Interaction of L-arginine with dihexadecylphosphate unilamellar liposomes: the effect of the lipid phase organization

The interaction of L-arginine with unilamellar liposomes of dihexadecylphosphate sodium salt (DHP-Na) has been investigated using calorimetric, light scattering, fluorescence spectroscopy and zeta-potential techniques. Heating from room temperature, the bilayer exhibits a phase transition from a subgel (L(c)) to the gel (L(beta')) phase as well as a pre-transition (L(beta')-P(beta')), which is followed by the main lipid phase transition (P(beta')-L(alpha)). Direct studies of the interaction of L-arginine with the DHP-Na bilayers via isothermal titration calorimetry at 27 degrees C depict significant differences between samples in the L(c) and the L(beta') phases reflecting the effect of molecular organization of the lipids upon the interaction. While L-arginine has only a small impact upon the L(c) to L(beta') phase transition, it affects more significantly the transition temperature as well as the shape of the DSC peaks of the main lipid phase transition. Based on fluorescence and zeta-potential studies, the permeability of L-arginine through the liposomal membrane is higher within the temperature range of the main lipid phase transition. Encapsulated l-arginine obstructs the formation of the subgel phase.     

Role of energetic coenzyme pools in the production of L-carnitine by Escherichia coli

The aim of this work was to understand the steps controlling the biotransformation of trimethylammonium compounds into L(-)-carnitine by Escherichia coli. The high-cell density reactor steady-state levels of carbon source (glycerol), biotransformation substrate (crotonobetaine), acetate (anaerobiosis product) and fumarate (as an electron acceptor) were pulsed by increasing them fivefold. Following the pulse, the evolution of the enzyme activities involved in the biotransformation process of crotonobetaine into L(-)-carnitine (crotonobetaine hydration), in the synthesis of acetyl-CoA (ACS: acetyl-CoA synthetase and PTA: ATP: acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid (ICDH: isocitrate dehydrogenase) and glyoxylate (ICL: isocitrate lyase) cycles was monitored. In addition, the levels of carnitine, the cell ATP content and the NADH/NAD(+) ratio were measured in order to assess the importance and participation of these energetic coenzymes in the catabolic system. The results provided an experimental demonstration of the important role of the glyoxylate shunt during biotransformation and the need for high levels of ATP to maintain metabolite transport and biotransformation. Moreover, the results obtained for the NADH/NAD(+) pool indicated that it is correlated with the biotransformation process at the NAD(+) regeneration and ATP production level in anaerobiosis. More importantly, a linear correlation between the NADH/NAD(+) ratio and the levels of the ICDH and ICL (carbon and electron flows) and the PTA and ACS (acetate and ATP production and acetyl-CoA synthesis) activity levels was assessed. The main metabolic pathway operating during cell metabolic perturbation with a pulse of glycerol and acetate in the high-cell density membrane reactor was that related to ICDH and ICL, both regulating the carbon metabolism, together with PTA and ACS enzymes (regulating ATP production).     

Biomechanical analysis of the Rolled (RLD) leaf phenotype of maize

The pleiotropic effects of the Rld1-O/+ mutation of Zea mays (Poaceae) on leaf phenotype include a suppression of normal transverse unrolling, a reversed top/bottom epidermal polarity, and an apparently straighter longitudinal shape. According to engineering shell theory, there might be mechanical coupling between transverse and longitudinal habit, i.e., the leaf rolling itself might produce the longitudinal straightening. We tested this possibility with quantitative curvature measurements and mechanical uncoupling experiments. The contributions of elastic bending under self weight, mechanical coupling, and rest state of leaf parts to the longitudinal and transverse habit were assessed in Rld1-O/+ mutants and a population of sibling +/+ segregants. Elastic bending and curvature coupling are shown to be relatively unimportant. The Rld1-O/+ mutation is shown to alter not only the unrolling process, but also the developmental longitudinal curving in the growing leaf, leading to a straighter midrib and a rolled lamina. The Rld1-O/+ mutant is thus a suitable model to study the relation between tissue polarity and differential curvature development in the maize leaf. Since on the abaxial side of the leaf, more abundant sclerenchyma is found in +/+ than in Rld1-O/+, a gradient in sclerification may contribute to the development of midrib curvature.     

