MicroRNA Evolution in the Human Genome


Micro ribonucleic acids (miRNAs) are a growing class of small RNA [∼22 nucleotide (nt)] that function as negative regulators in the genome by targeting messenger RNA (mRNA) for translational repression, cleavage and destabilization. Hundreds of miRNAs have been identified in the human genome. miRNAs can be conserved or nonconserved according to their cross‐species sequence conservation, and these two classes of miRNAs in the human genome are subject to distinct evolutionary patterns.

Keywords: miRNA; evolution; human genome

Figure 1.

The process for miRNA biogenesis. miRNA genes are transcribed by RNA pol II to generate pri‐miRNAs. The initiation‐processing step is mediated by the Drosha–DGCR8 complex. The product of this nuclear processing step is a ∼70‐nt pre‐miRNA. Pre‐miRNA constitutes a transport complex together with exportin‐5. Following export, the cytoplasmic Dicer participates in the second processing step to produce miRNA duplex. The strand of the miRNA duplex with the weakest base pairing at its 5′ terminus is preferably loaded into the effector complexes that are known as miRNP, whereas the other strand is mostly degraded. Finally, miRNP performs miRNA function as either repressing the translation or degrading the mRNAs.

Figure 2.

The rapid increase of identified miRNAs in the human genome registered in miRBase. From Version 3 (2004 January) to Version 9 (2007 February).

Figure 3.

The secondary structure of pre‐miRNA.

Figure 4.

The substitution pattern comparison between the conserved miRNA (A, miR‐194) and the nonconserved miRNA (B, miR‐510). There is an evident drop of conservation in the flanking sequences of miR‐194, but not in miR‐510. The degree of conservation is calculated and visualized by eshadow with default parameter. Pre‐miRNAs and mature miRNAs are marked as open and solid boxes, respectively.

Figure 5.

Copy number variation of the X‐linked miRNA cluster among primates. The number ‘1’ represents miR‐513, ‘2’ for miR‐506, ‘3’ for miR‐507, ‘4’ for miR‐508, ‘5’ for miR‐510L, ‘6’ for miR‐509, ‘7’ for miR‐510 and ‘8’ for miR‐514. YGM refers to Yunnan snub‐nosed monkey (Rhinopithecus bieti) (Reproduced from Zhang et al., , with permission from Cold Spring Harbor Laboratory Press).



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Further Reading

Bartel DP (2004) MicroRNAs: genomics, biogenesis, mechanism, and function. Cell 116: 281–297.

Berezikov E, Cuppen E and Plasterk RH (2006) Approaches to microRNA discovery. Nature Genetics 38(Supplements): S2–S7.

Li A and Mao L (2006) Evolution of plant microRNA gene families. Cell Research 17: 212–218.

Web Links

miRBase http://microrna.sanger.ac.uk/

miRGen http://www.diana.pcbi.upenn.edu/miRGen.html

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How to Cite close
Su, Bing, and Zhang, Rui(Mar 2008) MicroRNA Evolution in the Human Genome. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020788]