Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human

In 1871, the observation of yellowish nodules in the enlarged spleen of a cow was considered to be the first reported case of bovine leukemia. The etiological agent of this lymphoproliferative disease, bovine leukemia virus (BLV), belongs to the deltaretrovirus genus which also includes the related human T-lymphotropic virus type 1 (HTLV-1). This review summarizes current knowledge of this viral system, which is important as a model for leukemogenesis. Recently, the BLV model has also cast light onto novel prospects for therapies of HTLV induced diseases, for which no satisfactory treatment exists so far.     

Rodrigues fruit bats (<Emphasis Type="Italic">Pteropus rodricensis</Emphasis>, Megachiroptera: Pteropodidae) retain genetic diversity despite population declines and founder events

Fruit bats of the genus Pteropus are important contributors to ecosystem maintenance on islands through their roles as pollinators and seed dispersers. However, island faunas are the most prone to extinction and there is a real need to assess the possible genetic implications of population reductions in terms of extinction risk. An effective method of ameliorating extinction risk in endangered species is the establishment of captive populations ex situ. The effectiveness of captive breeding programmes may be assessed by comparing the genetic variability of captive colonies to that of wild counterparts. Here, we use polymorphic microsatellite loci to assess genetic variability in wild, critically endangered Rodrigues fruit bats (Pteropus rodricensis, Dobson 1878) and we compare this variability to that in a captive colony. We document remarkable conservation of genetic variability in both the wild and captive populations, despite population declines and founder events. Our results demonstrate that the wild population has withstood the negative effects of population reductions and that captive breeding programmes can fulfil the goals of retaining genetic diversity and limiting inbreeding.     

Alteration of the tertiary structure of the major bee venom allergen Api m 1 by multiple mutations is concomitant with low IgE reactivity

We have engineered a recombinant form of the major bee venom allergen (Api m 1) with the final goal of reducing its IgE reactivity. This molecule (Api mut) contains 24 mutations and one deletion of 10 amino acids. The successive introduction of these sequence modifications led to a progressive loss of specific IgE and IgG reactivity and did not reveal any immunodominant epitopes. However, Api mut exhibited a clear loss of reactivity for Api m 1-specific IgE and IgG. Injection of Api mut into mice induced specific antibody production. This humoral response was as high as that induced by the Api m 1 but the cross-reactivity of the antibodies was weak. As inferred by far UV circular dichroism, this mutant was correctly folded. However, near UV circular dichroism and denaturation curves of Api mut showed that it exhibits a dynamic tertiary structure and that it is a highly flexible molecule. Finally, as all the sequence modifications have been introduced outside the human and murine T cell epitope regions, we investigated its T cell properties in mice. We showed that Api mut-specific T lymphocytes induced in vivo were stimulated in vitro by both proteins. These data provide new insights in the design of hypoallergenic molecules.     

Metabolic Changes in <Emphasis Type="Italic">Clostridium absonum</Emphasis> ATCC 27555 Accompanying Induction of Epimerization of a Primary Bile Acid

Some parameters of fermentation have been determined for Clostridium absonum in a chemostat by using a chemically defined medium with glucose as the sole source of carbon and energy. Steady-state continuous cultures were achieved at two dilution rates (D). Trends of the carbon flow were determined by comparison of ratios between the specific rates of formation of the three products of metabolism (lactate, acetate, butyrate). Chenodeoxycholate induced the 7- and 7-hydroxysteroid dehydrogenases of C. absonum. In the presence of this inducer, the growth yield and the carbon recovery decreased, the carbon flow distribution was altered favoring acetate production, and a deficit in the reoxydation of nucleotidic cofactors was observed. In the presence of chenodeoxycholate, C. absonum would favor the production of energy at the expense of the reoxidation of nucleotidic cofactors so as to ensure its growth, and the epimerization of chenodeoxycholate to ursodeoxycholate.     

Microspatial genetic heterogeneity and gene flow in stray cats (Felis catus L.): a comparison of coat colour and microsatellite loci

We analysed levels of genetic differentiation between nine local urban colonies of stray cats using eight coat colour and nine microsatellite loci. Both types of markers revealed a strong differentiation between colonies (FST = 0.15 and 0.09 for coat colour and microsatellite loci, respectively). Three coat colour loci showed extreme levels of genetic differentiation comparatively to other loci and are strongly suspected to be under divergent selective pressures. Microsatellite loci showed significant heterozygote deficiency within colonies (FIS = 0.14), suggesting that coat colour loci are not appropriate to investigate genetic structure at a fine scale because coat colour allele frequencies are based on Hardy-Weinberg equilibrium. The reported pattern conformed to that predicted from the social structuring of cat colonies: aggressive exclusion of immigrants, inbreeding and very low dispersal rate.     

New nitrogen mustards structurally related to (L)-carnitine

Enantiopure nitrogen mustards which mimic (L)-carnitine framework are prepared by a multi-step synthesis from the (R)-di-tert-butyl malate and their antitumor properties evaluated.     

