The genome of Apis mellifera: dialog between linkage mapping and sequence assembly

Two independent genome projects for the honey bee, a microsatellite linkage map and a genome sequence assembly, have interactively produced an almost complete organization of the euchromatic genome

MoMuLV and HIV-1 nucleocapsid proteins have a common role in genomic RNA packaging but different in late reverse transcription

Retroviral nucleocapsid proteins harbor nucleic acid chaperoning activities that mostly rely on the N-terminal basic residues and the CCHC zinc finger motif. Such chaperoning is essential for virus replication, notably for genomic RNA selection and packaging in virions, and for reverse transcription of genomic RNA into DNA. Recent data revealed that HIV-1 nucleocapsid restricts reverse transcription during virus assembly--a process called late reverse transcription--suggesting a regulation between RNA packaging and late reverse transcription. Indeed, mutating the HIV-1 nucleocapsid basic residues or the two zinc fingers caused a reduction in RNA incorporated and an increase in newly made viral DNA in the mutant virions. MoMuLV nucleocapsid has an N-terminal basic region similar to HIV-1 nucleocapsid but a unique zinc finger. This prompted us to investigate whether the N-terminal basic residues and the zinc finger of MoMuLV and HIV-1 nucleocapsids play a similar role in genomic RNA packaging and late reverse transcription. To this end, we analyzed the genomic RNA and viral DNA contents of virions produced by cells transfected with MoMuLV molecular clones where the zinc finger was mutated or completely deleted or with a deletion of the N-terminal basic residues of nucleocapsid. All mutant virions showed a strong defect in genomic RNA content indicating that the basic residues and zinc finger are important for genomic RNA packaging. In contrast to HIV-1 nucleocapsid-mutants, the level of viral DNA in mutant MoMuLV virions was only slightly increased. These results confirm that the N-terminal basic residues and zinc finger of MoMuLV nucleocapsid are critical for genomic RNA packaging but, in contrast to HIV-1 nucleocapsid, they most probably do not play a role in the control of late reverse transcription. In addition, these results suggest that virus formation and late reverse transcription proceed according to distinct mechanisms for MuLV and HIV-1

Superconception in mammalian pregnancy can be detected and increases reproductive output per breeding season

The concept of superfetation, a second conception during pregnancy, has been controversial for a long time. In this paper we use an experimental approach to demonstrate that female European brown hares (Lepus europaeus) frequently develop a second pregnancy while already pregnant and thereby increase their reproductive success. After a new, successful copulation, we confirmed additional ovulations before parturition in living, late-pregnant females by detecting a second set of fresh corpora lutea using high-resolution ultrasonography. The presence of early embryonic stages in the oviduct, demonstrated by oviduct flushing, next to fully developed fetuses in the uterus is best explained by passage of semen through the late-pregnant uterus; this was confirmed by paternity analysis using microsatellite profiling. Subsequent implantation occurred after parturition. This superfetation, categorized as superconception, significantly increased litter size and permitted females to produce up to 35.4% more offspring per breeding season. It is therefore most likely an evolutionary adaptation

Murine leukemia virus RNA dimerization is coupled to transcription and splicing processes

Most of the cell biological aspects of retroviral genome dimerization remain unknown. Murine leukemia virus (MLV) constitutes a useful model to study when and where dimerization occurs within the cell. For instance, MLV produces a subgenomic RNA (called SD') that is co-packaged with the genomic RNA predominantly as FLSD' heterodimers. This SD' RNA is generated by splicing of the genomic RNA and also by direct transcription of a splice-associated retroelement of MLV (SDARE). We took advantage of these two SD' origins to study the effects of transcription and splicing events on RNA dimerization. Using genetic approaches coupled to capture of RNA heterodimer in virions, we determined heterodimerization frequencies in different cellular contexts. Several cell lines were stably established in which SD' RNA was produced by either splicing or transcription from SDARE. Moreover, SDARE was integrated into the host chromosome either concomitantly or sequentially with the genomic provirus. Our results showed that transcribed genomic and SD' RNAs preferentially formed heterodimers when their respective proviruses were integrated together. In contrast, heterodimerization was strongly affected when the two proviruses were integrated independently. Finally, dimerization was enhanced when the transcription sites were expected to be physically close. For the first time, we report that splicing and RNA dimerization appear to be coupled. Indeed, when the RNAs underwent splicing, the FLSD' dimerization reached a frequency similar to co-transcriptional heterodimerization. Altogether, our results indicate that randomness of heterodimerization increases when RNAs are co-expressed during either transcription or splicing. Our results strongly support the notion that dimerization occurs in the nucleus, at or near the transcription and splicing sites, at areas of high viral RNA concentration

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field

Fine Scale Analysis of Crossover and Non-Crossover and Detection of Recombination Sequence Motifs in the Honeybee (Apis mellifera)

BACKGROUND: Meiotic exchanges are non-uniformly distributed across the genome of most studied organisms. This uneven distribution suggests that recombination is initiated by specific signals and/or regulations. Some of these signals were recently identified in humans and mice. However, it is unclear whether or not sequence signals are also involved in chromosomal recombination of insects. METHODOLOGY: We analyzed recombination frequencies in the honeybee, in which genome sequencing provided a large amount of SNPs spread over the entire set of chromosomes. As the genome sequences were obtained from a pool of haploid males, which were the progeny of a single queen, an oocyte method (study of recombination on haploid males that develop from unfertilized eggs and hence are the direct reflect of female gametes haplotypes) was developed to detect recombined pairs of SNP sites. Sequences were further compared between recombinant and non-recombinant fragments to detect recombination-specific motifs. CONCLUSIONS: Recombination events between adjacent SNP sites were detected at an average distance of 92 bp and revealed the existence of high rates of recombination events. This study also shows the presence of conversion without crossover (i. e. non-crossover) events, the number of which largely outnumbers that of crossover events. Furthermore the comparison of sequences that have undergone recombination with sequences that have not, led to the discovery of sequence motifs (CGCA, GCCGC, CCGCA), which may correspond to recombination signals

Uranyl oxo activation and functionalization by metal cation coordination

International audienceThe oxo groups in the uranyl ion [UO$_2$]$^{2+}$ , one of many oxo cations formed by metals from across the periodic table—are particularly inert, which explains the dominance of this ion in the laboratory and its persistence as an environmental contaminant. In contrast, transition metal oxo (M=O) compounds can be highly reactive and carry out difficult reactions such as the oxygenation of hydrocarbons. Here we show how the sequential addition of a lithium metal base to the uranyl ion constrained in a ‘Pacman’ environment results in lithium coordination to the U=O bonds and single-electron reduction. This reaction depends on the nature and stoichiometry of the lithium reagent and suggests that competing reduction and C–H bond activation reactions are occurring

The macrophage in HIV-1 infection: From activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease

Control of Oxo-Group Functionalization and Reduction of the Uranyl Ion

yesUranyl complexes of a large, compartmental N8-macrocycle adopt a rigid, “Pacman” geometry that stabilizes the UV oxidation state and promotes chemistry at a single uranyl oxo-group. We present here new and straightforward routes to singly reduced and oxo-silylated uranyl Pacman complexes and propose mechanisms that account for the product formation, and the byproduct distributions that are formed using alternative reagents. Uranyl(VI) Pacman complexes in which one oxo-group is functionalized by a single metal cation are activated toward single-electron reduction. As such, the addition of a second equivalent of a Lewis acidic metal complex such as MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg−N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U−O−Zn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxogroup