PubMed Health⌕ Search

Biomedical subjects

T B Nesterova

Publications and source records attributed to T B Nesterova.

At least 19 recordsLinked to original sources
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↗
PubMed1994

[Prospects for obtaining a mapping panel for somatic cell marsupial-rodent hybrids for the short-tailed opossum Monodelphis domestica].

A possibility of obtaining a panel of marsupial-rodent somatic cell hybrid clones has been explored, with a view to mapping the genome of the opossum (Monodelphis domestica). Fusion of opossum cells (splenocytes, bone marrow cells, and fibroblasts) with fibroblasts of Chinese hamster or vole (HGPRT- and TK- mutants, respectively) produced 146 hybrid clones. The majority of marsupial-mammalian somatic cell hybrids were characterized by pronounced fragmentation and segregation of marsupial chromosomes. To overcome this difficulty, a method for rapid screening was developed, which allowed the early selection of clones rich in chromosomal material of opossum. Based on the screening results, 25 clones of independent origin were selected. A detailed genetic analysis, which included chromosome G-banding and in situ hybridization of biotin-labeled opossum DNA on metaphase chromosomes, allowed further selection of seven hybrid clones containing one to six intact chromosomes of M. domestica. Opossum chromosomes were present in various combinations against the background of Chinese hamster or vole chromosomes. The clones will be included in the panel of opossum-rodent somatic cell hybrids, which is currently being created.

Animals↗
PubMed1994

[Rapid karyotyping of mammalian cells].

The use of "pipette" method ensures rapid preparation of standardized whole metaphase spreads. Experiments with human, murine, Chinese hamster, American mink, green African monkey, dog, and vole cells demonstrated that G-banded whole metaphase spreads can be obtained in less than two hours after the beginning of work with cell or tissue culture. Due to that, it became possible to start karyotyping of animal tissue explants, as well as fetal cells present in human amniotic fluid, on day 3 to 4 after their receiving.

Animals↗
PubMed1994

[X chromosome inactivation in mammals].

The most important results of the last 30 years of studies on mammalian X-chromosome inactivation are reviewed. The data on X-chromosome inactivation in cells of embryonic and extraembryonic tissues and in male and female germ cell lines are discussed. Special attention is paid to data on mapping and functioning of the X-inactivation center and of recently discovered gene XIST. The main hypotheses concerning the mechanisms responsible for X-chromosome inactivation are considered. A new model of X-inactivation is proposed, which regards heterochromatin as a nonspecific activator of nucleation of the X-chromosome on which it is located.

Animals↗