Politz, J.C., Zhang, F. & Pederson, T. MicroRNA-206 colocalizes with ribosome-rich regions in both the nucleolus and cytoplasm of rat myogenic cells. Proc. Natl. Acad. Sci. USA 103, 18957-18962

Department of Biochemistry and Molecular Pharmacology and Program in Cell Dynamics, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 01/2007; 103(50):18957-62. DOI: 10.1073/pnas.0609466103
Source: PubMed


MicroRNAs are small, approximately 21- to 24-nt RNAs that have been found to regulate gene expression. miR-206 is a microRNA that is expressed at high levels in Drosophila, zebrafish, and mouse skeletal muscle and is thought to be involved in the attainment and/or maintenance of the differentiated state. We used locked nucleic acid probes for in situ hybridization analysis of the intracellular localization of miR-206 during differentiation of rat myogenic cells. Like most microRNAs, which are presumed to suppress translation of target mRNAs, we found that miR-206 occupies a cytoplasmic location in cultured myoblasts and differentiated myotubes and that its level increases in myotubes over the course of differentiation, consistent with previous findings in muscle tissue in vivo. However, to our surprise, we also observed miR-206 to be concentrated in nucleoli. A probe designed to be complementary to the precursor forms of miR-206 gave no nucleolar signal. We characterized the intracellular localization of miR-206 at higher spatial resolution and found that a substantial fraction colocalizes with 28S rRNA in both the cytoplasm and the nucleolus. miR-206 is not concentrated in either the fibrillar centers of the nucleolus or the dense fibrillar component, where ribosomal RNA transcription and early processing occur, but rather is localized in the granular component, the region of the nucleolus where final ribosome assembly takes place. These results suggest that miR-206 may associate both with nascent ribosomes in the nucleolus and with exported, functional ribosomes in the cytoplasm.

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Article: Politz, J.C., Zhang, F. & Pederson, T. MicroRNA-206 colocalizes with ribosome-rich regions in both the nucleolus and cytoplasm of rat myogenic cells. Proc. Natl. Acad. Sci. USA 103, 18957-18962

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    • "However, recent studies also demonstrate roles for miRNAs in epigenetic modifications. Several studies described the localization and enrichment of certain miRNAs in the nucleus of different tissues or cells, such as miR-29b in HeLa cell nuclei and miR-206 in rat myogenic cell nuclei, suggesting a nuclear function for miRNAs, apart from their canonical roles in the cytoplasm (Hwang et al., 2007; Liao et al., 2010; Politz et al., 2006). Although there is no direct evidence for which protein can transport mature miRNA from the cytoplasm to the nucleus, some studies identified exportin-1 (Castanotto et al., 2009) and importin-8 (Wei et al., 2014; Weinmann et al., 2009) as possible transporters. "
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    • "Other examples of miRNAs found in the nucleus are miR-709, miR-690, miR-30e (Tang et al., 2012), and miR-122 (Földes-Papp et al., 2009). miRNAs can also be found in the nucleolus as precursor forms, like miR-494 and miR-664, and as mature miRNAs, like miR-21, miR-1, miR-351, miR-206 (Politz et al., 2006, 2009), and miR-320 (Marcon et al., 2008). Another intriguing subcellular localization of miRNAs is mitochondria, where they may modulate apoptosis processes in a coordinated way (Kren et al., 2009). "
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    • "The RNase P RNA assists in the 5′ processing of tRNA in the nucleolus [14]. At least one microRNA (miRNA) has been reported in the nucleolus of rat myoblasts [15], [16], and several nucleolar miRNAs were demonstrated in HeLa cells in a recent study [17]. Besides rRNA and ribosome biogenesis, a number of other functions that involve RNP assemblies have been associated with the nucleolus. "
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