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Regulation of microRNA biogenesis and function

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MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate the expression of complementary mRNAs and affect a great diversity of biological processes. Their biogenesis involves a nuclear phase catalyzed by the Microprocessor (Drosha/DGCR8) followed by a cytoplasmic step carried out by Dicer to produce the mature miRNA.

We have shown that hnRNP A1, a protein implicated in many aspects of RNA processing, promotes the Drosha-mediated processing of a miRNA precursor, pri-miR-18a, by binding to its conserved terminal loop (1,2). By contrast, hnRNP A1 can act as a negative regulator of Let-7a in differentiated cells by antagonizing the positive role of the KH-type splicing regulatory protein KSRP (3). Altogether, these data suggest the existence of auxiliary factors for the processing of specific miRNAs that can have a positive or negative role in the production of individual miRNAs.

We have used high-throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (HITS-CLIP) to identify endogenous RNA targets of the microprocessor component, DGCR8 in mammalian cells. As expected, most of the miRNAs known to be expressed in 293T cells were identified, as well as, the DGCR8 mRNA, which was known to be a target of the microprocessor complex. Other DGCR8 targets include several hundred mRNAs, non-coding RNAs, snoRNAs and retrotransposons. Further analysis and validation of these data will provide insights in the complex role of the DGCR8 in controlling the fate of different classes of cellular RNAs.

1. Guil,S. and Cáceres,J.F. (2007) The multifunctional RNA -binding protein hnRNP A1 is required for processing of miR-18a. Nat. Struct. Mol. Biol., 14, 591-596.

2. Michlewski,G. et al. (2008) Mol Cell, 32, 383-393.

3. Michlewski,G. and Cáceres,J.F. (2010) Nat. Struct. Mol. Biol., 17, 1011-1018.

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