PubMed Health⌕ Search

Biomedical subjects

S M Zakiian

Publications and source records attributed to S M Zakiian.

At least 19 recordsLinked to original sources
PubMed2006

[Chromatin modifications during X-chromosome inactivation in female mammals].

In female mammals, the process of dosage compensation occurs during early embryonic development. As a result of this, one of X-chromosomes becomes transcriptionally inactive. This process is accompanied by chromatin remodeling on inactivated X-chromosome, providing transcriptional silencing of the genes and maintenance of their inactive state. In the present review, the dynamics of modifications occurring during embryonic inactivation, their distribution over the inactive X-chromosome, interaction, and the role in establishing and maintening the inactive state are discussed. As an illustration, modifications on the inactive X-chromosome of the Microtus common vole are presented.

Animals↗
PubMed2004

[Evolution of mammalian sex chromosomes: cooperation of genetic and epigenetic factors].

The X and Y chromosomes of mammals, which significantly differ in structure and genetic composition, are thought to originate from a pair of autosomes. During evolution of sex chromosomes in placental mammals, the degradation of the Y chromosome and inactivation spreading along the X chromosome occurred gradually and in concert. Thus, at the molecular level, the genetic and epigenetic factors interacted toward greater differentiation of the X/Y pair. In this review, in context of a comparison permitting to trace this evolutionary pathway, we consider the structural features of mammalian sex chromosomes focusing on the X-chromosomal genes and the unique epigenetic mechanism of their regulation. Possible causes and consequences of the genes skipping inactivation and aspects of molecular mechanism of X-chromosome inactivation are discussed. A number of hypotheses are considered on evolutionary relationships of X-chromosome inactivation and other molecular processes in mammals.

Animals↗
PubMed2003

[SMC (structural maintenance of chromosomes) structural protein family and their role in chromatin reorganization].

Structural chromatin proteins of the SMC (Structural Maintenance of Chromosomes) family play an important role in structural DNA reorganization in pro- and eukaryotes. Eukaryotic SMC proteins are the core components of the cohesin and condensin complexes. The cohesin complex is responsible for sister chromatid and homolog cohesion in mitosis and meiosis. The condensin complex uses ATP energy to induce positive coiled-coils in DNA, which results in compaction of the latter and formation of mitotic chromosome scaffold. In addition, the SMC proteins constitute recombination and recombination repair complexes. In hermaphrodites of nematode Caenorhabditis elegans, the SMC protein-containing complex controls dosage compensation and inactivation of the X chromosome genes.

Adenosine Triphosphate↗
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↗
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↗
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

[Mapping the silver fox genome. IV. Determination of chromosomal location of genes for ornithine carbamoyltransferase and prion protein].

The location in chromosomes of genes encoding ornithine carbamoyltransferase (ornithine transcarbamylase, OTC) and prion protein (PrP) was determined by Southern blotting of DNAs obtained from a panel of hybrid (for x Chinese hamster) somatic cell clones, with human OTC and Chinese hamster PrP DNA fragments used as probes. The gene OTC was located in the X-chromosome and PrP was located in chromosome 14 of the fox.

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↗
PubMed1993

[Construction of a mapping panel of human-rodent hybrid cells].

A clone panel of 27 human-Chinese hamster and 4 human-mouse somatic cell hybrids which contained as minimum five discriminating clones for any chromosome pairs was set up. Segregation analysis of 45 human chromosome-specific isoenzymes and PCR markers in hybrid clones allowed to demonstrate a possibility to apply the obtained panel for chromosome mapping of human genes.

Animals↗
PubMed1993

[Establishment of linkage and the order of the genes GALA, G6PD, HPRT and PGK on the X-chromosome in two species of voles of the genus Microtus].

Localization of genes GALA, G6PD, HPRT and PGK on X-chromosome of Microtus subarvalis has been proved. Using the radiation hybrid mapping technique of Goss and Harris, the order of these genes for two species M. subarvalis and M. Kirgisorum was established. Statistical methods (program package RHMAP) result in the only gene order PKG--HPRT--G6PD--GALA for M. subarvalis. The same order was found to be the most probable for M. kirgisorum. Relative distances between these genes in two species appeared to be practically equal. A conservatism of a linear order of the X-linked genes in various mammalian taxons is discussed.

Animals↗
PubMed1993

[Statistical validation of a radiation mapping method].

Correct statistical treatment of results of Goss and Harris experiments on radiation hybrid mapping is proposed. Using stochastic simulation a problem of an optimal sample size is investigated. Reasons for a repetition of experiments with different doses of radiation are discussed.

Animals↗
PubMed1993

[The detection of the location of glucose-6-phosphate dehydrogenase in the fibroblasts of voles and mice and in rat myoblasts by using monoclonal antibodies against glucose-6-phosphate dehydrogenase].

