Emittance preservation in a plasma-wakefield accelerator.

Radio-frequency particle accelerators are engines of discovery, powering high-energy physics and photon science, but are also large and expensive due to their limited accelerating fields. Plasma-wakefield accelerators (PWFAs) provide orders-of-magnitude stronger fields in the charge-density wave behind a particle bunch travelling in a plasma, promising particle accelerators of greatly reduced size and cost. However, PWFAs can easily degrade the beam quality of the bunches they accelerate. Emittance, which determines how tightly beams can be focused, is a critical beam quality in for instance colliders and free-electron lasers, but is particularly prone to degradation. We demonstrate, for the first time, emittance preservation in a high-gradient and high-efficiency PWFA while simultaneously preserving charge and energy spread. This establishes that PWFAs can accelerate without degradation-an essential step toward energy boosters in photon science and multistage facilities for compact high-energy particle colliders.

Recovery time of a plasma-wakefield accelerator.

The interaction of intense particle bunches with plasma can give rise to plasma wakes1,2 capable of sustaining gigavolt-per-metre electric fields3,4, which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology5. Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology6,7. Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.

High-resolution sampling of beam-driven plasma wakefields.

Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. Such applications require particle beams with a well-controlled energy spectrum, which necessitates detailed tailoring of the plasma wakefield. Precise measurements of the effective wakefield structure are therefore essential for optimising the acceleration process. Here we propose and demonstrate such a measurement technique that enables femtosecond-level (15 fs) sampling of longitudinal electric fields of order gigavolts-per-meter (0.8 GV m-1). This method-based on energy collimation of the incoming bunch-made it possible to investigate the effect of beam and plasma parameters on the beam-loaded longitudinally integrated plasma wakefield, showing good agreement with particle-in-cell simulations. These results open the door to high-quality operation of future plasma accelerators through precise control of the acceleration process.

FLASHForward: plasma wakefield accelerator science for high-average-power applications.

The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

[Non-coding RNA in malignant tumors. A new world of tumor biomarkers and target structures in cancer cells]. / Nichtcodierende RNA in malignen Tumoren. Eine neue Welt von Tumor-Biomarkern und Zielstrukturen in Krebszellen.

Only about 2% of the human genome constitute protein-coding genes - nevertheless, medical research has focused mainly on this portion in recent decades. Since up to 70% of the human genome is transcribed into RNA, the genome contains much more non-coding information than coding, which is present in the cell as non-coding RNA (ncRNA). Many of these ncRNAs are highly expressed, specifically regulated and evolutionarily conserved, arguing in favor of their functional significance. MicroRNAs are the most well-known ncRNAs, but many other long ncRNAs exist. Differential ncRNA or microRNA expression patterns correlate with diagnosis or prognosis in many tumor entities and can thus serve as an extensive source of new biomarkers. The expression of the long ncRNA MALAT1 correlates with tumor development, progression or survival in lung, liver and breast cancer. Functionally active ncRNAs can provide novel insights into the mechanisms underlying tumor development. The large number of different, often as yet unidentified ncRNAs promises new stimuli for the diagnosis, prognosis and therapy of many diseases.

[Regenerative medicine in orthopaedics. Cell therapy - tissue engineering - in situ regeneration]. / Regenerative Medizin in der Orthopädie. Zelltherapie - Tissue Engineering - In-situ-Regeneration.

Therapeutic approaches in regenerative medicine, irrespective of specific fields, comprise cell therapy, tissue engineering and in situ regeneration. Regenerative orthopaedics often leads the way on the path to clinical application. In cell therapy primary cells could be replaced by adult mesenchymal stem cells exhibiting almost unlimited regeneration capacity. More sophisticated biomaterial design allowing specific control of cell morphology and tissue organisation is the current focus of advancements in tissue engineering, while signalling to cells by intelligent biomaterials is a main focus of in situ regeneration. These new approaches to the reconstruction of structures and function in damaged or dysfunctional tissue will make it more often possible to achieve a sustainable improvement in terms of real regeneration rather than an acceptable repair.

Mechanical strain using 2D and 3D bioreactors induces osteogenesis: implications for bone tissue engineering.

Fracture healing is a complicated process involving many growth factors, cells, and physical forces. In cases, where natural healing is not able, efforts have to be undertaken to improve healing. For this purpose, tissue engineering may be an option. In order to stimulate cells to form a bone tissue several factors are needed: cells, scaffold, and growth factors. Stem cells derived from bone marrow or adipose tissues are the most useful in this regard. The differentiation of the cells can be accelerated using mechanical stimulation. The first part of this chapter describes the influence of longitudinal strain application. The second part uses a sophisticated approach with stem cells on a newly developed biomaterial (Sponceram) in a rotating bed bioreactor with the administration of bone morphogenetic protein-2. It is shown that such an approach is able to produce bone tissue constructs. This may lead to production of larger constructs that can be used in clinical applications.

