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A feedback loop comprising lin-28 and let-7 controls pre-let-7 maturation during neural stem-cell commitment

Abstract

miRNA populations, including mammalian homologues of lin-4 (mir-125) and let-7, undergo a marked transition during stem-cell differentiation1. Originally identified on the basis of their mutational phenotypes in stem-cell maturation, mir-125 and let-7 are strongly induced during neural differentiation of embryonic stem (ES) cells and embryocarcinoma (EC) cells. We report that embryonic neural stem (NS) cells express let-7 and mir-125, and investigate post-transcriptional mechanisms contributing to the induction of let-7. We demonstrate that the pluripotency factor Lin-28 binds the pre-let-7 RNA and inhibits processing by the Dicer ribonuclease in ES and EC cells. In NS cells, Lin-28 is downregulated by mir-125 and let-7, allowing processing of pre-let-7 to proceed. Suppression of let-7 or mir-125 activity in NS cells led to upregulation of Lin-28 and loss of pre-let-7 processing activity, suggesting that let-7, mir-125 and lin-28 participate in an autoregulatory circuit that controls miRNA processing during NS-cell commitment.

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Figure 1: miRNA activity in neural progenitors.
Figure 2: Characterization of NS cell processing and precursor RNA-binding activity.
Figure 3: Reciprocal regulation of Lin-28 and let-7.
Figure 4: Lin-28 inhibits processing of pre-let-7.
Figure 5: Cell staining reveals cytoplasmic accumulation of pre-let-7 in EC cells.

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Acknowledgements

The authors would like to thank all members of the laboratories at the Institute for Cell and Neurobiology for support and cooperation. Brita Scholte and Anja Gräfe provided excellent technical assistance. We received invaluable help from Jutta Schüler with microscopy, from Jens Baron and Gudrun Ahnert-Hilger with densitometric quantification, and from Tina Rosenkrantz with LNA design. We thank Wei Chen and Nikolaus Rajewsky for advice and discussions, James Ari Liebkowsky and Elisa Cuevas for critical reading of the manuscript, and Scott Hammond for communicating unpublished results. L.S. and A.R. were partially supported as fellows of the Humboldt University Graduate Schools, Grant 238: Damage cascades in neurological disorders, and Grant 1123: Learning and Memory, respectively, awarded to R.N. Additional support was provided by SFB grant 665 to F.G.W. and R.N.

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Correspondence to F. Gregory Wulczyn.

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Supplementary Figures S1, S2, S3, S4, S5, S6, S7, S8, S9, S10 and Supplementary Methods (PDF 1370 kb)

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Rybak, A., Fuchs, H., Smirnova, L. et al. A feedback loop comprising lin-28 and let-7 controls pre-let-7 maturation during neural stem-cell commitment. Nat Cell Biol 10, 987–993 (2008). https://doi.org/10.1038/ncb1759

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