Negative control of CSL gene transcription by stress/DNA damage response and p53.

CSL is a key transcriptional repressor and mediator of Notch signaling. Despite wide interest in CSL, mechanisms responsible for its own regulation are little studied. CSL down-modulation in human dermal fibroblasts (HDFs) leads to conversion into cancer associated fibroblasts (CAF), promoting keratinocyte tumors. We show here that CSL transcript levels differ among HDF strains from different individuals, with negative correlation with genes involved in DNA damage/repair. CSL expression is negatively regulated by stress/DNA damage caused by UVA, Reactive Oxygen Species (ROS), smoke extract, and doxorubicin treatment. P53, a key effector of the DNA damage response, negatively controls CSL gene transcription, through suppression of CSL promoter activity and, indirectly, by increased p21 expression. CSL was previously shown to bind p53 suppressing its activity. The present findings indicate that p53, in turn, decreases CSL expression, which can serve to enhance p53 activity in acute DNA damage response of cells

Comparaison des sections efficaces des réactions (p, n) et (p, pn) induites sur le thorium par des protons de 30 à 150 MeV

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Tracking the phase-transition energy in disassembly of hot nuclei

In efforts to determine phase transitions in the disintegration of highly excited heavy nuclei, a popular practice is to parametrise the yields of isotopes as a function of temperature in the form $Y(z)=z^{-\tau}f(z^{\sigma}(T-T_0))$, where $Y(z)$'s are the measured yields and $\tau, \sigma$ and $T_0$ are fitted to the yields. Here $T_0$ would be interpreted as the phase transition temperature. For finite systems such as those obtained in nuclear collisions, this parametrisation is only approximate and hence allows for extraction of $T_0$ in more than one way. In this work we look in detail at how values of $T_0$ differ, depending on methods of extraction. It should be mentioned that for finite systems, this approximate parametrisation works not only at the critical point, but also for first order phase transitions (at least in some models). Thus the approximate fit is no guarantee that one is seeing a critical phenomenon. A different but more conventional search for the nuclear phase transition would look for a maximum in the specific heat as a function of temperature $T_2$. In this case $T_2$ is interpreted as the phase transition temperature. Ideally $T_0$ and $T_2$ would coincide. We invesigate this possibility, both in theory and from the ISiS data, performing both canonical ($T$) and microcanonical ($e=E^*/A$) calculations. Although more than one value of $T_0$ can be extracted from the approximate parmetrisation, the work here points to the best value from among the choices. Several interesting results, seen in theoretical calculations, are borne out in experiment.Comment: Revtex, 10 pages including 8 figures and 2 table

The cross sections for different channels in heavy ion nuclear reactions

Estimates have been made for the critical value lc of the orbital angular momentum above which a complete fusion nucleus cannot be formed. The results have been obtained by measurements of cross sections for noncompound inelastic processes (inelastic scattering, transfer. reactions, α particle emission) when Ag targets were bombarded by 86 MeV 12C ions and by 78 and 113 MeV 14N ions. The average value of lc was found between 38 and 45 ħ. A short discussion is given on the range of angular momenta at which transfer reactions occur. It is shown that quasi elastic single and multi-nucleon transfer reactions are possible only for large values of l called lT. When the bombarding energy is high enough, theses values lT are larger than lc and there is a region of l between l c and lT where a very inelastic mechanism takes place. A model called « fusion prompt scission » process is proposed. It is suggested that a deformed shape for the two fissioning nuclei is temporarly formed and breaks off very shortly after.La valeur critique lc du moment angulaire au-delà duquel un noyau composé de fusion ne peut plus être formé, a été estimée. Les résultats ont été obtenus selon une nouvelle méthode qui consiste à mesurer la section efficace de tous les processus ne faisant pas intervenir le noyau composé (diffusion inélastique, réactions de transfert, émission de particules alpha vers l'avant). L'étude a été effectuée au moyen d'ions 12C de 86 MeV et d'ions 14N de 78 et 113 MeV bombardant des cibles d'argent. On a trouvé lc compris entre 38 et 45 ħ quelque soit l'ion incident et l'énergie. On discute ensuite brièvement pour quelle région de moments angulaires les réactions de transfert ont lieu. On montre que les cas de transferts quasi élastiques sont possibles seulement pour des l élevés, de valeur moyenne lT dépendant de l'énergie incidente. lT devient très supérieur à lc lorsque l'énergie croit et un mécanisme d'échange de nucléons très inélastique intervient dans la région comprise entre lc et l T. Un modèle est proposé qui consiste en une fusion de durée très brève des deux noyaux sous la forme d'une configuration très déformée

Production de tritium dans le thorium par des protons de 135 MeV

We have measured the cross-section of tritium production by bombardement of thorium by 135 MeV protons in the Orsay synchro-cyclotron. The tritium was separated from the targets by heating in a graphite crucible with a high-frequency generator, under hydrogen gas pressure. Tritiated water was synthetised and the tritium was measured with liquid scintillator. A value of 19.5 ± 0.05 mbarns was obtained for the tritium-cross section and ten percent of tritons have energies higher than 35 MeV. This large cross-section is attributed to a double pick-up process.On a mesuré la section efficace de production de tritium après bombardment de thorium par des protons de 135 MeV accélérés au synchro-cyclotron d'Orsay. Le tritium était extrait des cibles par chauffage, dans un creuset de graphite, par courants H. F. sous atmosphère d'hydrogène. L'hydrogène tritié était ensuite transformé en eau tritiée et le tritium mesuré au moyen de scintillateur liquide. La section efficace obtenue est de 19,5 ± 0,5 mbarns et dix pour cent des tritons ont une énergie supérieure à 35 MeV. On attribue cette production à un processus de double pick-up

Interplay of initial deformation and Coulomb proximity on nuclear decay

Alpha particles emitted from an excited projectile-like fragment (PLF*) formed in a peripheral collision of two intermediate-energy heavy ions exhibit a strong preference for emission towards the target-like fragment (TLF). The interplay of the initial deformation of the PLF* caused by the reaction, Coulomb proximity, and the rotation of the PLF* results in the observed anisotropic angular distribution. Changes in the shape of the angular distribution with excitation energy are interpreted as being the result of forming more elongated initial geometries in the more peripheral collisions.Comment: 4 figure