The evolutionary radiation of Arvicolinae rodents (voles and lemmings): relative contribution of nuclear and mitochondrial DNA phylogenies

Background  

Mitochondrial and nuclear genes have generally been employed for different purposes in molecular systematics, the former to resolve relationships within recently evolved groups and the latter to investigate phylogenies at a deeper level. In the case of rapid and recent evolutionary radiations, mitochondrial genes like cytochrome b (CYB) are often inefficient for resolving phylogenetic relationships. One of the best examples is illustrated by Arvicolinae rodents (Rodentia; Muridae), the most impressive mammalian radiation of the Northern Hemisphere which produced voles, lemmings and muskrats. Here, we compare the relative contribution of a nuclear marker – the exon 10 of the growth hormone receptor (GHR) gene – to the one of the mitochondrial CYB for inferring phylogenetic relationships among the major lineages of arvicoline rodents.     

The abundance of additional N-acetyllactosamine units in N-linked tetraantennary oligosaccharides of human Tamm-Horsfall glycoprotein is a donor-specific feature

Previously, treatment of Tamm-Horsfall glycoprotein (THp) from different donors with endo-beta-galactosidase has been shown to liberate a tetra- and a Sd(a)-active pentasaccharide, concluding the presence of N-linked carbohydrate chains containing additional N - acetyllactosamine units. These type of oligosaccharides were not found in a detailed structure elucidation of the carbohydrate moiety of THp of one male donor, suggesting a donor-specific feature for these type of structures. Therefore, THp was isolated from four healthy male donors and each subjected to endo-beta-galactosidase treatment in order to release these tetra- and Sd(a)-active pentasaccharide. Differences were observed in the total amount of released tetra- and Sda-active pentasaccharide of the used donors (42, 470, 478, 718 microg/100 mg THp), indicating that the presence of repeating N-acetyllactosamine units incorporated into the N-glycan moiety of THp is donor specific. Furthermore, a higher expression of the Sd(a) determinant on antennae which display N-acetyllactosamine elongation was observed, suggesting a better accessibility for the beta-N-acetylgalactosaminyltransferase. In order to characterize the N-glycans containing repeating N- acetyllactosamine units, carbohydrate chains were enzymatically released from THp and isolated. The tetraantennary fraction, which accounts for more than 33% of the total carbohydrate moiety of THp, was used to isolate oligosaccharides containing additional N - acetyllactosamine units. Five N-linked tetraantennary oligosaccharides containing a repeating N-acetyllactosamine unit were identified, varying from structures bearing four Sd(a) determinants to structures containing no Sd(a) determinant (see below). One compound was used in order to specify the branch location of the additional N- acetyllactosamine unit, and it appeared that only the Gal-6' and Gal-8' residues were occupied by a repeating N -acetyllactosamine unit.      

Differential binding of lectins IL-2 and CSL to candida albicans and cancer cells

The demonstration that interleukin 2 (IL-2) is a lectin specific for oligomannosides allows to understand a new function for this cytokine: as a bifunctional molecule when bound to its receptor ss, IL-2 associates the latter which the CD3/TCR complex, interacting with oligosaccharides of CD3 through its carbohydrate-recognition domain (Zanetta et al. , 1996, Biochem. J., 318, 49-53). This induces the tyrosine phosphorylation of the IL-2R beta by ++p56(lck) , the first step of the IL-2-dependent signaling. Since this specific association is disrupted in vitro by oligomannosides with five and six mannose residues, we made the hypothesis that pathogenic cells or microorganisms could bind IL-2, consequently disturbing the IL-2- dependent response. This study shows that the pathogenic yeast Candida albicans (in contrast with nonpathogenic yeasts) binds high amounts of IL-2 as did cancer cells. In contrast with cancer cells, yeasts do not bind the Man6GlcNAc2-specific lectin CSL, an endogenous "amplifier of activation signals" (Zanetta et al. , 1995, Biochem. J., 311, 629-636).      

d-glucose uptake in human liver cell cultures

Summary The kinetic parameters ford-glucose uptake were studied in human liver cell cultures under strictly defined experimental conditions. Using a wide concentration range (0.005 to 30 mmol/l), the kinetic data obtained suggested strongly thatd-glucose in human liver cell cultures can be transported by two separate systems. For the high-affinity system, the apparentK _m was 0.645±0.21 mmol/l and the V_max, 12.49±3.74 nmol/mg protein per min. For the low-affinity system, the apparentK _m was 6.91±0.58 mmol/l and the V_max, 79.90±5.27 nmol/mg protein per min. At a concentration of 2.1×10⁻⁷ mol/l, cytochalasin B preferentially inhibited the high-affinityd-glucose site or transport system. The time course ofd-glucose uptake, studied in two cell lines from patients with hereditary fructose intolerance, was significantly higher than for the control lines. This work was supported by Grant I.N.S.E.R.M. CRL 77-5-210-4.     