Upregulation of miR-24 is associated with a decreased DNA damage response upon etoposide treatment in highly differentiated CD8(+) T cells sensitizing them to apoptotic cell death

The life-long homeostasis of memory CD8(+) T cells as well as persistent viral infections have been shown to facilitate the accumulation of highly differentiated CD8(+) CD28(-) T cells, a phenomenon that has been associated with an impaired immune function in humans. However, the molecular mechanisms regulating homeostasis of CD8(+) CD28(-) T cells have not yet been elucidated. In this study, we demonstrate that the miR-23～24～27 cluster is up-regulated during post-thymic CD8(+) T-cell differentiation in humans. The increased expression of miR-24 in CD8(+) CD28(-) T cells is associated with decreased expression of the histone variant H2AX, a protein that plays a key role in the DNA damage response (DDR). Following treatment with the classic chemotherapeutic agent etoposide, a topoisomerase II inhibitor, apoptosis was increased in CD8(+) CD28(-) when compared to CD8(+) CD28(+) T cells and correlated with an impaired DDR in this cell type. The reduced capacity of CD8(+) CD28(-) T cell to repair DNA was characterized by the automated fluorimetric analysis of DNA unwinding (FADU) assay as well as by decreased phosphorylation of H2AX at Ser139, of ATM at Ser1981, and of p53 at Ser15. Interleukin (IL)-15 could prevent etoposide-mediated apoptosis of CD8(+) CD28(-) T cells, suggesting a role for IL-15 in the survival and the age-dependent accumulation of CD8(+) CD28(-) T cells in humans.     

串果藤属(Sinofranchetia)叶的个体发育研究

对串果藤属(Sinofranchetia)叶的个体发育过程进行了观察,结果表明,其叶原基在发生时为不分裂的,其后叶原基两侧产生两个突起,形成两个侧生小叶原基,而中央部分形成中央小叶的原基。同时对串果藤属植物叶原基发生的类型等问题进行了讨论。     

Spinal Cord Transcriptome Analysis Using Suppression Subtractive Hybridization and Mirror Orientation Selection

Comparison of cDNA libraries derived from the spinal cord with those derived from the visual cortex by means of forward and reverse subtractive hybridization resulted in the cataloguing of 60 genes differentially expressed in the spinal cord. 1. The differentially expressed genes represent a mixture of novel and known sequences with known and unknown protein products. 2. The possibility that the subtraction process was simply overwhelmed by background sequences was significantly reduced by several observations including comparisons between suppression subtractive hybridization (SSH) and mirror orientation selection (MOS). 3. Nearly half of all genes up-regulated in the spinal cord are of myelin origin. 4. Twenty-five percent of all up-regulated clones in the spinal cord versus the visual cortex are for proteolipid protein. 5. Ten percent of all up-regulated clones in spinal cord versus visual cortex are for ferretin heavy chain, which is known to be produced in oligodendroglial cells in the CNS. 6. Two of the up-regulated sequences, proteolipid protein and N-myc down-regulated gene 4, are identified with genes known to directly affect neuron survival. 7. Two of the up-regulated genes, ferritin and transferrin, are indirectly associated with apoptosis through their ability to sequester iron and reduce free radical formation.     

Cellular Differentiation and Leaf Morphogenesis in Arabdopsis

A focused approach that exploits a single plant species, namely, Arabidopsis thaliana, as a means to understand how leaf cells differentiate and the factors that govern overall leaf morphogenesis has begun to generate a significant body of knowledge in this model plant. Although many studies have concentrated on specific cell types and factors that control their differentiation, some degree of consensus is starting to be reached. However, an understanding of specific mechanisms by which cells differentiate in relation to their position, that appears to be an overriding factor in this process, is not yet in place for cell types in the Arabidopsis leaf. It is clear that perturbations in cellular development within the leaf do not necessarily have a general effect on morphogenesis. Environmental factors, particularly light, have been known to affect leaf cell differentiation and expansion, and endogenous hormones also appear to play an important role, through mechanisms that are beginning to be uncovered. It is likely that continued identification of genes involved in leaf development and their regulation in relation to positional information or other cues will lead to a clearer understanding of the control of differentiation and morphogenesis in the Arabidopsis leaf.     

