Biomedical subjects

F Klein

Publications and source records attributed to F Klein.

At least 19 recordsLinked to original sources

PubMed2006

Measurement of the Gerasimov-Drell-Hearn Integrand for 2H from 200 to 800 MeV.

A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200<Egamma<800 MeV. The experiment used a 4pi detection system, a circularly polarized tagged photon beam and a frozen-spin target which provided longitudinally polarized deuterons. The contribution to the Gerasimov-Drell-Hearn sum rule for the deuteron determined from the data is 407+/-20(stat)+/-24(syst) mu b for 200<Egamma<800 MeV.

Journal Article↗

PubMed2006

BCR-ABL1 induces aberrant splicing of IKAROS and lineage infidelity in pre-B lymphoblastic leukemia cells.

Pre-B lymphoblastic leukemia cells carrying a BCR-ABL1 gene rearrangement exhibit an undifferentiated phenotype. Comparing the genome-wide gene expression profiles of normal B-cell subsets and BCR-ABL1+ pre-B lymphoblastic leukemia cells by SAGE, the leukemia cells show loss of B lymphoid identity and aberrant expression of myeloid lineage-specific molecules. Consistent with this, BCR-ABL1+ pre-B lymphoblastic leukemia cells exhibit defective expression of IKAROS, a transcription factor needed for early lymphoid lineage commitment. As shown by inducible expression of BCR-ABL1 in human and murine B-cell precursor cell lines, BCR-ABL1 induces the expression of a dominant-negative IKAROS splice variant, termed IK6. Comparing matched leukemia sample pairs from patients before and during therapy with the BCR-ABL1 kinase inhibitor STI571 (Imatinib), inhibition of BCR-ABL1 partially corrected aberrant expression of IK6 and lineage infidelity of the leukemia cells. To elucidate the contribution of IK6 to lineage infidelity in BCR-ABL1+ cell lines, IK6 expression was silenced by RNA interference. Upon inhibition of IK6, BCR-ABL1+ leukemia cells partially restored B lymphoid lineage commitment. Therefore, we propose that BCR-ABL1 induces aberrant splicing of IKAROS, which interferes with lineage identity and differentiation of pre-B lymphoblastic leukemia cells.

Alternative Splicing↗

PubMed2005

First measurement of the transverse spin asymmetries of the deuteron in semi-inclusive deep inelastic scattering.

First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.

Journal Article↗

PubMed2005

Measurement of helicity-dependent photoabsorption cross sections on the neutron from 815 to 1825 MeV.

Helicity-dependent total photoabsorption cross sections on the deuteron have been measured for the first time at ELSA (Bonn) in the photon energy range from 815 to 1825 MeV. Circularly polarized tagged photons impinging on a longitudinally polarized LiD target have been used together with a highly efficient 4pi detector system. The data around 1 GeV are not compatible with predictions from existing multipole analyses. From the measured energy range an experimental contribution to the GDH integral on the neutron of [33.9 +/- 5.5(stat) +/- 4.5(syst)] microb is extracted.

Journal Article↗

PubMed2005

Neutral-pion photoproduction off protons in the energy range 0.3 GeV<E(gamma)<3 GeV.

Single pi(0) photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of approximately 98% of 4pi. Differential cross sections dsigma/dOmega have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gammap-->N(*)(Delta(*))-->ppi(0). A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.

Journal Article↗

PubMed2005

Photoproduction of eta mesons off protons for 0.75 GeV<E(gamma)<3 GeV.

Total and differential cross sections for the reaction p(gamma,eta)p have been measured for photon energies in the range from 750 MeV to 3 GeV. The low-energy data are dominated by the S11 wave which has two poles in the energy region below 2 GeV. Eleven nucleon resonances are observed in their decay into peta. At medium energies we find evidence for a new resonance N(2070)D15 with (M,Gamma)=(2068+/-22, 295+/-40) MeV. At gamma energies above 1.5 GeV, a strong peak in the forward direction develops, signaling the exchange of vector mesons in the t channel.

Journal Article↗

PubMed2004

Experimental check of the Gerasimov-Drell-Hearn sum rule for 1H.

For the first time we checked the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the proton experimentally in the photon energy range from 0.2-2.9 GeV with the tagged photon facilities at MAMI (Mainz) and ELSA (Bonn). New data of the doubly polarized total cross section difference are presented in the energy range from 1.6 to 2.9 GeV. The contribution to the GDH integral from 0.2-2.9 GeV yields [254+/-5(stat)+/-12(syst)] microb with negative contributions in the Regge regime at photon energies above 2.1 GeV. This trend supports the validity of the GDH sum rule.

Journal Article↗

PubMed2004

GermOnline, a cross-species community knowledgebase on germ cell differentiation.