Study of vitamin E net mass transfer between alpha-tocopherol-enriched HDL and erythrocytes: application to asymptomatic hypercholesterolemic men

We previously showed that hypercholesterolemic asymptomatic men had lower erythrocyte vitamin E content, despite normal plasma concentrations compared to normocholesterolemic men. We hypothesized that the reduced erythrocyte vitamin E concentration could be due to an impairment of transfer of vitamin E from plasma lipoproteins. We first developed a model for testing the ability of erythrocytes to accept vitamin E from high-density lipoproteins (HDL) pre-enriched in vitamin E, which allows to measure a net mass transfer of vitamin E from HDL to erythrocytes. Vitamin E-enriched HDL were obtained in controlled conditions of concentration and incubation time with a good reproducibility (CV 相似文献   

Stoichiometry and compartmentation of NADH metabolism in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, reduction of NAD(+) to NADH occurs in dissimilatory as well as in assimilatory reactions. This review discusses mechanisms for reoxidation of NADH in this yeast, with special emphasis on the metabolic compartmentation that occurs as a consequence of the impermeability of the mitochondrial inner membrane for NADH and NAD(+). At least five mechanisms of NADH reoxidation exist in S. cerevisiae. These are: (1) alcoholic fermentation; (2) glycerol production; (3) respiration of cytosolic NADH via external mitochondrial NADH dehydrogenases; (4) respiration of cytosolic NADH via the glycerol-3-phosphate shuttle; and (5) oxidation of intramitochondrial NADH via a mitochondrial 'internal' NADH dehydrogenase. Furthermore, in vivo evidence indicates that NADH redox equivalents can be shuttled across the mitochondrial inner membrane by an ethanol-acetaldehyde shuttle. Several other redox-shuttle mechanisms might occur in S. cerevisiae, including a malate-oxaloacetate shuttle, a malate-aspartate shuttle and a malate-pyruvate shuttle. Although key enzymes and transporters for these shuttles are present, there is as yet no consistent evidence for their in vivo activity. Activity of several other shuttles, including the malate-citrate and fatty acid shuttles, can be ruled out based on the absence of key enzymes or transporters. Quantitative physiological analysis of defined mutants has been important in identifying several parallel pathways for reoxidation of cytosolic and intramitochondrial NADH. The major challenge that lies ahead is to elucidate the physiological function of parallel pathways for NADH oxidation in wild-type cells, both under steady-state and transient-state conditions. This requires the development of techniques for accurate measurement of intracellular metabolite concentrations in separate metabolic compartments.     

Oxidative Modification of Low-Density Lipoprotein by the Human Hepatoma Cell Line HepG2

The human hepatoblastoma cell line HepG2 is a liver model commonly used for lipid metabolism studies. Numerous cell types have been found to oxidize low-density lipoprotein (LDL) but, to our knowledge, the effects of HepG2 cells on LDL have not been investigated. We found that LDL is modified by HepG2 cells through a peroxidative mechanism, as judged by an increase in TBARS content (which was prevented in the presence of the antioxidants vitamin E, 2, 6-di-tert-butyl-cresol and probucol), increased degradation by J774 macrophages, decreased internalization by MRC5 fibroblasts, and aggregation of apo B. Aspirin and allopurinol, which inhibit cyclooxygenase and xanthine-oxidase activities, respectively, had no effect on HepG2-induced LDL modification, and neither did catalase, which dismutates hydrogen peroxide; or mannitol, which scavenges hydroxyl radicals. In contrast, superoxide dismutase, a superoxide anion scavenger, and glutamate and threonine, which alter cellular cystine uptake, prevented LDL modifications, as did the removal of cysteine/cystine from the culture medium. Oxidation of LDL by HepG2 cells might thus involve superoxide anion production and/or thiol metabolism.