Optimal window of caloric restriction onset limits its beneficial impact on T‐cell senescence in primates

We have recently shown in non‐human primates that caloric restriction (CR) initiated during adulthood can delay T‐cell aging and preserve naïve CD8 and CD4 T cells into advanced age. An important question is whether CR can be initiated at any time in life, and whether age at the time of onset would modulate the beneficial effects of CR. In the current study, we evaluated the impact of CR started before puberty or during advanced age on T‐cell senescence and compared it to the effects of CR started in early adulthood. Our data demonstrate that the beneficial effects of adult‐onset CR on T‐cell aging were lost by both early and late CR onset. In fact, some of our results suggest that inappropriate initiation of CR may be harmful to the maintenance of T‐cell function. This suggests that there may be an optimal window during adulthood where CR can delay immune senescence and improve correlates of immunity in primates.     

Trade‐off relationship between productivity and thallus toughness in Laminariales (Phaeophyceae)

Trade‐off relationships are considered key to understanding the mechanisms supporting the coexistence of multiple species within kelp beds. Thus, information on trade‐offs is expected to contribute to conservation of kelp bed diversity. To test the existence of a trade‐off between productivity and thallus toughness, thallus traits and relationships between the traits were examined for seven species of Laminariales including 24 populations. For each population, photosynthetic capacity per unit biomass (as A _mass) and nitrogen (i.e., photosynthetic nitrogen‐use efficiency, PNUE), nitrogen content (as N _mass), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as F _p, a common index of leaf toughness in land plants by punch test) were determined. A _mass increased with increasing N _mass. Blades with high N _mass showed high A _mass. These blades may invest a large proportion of nitrogen to the photosynthetic parts, and consequently exhibit high metabolic rates. Moreover, blades with high N _mass tended to be associated with low TMA, and N _mass decreased with increasing TMA. A significant negative correlation was observed between TMA and A _mass because of the linkage of high A _mass with high N _mass and high N _mass associated with low TMA, while a significant positive correlation was observed between TMA and F _p. The two correlations indicate the existence of a trade‐off between productivity and thallus toughness in Laminariales. PNUE showed a significant negative correlation with TMA, which also showed a significant positive correlation with F _p as the index of thallus toughness, and therefore a trade‐off relationship between productivity and thallus toughness.     

Cutting edge: Chk1 directs senescence and mitotic catastrophe in recovery from G2 checkpoint arrest

Besides the well‐understood DNA damage response via establishment of G₂ checkpoint arrest, novel studies focus on the recovery from arrest by checkpoint override to monitor cell cycle re‐entry. The aim of this study was to investigate the role of Chk1 in the recovery from G₂ checkpoint arrest in HCT116 (human colorectal cancer) wt, p53^–/– and p21^–/– cell lines following H₂O₂ treatment. Firstly, DNA damage caused G₂ checkpoint activation via Chk1. Secondly, overriding G₂ checkpoint led to (i) mitotic slippage, cell cycle re‐entry in G₁ and subsequent G₁ arrest associated with senescence or (ii) premature mitotic entry in the absence of p53/p21^WAF1 causing mitotic catastrophe. We revealed subtle differences in the initial Chk1‐involved G₂ arrest with respect to p53/p21^WAF1: absence of either protein led to late G₂ arrest instead of the classic G₂ arrest during checkpoint initiation, and this impacted the release back into the cell cycle. Thus, G₂ arrest correlated with downstream senescence, but late G₂ arrest led to mitotic catastrophe, although both cell cycle re‐entries were linked to upstream Chk1 signalling. Chk1 knockdown deciphered that Chk1 defines long‐term DNA damage responses causing cell cycle re‐entry. We propose that recovery from oxidative DNA damage‐induced G₂ arrest requires Chk1. It works as cutting edge and navigates cells to senescence or mitotic catastrophe. The decision, however, seems to depend on p53/p21^WAF1. The general relevance of Chk1 as an important determinant of recovery from G₂ checkpoint arrest was verified in HT29 colorectal cancer cells.