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. 2011;3(3):83-92.

MicroRNAs: Processing, Maturation, Target Recognition and Regulatory Functions

Girish C Shukla  1 , Jagjit Singh, Sailen Barik
Affiliations

MicroRNAs: Processing, Maturation, Target Recognition and Regulatory Functions

Girish C Shukla et al. Mol Cell Pharmacol. 2011.

Abstract

The remarkable discovery of small noncoding microRNAs (miRNAs) and their role in posttranscriptional gene regulation have revealed another fine-tuning step in the expression of genetic information VSports手机版. A large number of cellular pathways, which act in organismal development and are important in health and disease, appear to be modulated by miRNAs. At the molecular level, miRNAs restrain the production of proteins by affecting the stability of their target mRNA and/or by down-regulating their translation. This review attempts to offer a snapshot of aspects of miRNA coding, processing, target recognition and function in animals. Our goal here is to provide the readers with a thought-provoking and mechanistic introduction to the miRNA world rather than with a detailed encyclopedia. .

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Conflict of interest statement

Conflicts of interest

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1. General molecular mechanisms of miRNA biogenesis
miRNAs are transcribed by RNA polymerases II or III as pri-mRNA that are modified with cap structure and polyadenylation. Initial processing of pri-miRNA occurs in nucleus by the Drosha complex which crops the miRNA into a hairpin-shaped pre-miRNA. Next, pre-miRNA is exported to cytoplasm with Exportin-5/Ran-GTP complex for Dicer processing. Following this, one of the strands of the miRNA duplex is incorporated with Ago to form miRNA-RISC that engages on the target mRNA to mediate gene silencing either by translational repression or by mRNA degradation/deadenylation (detailed in Figs. 3, 4). Noncanonical intronic miRNAs, "mirtrons", are processed by the spliceosome, which is independent of the Drosha microprocessor complex.
Figure 2
Figure 2. Coding structure of intronic miRNAs
The Figure illustrates the coding patterns of intronic miRNAs. Intronic or intragenic miRNAs can be coded as: (A) a single standalone gene, or (B) in a cluster containing multiple miRNA genes.
Figure 3
Figure 3. Two modes of action of miRNAs. miRNAs can establish (A) imperfect or (B) perfect complementarity within the 3’ UTR of its target mRNAs
Depending upon the complementarity, miRNA can then modulate the translation and mRNA destabilization (mostly in animals) or degrade the target message (common in plants). Also see Fig. 4 for detailed mechanisms.
Figure 4
Figure 4. Suggested mechanisms of miRNA-mediated translational repression
(A) 3’ UTR of a mRNA engaged to RISC and miRNA; (B) CAF1/CCR4/NOT1 complex-mediated deadneylation and degradation of the target mRNA; (C) Dcp1/2 complex-mediated decapping; and (D) translational repression in actively translating polysomes at initiation and elongation stages by ribosome drop off.
See this image and copyright information in PMC

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