Temporal variability in a system of coupled mitotic timers

 Cell proliferation is considered a periodic process governed by a relaxation timer. The collective behavior of a system composed of three identical relaxation oscillators in numerically studied under the condition that diffusion of the slow mode dominates. We demonstrate: (1) the existence of three periodic regimes with different periods and phase relations and an unsymmetrical, stable steady-state (USSS); (2) the coexistence of in-phase oscillations and USSS; (3) the coexistence of periodic attractors; and (4) the emergence of a two-loop limit cycle coexisting with both in-phase oscillations and a stable steady-state. The qualitative reasons for such a diversitiy and its possible role in the generation of cell cycle variability are discussed. Received: 18 March 1992/Accepted in revised form: 16 April 1994     

Reagents For The Selective Immobilization Of Oligonucleotides On Solid Supports

New reagents (CPGs and phosphoramidites) for automatic solid phase synthesis of modified oligonucleotides were designed. Three oligonucleotides carrying fluorescent label at the 5′-terminus and an anchor group at the 3′-terminus were prepared and their immobilization in orthogonal conditions on solid supports was studied.     

Characterization of the mitochondrial genome of the MAX1 type of cytoplasmic male-sterile sunflower

Background

More than 70 cytoplasmic male sterility (CMS) types have been identified in Helianthus, but only for less than half of them, research of mitochondrial organization has been conducted. Moreover, complete mitochondrion sequences have only been published for two CMS sources – PET1 and PET2. It has been demonstrated that other sunflower CMS sources like MAX1, significantly differ from the PET1 and PET2 types. However, possible molecular causes for the CMS induction by MAX1 have not yet been proposed. In the present study, we have investigated structural changes in the mitochondrial genome of HA89 (MAX1) CMS sunflower line in comparison to the fertile mitochondrial genome.

Results

Eight significant major reorganization events have been determined in HA89 (MAX1) mtDNA: one 110 kb inverted region, four deletions of 439 bp, 978 bp, 3183 bp and 14,296 bp, respectively, and three insertions of 1999 bp, 5272 bp and 6583 bp. The rearrangements have led to functional changes in the mitochondrial genome of HA89 (MAX1) resulting in the complete elimination of orf777 and the appearance of new ORFs - orf306, orf480, orf645 and orf1287. Aligning the mtDNA of the CMS sources PET1 and PET2 with MAX1 we found some common reorganization features in their mitochondrial genome sequences.

Conclusion

The new open reading frame orf1287, representing a chimeric atp6 gene, may play a key role in MAX1 CMS phenotype formation in sunflower, while the contribution of other mitochondrial reorganizations seems to appear negligible for the CMS development.

     

Probiotic Intake Increases the Expression of Vitellogenin Genes in Laying Hens

Probiotics and Antimicrobial Proteins - A promising approach for slowing down the rate of reproductive aging is the use of probiotic bacteria as a feed additive. In the current study was...     

Miniaturized device for agitating a high-density yeast suspension that is suitable for in vivo nuclear magnetic resonance applications

In vivo nuclear magnetic resonance (NMR) monitoring requires a high-density cell suspension, where cell precipitation should be avoided. We have designed a miniaturized cell agitator that fits entirely into an 8-mm NMR probe but that, being mounted into the instrument, is situated outside of the sensitive area. The device consists of two glass tubes connected in a way that, when gas flow is blown through them, creates influx of cell suspension into the device that returns through apertures. This flow creates continuous circular vortex of the cell suspension in the whole sample volume, whereas there are no moving mechanical parts or gas bubbles crossing the instrument’s sensitive area. The gas flow controls conditions of the cell suspension and removes volatile waste metabolites.     

Mechanical Unfolding of Acylphosphatase Studied by Single-Molecule Force Spectroscopy and MD Simulations

Single-molecule manipulation methods provide a powerful means to study protein transitions. Here we combined single-molecule force spectroscopy and steered molecular-dynamics simulations to study the mechanical properties and unfolding behavior of the small enzyme acylphosphatase (AcP). We find that mechanical unfolding of AcP occurs at relatively low forces in an all-or-none fashion and is decelerated in the presence of a ligand, as observed in solution measurements. The prominent energy barrier for the transition is separated from the native state by a distance that is unusually long for α/β proteins. Unfolding is initiated at the C-terminal strand (β_T) that lies at one edge of the β-sheet of AcP, followed by unraveling of the strand located at the other. The central strand of the sheet and the two helices in the protein unfold last. Ligand binding counteracts unfolding by stabilizing contacts between an arginine residue (Arg-23) and the catalytic loop, as well as with β_T of AcP, which renders the force-bearing units of the protein resistant to force. This stabilizing effect may also account for the decelerated unfolding of ligand-bound AcP in the absence of force.     

Membrane cholesterol content plays a key role in the neurotoxicity of β-amyloid: implications for Alzheimer's disease

Beta amyloid (βA) plays a central role in the pathogenesis of the most common and devastating neurodegenerative disorder, Alzheimer's disease (AD). The mechanisms of βA neurotoxicity remain controversial, but include dysregulation of calcium homeostasis and oxidative stress. A large body of data suggest that cholesterol plays a significant role in AD. In mixed cultures containing hippocampal neurons and astrocytes, we have shown that neurotoxic βA peptides (1-42 and 25-35) cause sporadic cytosolic calcium ([Ca(2+) ](c) ) signals in astrocytes but not in neurons, initiating a cascade that ends in neuronal death. We now show, using the cholesterol-sensitive fluorescent probe, Filipin, that membrane cholesterol is significantly higher in astrocytes than in neurons and mediates the selective response of astrocytes to βA. Thus, lowering [cholesterol] using mevastatin, methyl-β-cyclodextrin or filipin prevented the βA-induced [Ca(2+) ](c) signals, while increased membrane [cholesterol] increased βA-induced [Ca(2+) ](c) signals in both neurons and astrocytes. Addition of βA to lipid bilayers caused the appearance of a conductance that was significantly higher in membranes containing cholesterol. Increasing membrane [cholesterol] significantly increased βA-induced neuronal and astrocytic death. We conclude that a high membrane [cholesterol] promotes βA incorporation into membranes and increased [Ca(2+) ](c) leading to cell death.     

Simplified absolute metabolite quantification by gas chromatography-isotope dilution mass spectrometry on the basis of commercially available source material

In the field of metabolomics, GC-MS has rather established itself as a tool for semi-quantitative strategies like metabolic fingerprinting or metabolic profiling. Absolute quantification of intra- or extracellular metabolites is nowadays mostly accomplished by application of diverse LC-MS techniques. Only few groups have so far adopted GC-MS technology for this exceptionally challenging task. Besides numerous and deeply investigated problems related to sample generation, the pronounced matrix effects in biological samples have led to the almost mandatory application of isotope dilution mass spectrometry (IDMS) for the accurate determination of absolute metabolite concentrations. Nevertheless, access to stable isotope labeled internal standards (ILIS), which are in many cases commercially unavailable, is quite laborious and very expensive. Here we present an improved and simplified gas chromatography-isotope dilution mass spectrometry (GC-IDMS) protocol for the absolute determination of intra- and extracellular metabolite levels. Commercially available (13)C-labeled algal cells were used as a convenient source for the preparation of internal standards. Advantages as well as limitations of the described method are discussed.