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Published online on November 29, 2006, 10.1073/pnas.0609466103
PNAS | December 12, 2006 | vol. 103 | no. 50 | 18957-18962


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BIOLOGICAL SCIENCES / CELL BIOLOGY
MicroRNA-206 colocalizes with ribosome-rich regions in both the nucleolus and cytoplasm of rat myogenic cells

Joan C. Ritland Politz*, Fan Zhang, and Thoru Pederson

Department of Biochemistry and Molecular Pharmacology and Program in Cell Dynamics, University of Massachusetts Medical School, Worcester, MA 01605

Communicated by Masayasu Nomura, University of California, Irvine, CA, October 25, 2006 (received for review August 2, 2006)

MicroRNAs are small, {approx}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.

microRNA | myogenesis | nuclear structure | RNA localization | ribosomal RNA

Author contributions: J.C.R.P. and T.P. designed research; J.C.R.P. and F.Z. performed research; J.C.R.P., F.Z., and T.P. analyzed data; and J.C.R.P. and T.P. wrote the paper.

The authors declare no conflict of interest.

*To whom correspondence should be addressed. E-mail: joan.politz{at}umassmed.edu

© 2006 by The National Academy of Sciences of the USA


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