Radiation induction of delayed recombination in Schizosaccharomyces pombe.

Ionizing radiation is known to induce delayed chromosome and gene mutations in the descendants of the irradiated tissue culture cells. Molecular mechanisms of such delayed mutations are yet to be elucidated, since high genomic complexity of mammalian cells makes it difficult to analyze. We now tested radiation induction of delayed recombination in the fission yeast Schizosaccharomyces pombe by monitoring the frequency of homologous recombination after X-irradiation. A reporter with 200 bp tandem repeats went through spontaneous recombination at a frequency of 1.0 x 10(-4), and the frequency increased dose-dependently to around 10 x 10(-4) at 500 Gy of X-irradiation. Although the repair of initial DNA damage was thought to be completed before the restart of cell division cycle, the elevation of the recombination frequency persisted for 8-10 cell generations after irradiation (delayed recombination). The delayed recombination suggests that descendants of the irradiated cells keep a memory of the initial DNA damage which upregulates recombination machinery for 8-10 generations even in the absence of DNA double-strand breaks (DSBs). Since radical scavengers were ineffective in inhibiting the delayed recombination, a memory by continuous production of DNA damaging agents such as reactive oxygen species (ROS) was excluded. Recombination was induced in trans in a reporter on chromosome III by a DNA DSB at a site on chromosome I, suggesting the untargeted nature of delayed recombination. Interestingly, Rad22 foci persisted in the X-irradiated population in parallel with the elevation of the recombination frequency. These results suggest that the epigenetic damage memory induced by DNA DSB upregulates untargeted and delayed recombination in S. pombe

Delayed and stage specific phosphorylation of H2AX during preimplantation development of gamma-irradiated mouse embryos

Within minutes of the induction of DNA double-strand breaks in somatic cells, histone H2AX becomes phosphorylated in the serine 139 residue at the damage site. The phosphorylated H2AX, designated as gamma-H2AX, is visible as nuclear foci in the irradiated cells which are thought to serve as a platform for the assembly of proteins involved in checkpoint response and DNA repair. It is known that early stage mammalian embryos are highly sensitive to radiation but the mechanism of radiosensitivity is not well understood. Thus, we investigated the damage response of the preimplantation stage development by analyzing focus formation of gamma-H2AX in mouse embryos gamma-irradiated in utero. Our analysis revealed that although H2AX is present in early preimplantation embryos, its phosphorylation after 3 Gy gamma-irradiation is hindered up to the two cell stage of development. When left in utero for another 24-64 h, however, these irradiated embryos showed delayed phosphorylation of H2AX. In contrast, phosphorylation of H2AX was readily induced by radiation in post-compaction stage embryos. It is possible that phosphorylation of H2AX is inefficient in early stage embryos. It is also possible that the phosphorylated H2AX exists in the dispersed chromatin structure of early stage embryonic pronuclei, so that it cannot readily be detected by conventional immunostaining method. In either case, this phenomenon is likely to correlate with the lack of cell cycle arrest, apoptosis and high radiosensitivity of these developmental stages

Genome-Wide Redistribution of Meiotic Double-Strand Breaks in Saccharomyces cerevisiae

Meiotic recombination is initiated by the formation of programmed DNA double-strand breaks (DSBs) catalyzed by the Spo11 protein. DSBs are not randomly distributed along chromosomes. To better understand factors that control the distribution of DSBs in budding yeast, we have examined the genome-wide binding and cleavage properties of the Gal4 DNA binding domain (Gal4BD)-Spo11 fusion protein. We found that Gal4BD-Spo11 cleaves only a subset of its binding sites, indicating that the association of Spo11 with chromatin is not sufficient for DSB formation. In centromere-associated regions, the centromere itself prevents DSB cleavage by tethered Gal4BD-Spo11 since its displacement restores targeted DSB formation. In addition, we observed that new DSBs introduced by Gal4BD-Spo11 inhibit surrounding DSB formation over long distances (up to 60 kb), keeping constant the number of DSBs per chromosomal region. Together, these results demonstrate that the targeting of Spo11 to new chromosomal locations leads to both local stimulation and genome-wide redistribution of recombination initiation and that some chromosomal regions are inherently cold regardless of the presence of Spo11