Accelerated growth of preosteoblastic cells on ultrafine grained titanium.

This work is part of a general effort to demonstrate the effect of the bulk microstructure of titanium as a model bone implant material on viability of osteoblasts (bone-forming cells). The objective of this work was to study the proliferation of preosteoblastic MC3T3-E1 cells extracted from mice embryos on commercial purity titanium substrates. Two distinct states of titanium were considered: as-received material with an average grain size of 4.5 microm and that processed by equal channel angular pressing (ECAP), with an average grain size of 200 nm. We report the first results of an in vitro study into the effect of this extreme grain refinement on viability and proliferation of MC3T3-E1 cells. By means of MTT assays it was demonstrated that ECAP processing of titanium enhances MC3T3-E1 culture proliferation in a spectacular way. This finding suggests that bone implants made from ECAP processed titanium may promote bone tissue growth.

Evaluation of an in situ setting injectable calcium phosphate as a new carrier material for gentamicin in the treatment of chronic osteomyelitis: studies in vitro and in vivo.

A study was performed to investigate the effectiveness of hydroxyapatite cement (HAC) as a new carrier system in the treatment of chronic, posttraumatic osteomyelitis. In the in vitro study, release of gentamicin from standard cylinders of HAC were measured by agar diffusion test. As a representative for mechanical properties, compression strength was measured in order to detect changes when mixing HAC with gentamicin. In the in vivo study, bone infection was induced according to the model of Norden by injection of 1 ml Na-morrhuat and 3 x 10(6)CFU Staphylococcus aureus. After 3 weeks, when chronic stage of infection was obtained, 17 animals were treated by debridement and filling the marrow either with HAC alone or HAC mixed with gentamicin (32 mg/g). Animals of the control groups were left untreated. After 6 weeks, all animals were sacrificed. Hematological, radiological, microbiological and histological examinations were carried out by covered investigation. Best evidence of the efficiency of treatment was observed in histopathological and microbiological findings. In all swabs of the control groups, taken 6 weeks following infection S. aureus were detected which were clonal to the strain used for induction of osteomyelitis. In HAC/gentamicin-treated animals, no growth was detectable after 7 days of culturing in BHI bouillon. In the HAC/gentamicin-treated group, there was no histopathological evidence of infection. In all other groups different stages of chronic osteomyelitis were found. No side effect was observed, neither locally nor systemically by HAC or gentamicin. Therefore, HAC is considered to be a very effective carrier for antibiotics in treatment of chronic, posttraumatic osteomyelitis.

[Follow-up treatment with physiotherapy after arthroscopic reconstruction in SLAP lesions]. / Physiotherapeutische Nachbehandlung nach arthroskopischer Wiederherstellung bei SLAP-Läsionen.

An appropriate physiotherapeutic treatment program complements an optimal operative result. In the instance of SLAP lesions, a differentiated therapy is only possible on consultation with the surgeon. A detailed treatment design allows optimal guidance of the patient to his or her personal goal. Important treatment elements include the optimization of the ability of the humerus head to centralize and the proprioception of the shoulder joint, as well as reinstatement of strength and endurance, especially of the rotator cuff.

Loss of expression of HDAC-recruiting methyl-CpG-binding domain proteins in human cancer.

Dysregulation of CpG-methylation is a common feature of many human cancers and tumour suppressor genes can be silenced by hypermethylation. Recently, 2 methyl-CpG-binding domain proteins have been linked to gene inactivation by their ability to recruit co-repressors and HDAC-activity to methylated gene promoters. Here, we have analysed mRNA expression of these genes, MeCP2 and MBD2, in a wide variety of primary human tumours. In solid tumours, expression levels of MBD2 (57/71) and MeCP2 (64/71) were significantly reduced in the majority of primary tumours as detected by quantitative real-time RT-PCR. Western blot analyses of MeCP2 in matched tumour-normal samples of patients with non-small-cell lung cancer (NSCLC) indicated reduced protein in a significant percentage of patients. In acute myelogenous leukaemia (n = 26), expression levels were only slightly reduced and did not differ between samples analysed at diagnosis or at the time of relapse. In early-stage NSCLC (n = 70) expression of MeCP2 and MBD2 was significantly lower in squamous cell carcinoma than in adenocarcinoma or large cell carcinoma (P = 0.03 and P = 0.01). To further elucidate the mechanisms of gene regulation, we analysed MeCP2 and MBD2 regulation during haematopoietic differentiation. No significant changes in MeCP2 or MBD2 expression were found when NB4 cells were differentiated toward granulocytes suggesting that neither differentiation nor cell cycle status were relevant for the reduced expression of these genes in human cancer. In conclusion, the significant loss of MeCP2 and MBD2 expression in human cancers suggests a potential role of this phenomenon in the development of solid human tumours.

