Apoptosis of cells lacking mitochondrial DNA

The mitochondrial genome of animals encodes a few subcomponents of the respiratory chain complexes I, III and IV, whereas nuclear DNA encodes the overwhelming majority, both in quantitative and qualitative terms, of mitochondrial proteins. Complete depletion of mitochondrial DNA (mtDNA) can be achieved by culturing cells in the presence of inhibitors of mtDNA replication or mitochondrial protein synthesis, giving rise to mutant cells (ϱ∘ cells) which carry morphological near-to-intact mitochondria with respiratory defects. Such cells can be used to study the impact of mitochondrial respiration on apoptosis. ϱ∘ cells do not undergo cell death in response to determined stimuli, yet they conserve their potential to undergo full-blown apoptosis in many experimental systems. This indicates that mtDNA and associated functions (in particular mitochondrial respiration) are irrelevant to apoptosis execution. However, the finding that mtDNA-deficient mitochondria can undergo apoptosis does not argue against the involvement of mitochondria in the apoptotic process, since mitochondria from ϱ∘ cells conserve most of their functions including those involved in the execution of the death programme: permeability transition and release of one or several intermembrane proteins causing nuclear apoptosis. Supported by ARC, ANRS, CNRS, FRM, Fondation de France, INSERM, NATO, Ligue contre le Cancer Ministère de la Recherche et de l'Industrie (France), and Sidaction (to GK). SAS receives a fellowship from the Spanish Government (Ministerio de Ciencia y Educación).     

Relationships between biotin and vitamin B12. Effects of biotin and vitamin B12 on folic acid metabolism

1. The effects of dietary biotin compared with vitamin B₁₂ on the total content and on the distribution of the various folate derivatives in the liver of rats given a biotin-free diet have been studied. The effect of both vitamins on the conversion in vitro of folic acid into citrovorum factor in the same experimental conditions was also examined. 2. In biotin-treated rats as well as in vitamin B₁₂-treated rats the total content of folic acid-active substances measured microbiologically by Pediococcus cerevisiae, Streptococcus faecalis and Lactobacillus casei is significantly higher than that in biotin-deficient rats. The liver distribution of various folate derivatives in the three groups of animals is also markedly modified. 3. The amount of citrovorum factor formed in systems with liver homogenate of rats receiving biotin or vitamin B₁₂ is higher than that with liver homogenates of deficient rats. 4. The results obtained demonstrate the influence of biotin in the metabolism of folic acid, and the similar actions at this level of both biotin and vitamin B₁₂. These results are discussed in relation to the participation of the two vitamins in the metabolism of C₁ units, as a biochemical interpretation of the relationships between vitamin B₁₂ and biotin.     

Synthesis and structural characterization of adducts of silver(I) nitrate with ER3 (E = P, As, Sb; R = Ph, cy, o-tolyl, mes) and oligodentate aromatic bases derivative of 2,2′-bipyridyl, L, AgNO3:ER3:L (1:1:1)

Twenty-one adducts of the form AgNO₃:ER₃:L (1:1:1) (E = P, As, Sb; R = Ph, cy, o-tolyl, mes; L = 2,2′-bipyridyl (‘bpy’)-based ligand), together with AgNO₃:Pcy₃:tpy (2:2:1) and AgNO₃:PPh₃:tpy (1:2:1) (‘tpy’ ≡ (2,2′:6,2″-terpyridine)), have been synthesized and characterized by analytical, spectroscopic (IR, far-IR, ¹H and ³¹P NMR) and single crystal X-ray diffraction studies. The resulting complexes are predominantly of the form , with trigonal EAgN₂ coordination environments, the planarity of which is perturbed by the approach of the nitrate anion. The nitrate ion shows uni- or (semi-)bidentate coordination, excepting the complex AgNO₃:P(o-tol)₃:dpca (1:1:1) (dpca = bis(2-picolyl)amine) where the anion is uncoordinated, the donor dpca being a pincer-tridentate. The complex AgNO₃:Pcy₃:tpy (2:2:1), also reported, is dinuclear with a bridging unidentate nitrate and a terpyridine, the latter bridging through its central ring, with the peripheral rings forming chelates to either side, whereas the complex AgNO₃:PPh₃:tpy (1:2:1) is ionic with a five-coordinate silver, bonded to tridentate tpy and two phosphines.     

