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During the last decade of the 20th century a totally novel way of gene regulation was revealed. Findings that at frst glance appeared freak features of plants or C. elegans turned out to be mechanistically related and deeply conserved throughout evolution. this important insight was primed by the landmark discovery of RNA interference, or RNAi, in 1998. This work started an entire novel feld of research,...
microRNAs (miRNAs) are small (∼22 nucleotides (nt)), noncoding RNAs that play a critical role in diverse biological functions by modulating mRNA stability and translational control. Numerous miRNA profiling studies have indicated that the levels of miRNAs are tightly controlled during developmental stages and various pathophysiological and physiological conditions. Following transcription, the long...
Recent evidence suggests that the canonical miRNA processing pathway can be regulated by a number of positive and negative trans-acting factors. This chapter provides an overview of hnRNP Al-mediated regulation of miR-18a biogenesis. Our laboratory has recently established that the multifunctional RNA-binding protein hnRNP Al is required for the processing of miR-18a at the nuclear step of Drosha-mediated...
microrNNA (mirNAs) are small noncoding RNAs that down-regulate gene expression by reducing stability and/or translation of target mRNAs. In animals, miRNAs arise from sequential processing of hairpin primary transcripts by two rNase III domain-containing enzymes, namely Drosha and Dicer, to generate a mature form of about 22 nucleotides. In this chapter we discuss our latest fndings indicating that...
The maturation of primary microrRNAs (pri-miRNAs) to precursor miRNAs (pre-miRNAs) is mediated by the “microprocessor” complex minimally comprimising two core components, Drosha and DGCR8. However, the roles of RNA-binding proteins associated with these core units in the large Drosha complex remain to be defined. While signal-dependent regulation of miRNA biogenesis is assumed, such regulation remains...
The Microprocessor, comprising the ribonuclease Drosha and its essential cofactor, the double-stranded RNA-binding protein, DGCR8, is essential for the first step of the miRNA biogenesis pathway. It specifically cleaves double-stranded RNA within stem-loop structures of primary miRNA transcripts (pri-miRNAs) to generate precursor (pre-miRNA) intermediates. Pre-miRNAs are subsequently processed by...
microRNAs are endogenously expressed ∼21 nucleotide noncoding RNAs. microRNA-mediated regulation of the translation of specific mRNA is implicated in a range of developmental processes and pathologies. As such, miRNA expression is tightly controlled in normal development by both transcriptional and post-transcriptional mechanisms. This chapter is concerned with the control of pre-miRNA processing...
From analysis of deep-sequencing data it is apparent that sequence differences occur between the genome and miRNAs. Changes from genomic A to an apparent G in miRNA can be accounted for by the editing activity of ADARs. Questions that arise from this observation are: How many miRNAs are edited and to what frequency? Is there a specific step in the biogenesis of miRNAs that is preferentially susceptible...
Trim-NHL proteins are defined by RING, B-Box and Coiled-coil protein motifs (referred to collectively as the Trim domain) coupled to an NHL domain. The C. elegans, D. melanogaster, mouse and human Trim-NHL proteins are potential and in several cases confirmed, E3 ubiquitin ligases. Current research is focused on identifying targets and pathways for Trim-NHL-mediated ubiquitination and in assessing...
Gene expression in eukaryotes is subject to extensive regulation at posttranscriptional levels. One of the most important sites of control involves mRNA 3′ untranslated regions (3′utrs), which are recognized by RNA-binding proteins (RBPs) and microRNAs (miRNAs). These factors greatly influence translational efficiency and stability of target mRNAs and often also determine their cellular localization...
microRNAs (miRNAs) and small interfering RNAs (siRNAs) play important roles in gene regulation and defense responses against transposons and viruses in eukaryotes. These small RNAs generally trigger the silencing of cognate sequences through a variety of mechanisms, including RNA degradation, translational inhibition and transcriptional repression. In the past few years, the synthesis and the mode...
microRNAs (miRNAs) are small noncoding RNAs that regulate numerous target mRNAs through an antisense mechanism. Initially thought to be very stable with half-lives on the orderof days, mature miRNAs haverecently been shown to be subject to degradation by ‘microRNases’ (miRNases) in plants (the small RNA degrading nucleases, SDN) and animals (exoribonuclease 2/XRN-2/XRN2). Interference with these miRNA...
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