Cyclin A1 directly interacts with B-myb and cyclin A1/cdk2 phosphorylate B-myb at functionally important serine and threonine residues: tissue-specific regulation of B-myb function.

Cyclin A1 is tissue-specifically expressed during spermatogenesis, but it is also highly expressed in acute myeloid leukemia (AML). Its pathogenetic role in AML and in the cell cycle of leukemic blasts is unknown. B-myb is essential for G1/S transition and has been shown to be phosphorylated by the cyclin A2/cdk2 complex. Here it is demonstrated that cyclin A1 interacts with the C-terminal portion of B-myb as shown by glutathione S-transferase (GST) precipitation. This interaction is confined to cyclin A1 because binding could not be detected between cyclin A2 and B-myb. Also, cdk2 was not pulled down by GST-B-myb from U937 lysates. In addition, co-immunoprecipitation of cyclin A1 and B-myb in leukemic cells evidenced protein interaction in vivo. Baculovirus-expressed cyclin A1/cdk2 complexes were able to phosphorylate human as well as murine B-myb in vitro. Tryptic phosphopeptide mapping revealed that cyclin A1/cdk2 complexes phosphorylated the C-terminal part of B-myb at several sites including threonine 447, 490, and 497 and serine 581. These phosphorylation sites have been demonstrated to be important for the enhancement of B-myb transcriptional activity. Further studies showed that cyclin A1 cooperated with B-myb to transactivate myb binding site containing promoters including the promoter of the human cyclin A1 gene. Taken together, the data suggest that cyclin A1 is a tissue-specific regulator of B-myb function and activates B-myb in leukemic blasts. (Blood. 2001;97:2091-2097)

Cyclin E is the only cyclin-dependent kinase 2-associated cyclin that predicts metastasis and survival in early stage non-small cell lung cancer.

Progression through G1-S transition and S phase of the cell cycle is mediated by cyclin-dependent kinase 2 (cdk2), which interacts with several cyclins. Two of these, cyclin E and cyclin A2 (also known as cyclin A), are overexpressed in many cancers. Cyclin E2 and cyclin A1 are recently discovered cdk2-interacting cyclins that are found in malignant tumor cell lines and in acute myeloid leukemia, respectively. Expression and prognostic role of these cyclins in solid tumors is unknown. Here, we have analyzed expression and prognostic relevance of the cdk2-associated cyclins in non-small cell lung cancer (NSCLC). Fresh-frozen biopsies (n = 70) from completely resected tumors with stage I to IIIA NSCLC were studied. Gene expression was analyzed by quantitative real-time reverse transcription-PCR. Expression levels of cyclin E (P = 0.04) and cyclin A2 (P = 0.004) were significantly higher in the tumor samples than in normal controls. Cyclin A1, cyclin A2, and cyclin E2 expression levels did not have prognostic relevance for survival. The mean survival time associated with low and high levels of cyclin E was 69.4 and 47.2 months, respectively, which was statistically significant (P = 0.03). Differences in survival were particularly pronounced in stages I and II. Cyclin E was also closely associated with the development of distant metastasis (P = 0.01). Finally, we confirmed by immunohistochemistry analyses that cyclin E mRNA expression was closely associated with cyclin E protein expression. In conclusion, cyclin E is a strong independent prognostic indicator in patients with early-stage NSCLC, whereas cyclin E2, cyclin A1, and cyclin A2 do not have a prognostic role in NSCLC.

Analyses of the genomic methylation status of the human cyclin A1 promoter by a novel real-time PCR-based methodology.

