Interaction of clinically important human DNA topoisomerase I poison, topotecan, with double-stranded DNA

Topotecan (TPT), a water-soluble derivative of camptothecin, is a potent antitumor poison of human DNA topoisomerase I (top1) that stabilizes the cleavage complex between the enzyme and DNA. The role of the recently discovered TPT affinity to DNA remains to be defined. The aim of this work is to clarify the molecular mechanisms of the TPT-DNA interaction and to propose the models of TPT-DNA complexes in solution in the absence of top1. It is shown that TPT molecules form dimers with a dimerization constant of (4.0 +/- 0.7) x 10(3) M(-1) and the presence of DNA provokes more than a 400-fold increase of the effective dimerization constant. Flow linear dichroism spectroscopy accompanied by circular dichroism, fluorescence, and surface-enhanced Raman scattering experiments provide evidence that TPT dimers are able to bind DNA by bridging different DNA molecules or distant DNA structural domains. This effect may provoke modification of the intrinsic geometry of the cruciform DNA structures, leading to the appearance of new crossover points that serve as the sites of the top1 loading position. The data presume the hypothesis of TPT-mediated modulation of top1-DNA recognition before ternary complex formation.     

Evaluation of the role of uniparental disomy in early embryolethality of man

We carried out systematic studies of the contribution of uniparental disomy for eight human chromosomes, 2, 9, 11, 15, 16, 19, 20, and 21, to the etiology of spontaneous mortality of human embryos. Most of these chromosomes have regions with orthologous imprinted genes syntenic with those on mouse chromosomes, the disturbed expression of which is related to embryolethality in mice. Screening of uniparental disomy in spontaneous 5- to 16-week abortuses was performed by evaluation of the pattern of inheritance of alleles of polymorphic microsatellite loci located in the studied chromosomes. A total of 100 human embryos with cytogenetically determined normal karyotype were studied, in which arrest at the early stages of intrauterine development was determined by ultrasound examination of pregnant women. During this study, 13 embryos were discarded due to karyotype anomalies or nonpaternity. No cases of uniparental disomy were found among the 87 studied abortuses for any of chromosomes studied. The analysis of the results of this study and four other studies concerning the search for uniparental disomy in dead embryos and fetuses did not reveal its elevated frequency in spontaneous abortuses as compared to the theoretically expected value based on evaluation of the probable combination of meiotic errors in human gametes. The data we obtained suggest that, first, uniparental disomies for human chromosomes that have regions with orthologous imprinted genes syntenic with mouse chromosomes do not contribute noticeably to the death of human embryos at the early developmental stages and, second, the mechanisms underlying embryolethality as a result of disturbed expression of imprinted loci differ markedly in mammals evolutionarily remote from one other.     

Protein interaction with hydrated C60 fullerene in aqueous solutions

Physicochemical effects of hydrated C(60) fullerenes (HyFn) on serum albumin molecules were studied using ESR spin labeling and differential scanning microcalorimetry. Molecular-colloidal solution of hydrated C(60) fullerenes and their small spherical fractal clusters in water (C(60)FWS), was shown to stabilize protein hydration, and decrease specific surface energy in water-protein matrix in salt solutions. The mechanism of HyFn interaction with protein is discussed in terms of HyFn induced formation of protein clusters and phase transition of hydration water.     

DNA binding induces conformational transition within human DNA topoisomerase I in solution

We employed Raman and circular dichroism (CD) spectroscopy to probe the molecular structure of 68-kDa recombinant human DNA topoisomerase I (TopoI) in solution, in a complex with a 16-bp DNA fragment containing a camptothecin-enhanced TopoI cleavage site, and in a ternary complex with this oligonucleotide and topotecan. Raman spectroscopy reveals a TopoI secondary structure transition and significant changes in the hydrogen bonding of the tyrosine residues induced by the DNA binding. CD spectroscopy confirms the Raman data and identifies a DNA-induced (>7%) decrease of the TopoI alpha helix accompanied by at least a 6% increase of the beta structure. The Raman DNA molecular signatures demonstrated a bandshift that is expected for a net change in the environment of guanine C6 [double bond] O groups from pairing to solvent exposure. The formation of a ternary cleavage complex with TopoI, DNA, and topotecan as probed by CD spectroscopy reveals neither additional modifications of the TopoI secondary structure nor of the oligonucleotide structure, compared to the TopoI-oligonucleotide complex.     

