Parasitoid polydnaviruses: evolution,pathology and applications

One of the more unusual groups of insect pathogens consists of members of the family Polydnaviridae, insect DNA viruses that live in mutual symbioses with their associated parasitoid wasp (Hymentoptera) carriers until they are injected into specific lepidopteran hosts. Once inside this secondary host, polydnaviruses cause a wide variety of negative effects that ultimately ensure the survival of the parasitoid larvae. Because of their unusual life strategy and genetic features, it had been difficult to fully characterise polydnaviruses in terms of evolutionary history, replication cycle and functions in the host that might normally be well characterised for more conventional viruses. Recently, our understanding of polydnavirus evolutionary origins, gene content, genome organisation and functions in parasitism has greatly increased. Key findings are summarised in this review with emphasis on evolution of polydnavirus genes and genomes, their functional roles in insect pathology and their potential applications in insect biological control and biotechnology.     

Exploring nucleo-cytoplasmic large DNA viruses in Tara Oceans microbial metagenomes

Nucleo-cytoplasmic large DNA viruses (NCLDVs) constitute a group of eukaryotic viruses that can have crucial ecological roles in the sea by accelerating the turnover of their unicellular hosts or by causing diseases in animals. To better characterize the diversity, abundance and biogeography of marine NCLDVs, we analyzed 17 metagenomes derived from microbial samples (0.2–1.6 μm size range) collected during the Tara Oceans Expedition. The sample set includes ecosystems under-represented in previous studies, such as the Arabian Sea oxygen minimum zone (OMZ) and Indian Ocean lagoons. By combining computationally derived relative abundance and direct prokaryote cell counts, the abundance of NCLDVs was found to be in the order of 10⁴–10⁵ genomes ml⁻¹ for the samples from the photic zone and 10²–10³ genomes ml⁻¹ for the OMZ. The Megaviridae and Phycodnaviridae dominated the NCLDV populations in the metagenomes, although most of the reads classified in these families showed large divergence from known viral genomes. Our taxon co-occurrence analysis revealed a potential association between viruses of the Megaviridae family and eukaryotes related to oomycetes. In support of this predicted association, we identified six cases of lateral gene transfer between Megaviridae and oomycetes. Our results suggest that marine NCLDVs probably outnumber eukaryotic organisms in the photic layer (per given water mass) and that metagenomic sequence analyses promise to shed new light on the biodiversity of marine viruses and their interactions with potential hosts.     

Synapto-Protective Drugs Evaluation in Reconstructed Neuronal Network

Chronic neurodegenerative syndromes such as Alzheimer’s and Parkinson’s diseases, or acute syndromes such as ischemic stroke or traumatic brain injuries are characterized by early synaptic collapse which precedes axonal and neuronal cell body degeneration and promotes early cognitive impairment in patients. Until now, neuroprotective strategies have failed to impede the progression of neurodegenerative syndromes. Drugs preventing the loss of cell body do not prevent the cognitive decline, probably because they lack synapto-protective effects. The absence of physiologically realistic neuronal network models which can be easily handled has hindered the development of synapto-protective drugs suitable for therapies. Here we describe a new microfluidic platform which makes it possible to study the consequences of axonal trauma of reconstructed oriented mouse neuronal networks. Each neuronal population and sub-compartment can be chemically addressed individually. The somatic, mid axon, presynaptic and postsynaptic effects of local pathological stresses or putative protective molecules can thus be evaluated with the help of this versatile “brain on chip” platform. We show that presynaptic loss is the earliest event observed following axotomy of cortical fibers, before any sign of axonal fragmentation or post-synaptic spine alteration. This platform can be used to screen and evaluate the synapto-protective potential of several drugs. For instance, NAD⁺ and the Rho-kinase inhibitor Y27632 can efficiently prevent synaptic disconnection, whereas the broad-spectrum caspase inhibitor zVAD-fmk and the stilbenoid resveratrol do not prevent presynaptic degeneration. Hence, this platform is a promising tool for fundamental research in the field of developmental and neurodegenerative neurosciences, and also offers the opportunity to set up pharmacological screening of axon-protective and synapto-protective drugs.     

Age and sex-dependent effects of landscape cover and trapping on the spatial genetic structure of the stone marten (<Emphasis Type="Italic">Martes foina</Emphasis>)

Maintenance of genetic variation is of critical importance for wild populations since low levels limit the species’ ability to respond to different threats (diseases, predators, environmental changes) in both the long and the short term. Human activities could impact the genetic variation of wild species in multiple ways, including via fragmentation and harvesting. We used an individual-based landscape genetics approach to describe the impact of landscape elements and trapping pressure on the spatial genetic structure of a large sample (n = 370) of the stone marten (Martes foina) in central-eastern France (Bresse). An analysis of isolation-by-resistance using a causal modeling approach showed an influence of landscape cover and/or trapping pressure on gene flow according to age and sex class. Overall, the connectivity in the study area is provided mainly by vegetation cover, while roads and open areas partially impede it. Unexpectedly for this “urban adapter” species, buildings could reduce gene flow. We also emphasized the sex-dependent effect of trapping on gene flow. Genetic differentiation in males was influenced by trapping pressure and landscape structure while only the latter influenced genetic differentiation in females. A stronger isolation by distance in males than in females suggested that at the scale of the study area, males are more exposed to trapping pressure, which reduces effective dispersal. Overall, the combination of both landscape and trapping costs might create an ‘ecological trap’ that could disrupt gene flow, leading to a north–south division in the study area.     

AtCCMA interacts with AtCcmB to form a novel mitochondrial ABC transporter involved in cytochrome c maturation in Arabidopsis

ABC transporters make a large and diverse family of proteins found in all phylae. AtCCMA is the nucleotide binding domain of a novel Arabidopsis mitochondrial ABC transporter. It is encoded in the nucleus and imported into mitochondria. Sub-organellar and topology studies find AtCCMA bound to the mitochondrial inner membrane, facing the matrix. AtCCMA exhibits an ATPase activity, and ATP/Mg(2+) can facilitate its dissociation from membranes. Blue Native PAGE shows that it is part of a 480-kDa complex. Yeast two-hybrid assays reveal interactions between AtCCMA and domains of CcmB, the mitochondria-encoded transmembrane protein of a conserved ABC transporter. All these properties designate the protein as the ortholog in plant mitochondria of the bacterial CcmA required for cytochrome c maturation. The transporter that involves AtCCMA defines a new category of eukaryotic ABC proteins because its transmembrane and nucleotide binding domains are encoded by separate genomes.