ABSTRACT
MicroRNAs (miRNAs) are a family of 21- to 25-nucleotide-long RNAs expressed in a wide variety of organisms. These account for more than 3% of all human genes, and many of them are highly conserved across species. These are transcribed as precursor RNAs from intergenic, intronic, or polycistronic genomic loci by the enzyme RNA polymerase II in a multistage process that involves both the nuclear and cytoplasmic compartments. MicroRNAs have important functions in humans, with some of them involved in biological processes such as cellular growth and development, differentiation, embryogenesis, stem cell maintenance, hematopoietic cell differentiation, brain development, proliferation, and apoptosis. MicroRNAs are also at the center of studies for determining how patients react to and metabolize drugs, since the drug metabolism can involve a group of genes.
