Small RNAs and Transgenerational Epigenetic Variation

Small RNAs are found in eukaryotes and are responsible for regulation of chromatin structure, RNA processing and stability, translation and transcription. 24-nt small interfering RNA (siRNA) are known to mediate gene inactivation via the RNA-directed DNA methylation pathway (RdDM) and are important for natural heritable changes in plant species. DNA cytosine methylation can be maintained between generations and this may be important for accelerated adaption to stress conditions. Research is currently focused toward the epigenetic response to disease, the stability of DNA methylation over generations, the elucidation of newly discovered pathways for de novo DNA methylation, and the application of epigenetic variation to breeding programs. This review aims to give a brief but comprehensive examination on small RNAs and transgenerational epigenetic variation.

Effect of austenitizing condition on mechanical properties,microstructure and precipitation behavior of AISI H13 steel

The effects of austenitizing temperature(1223,1303,and 1373 K)and holding time(1-1500 s)on the microstructure,mechanical properties,and precipitation behavior of the H13 hot work die steel were investigated.The results indicate a softening phenomenon when H13 steel is austenitized at 1303 K beyond 900 s and 1373 K beyond 600 s,respectively.For the sample held for 1200 s,the tensile strength is found capable of reaching up to 2.2 GPa when quenched from a temperature above 1303 K.Meanwhile,prior-austenite grain size increases with the increase in austenitizing temperature.The kinetic behavior of the precipitates(mainly MC-type carbides)in H13 steel could be elaborated through the principles set forth by the Arrhenius and Avrami equations.Finally,the comprehensive strengthening of the H13 steel was discussed in detail.The results show that the activation energy of the transformed fraction of carbides is higher than that of the diffusion process for common alloying elements(Cr,V,Mo,and Ni)found in the austenite.This suggests that it would be difficult for precipitates to dissolve into the matrix when H13 steel is austenitized at high temperatures.With the increasing austenitizing temperature,the precipitation fraction decreases,and the dislocation density increases.The dislocation strengthening is regarded as the dominant strengthening contributed to yield strength in as-quenched H13 steel.

Efficient Silencing of Endogenous MicroRNAs Using Artificial MicroRNAs in Arabidopsis thaliana

We report here that the expression of endogenous microRNAs （miRNAs） can be efficiently silenced in Arabi- dopsis thaliana （Arabidopsis） using artificial miRNA （amiRNA） technology. We demonstrate that an amiRNA designed to target a mature miRNA directs silencing against all miRNA family members, whereas an amiRNA designed to target the stem-loop region of a miRNA precursor transcript directs silencing against only the individual family member targeted. Furthermore, our results indicate that amiRNAs targeting both the mature miRNA and stem-loop sequence direct RNA silencing through cleavage of the miRNA precursor transcript, which presumably occurs in the nucleus of a plant cell during the initial stages of miRNA biogenesis. This suggests that small RNA （sRNA）-guided RNA cleavage in plants occurs not only in the cytoplasm, but also in the nucleus. Many plant miRNA gene families have been identified via sequencing and bio- informatic analysis, but, to date, only a small tranche of these have been functionally characterized due to a lack of ef- fective forward or reverse genetic tools. Our findings therefore provide a new and powerful reverse-genetic tool for the analysis of miRNA function in plants.

Precise Construction and Tuning of an Aerolysin Single-Biomolecule Interface for Single-Molecule Sensing

Membrane protein molecules can self-assemble to form a single-biomolecule interface,which can accommodate one single molecule at a time and provide a suitable sensing environment for single-molecule measurements.To achieve the high temporal and spatial resolution for revealing the heterogenous of single molecules,one of the most important challenge is to construct a functional single-biomolecule interface.

RNA silencing in fungi

RNA silencing is an evolutionarily conserved mechanism in eukaryotic organisms induced by double-stranded RNA(dsRNA)and plays an essential role in regulating gene expression and maintaining genome stability.RNA silencing occurs at both posttranscriptional levels through sequence-specific RNA degradation or translational repression and at transcriptional levels through RNA-directed DNA methylation and/or hetero-chromatin formation.RNA silencing pathways have been relatively well characterized in plants and animals,and are now also being widely investigated in diverse fungi,some of which are important plant pathogens.This review focuses primarily on the current understanding of the dsRNA-mediated posttranscriptional gene silencing pro-cesses in fungi,but also discusses briefly the known gene silencing pathways that appear to be independent of the RNA silencing machineries.We review RNA silencing studies for a variety of fungi and highlight some of the mechanistic differences observed in different fungal organisms.As RNA silencing is being exploited as a technology in gene function studies in fungi as well as in engineering anti-fungal resistance in plants and animals,we also discuss the recent progress towards understanding dsRNA uptake in fungi.

Mobile silencing in plants:what is the signal and what defines the target

RNA-mediated silencing in plants can spread from cell to cell and over a long distance,and such mobile silencing has been extensively studied in the past decade.However,major questions remain as to what is the exact nature of the mobile silencing signals,how the components of the RNA-directed DNA methylation pathway are involved,and why systemic spread of silencing has only been observed for transgenes but not endogenous genes.In this review,we provide an overview of the current knowledge on mobile gene silencing in plants and present a model where systemic silencing involves long nuclear RNA transcripts that serve as a template to amplify primary siRNA signals.

Regulatory giants join forces

Numerous disease states are characterized by ectopic expression of genes.Recent findings suggest that crosstalk between systems that regulate gene expression during animal development ensures responsiveness to environmental cues.