International round-robin experiment for angle-resolved light scattering measurement

International audienc

Endogenous viral elements in shrew genomes provide insights into Pestivirus ancient history

As viral genomic imprints in host genomes, endogenous viral elements (EVEs) shed light on the deep evolutionary history of viruses, ancestral host ranges, and ancient viral-host interactions. In addition, they may provide crucial information for calibrating viral evolutionary timescales. In this study, we conducted a comprehensive in silico screening of a large dataset of available mammalian genomes for EVEs deriving from members of the viral family Flaviviridae, an important group of viruses including well-known human pathogens, such as Zika, dengue, or hepatitis C viruses. We identified two novel pestivirus-like EVEs in the reference genome of the Indochinese shrew (Crocidura indochinensis). Homologs of these novel EVEs were subsequently detected in vivo by molecular detection and sequencing in 27 shrew species, including 26 species representing a wide distribution within the Crocidurinae subfamily and one in the Soricinae subfamily on different continents. Based on this wide distribution, we estimate that the integration event occurred before the last common ancestor of the subfamily, about 10.8 million years ago, attesting to an ancient origin of pestiviruses and Flaviviridae in general. Moreover, we provide the first description of Flaviviridae-derived EVEs in mammals even though the family encompasses numerous mammal-infecting members. This also suggests that shrews were past and perhaps also current natural reservoirs of pestiviruses. Taken together, our results expand the current known Pestivirus host range and provide novel insight into the ancient evolutionary history of pestiviruses and the Flaviviridae family in general

Compensation of loss to approach –1 effective index by gain in metal-dielectric stacks

We propose a theoretical study of optimization of metal-dielectric multilayer in order to approach -1 effective refractive index for transverse magnetic waves and a wavelength in the visible. The absorption losses of metal appear to be a crucial factor that affects the effective properties of the multilayer. Taking advantage of the dispersion relation of Bloch modes, we show that the losses not only decrease the transmission of the stack, but also change the negatively refracted angle. Then, we propose that using a gain-providing semiconductor (GaN) may allow compensating for the losses in metal layers. In theory, the performances of the structure can be improved greatly when gain is involved. When considering finite thickness structures, and with appropriate thickness for the terminating layers, it is possible to obtain a high transmission of the structure. A near -1 effective index metal-dielectric stack with high transmission may pave the way to the realization of negative quasi-isotropic refraction in the visible or ultraviolet wavelength range

In-situ interferometric monitoring of optical coatings

International audienceWe present a new method for the in situ measurement of the amplitude and phase of the reflection coefficient of a plane substrate installed in a mechanical holder rotating at high speed (120 turns per minute) during the deposition of an optical thin-film stack. Our method is based on digital holography and uses a self-referenced scheme to cancel the effects of the severe constraints generated by the vibrational and thermal environment of the deposition machine

Evolution and phylogeography of Culex pipiens densovirus

Viruses of the Parvoviridae family infect a wide range of animals including vertebrates and invertebrates. So far, our understanding of parvovirus diversity is biased towards medically or economically important viruses mainly infecting vertebrate hosts, while invertebrate infecting parvoviruses-namely densoviruses-have been largely neglected. Here, we investigated the prevalence and the evolution of the only mosquito-infecting ambidensovirus, Culex pipiens densovirus (CpDV), from laboratory mosquito lines and natural populations collected worldwide. CpDV diversity generally grouped in two clades, here named CpDV-1 and -2. The incongruence of the different gene trees for some samples suggested the possibility of recombination events between strains from different clades. We further investigated the role of selection on the evolution of CpDV genome and detected many individual sites under purifying selection both in non-structural and structural genes. However, some sites in structural genes were under diversifying selection, especially during the divergence of CpDV-1 and -2 clades. These substitutions between CpDV-1 and -2 clades were mostly located in the capsid protein encoding region and might cause changes in host specificity or pathogenicity of CpDV strains from the two clades. However, additional functional and experimental studies are necessary to fully understand the protein conformations and the resulting phenotype of these substitutions between clades of CpDV

Genetic Drift, Purifying Selection and Vector Genotype Shape Dengue Virus Intra-host Genetic Diversity in Mosquitoes

International audienceDue to their error-prone replication, RNA viruses typically exist as a diverse population of closely related genomes, which is considered critical for their fitness and adaptive potential. Intra-host demographic fluctuations that stochastically reduce the effective size of viral populations are a challenge to maintaining genetic diversity during systemic host infection. Arthropod-borne viruses (arboviruses) traverse several anatomical barriers during infection of their arthropod vectors that are believed to impose population bottlenecks. These anatomical barriers have been associated with both maintenance of arboviral genetic diversity and alteration of the variant repertoire. Whether these patterns result from stochastic sampling (genetic drift) rather than natural selection, and/or from the influence of vector genetic heterogeneity has not been elucidated. Here, we used deep sequencing of full-length viral genomes to monitor the intra-host evolution of a wild-type dengue virus isolate during infection of several mosquito genetic backgrounds. We estimated a bottleneck size ranging from 5 to 42 founding viral genomes at initial midgut infection, irrespective of mosquito genotype, resulting in stochastic reshuffling of the variant repertoire. The observed level of genetic diversity increased following initial midgut infection but significantly differed between mosquito genetic backgrounds despite a similar initial bottleneck size. Natural selection was predominantly negative (purifying) during viral population expansion. Taken together, our results indicate that dengue virus intra-host genetic diversity in the mosquito vector is shaped by genetic drift and purifying selection, and point to a novel role for vector genetic factors in the genetic breadth of virus populations during infection. Identifying the evolutionary forces acting on arboviral populations within their arthropod vector provides novel insights into arbovirus evolution

Transfer process of multilayer optical coatings for patterned components

International audienceThe capability to transfer a multilayer coating from the initial substrate on which it was deposited to another one is an interesting technique for the manufacturing of patterned components with a high number of different filters such as stripe filters. The two major technological steps of the transfer, namely the removal from the initial substrate, and the bonding onto the new one, are described in this paper. The principle of this approach is validated by the transfer of a band-pass filter with the typical sizes of a stripe