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161.
Jochen Schulze Sebastian Seitz Hiroaki Saito Michael Schneebauer Robert P. Marshall Anke Baranowsky Bjoern Busse Arndt F. Schilling Felix W. Friedrich Joachim Albers Alexander S. Spiro Jozef Zustin Thomas Streichert Kristina Ellwanger Christof Niehrs Michael Amling Roland Baron Thorsten Schinke 《PloS one》2010,5(4)
Wnt signalling is a key pathway controlling bone formation in mice and humans. One of the regulators of this pathway is Dkk1, which antagonizes Wnt signalling through the formation of a ternary complex with the transmembrane receptors Krm1/2 and Lrp5/6, thereby blocking the induction of Wnt signalling by the latter ones. Here we show that Kremen-2 (Krm2) is predominantly expressed in bone, and that its osteoblast-specific over-expression in transgenic mice (Col1a1-Krm2) results in severe osteoporosis. Histomorphometric analysis revealed that osteoblast maturation and bone formation are disturbed in Col1a1-Krm2 mice, whereas bone resorption is increased. In line with these findings, primary osteoblasts derived from Col1a1-Krm2 mice display a cell-autonomous differentiation defect, impaired canonical Wnt signalling and decreased production of the osteoclast inhibitory factor Opg. To determine whether the observed effects of Krm2 on bone remodeling are physiologically relevant, we analyzed the skeletal phenotype of 24 weeks old Krm2-deficient mice and observed high bone mass caused by a more than three-fold increase in bone formation. Taken together, these data identify Krm2 as a regulator of bone remodeling and raise the possibility that antagonizing KRM2 might prove beneficial in patients with bone loss disorders. 相似文献
162.
Jochen Langbein Simon J. Thirgood 《Ethology : formerly Zeitschrift fur Tierpsychologie》1989,83(3):195-214
Variation in mating systems of fallow deer (Dama dama L.) was studied in wild and park populations and could be broadly distinguished into 7 categories: following, harems, dominance groups, stands, temporary stands, multiple stands, and leks. The ecological factors which exerted the greatest influence on mating systems were buck density, doe density, and habitat structure and tree cover, resulting in pronounced changes in the degree and type of territoriality observed. Individual male reproductive success was highly skewed in all systems. A greater range of concurrent mating strategies was observed in wild populations than in parks. 相似文献
163.
Effect of elevated dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum on D-glucose and L-lactate 总被引:1,自引:0,他引:1
Bäumchen C Knoll A Husemann B Seletzky J Maier B Dietrich C Amoabediny G Büchs J 《Journal of biotechnology》2007,128(4):868-874
The effect of increased dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum was studied with continuous turbidostatic cultures. The carbon sources were either l-lactate or d-glucose. To increase the dissolved carbon dioxide concentration the carbon dioxide partial pressure of the inlet gas stream pCO2,IN was increased stepwise from 0.0003 bar (air) up to 0.79 bar, while the oxygen partial pressure of the inlet gas stream was kept constant at 0.21 bar. For each resulting carbon dioxide partial pressure pCO2 the maximum specific growth rate mu(max) was determined from the feed rate resulting from the turbidostatic control. On d-glucose and pCO2 up to 0.26 bar, mu(max) was mostly constant around 0.58 h(-1). Higher pCO2 led to a slight decrease of mu(max). On l-lactate mu(max) increased gradually with increasing carbon dioxide partial pressures from 0.37 h(-1) under aeration with air to a maximum value of 0.47 h(-1) at a pCO2 of 0.26 bar. At very high pCO2 (0.81 bar) mu(max) decreased down to 0.35 h(-1) independent of the carbon source. 相似文献
164.
Plasmid DNA for biopharmaceutical applications is mainly produced in E. coli cells. The first and most crucial step for recovering the plasmid is the cell lysis. Governed by the physico-chemical properties of the polynucleotide, alkaline lysis has been the lysis-method of choice. This chemical disintegration technique was initially developed for the lab scale and non-pharmaceutical applications. A continuous, fully automated and closed system combining alkaline lysis, neutralization and clarification in one gentle and generic operation was developed. This system consists of a three units. One unit controls mixing and contact time during the alkaline treatment, another one controls the neutralization and the concurrent formation of flocs and a third one the separation of flocs and pDNA containing lysate. Based on optimization experiments the selected process parameters resulted in yields up to 100% and homogeneities comparable to that obtained by gentle manual lysis. The process does not need enzymes and it is scalable and routinely used for cGMP-production of pharmaceutical grade plasmid DNA from 200 L fermentations. 相似文献
165.