Effect of external environmental factors on DNA content in Euglena]

The chromosome number and DNA content in Euglena gracilis cell have been shown by the number of investigators to vary essentially under the influence of some environmental factors (low phosphate and acetate concentrations, density of culture, temperature, light/dark regime, streptomycin treatment). Variability in the nuclear DNA quantity is supposed to be an important peculiarity of the structure and functional activity of the genome of Euglena gracilis.     

红腹锦鸡肺的组织结构与微血管构筑

为了了解红腹锦鸡(Chroysolophus pictus)肺的微细结构和微血管构筑特征,为呼吸生物学研究提供形态学依据,用组织学方法和微血管铸型技术在光镜和扫描电镜下观察研究了红腹锦鸡肺的组织结构与微血管构筑情况。结果表明,红腹锦鸡肺主要由各级支气管构成,从三级支气管上呈辅射状分出许多呼吸毛细管(微气管),并相互吻合成网状,呼吸毛细管外面包围有丰富的毛细血管;红腹锦鸡肺毛细血管垂直围绕在各微气管外,并相互吻合成密集的立体微血管网;毛细血管管径4.5~7.0μm,微气管直径11~50μm。并对肺微血管构筑情况与呼吸效率的关系作了探讨。     

Effect of the frequency of X-monosomal cell clone on variability of anthropometric indicators in Shereshevsky-Turner syndrome]

Using methods of mathematical statistics the relationships were determined between 31 anthropometric traits (ATs) and the frequency of the X-monosome cell clone in 53 patients with either 45, X-monosomy or mosaic forms (45,X/46,XX) of the Shereshevsky-Turner syndrome (STS). AT variations were studied in patients untreated with growth hormone and in 25 control fertile healthy women. In 29 patients, the degree of mosaicism was assessed by interphase FISH analysis using X-centromer-specific DNA probe hybridized to the cell nuclei of two types of tissues differing in embryonic origin (lymphocytes and oral epithelium, originating from meso- and ectoderm, respectively). The level of X-monosome mosaicism had a substantial effect on some AT, which depended similarly on the proportion of X-monosome cells in tissues of different embryonic origin. Statistically significant negative correlations were revealed between the size of X-monosome clone and 13 height-weight, longitudinal, and circumference traits, whereas positive correlations were characteristic of seven mostly width traits. Eleven ATs showed no correlation with the X-monosome cell clone. Discriminant analysis of all ATs, whose variations depended on the frequency of X-monosome cell clone, was found to be an essential tool for precise classification of both STS patients with different degree of mosaicism and healthy women. Based on these results, the set of ATs characteristic of the STS phenotype was identified.     

Stress-reactivity of a Drosophila melanogaster strain with impaired juvenile hormone action

Met(27) is a null allele of the Methoprene-tolerant gene of D. melanogaster that shows resistance to the toxic effects of both juvenile hormone (JH) and a JH analog, methoprene. The mechanism of resistance appears to be altered JH reception. We measured fertility, JH-hydrolyzing activity, and dopamine (DA) levels in Met(27) and Met(+) flies under normal (25 degrees C) and heat-stress (38 degrees C) conditions. We show that under normal conditions Met(27) females have JH-hydrolyzing activity and fertility lower than Met(+), but DA content did not differ between the two strains. At 38 degrees C Met(27) flies show no impairment in JH-hydrolyzing activity in response to stress, but they do show lower DA levels and impaired reproduction. The results with Met(27) are consistent with the previous hypothesis that the alteration in fertility that follows heat stress in D. melanogaster could result from alteration in the JH endocrine system.     

Biogenic amines in Drosophila virilis under stress conditions

The effect of heat stress (38 degrees C) on the content of DL-beta-(3,4-dihydroxyphenyl)alanine (DOPA), dopamine, tyramine, octopamine, and their precursor Tyr was studied in adults of two lines of Drosophila virilis contrasting in their stress response. In individuals of line 101 responding to stress by a hormonal stress reaction, the contents of DOPA, dopamine, octopamine, and Tyr were lower than those of line 147 that did not respond to the stress. However, heat stress caused an increase in the contents of DOPA, dopamine, octopamine, and Tyr in line 101, whereas the equivalent titers in line 147 remain unchanged.