The effect of electron backscatter and charge build up in media on beam current transformer signal for ultra-high dose rate (FLASH) electron beam monitoring

Objective.Beam current transformers (BCT) are promising detectors for real-time beam monitoring in ultra-high dose rate (UHDR) electron radiotherapy. However, previous studies have reported a significant sensitivity of the BCT signal to changes in source-to-surface distance (SSD), field size, and phantom material which have until now been attributed to the fluctuating levels of electrons backscattered within the BCT. The purpose of this study is to evaluate this hypothesis, with the goal of understanding and mitigating the variations in BCT signal due to changes in irradiation conditions.Approach.Monte Carlo simulations and experimental measurements were conducted with a UHDR-capable intra-operative electron linear accelerator to analyze the impact of backscattered electrons on BCT signal. The potential influence of charge accumulation in media as a mechanism affecting BCT signal perturbation was further investigated by examining the effects of phantom conductivity and electrical grounding. Finally, the effectiveness of Faraday shielding to mitigate BCT signal variations is evaluated.Main Results.Monte Carlo simulations indicated that the fraction of electrons backscattered in water and on the collimator plastic at 6 and 9 MeV is lower than 1%, suggesting that backscattered electrons alone cannot account for the observed BCT signal variations. However, our experimental measurements confirmed previous findings of BCT response variation up to 15% for different field diameters. A significant impact of phantom type on BCT response was also observed, with variations in BCT signal as high as 14.1% when comparing measurements in water and solid water. The introduction of a Faraday shield to our applicators effectively mitigated the dependencies of BCT signal on SSD, field size, and phantom material.Significance.Our results indicate that variations in BCT signal as a function of SSD, field size, and phantom material are likely driven by an electric field originating in dielectric materials exposed to the UHDR electron beam. Strategies such as Faraday shielding were shown to effectively prevent these electric fields from affecting BCT signal, enabling reliable BCT-based electron UHDR beam monitoring.

Vesicle Dynamics during Plant Cell Cytokinesis Reveals Distinct Developmental Phases

Cell division in plant cells requires the deposition of a new cell wall between the two daughter cells. The assembly of this plate requires the coordinated movement of cargo vesicles whose size is below the diffraction-limited resolution of the optical microscope. We combined high spatial and temporal resolution confocal laser scanning microscopy with advanced image-processing tools and fluorescence fluctuation methods and distinguished three distinct phases during cell plate expansion in tobacco (Nicotiana tabacum) 'Bright Yellow-2' cells: massive delivery of preexisting vesicles to a disk-shaped region at the equatorial plane precedes a primary rapid expansion phase followed by a secondary, slow expansion phase during which the extremity of the circular plate seeks contact with the mother wall and brings about the separation of the two portions of cytoplasm. Different effects of pharmacological inhibition emphasize the distinct nature of the assembly and expansion mechanisms characterizing these phases.

Actomyosin-dependent dynamic spatial patterns of cytoskeletal components drive mesoscale podosome organization

Podosomes are cytoskeletal structures crucial for cell protrusion and matrix remodelling in osteoclasts, activated endothelial cells, macrophages and dendritic cells. In these cells, hundreds of podosomes are spatially organized in diversely shaped clusters. Although we and others established individual podosomes as micron-sized mechanosensing protrusive units, the exact scope and spatiotemporal organization of podosome clustering remain elusive. By integrating a newly developed extension of Spatiotemporal Image Correlation Spectroscopy with novel image analysis, we demonstrate that F-actin, vinculin and talin exhibit directional and correlated flow patterns throughout podosome clusters. Pattern formation and magnitude depend on the cluster actomyosin machinery. Indeed, nanoscopy reveals myosin IIA-decorated actin filaments interconnecting multiple proximal podosomes. Extending well-beyond podosome nearest neighbours, the actomyosin-dependent dynamic spatial patterns reveal a previously unappreciated mesoscale connectivity throughout the podosome clusters. This directional transport and continuous redistribution of podosome components provides a mechanistic explanation of how podosome clusters function as coordinated mechanosensory area.

Collapsin response mediator protein 4 regulates growth cone dynamics through the actin and microtubule cytoskeleton

Coordinated control of the growth cone cytoskeleton underlies axon extension and guidance. Members of the collapsin response mediator protein (CRMP) family of cytosolic phosphoproteins regulate the microtubule and actin cytoskeleton, but their roles in regulating growth cone dynamics remain largely unexplored. Here, we examine how CRMP4 regulates the growth cone cytoskeleton. Hippocampal neurons from CRMP4-/- mice exhibited a selective decrease in axon extension and reduced growth cone area, whereas overexpression of CRMP4 enhanced the formation and length of growth cone filopodia. Biochemically, CRMP4 can impact both microtubule assembly and F-actin bundling in vitro. Through a structure function analysis of CRMP4, we found that the effects of CRMP4 on axon growth and growth cone morphology were dependent on microtubule assembly, whereas filopodial extension relied on actin bundling. Intriguingly, anterograde movement of EB3 comets, which track microtubule protrusion, slowed significantly in neurons derived from CRMP4-/- mice, and rescue of microtubule dynamics required CRMP4 activity toward both the actin and microtubule cytoskeleton. Together, this study identified a dual role for CRMP4 in regulating the actin and microtubule growth cone cytoskeleton.

Thermal Activation of the Crystallization Kinetics of Amorphous Silicon

Solid Phase Crystallization of amorphous silicon films, deposited by the Low Pressure Chemical Vapor Deposition technique, is studied by in-situ monitoring the film conductance. The crystal growth rate VG, deduced from this measurement, was found to be thermally activated. The activation energy E behaviour for films with different doping varying in a great range, from undoped to 4×1019 cm−3, was then deduced. This behaviour, described for the first time in this work, shows a constant E for undoped and weak doping, then a high decrease after a doping value threshold. The undoped films show a decreasing E when the deposition rate increases i.e. when the structure of the amorphous deposited film tends to correspond to the relaxed amorphous network. All these new results are used to introduce a crystallization model based on a crystalline-amorphous double phase and on the charge of defects at the crystal-amorphous interface.

Hsp27 (HspB1) and alphaB-crystallin (HspB5) as therapeutic targets

Hsp27 and alphaB-crystallin are molecular chaperones that are constitutively expressed in several mammalian cells, particularly in pathological conditions. These proteins share functions as diverse as protection against toxicity mediated by aberrantly folded proteins or oxidative-inflammation conditions. In addition, these proteins share anti-apoptotic properties and are tumorigenic when expressed in cancer cells. This review summarizes the current knowledge about Hsp27 and alphaB-crystallin and the implications, either positive or deleterious, of these proteins in pathologies such as neurodegenerative diseases, myopathies, asthma, cataracts and cancers. Approaches towards therapeutic strategies aimed at modulating the expression and/or the activities of Hsp27 and alphaB-crystallin are presented.

Current practice in Marfan's syndrome and annulo-aortic ectasia: aortic root replacement with a composite graft over a twenty-year period

BACKGROUND

From October 1973 to December 1995, 251 patients (204 male, 47 female) aged from 10 to 75 years (mean: 46.6 +/- 15) underwent an ascending aortic replacement with a composite graft for: dystrophic aneurysm (AN), 168 cases (66.9%); chronic dissection (CD), 36 cases (14%); and type A acute dissection (AD), 48 cases (19.1%). Fifty-one patients (20.3%) suffered from Marfan's disease (25 AN, 17 AD, 9 CD). Thirty-seven patients (14.7%) had undergone a previous cardiac or aortic operation. The ascending aortic replacement was extended to the transverse arch in 31 patients (12.3%). A mechanical valve was used in 233 patients (92.8%). The classic "Bentall" technique was used in 87 patients (34.6%), the "button" technique in 121 patients (48.2%), the "Cabrol" technique in 26 patients (10.3%) and a "mixed" technique in 17 patients (6.2%).

RESULTS

The hospital mortality accounts for 7.2% (18 out of 251) (AN: 4 out of 68, 2.3%, CD: 4 out of 36, 11.1%, AD: 9 out of 48, 18.7%). When emergencies are considered, the hospital mortality is 12 out of 54 (22.2%) versus 6 out of 197 (3%) in elective procedures. The predictors of hospital death were emergency, AD (p < 0.03) and arch replacement (p < 0.02). Mean follow up is 38 +/- 15 months (4-262). The overall long term survival rate is (Kaplan Meïer): 92 +/- 6% at one year, 77.9% +/- 9% at 5 years, 67.7 +/- 12% at 10 years, and 61.3 +/- 15% at 12 years. The 10-year survival rate is significantly higher in patients with AN (93 +/- 6%) than in patients with AD (61.6 +/- 17%) (p < 0.01). The late survival rate is also significantly higher after the "button" (93.8 +/- 5%) or Bentall's reimplantation (88.7 +/- 6%, 83.8 +/- 9%, and 76.6 +/- 12%) than after the "Cabrol" procedure (80 +/- 18%, 63 +/- 21% and 58 +/- 35%) at 1, 5, and 8 years, respectively.

CONCLUSION

Ascending aortic replacement with a composite graft is a safe procedure, especially when performed electively in patients with dystrophic aneurysm or Marfan's disease. The technique of coronary reimplantation has a significant influence of the long-term results, with the reimplantation of choice being the "button" technique. The "Cabrol" technique must be used when the "button" or the "Bentall" reimplantation is not feasible.

Tumor necrosis factor-alpha induces changes in the phosphorylation, cellular localization, and oligomerization of human hsp27, a stress protein that confers cellular resistance to this cytokine

The stress protein hsp27 is constitutively expressed in several human cells and shows a rapid phosphorylation following treatment with tumor necrosis factor-alpha (TNF-alpha). hsp27 usually displays native molecular mass ranging from 100 to 700 kDa. Here, we have analyzed the TNF-alpha-mediated changes in the phosphorylation, cellular localization, and structural organization of hsp27 in HeLa cells. We report that the TNF-alpha-mediated hsp27 phosphorylation is a long-lasting phenomenon that correlates with the cytostatic effect of this cytokine. Following TNF-alpha treatment, the rapid phosphorylation of hsp27 occurred concomitantly with complex changes in the intracellular distribution and structural organization of this protein. This resulted in the quantitative redistribution of hsp27 toward the soluble phase of the cytoplasm. In addition, during the first 2 h of TNF-alpha treatment, a transient increase in the native molecular mass of most hsp27 molecules (< or = 700 kDa) occurred. Then, by 4 h of TNF-alpha treatment, the native size of this stress protein drastically regressed (< 200 kDa). During this phenomenon, the phosphorylated isoforms of hsp27 remained concentrated in the small or medium-sized oligomers (< 300 kDa) of this protein. We also analyzed the properties of human hsp27 in transfected murine L929 cell lines that constitutively express this protein. In these cells, TNF-alpha induced modifications in the phosphorylation, intracellular distribution, and oligomerization of human hsp27 similar to those observed in HeLa cells. Moreover, the expression of hsp27 in L929 cells was found to correlate with a reduced cytotoxicity of this cytokine. Hence, the complex changes in the phosphorylation, intracellular locale and structural organization of human hsp27 may be related to the protective activity of this protein against the deleterious effects induced by TNF-alpha.