Reactome | MicroRNA (miRNA) biogenesis

MicroRNA (miRNA) biogenesis

Stable Identifier

R-HSA-203927

DOI

10.3180/REACT_12417.1

Type

Pathway

Species

Homo sapiens

Compartment

nucleoplasm, nuclear envelope, cytosol

ReviewStatus

5/5

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Biogenesis of microRNAs (miRNAs) can be summarized in five steps (reviewed in Ketting 2011, Nowotny and Yang 2009, Kim et al. 2009, Chua et al. 2009, Hannon and He 2004):
1. Transcription. miRNA transcripts may come from autonomously transcribed genes, they may be contained in cotranscripts with other genes, or they may be located in introns of host genes. Most miRNAs are transcribed by RNA polymerase II, however a few miRNAs originate as RNA polymerase III cotranscripts with neighboring repetitive elements. The initial transcript, termed a primary microRNA (pri-miRNA), contains an imperfectly double-stranded region within a hairpin loop. Longer sequences extend from the 5' and 3' ends of the hairpin and may also contain double-stranded regions.
2. Cleavage by DROSHA. The 5' and 3' ends of the pri-miRNA are removed during endoribonucleolytic cleavage by the DROSHA nuclease in a complex with the RNA-binding protein DGCR8 (the Microprocessor complex). The cleavage product is a short hairpin of about 60 to 70 nt called the pre-microRNA (pre-miRNA).
3. Nuclear export by Exportin-5. The resulting pre-miRNA is bound by Exportin-5 in a complex with Ran and GTP. The complex translocates the pre-miRNA through the nuclear pore into the cytoplasm.
4. Cleavage by DICER1. Once in the cytoplasm the pre-miRNA is bound by the RISC loading complex which contains DICER1, an Argonaute protein and either TARBP2 or PRKRA. DICER1 cleaves the pre-miRNA to yield an imperfectly double-stranded miRNA of about 21 to 23 nucleotides. At this stage the double-stranded miRNA has protruding single-stranded 3' ends of 2-3 nt.
5. Incorporation into RNA-Induced Silencing Complex (RISC) and strand selection. The double-stranded miRNA is passed to a Argonaute protein contained in the RISC loading complex. One strand, the passenger strand, will be removed and degraded; the other strand, the guide strand, will be retained and will guide the Argonaute:miRNA complex (RISC) to target mRNAs.
The human genome encodes 4 Argonaute proteins (AGO1 (EIF2C1), AGO2 (EIF2C2), AGO3 (EIF2C3), AGO4 (EIF2C4)), however only AGO2 (EIF2C2) can cleave target mRNAs with perfect or nearly perfect complementarity to the guide miRNA. For complexes that contain AGO2, cleavage of the passenger strand of the double-stranded miRNA accompanies removal of the passenger strand. Complexes containing other Argonautes may use a helicase to remove the passenger strand but this is not fully known. The resulting miRNA-loaded AGO2 is predominantly located in complexes with TARBP2 or PRKRA at the cytosolic face of the rough endoplasmic reticulum. AGO2, TARBP2, and DICER1 are also observed in the nucleus.

Literature References

PubMed ID	Title	Journal	Year
15364901	Identification of mammalian microRNA host genes and transcription units Bradley, A, Griffiths-Jones, S, Ashurst, JL, Rodriguez, A	Genome Res	2004
15211354	MicroRNAs: small RNAs with a big role in gene regulation Hannon, GJ, He, L	Nat Rev Genet	2004
17057362	Intronic microRNA (miRNA) Lin, SL, Miller, JD, Ying, SY	J Biomed Biotechnol	2006
19165215	Biogenesis of small RNAs in animals Han, J, Kim, VN, Siomi, MC	Nat Rev Mol Cell Biol	2009
21755468	microRNA Biogenesis and Function : An overview Ketting, RF	Adv Exp Med Biol	2011
8252621	The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14 Lee, RC, Ambros, V, Feinbaum, RL	Cell	1993
19330724	MicroRNAs: biogenesis, function and applications Chua, JH, Jeyaseelan, K, Armugam, A	Curr Opin Mol Ther	2009
15944707	A microRNA polycistron as a potential human oncogene Hammond, SM, Cordon-Cardo, C, Powers, S, Hannon, GJ, Lowe, SW, Goodson, S, Hernando-Monge, E, Thomson, JM, He, L, Hemann, MT, Mu, D	Nature	2005
23511973	The rough endoplasmatic reticulum is a central nucleation site of siRNA-mediated RNA silencing Hean, J, Aeschimann, F, Basselet, P, Stalder, L, Hintersteiner, M, Heusermann, W, Meisner-Kober, NC, Wirz, J, Morrissey, DV, Sokol, L, Pfanzagl, V, Trojer, D, Fritzsche, A, Weiler, J	EMBO J.	2013
24388755	RNAi factors are present and active in human cell nuclei Chu, Y, Janowski, BA, Gagnon, KT, Li, L, Corey, DR	Cell Rep	2014