Lower Extremity Power Training Improves Healthy Old Adults’ Gait Biomechanics

Purpose: Age-related slowing of gait speed predicts many clinical conditions in later life. We examined the kinematic and kinetic mechanisms of how lower extremity power training increases healthy old adults’ gait speed. Methods: We randomly allocated old adults to a training (age 74.3 y, 9 males, 6 females) and a control group (age 73.6 y, 3 males, 4 females) and compared the biomechanics of habitual and fast gait before and after 16 sessions (8 weeks) of lower extremity power training. Results: Training increased maximal leg press load by ∼40% (P \u3c 0.05) and maximal voluntary force in five groups of leg muscles by ∼32% (P \u3c 0.05) in the training group. Training vs. control tended to increase habitual (10.8 vs. 7.6%) and fast gait speed (17.6 vs. 9.0%; all P \u3c 0.05) more. In the training group only, these increases in gait speed correlated with increases in stride length (habitual: r2 = 0.84, fast: r2 = 0.89). Training made old adults’ gait more erect: hip and knee extension increased in the stance phase of gait. Training increased ankle joint positive work by 3.3 J (control: −0.4 J, Group by Time interaction: P \u3c 0.05), which correlated r2 = 0.58 and r2 = 0.67 with increases in habitual and fast gait speed without changes in hip and knee joint powers. Conclusion: Increases in leg muscle power increased healthy old adults’ gait speed through correlated increases in stride length and ankle plantarflexor work generation

La créativité altermondialiste (discours, organisation, action directe)

La thèse porte sur les pratiques créatives à l'œuvre dans certains groupes altermondialistes, à la lumière d'un rapport entre discours et action qui se transforme au cours de l'histoire de ces mouvements. Au cours de leur brève existence, les mouvements altermondialistes ont connu une croissance rapide, mais ont été confrontés à des problèmes qui les ont fait entrer en crise. On examine les conditions et les contraintes pesant sur cette créativité dans trois sphères d'exercice: le discours, les structures organisationnelles et l'action directe. Le rapport au discours politique des altermondialistes se situe d'emblée en tension avec d'autres discours anti-mondialisation. Sur le plan organisationnel, les mouvements mettent volontiers en avant leur spécificité, en s'appuyant sur une éthique du pluralisme politique qui conduit à considérer comme un atout la diversité interne des positions politiques. Pour eux, l'action directe apparaît comme conjuguant l'efficacité à une définition de la protestation plurielle, ouverte et démocratique. De fait, cette définition de l'action directe pose immédiatement des problèmes et occasionne des tensions internes.The dissertation studies creative practices within certain alter-globalization movements in a context marked by a changing relationship between discourse and action. During their brief history, alter-globalization movements have grown rapidly but they have met with some challenges which prompted their crisis. The aim is to examine the conditions and the constraints which shape this creativity in three realms: discourse, organizational structures and direct action. The movements' relation to discourse is marked by a tension with other anti-discrimination discourses. On the organizational level, the movements are keen on emphasizing their specificity by drawing on an ethics of political pluralism which leads them to consider the internaI diversity of political orientations as a strength. For them, direct action appears to conjugate efficiency with a plural, open and democratic form of protest. However, this definition meets with problems and leads to internaI tension.PARIS3-BU (751052102) / SudocSudocFranceF

p53-Dependent S-Phase Damage Checkpoint and Pronuclear Cross Talk in Mouse Zygotes with X-Irradiated Sperm

One difficulty in analyzing the damage response is that the effect of damage itself and that of cellular response are hard to distinguish in irradiated cells. In mouse zygotes, damage can be introduced by irradiated sperm, while damage response can be studied in the unirradiated maternal pronucleus. We have analyzed the p53-dependent damage responses in irradiated-sperm mouse zygotes and found that a p53-responsive reporter was efficiently activated in the female pronucleus. [(3)H]thymidine labeling experiments indicated that irradiated-sperm zygotes were devoid of G(1)/S arrest, but pronuclear DNA synthesis was suppressed equally in male and female pronuclei. p53(−/−) zygotes lacked this suppression, which was corrected by microinjection of glutathione S-transferase-p53 fusion protein. In contrast, p21(−/−) zygotes exhibited the same level of suppression upon fertilization by irradiated sperm. About a half of the 6-Gy-irradiated-sperm zygotes managed to synthesize a full DNA content by prolonging S phase, while the other half failed to do so. Regardless of the DNA content, all the zygotes cleaved to become two-cell-stage embryos. These results revealed the presence of p53-dependent pronuclear cross talk and a novel function of p53 in the S-phase DNA damage checkpoint of mouse zygotes

Pearson product moment correlation coefficients between maximal leg strength and gait speed before and after exercise intervention (n = 15).

<p>p, 2-tailed probability values for the correlation coefficient.</p><p>Pearson product moment correlation coefficients between maximal leg strength and gait speed before and after exercise intervention (n = 15).</p