MicroRNA and Its Biogenesis

MicroRNAs (miRNAs) belong to the family of small noncoding RNAs, about 19–23 nucleotides long when eventually processed as functioning mature miRNA. Though not coding for proteins, miRNAs play important roles in regulating gene expression at the posttranscriptional level through complementary base-pairing within 3’ untranslated region (3’UTR) of target mRNA. There are more than 2,000 annotated miRNAs from the human genome and the number is still increasing. It is estimated that human miRNAs regulate as much as 60 % of genes and play pivotal roles in various physiological processes such as cell proliferation, differentiation, genomic stability, metabolism, apoptosis, and aging. Not surprisingly, deregulation of miRNA has been associated with many pathological conditions including OA [7].

There are three forms of miRNAs which are long primary miRNAs (pri-miRNA), hairpin precursor miRNAs (pre-miRNA), and short mature miRNAs. In the nucleus, the miRNA gene is transcribed into large pri-miRNA which is subsequently cleaved to make pre-miRNA.