Mammalian telomere biology

The review considers the function of the important chromosome regions telomeres in normal and immortal cells. Telomeres are dynamic nucleoprotein structures that cap the ends of eukaryotic chromosomes, protecting them from degradation and end-to-end fusion. The functional state of telomeres depends on many interrelated parameters such as telomerase activity, the status of the telomere safety complex shelterin, and telomere-associated proteins (replication, recombination, DNA break repair factors, etc.). Special attention is paid to the mechanisms that control the telomere length in normal and immortal cells as well as in cells containing or lacking active telomerase. The features attributed to an alternative telomere length control are analyzed, in particular, in view of a recently discovered additional mechanism of telomere shortening by t-cycle trimming. The possibility of expressing both telomerase-dependent and recombinational pathways of telomere length control in normal mammalian cells is considered, as well as the role of shelterin proteins in choosing one of them to be dominant. The review additionally discusses the role of telomeres in the spatial organization of the nucleus during mitosis and meiosis and specific telomere organizations in mammals, including Iberian shrews with their unusual or rare chromosome structures.     

Recombinogenic Telomeres in Diploid Sorex granarius (Soricidae,Eulipotyphla) Fibroblast Cells

The telomere structure in the Iberian shrew Sorex granarius is characterized by unique, striking features, with short arms of acrocentric chromosomes carrying extremely long telomeres (up to 300 kb) with interspersed ribosomal DNA (rDNA) repeat blocks. In this work, we investigated the telomere physiology of S. granarius fibroblast cells and found that telomere repeats are transcribed on both strands and that there is no telomere-dependent senescence mechanism. Although telomerase activity is detectable throughout cell culture and appears to act on both short and long telomeres, we also discovered that signatures of a recombinogenic activity are omnipresent, including telomere-sister chromatid exchanges, formation of alternative lengthening of telomeres (ALT)-associated PML-like bodies, production of telomere circles, and a high frequency of telomeres carrying marks of a DNA damage response. Our results suggest that recombination participates in the maintenance of the very long telomeres in normal S. granarius fibroblasts. We discuss the possible interplay between the interspersed telomere and rDNA repeats in the stabilization of the very long telomeres in this organism.     

Subcellular localization and self-interaction of plant-specific Nt-4/1 protein

The Nicotiana tabacum Nt-4/1 protein is a plant-specific protein of unknown function. Analysis of bacterially expressed Nt-4/1 protein in vitro revealed that the protein secondary structure is mostly alpha-helical and suggested that it could consist of three structural domains. Earlier studies of At-4/1, the Arabidopsis thaliana-encoded ortholog of Nt-4/1, demonstrated that GFP-fused At-4/1 was capable of polar localization in plant cells, association with plasmodesmata, and cell-to-cell transport. Together with the At-4/1 ability to interact with a plant virus movement protein, these data supported the hypothesis of the At-4/1 protein involvement in viral transport through plasmodesmata. Studies of the Nt-4/1-GFP fusion protein reported in this paper revealed that the protein was localized to cytoplasmic bodies, which were co-aligned with actin filaments and capable of actin-dependent intracellular movement. The Nt-4/1-GFP bodies, being non-membrane structures, were found in association with the plasma membrane, the tubular endoplasmic reticulum and endosome-like structures. Bimolecular fluorescence complementation experiments and inhibition of nuclear export showed that the Nt-4/1 protein was capable of nuclear-cytoplasmic transport. The nuclear export signal (NES) was identified in the Nt-4/1 protein by site-directed mutagenesis. The Nt-4/1 NES mutant was localized to the nucleoplasm forming spherical bodies. Immunogold labeling and electron microscopy of cytoplasmic Nt-4/1-containing bodies and nuclear structures containing the Nt-4/1 NES mutant revealed differences in their fine structure. In mammalian cells, Nt-4/1-GFP formed cytoplasmic spherical bodies similar to those found for the Nt-4/1 NES mutant in plant cell nuclei. Using dynamic laser light scattering and electron microscopy, the Nt-4/1 protein was found to form multimeric complexes in vitro.     

Genotoxic and Carcinogenic Effects of Industrial Factors in Coal Mining and Coal-Processing Industry (Review)

Russian Journal of Genetics - This paper presents a review of research devoted to the study of genotoxic and carcinogenic effects of exposure to factors of the production environment of the coal...     

