microRNAs (miRNA) are abundant RNA molecules around 21 nucleotides long that regulate specific mRNA expression by directly interacting with the mRNA molecule. Our understanding of miRNA function in mRNA regulation has grown exponentially as more miRNA molecules have been described. As of 2013, more than 24,000 miRNA molecules had been described from more than 140 separate species, indicating that miRNA regulation is conserved across species. In humans, 2,500 mature miRNAs have been described, and researchers predict that 60% of human protein-coding genes may be targets of miRNA regulation. Most often miRNA regulation of an mRNA results in decreased expression, either by destabilizing the mRNA or by inducing translational repression. Very recently, some researchers have reported up regulation of mRNA through miRNA activity.
Since miRNA molecules are so abundant within cells and across species and their target sequences are found in so many protein-coding genes, understanding how miRNA regulation of mRNAs acts in concert with the many other levels of gene expression regulation becomes a complex, but fundamental, biological question.
To probe miRNA regulation of mRNA, the proper tools and experimental design are essential. Continue reading