High cell density cultivation of recombinant yeasts and bacteria under non-pressurized and pressurized conditions in stirred tank bioreactors 总被引:1,自引:0,他引:1
Knoll A Bartsch S Husemann B Engel P Schroer K Ribeiro B Stöckmann C Seletzky J Büchs J 《Journal of biotechnology》2007,132(2):167-179
This study demonstrates the applicability of pressurized stirred tank bioreactors for oxygen transfer enhancement in aerobic cultivation processes. The specific power input and the reactor pressure was employed as process variable. As model organism Escherichia coli, Arxula adeninivorans, Saccharomyces cerevisiae and Corynebacterium glutamicum were cultivated to high cell densities. By applying specific power inputs of approx. 48kWm(-3) the oxygen transfer rate of a E. coli culture in the non-pressurized stirred tank bioreactor was lifted up to values of 0.51moll(-1)h(-1). When a reactor pressure up to 10bar was applied, the oxygen transfer rate of a pressurized stirred tank bioreactor was lifted up to values of 0.89moll(-1)h(-1). The non-pressurized stirred tank bioreactor was able to support non-oxygen limited growth of cell densities of more than 40gl(-1) cell dry weight (CDW) of E. coli, whereas the pressurized stirred tank bioreactor was able to support non-oxygen limited growth of cell densities up to 225gl(-1) CDW of A. adeninivorans, 89gl(-1) CDW of S. cerevisiae, 226gl(-1) CDW of C. glutamicum and 110gl(-1) CDW of E. coli. Compared to literature data, some of these cell densities are the highest values ever achieved in high cell density cultivation of microorganisms in stirred tank bioreactors. By comparing the specific power inputs as well as the k(L)a values of both systems, it is demonstrated that only the pressure is a scaleable tool for oxygen transfer enhancement in industrial stirred tank bioreactors. Furthermore, it was shown that increased carbon dioxide partial pressures did not remarkably inhibit the growth of the investigated model organisms. 相似文献
166.
Stich B Melchinger AE Piepho HP Hamrit S Schipprack W Maurer HP Reif JC 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2007,115(4):529-536
Knowledge about the forces generating and conserving linkage disequilibrium (LD) is important for drawing conclusions about
the prospects and limitations of association mapping. The objectives of our research were to examine the importance of (1)
selection, (2) mutation, and (3) genetic drift for generating LD in a typical maize breeding program. We conducted computer
simulations based on genotypic data of Central European maize open-pollinated varieties which have played an important role
as founders of the European flint heterotic group. The breeding scheme and the dimensioning underlying our simulations reflect
essentially the maize breeding program of the University of Hohenheim. Results suggested that in a plant breeding program
of the examined dimension and breeding scheme, genetic drift and selection are major forces generating LD. The currently used
population-based association mapping tests do not explicitly correct for LD caused by these two forces. Therefore, increased
type I error rates are expected if these tests are applied to plant breeding populations. As a consequence, we recommend to
use family-based association tests for association mapping approaches in plant breeding populations. 相似文献
167.
Reichert J Grasnick D Afonin S Buerck J Wadhwani P Ulrich AS 《European biophysics journal : EBJ》2007,36(4-5):405-413
It is generally assumed that fusogenic peptides would require a certain conformation, which triggers or participates in the
rate-determining step of membrane fusion. Previous structure analyses of the viral fusion peptide from gp41 of HIV-1 have
yielded contradictory results, showing either an α-helical or a β-stranded conformation under different conditions. To find
out whether either of these conformations is relevant in the actual fusion process, we have placed sterically demanding substitutions
into the fusion peptide FP23 to prevent or partially inhibit folding and self-assembly. A single substitution of either D- or L-CF3-phenylglycine was introduced in different positions of the sequence, and the capability of these peptide analogues to fuse
large unilamellar vesicles was monitored by lipid mixing and dynamic light scattering. If fusion proceeds via a β-stranded
oligomer, then the D- and L-epimers are expected to differ systematically in their activity, since the D-epimers should be unable to form β-structures due to sterical hindrance. If an α-helical conformation is relevant for fusion,
then the D-epimers would be slightly disfavoured compared to the L-forms, hence a small systematic difference in fusion activity should be observed. Interestingly, we find that (1) all D- and L-epimers are fusogenically active, though to different extents compared to the wild type, and – most importantly – (ii) there
is no systematic preference for either the D- or L-forms. We therefore suggest that a well-structured α-helical peptide conformation or a β-stranded oligomeric assembly can
be excluded as the rate-determining state. Instead, fusion appears to involve conformationally disordered peptides with a
pronounced structural plasticity.
Dedicated to Prof. K. Arnold on the occasion of this 65th birthday. 相似文献
168.
