Mitochondrial DNA evolution in lagomorphs: Origin of systematic heteroplasmy and organization of diversity in European rabbits

Summary A characterization was conducted on mitochondrial DNA (mtDNA) molecules extracted separately from 107 European rabbits (Oryctolagus cuniculus) both wild and domestic, 13 European hares (Lepus capensis), and 1 eastern cottontail (Sylvilagus floridanus). Experimentally this study took into account restriction site polymorphism, overall length variation of the noncoding region, and numbers of repeated sequences. Nucleotide divergences indicate that the mtDNAs from the three species derived from a common ancestor some 6–8 million years (Myr) ago. Every animal appeared heteroplasmic for a set of molecules with various lengths of the noncoding region and variable numbers of repeated sequences that contribute to them. This systematic heteroplasmy, most probably generated by a rate of localized mtDNA rearrangements high enough to counterbalance the cellular segregation of rearranged molecules, is a shared derived character of leporids.The geographic distribution of mtDNA polymorphism among wild rabbit populations over the western European basin shows that two molecular lineages are represented, one in southern Spain, the second over northern Spain, France, and Tunisia. These two lineages derived from a common ancestor some 2 Myr ago. Their present geographical distribution may be correlated to the separation of rabbits into two stocks at the time of Mindel glaciation.Finally the distribution of mtDNA diversity exhibits a mosaic pattern both at inter- and intrapopulation levels.     

Structural characterization of a novel class of glycophosphosphingolipids from the protozoan Leptomonas samueli.

Aqueous phenol extraction of the lower trypanosomatid Leptomonas samueli released into the aqueous layer a chloroform/methanol/water-soluble glycophosphosphingolipid fraction. Alkaline degradation and purification by gel filtration chromatography resulted in a tetrasaccharide (phosphatidylinositol (PI)-oligosaccharide A), and a pentasaccharide (PI-oligosaccharide B), each containing 2 mol of 2-aminoethylphosphonate and 1 mol of phosphate. Nuclear magnetic resonance spectroscopy and fast atom bombardment-mass spectrometry suggested that the structure of PI-oligosaccharide A is [formula: see text] and that of PI-oligosaccharide B is as shown. [formula: see text] Both compounds contain an inositol unit linked to ceramide via a phosphodiester bridge. The major aliphatic components of the ceramide portion are stearic acid, lignoceric acid, and C20-phytosphingosine. These novel glycolipids fall within the glycosylated phosphatidylinositol (GPI) family, since they contain the core structure Man alpha (1-->4)GlcNH2 alpha (1-->6)myo-inositol-1-PO4, which is also found in the glycoinositolphospholipids and lipophosphoglycan of Leishmania spp., the L. major promastigote surface protease, the glycosylphosphatidylinositol anchor of Trypanosoma brucei variant surface glycoprotein, and the lipopeptidophosphoglycan of Trypanosoma cruzi. The glycophosphosphingolipids of Leptomonas have features in common with the glycolipids of both Leishmania and T. cruzi, resembling the former by the alpha (1-->3) linkage of mannose to the GPI core, while the 2-aminoethylphosphonate substituent on O-6 of glucosamine and the presence of ceramide in place of glycerol lipids is more reminiscent of T. cruzi. Thus these data lend some support to the hypothesis that both T. cruzi and Leishmania evolved from a Leptomonas-like ancestor.     

Amphibian oocytes and sphere organelles: are the U snRNA genes amplified?

The sphere organelles (spheres) ofXenopus and other amphibian oocytes are known to contain small nuclear ribonucleoprotein particles (snRNPs) and have been suggested to play a role in snRNP complex assembly. Coupled with the similarities that exist between spheres and nucleoli and the quantitative and kinetic aspects of snRNA synthesis in theXenopus oocyte, we have investigated whether or not the U snRNA encoding genes are amplified inXenopus oogenesis, the spheres being possible sites for the location of such extrachromosomal gene copies. By applying a number of quantitative nucleic acid hybridization procedures to both total and fractionated oocyte and somatic DNA, employing both homologous and heterologous U snRNA gene probes and suitable amplification and non-amplification control probes, we show that the U snRNA genes do not undergo any major amplification inXenopus oogenesis. Therefore, the analogy between the sphere organelles and nucleoli appears to be limited. The role of the spheres and their relationship to other snRNP containing structures, specifically B snurposomes, and the sphere organizer loci remains obscure.by A. Spradling     

Uridine transport in basolateral plasma membrane vesicles from rat liver

Summary The characteristics of uridine transport were studied in basolateral plasma membrane vesicles isolated from rat liver. Uridine was not metabolized under transport measurement conditions and was taken up into an osmotically active space with no significant binding of uridine to the membrane vesicles. Uridine uptake was sodium dependent, showing no significant stimulation by other monovalent cations. Kinetic analysis of the sodium-dependent component showed a single system with Michaelis-Menten kinetics. Parameter values were K _M 8.9 m and V _max 0.57 pmol/mg prot/sec. Uridine transport proved to be electrogenic, since, firstly, the Hill plot of the kinetic data suggested a 1 uridine: 1 Na⁺ stoichiometry, secondly, valinomycin enhanced basal uridine uptake rates and, thirdly, the permeant nature of the Na⁺ counterions determined uridine transport rates (SCN^– > NO ₃ ^– > Cl^– > SO ₄ ^2– ). Other purines and pyrimidines cis-inhibited and trans-stimulated uridine uptake.This work has been partially supported by grant PM90-0162 from D.G.I.C.Y.T. (Ministerio de Educación y Ciencia, Spain). B.R.-M. is a research fellow supported by the Nestlé Nutrition Research Grant Programme.     

