Circulating MicroRNAs: Potential and Emerging Biomarkers for Diagnosis of Cardiovascular and Cerebrovascular Diseases

Figure 1

Biogenesis of miRNAs. In the nucleus, miRNAs are transcribed by RNA polymerase II to generate long primary transcripts (pri-miRNAs), which may contain more than one miRNA. Pri-miRNAs are subsequently processed by the RNase III enzyme (Drosha) and its binding partner DGCR8, forming hairpin-like precursor miRNAs (pre-miRNAs). Pre-miRNAs are exported into the cytoplasm by exportin-5 with a Ran-GTP-dependent mechanism. Pre-miRNAs are cleaved by the RNase III enzyme (Dicer) to mature miRNAs. A single strand of the short interfering RNA (siRNA) or miRNA duplex forms RNA-induced silencing complexes (RISC). Then miRNAs guide RISC to complementary sites of the target mRNAs, initiating degradation or cleavage of mRNA.