Weickert MO Loeffelholz CV Roden M Chandramouli V Brehm A Nowotny P Osterhoff MA Isken F Spranger J Landau BR Pfeiffer AF Möhlig M 《American journal of physiology. Endocrinology and metabolism》2007,293(4):E1078-E1084
Liver fatty acid-binding protein (L-FABP) is a highly conserved key factor in lipid metabolism. Amino acid replacements in L-FABP might alter its function and thereby affect glucose metabolism in lipid-exposed subjects, as indicated by studies in L-FABP knockout mice. Amino acid replacements in L-FABP were investigated in a cohort of 1,453 Caucasian subjects. Endogenous glucose production (EGP), gluconeogenesis, and glycogenolysis were measured in healthy carriers of the only common Thr(94)-to-Ala amino acid replacement (Ala/Ala(94)) vs. age-, sex-, and BMI-matched wild-type (Thr/Thr(94)) controls at baseline and after 320-min lipid/heparin-somatostatin-insulin-glucagon clamps (n = 18). Whole body glucose disposal was further investigated (subset; n = 13) using euglycemic-hyperinsulinemic clamps without and with lipid/heparin infusion. In the entire cohort, the only common Ala/Ala(94) mutation was significantly associated with reduced body weight, which is in agreement with a previous report. In lipid-exposed, individually matched subjects there was a genotype vs. lipid-treatment interaction for EGP (P = 0.009) driven mainly by reduced glycogenolysis in Ala/Ala(94) carriers (0.46 +/- 0.05 vs. 0.59 +/- 0.05 mgxkg(-1)xmin(-1), P = 0.013). The lipid-induced elevation of plasma glucose levels was smaller in Ala/Ala(94) carriers compared with wild types (P < 0.0001). Whole body glucose disposal was not different between lipid-exposed L-FABP genotypes. In summary, the Ala/Ala(94)-mutation contributed significantly to reduced glycogenolysis and less severe hyperglycemia in lipid-exposed humans and was further associated with reduced body weight in a large cohort. Data clearly show that investigation of L-FABP phenotypes in the basal overnight-fasted state yielded incomplete information, and a challenge test was essential to detect phenotypical differences in glucose metabolism between L-FABP genotypes. 相似文献
169.
St Martin JL Klucken J Outeiro TF Nguyen P Keller-McGandy C Cantuti-Castelvetri I Grammatopoulos TN Standaert DG Hyman BT McLean PJ 《Journal of neurochemistry》2007,100(6):1449-1457
Several transgenic mouse lines with altered alpha-synuclein expression have been developed that show a variety of Parkinson's disease-like symptoms without specific loss of dopaminergic neurons. Targeted over-expression of human alpha-synuclein using viral-vector mediated gene delivery into the substantia nigra of rats and non-human primates leads to dopaminergic cell loss and the formation of alpha-synuclein aggregates reminiscent of Lewy bodies. In the context of these recent findings, we used adeno-associated virus (AAV) to over-express wild type human alpha-synuclein in the substantia nigra of mice. We hypothesized that this over-expression would recapitulate pathological hallmarks of Parkinson's disease, creating a mouse model to further characterize the disease pathogenesis. Recombinant AAV expressing alpha-synuclein was stereotaxically injected into the substantia nigra of mice, leading to a 25% reduction of dopaminergic neurons after 24 weeks of transduction. Furthermore, examination of mRNA levels of stress-related proteins using laser capture microdissection and quantitative PCR revealed a positive correlation of Hsp27 expression with the extent of viral transduction at 4 weeks and a positive correlation of Hsp40, Hsp70 and caspase 9 with the extent of viral transduction at 24 weeks. Taken together, our findings suggest that targeted over-expression of alpha-synuclein can induce pathology at the gross anatomical and molecular level in the substantia nigra, providing a mouse model in which upstream changes in Parkinson's disease pathogenesis can be further elucidated. 相似文献
170.
Löw C Weininger U Zeeb M Zhang W Laue ED Schmid FX Balbach J 《Journal of molecular biology》2007,373(1):219-231
The p19(INK4d) protein consists of five ankyrin repeats (ANK) and controls the human cell cycle by inhibiting the cyclin D-dependent kinases (CDK) 4 and 6. We investigated the folding of p19(INK4d) by urea-induced unfolding transitions, kinetic analyses of unfolding and refolding, including double-mixing experiments and a special assay for folding intermediates. Folding is a sequential two-step reaction via a hyperfluorescent on-pathway intermediate. This intermediate is present under all conditions, during unfolding, refolding and at equilibrium. The folding mechanism was confirmed by a quantitative global fit of a consistent set of equilibrium and kinetic data revealing the thermodynamics and intrinsic folding rates of the different states. Surprisingly, the N<-->I transition is much faster compared to the I<-->U transition. The urea-dependence of the intrinsic folding rates causes population of the intermediate at equilibrium close to the transition midpoint. NMR detected hydrogen/deuterium exchange and the analysis of truncated variants showed that the C-terminal repeats ANK3-5 are already folded in the on-pathway intermediate, whereas the N-terminal repeats 1 and 2 are not folded. We suggest that during refolding, repeats ANK3-ANK5 first form the scaffold for the subsequent assembly of repeats ANK1 and ANK2. The binding function of p19(INK4d) resides in the latter repeats. We propose that the graded stability and the facile unfolding of repeats 1 and 2 is a prerequisite for the down-regulation of the inhibitory activity of p19(INK4d) during the cell-cycle. 相似文献