GermOnline provides information and microarray expression data for genes involved in mitosis and meiosis, gamete formation and germ line development across species. The database has been developed, and is being curated and updated, by life scientists in cooperation with bioinformaticists. Information is contributed through an online form using free text, images and the controlled vocabulary developed by the GeneOntology Consortium. Authors provide up to three references in support of their contribution. The database is governed by an international board of scientists to ensure a standardized data format and the highest quality of GermOnline's information content. Release 2.0 provides exclusive access to microarray expression data from Saccharomyces cerevisiae and Rattus norvegicus, as well as curated information on approximately 700 genes from various organisms. The locus report pages include links to external databases that contain relevant annotation, microarray expression and proteome data. Conversely, the Saccharomyces Genome Database (SGD), S.cerevisiae GeneDB and Swiss-Prot link to the budding yeast section of GermOnline from their respective locus pages. GermOnline, a fully operational prototype subject-oriented knowledgebase designed for community annotation and array data visualization, is accessible at http://www.germonline.org. The target audience includes researchers who work on mitotic cell division, meiosis, gametogenesis, germ line development, human reproductive health and comparative genomics.

Animals↗

PubMed2003

First Measurement of the Gerasimov-Drell-Hearn Sum Rule for 1H from 0.7 to 1.8 GeV at ELSA.

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.

Journal Article↗

PubMed2002

Helicity amplitudes A1/2 and A3/2 for the D13(1520) resonance obtained from the gamma-->p-->-->ppi(0) Reaction.

The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.

Journal Article↗

PubMed2002

Measurement of the beam-helicity asymmetry in the p((-->)e,e'p)pi(0) reaction at the energy of the Delta(1232) resonance.

In a p((-->)e,e'p)pi(0) out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of the Delta(1232) resonance and Q(2) = 0.2(GeV/c)(2). The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.

Journal Article↗

PubMed2002

Cardiovascular and respiratory consequences of bilateral involvement of the medullary intermediate reticular formation in syringobulbia.

We studied five patients with clinical and radiological evidence of syringobulbia (SB) to determine whether the distribution of lesions in relationship to the cardiorespiratory control networks in the medullary intermediate reticular zone (IRt) correlates with the presence of abnormalities in autonomic cardiovascular and respiratory control in these patients. All patients underwent high resolution MRI to characterize the size, volume and distribution of the SB lesions, cardiovascular autonomic function testing and polysomnography. One patient with bilateral IRt involvement at both the rostral and caudal medulla had orthostatic hypotension (OH), absent HR(DB), abnormal Valsalva ratio, exaggerated fall of BP during phase II and absent phase IV during VM, and a dramatic fall of BP during head up tilt; this patient also had severe obstructive sleep apnea (OSA) and exhibited BP drops during each respiratory effort. A second patient, with bilateral IRt involvement restricted to the caudal medulla, had less severe cardiovascular autonomic dysfunction but also exhibited severe OSA. The other three patients had small SB cavities sparing the IRt and had sleep apnea but no autonomic dysfunction. Autonomic dysfunction could not be related to the size of the syrinx or the degree of atrophy in the cervical spinal cord in any of the five patients. Bilateral involvement of the IRt by SB produces cardiovascular autonomic failure and sleep apnea. In patients with more restricted lesions, autonomic and respiratory dysfunction may be dissociated. Clinico-radiological correlations using high resolution MRI assessment of medullary lesions can provide insight into the central organization of cardiovascular and respiratory control in humans.

Adult↗

PubMed2002

[Comparative analysis of the sensitivity and accuracy of clinical, radiographic and histometric measurements in assessing periodontal attachment levels].

The ultimate goal of the regenerative periodontal treatment is the de novo formation of new connective tissue attachment with the regrowth of the alveolar bone. Clinically it is very difficult to evaluate the nature of clinical healing and prove the occurrence of real periodontal regeneration. The aim of the present study was to compare the clinical and radiographic parameters with the histometric findings following two different periodontal regenerative procedures in humans.

Adult↗

PubMed2001

A screen for genes required for meiosis and spore formation based on whole-genome expression.

BACKGROUND: Meiosis is the process by which gametes are generated with half the ploidy of somatic cells. This reduction is achieved by three major differences in chromosome behavior during meiosis as compared to mitosis: the production of chiasmata by recombination, the protection of centromere-proximal sister chromatid cohesion, and the monoorientation of sister kinetochores during meiosis I. Mistakes in any of these processes lead to chromosome missegregation. RESULTS: To identify genes involved in meiotic chromosome behavior in Saccharomyces cerevisiae, we deleted 301 open reading frames (ORFs) which are preferentially expressed in meiotic cells according to microarray gene expression data. To facilitate the detection of chromosome missegregation mutants, chromosome V of the parental strain was marked by GFP. Thirty-three ORFs were required for the formation of wild-type asci, eight of which were needed for proper chromosome segregation. One of these (MAM1) is essential for the monoorientation of sister kinetochores during meiosis I. Two genes (MND1 and MND2) are implicated in the recombination process and another two (SMA1 and SMA2) in prospore membrane formation. CONCLUSIONS: Reverse genetics using gene expression data is an effective method for identifying new genes involved in specific cellular processes.

