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

MicroRNAs in brain development and function: a matter of flexibility and stability

International audienceFine-tuning of gene expression is a fundamental requirement for development and function of cells and organs. This requirement is particularly obvious in the nervous system where originally common stem cell populations generate thousands of different neuronal and glial cell types in a temporally and quantitatively perfectly orchestrated manner. Moreover, after their generation, young neurons have to connect with pre-determined target neurons through the establishment of functional synapses, either in their immediate environment or at distance. Lastly, brain function depends not only on static circuitries, but on plastic changes at the synaptic level allowing both, learning and memory. It appears evident that these processes necessitate flexibility and stability at the same time. These two contrasting features can only be achieved by complex molecular networks, superposed levels of control and tight interactions between regulatory mechanisms. Interactions between microRNAs and their target mRNAs fulfill these requirements. Here we review recent literature dealing with the involvement of microRNAs in multiple aspects of brain development and connectivity

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

Routine transformation of rapid cycling cabbage (Brassica oleracea) molecular evidence for regeneration of chimeras

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A2B5 cells from human glioblastoma have cancer stem cell properties

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