Interactions of surfactin,a biosurfactant fromBacillus subtilis,with inorganic cations

Summary The properties of surfactin, a biosurfactant lipopeptide, were highly modified in the presence of inorganic cations. The micellization of surfactin was favoured by monovalent and, especially by divalent cations with a modification of the molecular area at the air-water interface. Haemolysis of erythrocytes by surfactin was enhanced by low concentrations of divalent cations with an increase of the binding of the lipopeptide to membrane. Inorganic ions induced conformational rearrangements probably due to ion-surfactin associations which modify the surface-active properties.     

Cell suspension cultures ofOnonis natrix L. subspeciesramosissima: Establishment and culture conditions

Summary Explants from petioles, folioles or hypocotyls ofOnonis natrix have been used for calli initiation. Hypocotyls inoculated on MS medium supplemented with 2% sucrose and 0.5 mg.1^–1 2,4-D / 1 mg.1^–1 Kin showed to be the best primary explant. Cell suspension cultures were established in MS basal medium supplemented with 2% sucrose, 0.5 mg.1^–1 NAA or 2,4-D and 1 mg.1^–1 Kin. Different subculturing periods, inoculum density, hormonal supplementation and sucrose concentration were assayed in order to obtain the best culture growth conditions. The optimal conditions were achieved with cultures initiated with 40 g.1^–1 of initial inoculum, growing in MS basal medium supplemented with 4% sucrose, 0.5 mg.1^–1 NAA and 1 mg.1^–1 Kin subcultured every twelve days. Under these experimental conditions, the cultures showed a doubling time of 36.3 hours.     

The xylanase introns from Cryptococcus albidus are accurately spliced in transgenic tobacco plants

The xylanase gene from Cryptococcus albidus contains seven introns. Genomic and cDNA clones under the control of the CaMV 35S promoter were transferred into tobacco plants using Agrobacterium-mediated cell transformation. The genes were transcribed and the mRNAs were amplified by the polymerase chain reaction using primers on each side of the intron region. About 90% of the amplification products from plants transformed with the genomic clone corresponded to the size of the pre-mRNA (1.2 kb) and 10% represented the spliced product (0.85 kb). The 0.85 kb fragment was cloned and sequenced and the result indicated that the introns from the xylanase gene were accurately spliced by the plant cells.     

Structure and nonlinear optical properties of copper phthalocyanine thin films

This paper describes a joint study of the structure and nonlinear optical properties of vacuum evaporated thin films of copper phthalocyanine (CuPc for brevity). Film thickness ranges from 50 to 500 nm. The anisotropic paramagnetic resonance of Cu⁺⁺ ions reveals that the Pc rings lie almost parallel to the substrate plane with however a large angular distribution (30° FWHM). Third harmonic optical generation measurements performed at 1.064 m and 1.907 m fundamental wavelengths give respectively an average value of the cubic susceptibility ⁽³⁾(-3,)=(4±0.4)·10^–12 e.s.u. and (2.1+-0.2) · 10^-12 These values, although significantly higher than for a common ionic crystal, are about one order of magnitude lower than in conjugated 1-D systems, which shows that the 2-D -electron delocalization is less profitable than the 1-D one. Besides third harmonic, we have also observed second harmonic generation. Its polarization dependence is characteristic of a quadratic susceptibility enhanced in one direction, almost perpendicular to the substrate, withd _eff comprised between 30 and 60 · 10^-9 e.s.u. The possible origins ofd _eff are discussed.     

Experimental paracoccidioidomycosis in the Syrian hamster

Male hamsters (105) received intratesticular injection of suspension of a live yeast phase culture ofParacoccidioides brasiliensis and were sacrificed weekly during 20 weeks. Humoral immunity was studied by the agar-gel immunodiffusion (ID) and indirect immunofluorescence (IF) tests. Cell-mediated immunity was determined by the macrophage migration inhibition test in the presence of phytohemagglutinin (PHA) andParacoccidioides brasiliensis soluble antigen (PbAg). The morphology of the lesions was studied in the inoculation site, lymph nodes, lung, liver, spleen and kidneys.Disseminated paracoccidioidomycosis was observed in 100% of the animals after the first week. The lesions were initially made up of fungi surrounded by polymorphonuclear neutrophils and macrophages. Up to the 10th week the majority of the lesions appeared as compact confluent ephitelioid granulomas containing rare large fungi, some showing signs of degeneration. At this time, the specific antibody titers and the cellular immune response to PHA and PbAg were highest.From the 11th week on the granulomas became less compact, edematous with the epithelioid cells loosely arranged. This change was accompanied by an increase in the number of fungi showing reproductive activity and was associated with renal amyloidosis and progressive decline of cellular immune response both to PHA and PbAg. Contrariwise the titers of circulating antibodies were maintained.In the present model, disseminated paracoccidioidomycosis of the hamster was associated with depression of cellular immunity, change in the pattern of the granuloma, intense fungi proliferation and amyloidosis.