The role of CpG methylation in the regulation of tissue-specific gene expression is highly controversial. Cyclin A1 is a tissue-specifically expressed gene that is strongly methylated in non-expressing tumor cell lines. We have established a novel real-time PCR method to quantitate genomic CpG methylation of the cyclin A1 promoter. Genomic DNA samples from different human organs were treated with bisulfite and amplified with methylation-specific primers and with primers amplifying methylated as well as non-methylated DNA. PCR product quantitation was obtained by using a fluorogenic probe labeled with FAM and TAMRA. These analyses demonstrated that the human cyclin A1 promoter was methylated in kidney, colon, spleen, testis, and small intestine, but not in brain, liver, pancreas, or heart. Expression of cyclin A1 was predominantly found in testis. Low level expression of cyclin A1 was present in spleen, prostate, leukocytes, colon, and thymus. Taken together, our data provide evidence that CpG methylation patterns of the human cyclin A1 promoter in human organs do not generally correlate with cyclin A1 gene expression in vivo.

Methylation of the cyclin A1 promoter correlates with gene silencing in somatic cell lines, while tissue-specific expression of cyclin A1 is methylation independent.

Gene expression in mammalian organisms is regulated at multiple levels, including DNA accessibility for transcription factors and chromatin structure. Methylation of CpG dinucleotides is thought to be involved in imprinting and in the pathogenesis of cancer. However, the relevance of methylation for directing tissue-specific gene expression is highly controversial. The cyclin A1 gene is expressed in very few tissues, with high levels restricted to spermatogenesis and leukemic blasts. Here, we show that methylation of the CpG island of the human cyclin A1 promoter was correlated with nonexpression in cell lines, and the methyl-CpG binding protein MeCP2 suppressed transcription from the methylated cyclin A1 promoter. Repression could be relieved by trichostatin A. Silencing of a cyclin A1 promoter-enhanced green fluorescent protein (EGFP) transgene in stable transfected MG63 osteosarcoma cells was also closely associated with de novo promoter methylation. Cyclin A1 could be strongly induced in nonexpressing cell lines by trichostatin A but not by 5-aza-cytidine. The cyclin A1 promoter-EGFP construct directed tissue-specific expression in male germ cells of transgenic mice. Expression in the testes of these mice was independent of promoter methylation, and even strong promoter methylation did not suppress promoter activity. MeCP2 expression was notably absent in EGFP-expressing cells. Transcription from the transgenic cyclin A1 promoter was repressed in most organs outside the testis, even when the promoter was not methylated. These data show the association of methylation with silencing of the cyclin A1 gene in cancer cell lines. However, appropriate tissue-specific repression of the cyclin A1 promoter occurs independently of CpG methylation.

c-myb transactivates the human cyclin A1 promoter and induces cyclin A1 gene expression.

Cyclin A1 differs from other cyclins in its highly restricted expression pattern. Besides its expression during spermatogenesis, cyclin A1 is also expressed in hematopoietic progenitor cells and in acute myeloid leukemia. We investigated mechanisms that might contribute to cyclin A1 expression in hematopoietic cells. Comparison of cyclin A1 and cyclin A promoter activity in adherent and myeloid leukemia cell lines showed that the cyclin A1 promoter is preferentially active in myeloid cell lines. This preferential activity was present in a small, 335-bp cyclin A1 promoter fragment that contained several potential c-myb binding sites. Coexpression of a c-myb expression vector with the cyclin A1 promoter constructs significantly increased the reporter activity in adherent CV-1 as well as in myeloid U937 cells. Gel-shift assays demonstrated that c-myb could bind to the cyclin A1 promoter at a binding site located near the transcription start site. Site-directed mutagenesis of this site decreased promoter transactivation by 50% in both KCL22 cells that express high levels of c-myb and in CV-1 cells that were transfected with c-myb. In addition, transfection of primary human embryonic fibroblasts with a c-myb expression vector led to induction of the endogenous cyclin A1 gene. Taken together, c-myb can directly transactivate the promoter of cyclin A1, and c-myb might be involved in the high-level expression of cyclin A1 observed in acute myeloid leukemia. These findings suggest that c-myb induces hematopoiesis-specific mechanisms of cell cycle regulation.

Three-dimensional acquisition and visualization of dental arch features from optically digitized models.

A method for the acquisition and evaluation of 3D coordinates from anatomically oriented plaster casts is presented, which is based on optical phase shifting profilometry (a fringe projection technique). With the computer-controlled setup, measurements from different views can be combined to obtain a complete three dimensional reconstruction of the model surface. To allow faster evaluation, the result is converted into a range image. From this digital data set the characteristic features like cusp tips can be identified and located semi-automatically. Based on these marks, quantitative values for differences between situation models like local displacements, e.g. during orthodontic treatment, can be determined. The results are visualized as interactively controllable 3D computer graphics, which helps to make spatial relations clearer.