Benzyl butyl phthalate influences actin distribution and cell proliferation in rat Py1a osteoblasts

We previously reported that transient administration of phthalates induced actin cytoskeleton disruption in Py1a osteoblasts. However, the mechanism of this transient effect was not elucidated. In this study we provided evidence that the actin cytoskeletal re-established conditions are dependent on new actin expression and synthesis. To assess the role of phthalates in modulating the distribution of actin, confocal and electron microscopy studies were carried out. Results indicated a modification of actin distribution after phthalate administration. In addition, a relation with the nucleoskeletal component lamin A supports the hypothesis that phthalates may participate in regulatory cell processes involving actin in Py1a osteoblasts. The present study also supports the mitogenic effects of phthalates, which involve microfilament disruption, nuclear actin and lamin A. In particular, the increased levels of cyclin D3, which in mammalian cells plays a critical role in G1 to S transition and is a putative proto-oncogene in benzyl butyl phthalate treated cells, suggested a possible effect of the endocrine disruptor in cancer processes.     

A composite sensor array impedentiometric electronic tongue Part I. Characterization

A study aimed at the characterization of five compounds with different chemical characteristics and gustative perceptions by measuring the variations of the electrical impedance of a composite sensor array is presented. The array was composed of five sensors of three different types based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes. Measurements were carried out by evaluating the electrical impedance of the sensor array at a frequency of 150 Hz, and the data acquisition process was automated; a mechanical arm and a rotating platform controlled by a data acquisition card and a dedicated software allowed the sequential dipping of sensors in the test solutions. Fifty different solutions eliciting the 5 basic tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter, respectively) at 10 concentration levels comprising the human perceptive range were analysed. More than 100 measurements were carried for each sample in a 4-month period to evaluate the system repeatability and robustness. The impedentiometric composite sensor array is shown to be sensitive, selective and stable for use in an electronic tongue.     

Effect of multiple prolyl isomerization reactions on the stability and folding kinetics of the notch ankyrin domain: experiment and theory

Studies on the folding kinetics of the Notch ankyrin domain have demonstrated that the major refolding phase is slow, the minor refolding phase is limited by the isomerization of prolyl peptide bonds, and that unfolding is multiexponential. Here, we explore the relationship between prolyl isomerization and folding heterogeneity using a combination of experiment and simulation. Proline residues were replaced with alanine, both singly and in various combinations. These destabilizing substitutions combine to eliminate the minor refolding phase, although unfolding heterogeneity persists even when all seven proline residues are replaced. To test whether prolyl isomerization influences the major refolding phase, we modeled folding and prolyl isomerization as a system of sequential reactions. Simulations that use rate constants of the major folding phase of the Notch ankyrin domain to represent intrinsic folding indicate that even with seven prolyl isomerization reactions, only two significant phases should be observed, and that the fast observed phase provides a good approximation of the intrinsic folding in the absence of prolyl isomerization. These results indicate that the major refolding phase of the Notch ankyrin domain reflects an intrinsically slow folding transition, rather than coupling of fast folding events with slow prolyl isomerization steps. This is consistent with the observation that the single observed refolding phase of a construct in which all proline residues are replaced remains slow. Finally, the simulation fails to produce a second unfolding phase at high urea concentrations, indicating that prolyl isomerization does not play a role in the three-state mechanism that leads to this heterogeneity.     

Evolutionary importance of the relationship between cytogeography and climate: New insights on creosote bushes from North and South America

Relationships between genome size and environmental variables suggest that DNA content might be adaptive and of evolutionary importance in plants. The genus Larrea provides an interesting system to test this hypothesis, since it shows both intra- and interspecific variation in genome size. Larrea has an amphitropical distribution in North and South American deserts, where it is most speciose. Larrea tridentata in North America shows a gradient of increasing autopolyploidy; while three of the four studied South American species are diploids, Larrea divaricata, Larrea nitida, Larrea ameghinoi, and the fourth is an allopolyploid, Larrea cuneifolia. We downloaded available focal species’ georeferenced records from seven data reservoirs. We used these records to extract biologically relevant environmental variables from WorldClim at 30 arc seconds scale, to have a broad characterization of the variable climatic conditions of both regions, and a climatic envelope for each species. We estimated relative DNA content index and relative monoploid genome values, by flow cytometry, of four most abundant Larrea species throughout their respective ranges. Then we winnow the bioclimatic dataset down to uncorrelated variables and sampled locales, to analyse the degree of association between both intra- and interspecific relative DNA content and climatic variables that are functionally relevant in arid environments using Pearson correlations, general linear and mixed effects models. Within the genus Larrea, relative DNA content increases with rising temperature and decreases with rising precipitation. At the intraspecific level, all four species show relative DNA content variation across climatic conditions. Larrea is a genus that shows genome size variation correlated with climate. Our results are also consistent with the hypothesis that extreme environmental pressures may have facilitated repeated whole genome duplication events in North America, while in South America, reticulate evolution, as allopolyploidization, and speciation might have been climate-dependent since the Oligocene.