Cell Nucleus↗

PubMed2001

Measurement of the recoil polarization in the p(e-->, e'p-->)pi(0) reaction at the Delta(1232) resonance.

The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.

Journal Article↗

PubMed2001

B-type cyclins CLB5 and CLB6 control the initiation of recombination and synaptonemal complex formation in yeast meiosis.

BACKGROUND: The life cycle of most eukaryotic organisms includes a meiotic phase, in which diploid parental cells produce haploid gametes. During meiosis a single round of DNA replication is followed by two rounds of chromosome segregation. In the first, or reductional, division (meiosis I), which is unique to meiotic cells, homologous chromosomes segregate from one another, whereas in the second, or equational, division (Meiosis II) sister centromeres disjoin. Meiotic DNA replication precedes the initiation of recombination by programmed Spo11-dependent DNA double-strand breaks. Recent reports that meiosis-specific cohesion is established during meiotic S phase and that the length of S phase is modified by recombination factors (Spo11 and Rec8) raise the possibility that replication plays a fundamental role in the recombination process. RESULTS: To address how replication influences the initiation of recombination, we have used mutations in the B-type cyclin genes CLB5 and CLB6, which specifically prevent premeiotic replication in the yeast Saccharomyces cerevisiae. We find that clb5 and clb5 clb6 but not clb6 mutants are defective in DSB induction and prior associated changes in chromatin accessibility, heteroallelic recombination, and SC formation. The severity of these phenotypes in each mutant reflects the extent of replication impairment. CONCLUSIONS: This assemblage of phenotypes reveals roles for CLB5 and CLB6 not only in DNA replication but also in other key events of meiotic prophase. Links between the function of CLB5 and CLB6 in activating meiotic DNA replication and their effects on subsequent events are discussed.

Cyclin B↗

PubMed2001

Demonstration of heterogeneous genotypes of Taylorella equigenitalis isolated from horses in six European countries by pulsed-field gel electrophoresis.

Forty-six isolates of Taylorella equigenitalis were analysed by pulsed-field gel electrophoresis (PFGE) after separate digestion of the genomic DNA with ApaI and with NotI. The isolates had been obtained from horses in six European countries and were classified into 18 genotypes. In Belgium, 2 genotypes were detected in 2 isolates, in England 9 among 15, in Finland 2 in 2, in France 2 among 10, in Sweden 3 among 5, and in Switzerland 3 among 12. Two English isolates and 4 French isolates gave identical PFGE profiles to those of Kentucky 188 from the United States. A common genotype was found in 5 isolates from Belgium and England and also in 10 isolates from France and Switzerland. The analysis of genomic DNA from 12 isolates of T equigenitalis obtained from male horses in France, Sweden and Switzerland gave no evidence of a sex-related difference in the genomic DNA. Genomic DNA from 11 streptomycin (STM)-susceptible isolates obtained in Sweden and Switzerland were classified into four genotypes by PFGE. Each of the six genotypes determined among the 17 isolates from these two countries had single phenotypes for resistance or susceptibility to STM.

Animals↗

PubMed2001

[Mycotic aneurysms--A retrospective analysis].

12 patients (10 males and 2 females, average age 53 years) were operated upon in our hospital between 1994 and 1999 for mycotic aneurysms. The aneurysms were located in 7 patients in the aorto-iliac segment, 5 patients were treated for peripheral or visceral aneurysms. Two of these patients suffered from multiple aneurysms. When peripheral arteries were affected, a pulsatile tumour was felt. Most of these tumours developed in a relatively short period of time and sometimes a perivascular inflammation occurred. This was not the case when central arteries were attacked. A septic process or an infection, for example salmonella-enteritis, often preceded shortly the development of a mycotic aneurysm. In the case of an aneurysm of the aorto-iliac section we consider an in situ reconstruction with alloplastic material in combination with a perivascular debridement, lavage and omentum majus plastic as the treatment of choice. In peripheral arteries reconstruction should be performed with autologous vessels. Depending on the local findings, a perivascular debridement should also be performed in these cases. The reconstruction always should be combined with a calculated antibiotic therapy. Two of our patients died perioperatively. During follow up, 8 patients showed patent reconstructions and no signs of infection. The urgency of surgery depends on the level of inflammation and the existence of any secondary complications.

Adult↗