Insecticide resistance enhances male reproductive success in a beetle

Abstract.— Malathion-specific resistance in the red flour beetle, Tribolium castaneum , is widespread and stable in natural populations even in the absence of pesticide exposure. To understand this stability, both resistant and susceptible males were placed in competition for susceptible female fertilization. Females were then isolated and their progeny was tested for malathion susceptibility. Male reproductive success was estimated for populations originating from different geographic areas and for isogenic strains. In most cases, resistant males had a greater reproductive success rate than susceptibles. The results suggest that male reproductive success is not traded against the selection for malathion resistance, even resistant individuals are at an advantage for this fitness trait. This absence of fitness cost may be the result of postselection of (1) modifier gene which ameliorate the fitness of resistant individuals or (2) nondeleterious resistance gene. Resistant phenotype superiority could be due to increased male mating success, improved ability of resistant males in sperm competition, female mate choice, and/or cryptic female choice of resistance gene(s). The effect of male phenotypic frequency on male reproductive success was also examined. We observed that male fertilization success is frequency dependent and inversely related to their frequency. However, this "rare male" advantage did not counteract the superiority of the resistant males.     

Reactivity, secondary structure, and molecular topology of the Escherichia coli sulfite reductase flavodoxin-like domain

The flavodoxin-like domain, missing in the three-dimensional structure of the monomeric, simplified model of the Escherichia coli sulfite reductase flavoprotein component (SiR-FP), has now been expressed independently. This 168 amino acid protein was named SiR-FP18 with respect to its native molecular weight and represents the FMN-binding domain of SiR-FP. This simplified biological object has kept the main characteristics of its counterpart in the native protein. It could incorporate FMN exclusively and stabilize a neutral air-stable semiquinone radical. Both the radical and the fully reduced forms of SiR-FP18 were able to transfer their electrons to DCPIP or cytochrome c quantitatively. SiR-FP18 was able to form a highly stable complex with SiR-HP, the hemoprotein component of the sulfite reductase containing an iron-sulfur cluster coupled to a siroheme. In agreement with the postulated catalytic cycle of SiR-FP, only the fully reduced form of SiR-FP18 could transfer one electron to SiR-HP, the transferred electron being localized exclusively on the heme. As isolated SiR-FP18 has kept the main characteristics of the FMN-binding domain of the native protein, a structural analysis by NMR was performed in order to complete the partial structure obtained previously. Structural modeling was performed using sequence homologues, cytochrome P450 reductase (CPR; 29% identity) and bacterial cytochrome P450 (P450-BM3; 26% identity), as conformational templates. These sequences were anchored using common secondary structural elements identified from heteronuclear NMR data measured on the protein backbone. The resulting structural model was validated, and subsequently refined using residual (C(alpha)-C', N-H(N), and C'-H(N)) dipolar couplings measured in an anisotropic medium. The overall fold of SiR-FP18 is very similar to that of bacterial flavodoxins and of the flavodoxin-like domain in CPR or P450-BM3.     

Expression of a heterologous S-adenosylmethionine decarboxylase cDNA in plants demonstrates that changes in S-adenosyl-L-methionine decarboxylase activity determine levels of the higher polyamines spermidine and spermine

We posed the question of whether steady-state levels of the higher polyamines spermidine and spermine in plants can be influenced by overexpression of a heterologous cDNA involved in the later steps of the pathway, in the absence of any further manipulation of the two synthases that are also involved in their biosynthesis. Transgenic rice (Oryza sativa) plants engineered with the heterologous Datura stramonium S-adenosylmethionine decarboxylase (samdc) cDNA exhibited accumulation of the transgene steady-state mRNA. Transgene expression did not affect expression of the orthologous samdc gene. Significant increases in SAMDC activity translated to a direct increase in the level of spermidine, but not spermine, in leaves. Seeds recovered from a number of plants exhibited significant increases in spermidine and spermine levels. We demonstrate that overexpression of the D. stramonium samdc cDNA in transgenic rice is sufficient for accumulation of spermidine in leaves and spermidine and spermine in seeds. These findings suggest that increases in enzyme activity in one of the two components of the later parts of the pathway leading to the higher polyamines is sufficient to alter their levels mostly in seeds and, to some extent, in vegetative tissue such as leaves. Implications of our results on the design of rational approaches for the modulation of the polyamine pathway in plants are discussed in the general framework of metabolic pathway engineering.     

Activation of liver G-6-Pase in response to insulin-induced hypoglycemia or epinephrine infusion in the rat

This study was conducted to test the hypothesis of the activation of glucose-6-phosphatase (G-6-Pase) in situations where the liver is supposed to sustain high glucose supply, such as during the counterregulatory response to hypoglycemia. Hypoglycemia was induced by insulin infusion in anesthetized rats. Despite hyperinsulinemia, endogenous glucose production (EGP), assessed by [3-(3)H]glucose tracer dilution, was paradoxically not suppressed in hypoglycemic rats. G-6-Pase activity, assayed in a freeze-clamped liver lobe, was increased by 30% in hypoglycemia (P < 0.01 vs. saline-infused controls). Infusion of epinephrine (1 microg x kg(-1) x min(-1)) in normal rats induced a dramatic 80% increase in EGP and a 60% increase in G-6-Pase activity. In contrast, infusion of dexamethasone had no effect on these parameters. Similar insulin-induced hypoglycemia experiments performed in adrenalectomized rats did not induce any stimulation of G-6-Pase. Infusion of epinephrine in adrenalectomized rats restored a stimulation of G-6-Pase similar to that triggered by hypoglycemia in normal rats. These results strongly suggest that specific activatory mechanisms of G-6-Pase take place and contribute to EGP in situations where the latter is supposed to be sustained.