Monoclonal antibodies (MAs) were produced against glucose-6-phosphate dehydrogenase (G6PD) of two vole species--Microtus arvalis and M. subarvalis. The binding level of the MAs to G6PD in both species were almost the same, which suggested that these MAs may be specific for the antigenic determinants common to G6PD of these species. The MAs produced against the vole G6PD were used for its intracellular localization. The patterns obtained after staining cells with the use of MAs against G6PD were the same as those obtained after staining with the use of antibodies against F-actin. There was a good conformity between the results of light and electron microscopic immunoenzyme analyses with regard to the binding of MAs produced to the actin microfilaments. It is concluded that G6PD is closely associated with actin microfilaments of the cell cytoskeleton.

Animals↗
PubMed1993

[Comparative analysis of the level of heterozygosity for glucose phosphate isomerase (GPI) locus in silver foxes (Vulpes vulpes) of domesticated and control populations].

This communication is the first step of the studies on the correlation between protein polymorphism and the level of phenotypic diversity. The level of heterozygosity for glucose phosphate isomerase (GPI) locus was analysed in two populations of silver foxes. One of them has been selected for domestic behaviour during many years. This selection vector gave rise to many phenotypic novelties; 46% of the foxes analyzed has aberrant phenotypes. Another population was control bred under the same conditions of experimental farm of Siberian Dept. Russian Sci. with a commercial purpose. All the foxes analyzed from this population, except one, had a standard phenotype. Among 96 domestic foxes under analysis, only one heterozygotes for the GPI locus was detected. Among 112 control foxes, six were heterozygotes. In other words the data obtained indicate no correlation between the level of morphological diversity and the state of heterozygosity of the GPI locus.

Animals↗
PubMed1992

[Structural heterochromatin and X-chromosome inactivation].

Our previous studies on the expression of the G6PD and alpha-GAL genes from the X chromosome of inter-specific hybrids of voles of the Microtus genus have demonstrated an unusual pattern of X-inactivation in the parents. The observed phenomenon was explained as the presumable result of nonrandom inactivation of the X chromosomes with a heterochromatin block in crosses involving Microtus arvalis whose X lacks a heterochromatin region and also of random X inactivation when both parents had heterochromatin blocks on the Xs. Based on known models, we discuss here the possible mechanisms of the effect of heterochromatin on X-inactivation; we give preference to the model postulating binding of nonhistone protein to the inactivation centre as the key event. The hypothesis we offer suggests change in chromatin conformation in the inactivation centre during packaging of heterochromatic region of a chromosome; the protein molecules diffusing along the chromosome towards the heterochromatin region by the "facilitated diffusion" mechanism may happen to be in the region of the X-inactivation centre, which, being in a favorable state, binds specifically to it; as a consequence, the binding probability of protein to heterochromatin increases as compared to chromosome without heterochromatin block.

Animals↗
PubMed1991

[Heterochromatin as a factor influencing X-chromosome inactivation in hybrids of the common vole (Microtinae, Rodentia)].

Expression of X-linked genes for G6PD and alpha-GAL was studied in female interspecific hybrids of Microtus. The G6PD and alpha-GAL isozymes of Microtus arvalis were found to predominate in all cases when a species carrying a heterochromatin block on the X-chromosome served as one partner of hybridization and M. arvalis containing no heterochromatin block served as another. The proportions of G6PD and alpha-GAL parental forms were approx. equal in hybrid females when both species participating in hybridization contained heterochromatin blocks on X-chromosomes. Cytological analysis for revealing active and nonactive X-chromosomes on metaphase spreads of hybrid females supports the biochemical data. Non-random inactivation of X-chromosomes carrying the heterochromatin blocks in the interspecific hybrids with M. arvalis and a random one, when both parents contain heterochromatin blocks on the X-chromosomes are supposed to be the cause for the phenomenon observed. The study provided data supporting our previous hypothesis that heterochromatin affects the X-chromosome inactivation process in interspecific hybrid voles.

Animals↗
PubMed1991

[Morphology and behavior of the sex chromosomes in meiosis in four vole species of the genus Microtus].

Morphology and behaviour of the X and Y chromosomes of four species of genus Microtus were studied at pachytene, metaphase I and meiotic metaphase. The X chromosomes of the species varied with respect to their size and location of heterochromatic blocks. The axes of X and Y chromosomes of these species as well as Microtus agrestis never formed true synaptonemal complexes at any sub-stage of the pachytene. They approached each other at the start of the pachytene throughout to metaphase I, getting situated closely. At the end of the pachytene, they formed sex vesicle. The X and Y chromosomes kept their proximity during metaphase I, but never formed true bivalents. It is suggested that lack of synapsis of the X and Y chromosomes in the genus Microtus is the final step of evolutionary trend to reduction of the size of the pseudo-autosomal region. The abolition of restrictions on homology between the X and Y chromosomes is supposed to be a cause for the fast divergence in morphology of sex chromosomes in the genus.

Animals↗