Post-transcriptional gene silencing triggered by sense transgenes involves uncapped antisense RNA and differs from silencing intentionally triggered by antisense transgenes

Although post-transcriptional gene silencing (PTGS) has been studied for more than a decade, there is still a gap in our understanding of how de novo silencing is initiated against genetic elements that are not supposed to produce double-stranded (ds)RNA. Given the pervasive transcription occurring throughout eukaryote genomes, we tested the hypothesis that unintended transcription could produce antisense (as)RNA molecules that participate to the initiation of PTGS triggered by sense transgenes (S-PTGS). Our results reveal a higher level of asRNA in Arabidopsis thaliana lines that spontaneously trigger S-PTGS than in lines that do not. However, PTGS triggered by antisense transgenes (AS-PTGS) differs from S-PTGS. In particular, a hypomorphic ago1 mutation that suppresses S-PTGS prevents the degradation of asRNA but not sense RNA during AS-PTGS, suggesting a different treatment of coding and non-coding RNA by AGO1, likely because of AGO1 association to polysomes. Moreover, the intended asRNA produced during AS-PTGS is capped whereas the asRNA produced during S-PTGS derives from 3' maturation of a read-through transcript and is uncapped. Thus, we propose that uncapped asRNA corresponds to the aberrant RNA molecule that is converted to dsRNA by RNA-DEPENDENT RNA POLYMERASE 6 in siRNA-bodies to initiate S-PTGS, whereas capped asRNA must anneal with sense RNA to produce dsRNA that initiate AS-PTGS

MiR-200 family controls late steps of postnatal forebrain neurogenesis via Zeb2 inhibition

During neurogenesis, generation, migration and integration of the correct numbers of each neuron sub-Type depends on complex molecular interactions in space and time. MicroRNAs represent a key control level allowing the flexibility and stability needed f

Two Plant Viral Suppressors of Silencing Require the Ethylene-Inducible Host Transcription Factor RAV2 to Block RNA Silencing

RNA silencing is a highly conserved pathway in the network of interconnected defense responses that are activated during viral infection. As a counter-defense, many plant viruses encode proteins that block silencing, often also interfering with endogenous small RNA pathways. However, the mechanism of action of viral suppressors is not well understood and the role of host factors in the process is just beginning to emerge. Here we report that the ethylene-inducible transcription factor RAV2 is required for suppression of RNA silencing by two unrelated plant viral proteins, potyvirus HC-Pro and carmovirus P38. Using a hairpin transgene silencing system, we find that both viral suppressors require RAV2 to block the activity of primary siRNAs, whereas suppression of transitive silencing is RAV2-independent. RAV2 is also required for many HC-Pro-mediated morphological anomalies in transgenic plants, but not for the associated defects in the microRNA pathway. Whole genome tiling microarray experiments demonstrate that expression of genes known to be required for silencing is unchanged in HC-Pro plants, whereas a striking number of genes involved in other biotic and abiotic stress responses are induced, many in a RAV2-dependent manner. Among the genes that require RAV2 for induction by HC-Pro are FRY1 and CML38, genes implicated as endogenous suppressors of silencing. These findings raise the intriguing possibility that HC-Pro-suppression of silencing is not caused by decreased expression of genes that are required for silencing, but instead, by induction of stress and defense responses, some components of which interfere with antiviral silencing. Furthermore, the observation that two unrelated viral suppressors require the activity of the same factor to block silencing suggests that RAV2 represents a control point that can be readily subverted by viruses to block antiviral silencing

Design of bossed silicon membranes for high sensitivity microphone applications

This paper deals with the design optimization of new high sensitivity microphones in SOI technology for gas sensing applications. A novel geometry of bossed silicon membranes used as mechanical transducer has been studied by Finite Element Modelling. Device fabrication is achieved from SOI substrates through deep backside anisotropic etching and shallow front side RIE to define a bossed sensing membrane with two reinforced areas. Thus, the influence of thin film stresses on the device performance is largely decreased. Polysilicon gauges are located on the reinforced areas to get a better linearity in pressure

Design of bossed silicon membranes for high sensitivity microphone applications

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Energy transfer between semiconductor nanoparticles (ZnS or CdS) and Eu³⁺ ions in sol–gel derived ZrO₂ thin films

Semiconductor nanoparticles (CdS or ZnS) and Eu3+ co-doped zirconia thin films were prepared using the sol–gel route by an in situ method. We demonstrated that the energy exchange is more efficient between ZnS nanocrystals and Eu3+ ions than between CdS and Eu3+. The Eu3+ luminescence increased with the ion concentration up to 10 mol% (for 10 mol% ZnS). Moreover, the intensity of the europium emission increased as the ZnS nanoparticles concentration increased up to 15 mol% (for 5 mol% Eu3+). For The 15% ZnS–5% Eu3+ co-doped ZrO2 sample, the europium emissions were enhanced 42 times through energy transfer at 10 K. The defect states in semiconductor nanoparticles (CdS or ZnS) were found to play an important role in the energy transfer process

Arabidopsis HEN1: a genetic link between endogenous miRNA controlling development and siRNA controlling transgene silencing and virus resistance

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Controlled growth of SnO₂ nanocrystals in Eu³⁺-Doped SiO₂-SnO₂ planar waveguides: a spectroscopic investigation

We report on the fabrication of Eu³⁺-doped SiO₂−SnO₂ low-loss (0.8 dB/cm at 632.8 nm) glass-ceramic planar waveguides, fabricated by the sol−gel technique and dip-coating processing. The effects of heat treatments on the growth and evolution of SnO₂ nanocrystals in the matrix were investigated using different spectroscopic tools. In situ high-temperature X-ray diffraction allowed for the determination of the crystallization temperature and confirmed the formation of tetragonal rutile SnO₂ crystals. The effect of crystallization on the optical properties and on the photoluminescence of Eu³⁺ ions was also studied. Low-frequency Raman scattering was successfully used to determine the crystal size, and the results obtained were found to be consistent with transmission electron microscopy measurements. The breakage of Si−O−Sn linkages during the formation of SnO₂ nanocrystals in the matrix was investigated by Fourier-transform infrared spectroscopy