT-deficient or TK-deficient Chinese hamster, mouse, American mink, or common vole fibroblast lines. Because extreme segregation and fragmentation of marsupial chromosomes commonly occurs in eutherian x marsupial somatic cells hybrids, we developed a rapid primary screening method that enables the identification of primary clones containing a large amount of opossum DNA 20-25 d after fusion. This method, which depends on in situ hybridization of biotin-labeled total opossum DNA on interphase nuclei of hybrid cells fixed on the bottom of microwell plates, was used to screen the 237 hybrid clones; 52 of them had a substantial amount of opossum DNA. G-banding and in situ hybridization of biotin-labeled total opossum DNA on metaphase spreads of the clones enabled identification of 17 hybrid clones containing from two to seven intact chromosomes of M. domestica on the background of Chinese hamster or vole chromosomes. The hybrid clones with intact opossum chromosomes are used in a panel constructed for mapping the opossum genome. Initial mapping results from these clones have led to the tentative assignment of GPI and GOT1 to chromosome 1; 6PGD to chromosome 4; LDHA to chromosome 5; LDHB to chromosome 8; and PGK and G6PD to the X chromosome. On the basis of indirect evidence we also tentatively assigned HPRT to the X chromosome and TK to chromosome 5 of M. domestica. These are the first tentative chromosomal assignments by any technique for this species.

Animals↗
PubMed1996

Organization and chromosomal localization of a B1-like containing repeat of Microtus subarvalis.

A repetitive DNA sequence, MS2, was isolated from EcoRI-digested genomic DNA of the vole, Microtus subarvalis. The fragment was cloned and sequenced. Sequence analysis of this 1194-bp fragment revealed a 156-bp region demonstrating a 55% homology with the mouse B1 repeat. The remaining MS2 sequence shows no significant homology with other known GenBank sequences. The results of in situ hybridization of MS2 on vole metaphase chromosomes indicate the fragment is confined to heterochromatin blocks of the sex chromosomes in all but one species (M. arvalis). Distribution of MS2 sequences provides evidence for heterogeneity of the giant heterochromatin blocks of the XY Chromosomes (Chrs) in voles, for the unique cluster-like localization of MS2 within these blocks.

Amino Acid Sequence↗
PubMed1995

[High resolution GTG banding and nucleolus organizer regions of chromosomes from the vole Microtus kirgisorum].

The use of GTG-banding of chromosomes in combination with the pipette method of chromosome preparation at the early metaphase made it possible to distinguish about 520 segments in the haploid chromosome set of vole Microtus kirgisorum. The ideogram of M. kirgisorum chromosomes was obtained on the basis of detailed investigation of chromosomes at different condensation levels. Data of the localization and the number of nucleolus-organizer regions are given.

Animals↗
PubMed1995

High-resolution G-banding of chromosomes in Microtus subarvalis (Rodentia, Arvicolidae)

Karyotypes of six females and four males of the East European vole (Microtus subarvalis) were prepared from spleen cell cultures. G-banding of early metaphase chromosomes has allowed us to distinguish 488 bands in the haploid set of chromosomes of M. subarvalis. Based on the detailed study of chromosomes at various levels of condensation, an idiogram has been built up for the chromosomes of the East European vole.

Animals↗
PubMed1994

Demonstration of the X-linkage and order to the genes GLA, G6PD, HPRT, and PGK in two vole species of the genus Microtus.

Using a variety of genetic methods, it is shown in this paper that the genes GLA, G6PD, HPRT, and PGK are X-linked in the vole Microtus subarvalis. The order of these genes has been investigated in two vole species, M. subarvalis and M. kirgisorum, by using the mapping technique of Goss and Harris (1977a, b), which depends on the analysis of gamma-ray-induced gene segregation. The experimental data were processed with the computer programme RHMAP (Ginsburg et al., 1993). The analysis indicated that the correct gene order in M. subarvalis is PGK-HPRT-G6PD-GLA, and the same gene order was found to be the most probable for M. kirgisorum. The relative distances between the genes in the two vole species are apparently the same. The RHMAP programme has also been applied to data previously reported for the same set of X-linked genes in the American mink (Zhdanova et al., 1988), the Australian marsupial Planigale maculata (Dobrovic and Graves, 1986), and man. The evolutionary conservation of the linear order of these X-linked genes in different mammalian taxa is discussed.

Animals↗