Carbohydrate and pyruvic acid degradation pathways in Fusidium coccineum strains with varying levels of antibiotic synthesis]

A number of enzymes and reactions of glycolysis, pentose-phosphate cycle and degradation of pyruvic acid in strains of F. coccineum with various levels of antibiotic production was studied comparatively. The experiments showed that highly productive strains were characterized by higher activity of the NADP-deficient enzymes of the pentoze-phosphate cycle as compared to the low active strains. The activity levels of glycolytic enzymes, such as fructose-diphosphate-aldolase and 3-phosphoglycerolaldehydehydrogenase did not practically differ. Significant differences were found in the reactions of puryvic acid degradation: the activity of cytoplasmic pyruvatedecarboxylase in the mutant with high antibiotic production level was lower than that in the low productive strain, while oxidation of the pyruvate of the mitochondrial fraction was on the contrary more intensive than in the highly productive strain. Therefore, metabilism in the strains studied was characterized by ever-increasing biochemical changes with an increase in their antibiotic productivity. Lowering of the growth rate of the mutants as their capacity for antibiotic supersynthesis increased and subsequently the anabolic processes became more intensive was accompanied by increasing derepression of the key enzymes of carbohydrate metabolism and in particular NADR-deficient dehydrogenase of the pentose cycle and pyruvatedehydrogenase, significant for fusidin biosynthesis and providing production of the antibiotic of steroid nature by cofactor NADP-H and acetyl-KoA, the primary precursor.     

Synthesis of a lens-specific antigen (delta-crystallin) in rudimentary chicken adenohypophysis

The synthesis of two lens-specific proteins, delta- and beta-crystallins, by adenohypophyseal anlage of 4-day chick embryos was studied by the immunofluorescence technique in conjunction with autoradiography. Isolated anlages were incubated for 16 hours in a culture medium containing 14c-leucine. The synthesis was determined with the use of an unlabelled carrier, extract of chick lens, as well as of antisera against delta- and beta-crystallins. 14C-Leucine incorporation was found to occur only in delta-crystalline precipitation line rather than in beta-crystallin line. This evidence attests to the synthesis of delta-crystalline by the chick embryo adenohypophyseal anlage. The results are in agreement with the previously obtained immunohistochemical data on delta-crystalline localization in cells of the developing adenohypophysis.     

Interaction of pregna-D'-pentaranes--pentacyclic derivatives of progesterone--with gestagen-binding sites of uterine cytosol

The interaction of promegestone (R-5020), progesterone (P) and its derivatives having and additional carbocyclic D' (pregna-D'-pentrans) with progestin-binding cytosol system of the uterus was studied in different species (rabbits, rats, guinea-pigs and men). A comparative analysis of the competitive binding data for the mentioned compounds has shown interspecies differences in ligand specificity. Two types of binding sites for 3H-D'-pentran (in contrast to R-5020 and P) have been detected in rabbit uterus cytosol, both in intact and estrogenized animals. However, in rabbits, estrogenization altered the values of the apparent equilibrium constants and binding capacities. At the same time, the interaction of pentran with progestin-binding sites in guinea-pig and human uterus cytosol is nonspecific. It is suggested that the features of the interaction of 3H-D'-pentran with its binding sites in rabbit uterus cytosol may be determined by an increase in hydrophobic bond.     

The structure of long telomeres in chromosomes of the Iberian shrew

It is shown that the size, localization, and structure of telomeres in the Iberian shrew (Sorex granarius) are not characteristic of mammals. In this species, long telomeres of an average size of 213 kb are localized on the short arms of all 32 acrocentrics; ribosomal blocks and active nucleolus-organizing regions (NORs) were also discovered there. At the remaining chromosome ends the average size of telomeres is 3.8 kb. However, in a closely related species, Sorex araneus, all telomeres have size similar to that of human telomeres, i.e., 6.8–15.2 kb. Despite the fact that some long telomeres contain ribosomal repeats in addition to telomeric ones, the long telomeres have preserved asymmetry of G- and C-rich strands as in functional telomeres. It is probable that long telomeres were formed in meiosis at the stage of chromosome bouquet as a result of global reorganization of the chromosome ends. The provoking factors for such reorganization might be the fission of several metacentrics and the necessity of telomerization of the resulting acrocentrics.