Differential effect of ionizing radiation on transcription in repair-deficient and repair-proficient mice

Experiments were designed to examine in vivo changes in total transcription and in the expression of the c-fos gene following whole-body exposure of mice to JANUS fission-spectrum neutrons. Radiation repair-deficient (wst/wst) and -proficient (wst/., C57BL/6 x C3H F1) mice were exposed to JANUS fission-spectrum neutrons calibrated to deliver a gut dose of 50 cGy. Animals were sacrificed less than 10 or at 60 min postirradiation, and gut tissues were removed for study. Our results revealed that, in repair-proficient mice, an immediate depression (relative to untreated control) in total transcription was evident that continued through 1 h postirradiation. Conversely, radiation-sensitive wst/wst mice displayed doubled transcription levels postirradiation. Expression of c-fos was consistently depressed following radiation exposure in control and wst/wst mice. However, the depression of c-fos mRNA was delayed in wst/wst mice relative to controls. These results demonstrate abnormal regulation of transcription and of c-fos mRNA accumulation in repair-deficient wasted mice following exposure to ionizing radiation. In addition, this work documents rapid total transcriptional depression in normal mice following radiation exposure

The neutron imaging system fielded at the National Ignition Facility

We have fielded a neutron imaging system at the National Ignition Facility to collect images of fusion neutrons produced in the implosion of inertial confinement fusion experiments and scattered neutrons from (n, n′) reactions of the source neutrons in the surrounding dense material. A description of the neutron imaging system is presented, including the pinhole array aperture, the line-of-sight collimation, the scintillator-based detection system and the alignment systems and methods. Discussion of the alignment and resolution of the system is presented. We also discuss future improvements to the system hardware

The neutron imaging system fielded at the National Ignition Facility

We have fielded a neutron imaging system at the National Ignition Facility to collect images of fusion neutrons produced in the implosion of inertial confinement fusion experiments and scattered neutrons from (n, n′) reactions of the source neutrons in the surrounding dense material. A description of the neutron imaging system is presented, including the pinhole array aperture, the line-of-sight collimation, the scintillator-based detection system and the alignment systems and methods. Discussion of the alignment and resolution of the system is presented. We also discuss future improvements to the system hardware

Comparing neutron and X-ray images from NIF implosions

Directly laser driven and X-radiation driven DT filled capsules differ in the relationship between neutron and X-ray images. Shot N110217, a directly driven DT-filled glass micro-balloon provided the first neutron images at the National Ignition Facility. As seen in implosions on the Omega laser, the neutron image can be enclosed inside time integrated X-ray images. HYDRA simulations show the X-ray image is dominated by emission from the hot glass shell while the neutron image arises from the DT fuel it encloses. In the absence of mix or jetting, X-ray images of a cryogenically layered THD fuel capsule should be dominated by emission from the hydrogen rather than the cooler plastic shell that is separated from the hot core by cold DT fuel. This cool, dense DT, invisible in X-ray emission, shows itself by scattering hot core neutrons. Germanium X-ray emission spectra and Ross pair filtered X-ray energy resolved images suggest that germanium doped plastic emits in the torus shaped hot spot, probably reducing the neutron yield

Regulation of gene expression in Vibrio cholerae by ToxT involves both antirepression and RNA polymerase stimulation

Co-ordinate expression of many virulence genes in the human pathogen Vibrio cholerae is under the direct control of the ToxT protein, including genes whose products are required for the biogenesis of the toxin-co-regulated pilus (TCP) and cholera toxin (CTX). This work examined interactions between ToxT and the promoters of ctx and tcpA genes. We found that a minimum of three direct repeats of the sequence TTTTGAT is required for ToxT-dependent activation of the ctx promoter, and that the region from –85 to –41 of the tcpA promoter contains elements that are responsive to ToxT-dependent activation. The role of H-NS in transcription of ctx and tcpA was also analysed. The level of activation of ctx–lacZ in an E. coli hns – strain was greatly increased even in the absence of ToxT, and was further enhanced in the presence of ToxT. In contrast, H-NS plays a lesser role in the regulation of the tcpA promoter. Electrophoretic mobility shift assays demonstrated that 6 × His-tagged ToxT directly, and specifically, interacts with both the ctx and tcpA promoters. DNase I footprinting analysis suggests that there may be two ToxT binding sites with different affinity in the ctx promoter and that ToxT binds to –84 to –41 of the tcpA promoter. In vitro transcription experiments demonstrated that ToxT alone is able to activate transcription from both promoters. We hypothesize that under conditions appropriate for ToxT-dependent gene expression, ToxT binds to AT-rich promoters that may have a specific secondary conformation, displaces H-NS and stimulates RNA polymerase resulting in transcription activation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71500/1/j.1365-2958.2002.02721.x.pd

Comparing neutron and X-ray images from NIF implosions

Directly laser driven and X-radiation driven DT filled capsules differ in the relationship between neutron and X-ray images. Shot N110217, a directly driven DT-filled glass micro-balloon provided the first neutron images at the National Ignition Facility. As seen in implosions on the Omega laser, the neutron image can be enclosed inside time integrated X-ray images. HYDRA simulations show the X-ray image is dominated by emission from the hot glass shell while the neutron image arises from the DT fuel it encloses. In the absence of mix or jetting, X-ray images of a cryogenically layered THD fuel capsule should be dominated by emission from the hydrogen rather than the cooler plastic shell that is separated from the hot core by cold DT fuel. This cool, dense DT, invisible in X-ray emission, shows itself by scattering hot core neutrons. Germanium X-ray emission spectra and Ross pair filtered X-ray energy resolved images suggest that germanium doped plastic emits in the torus shaped hot spot, probably reducing the neutron yield