Molecular Basis for Interaction of let-7 MicroRNAs with Lin28

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Cell (Impact Factor: 32.24). 11/2011; 147(5):1080-91. DOI: 10.1016/j.cell.2011.10.020
Source: PubMed

ABSTRACT MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate gene expression. Among these, members of the let-7 miRNA family control many cell-fate determination genes to influence pluripotency, differentiation, and transformation. Lin28 is a specific, posttranscriptional inhibitor of let-7 biogenesis. We report crystal structures of mouse Lin28 in complex with sequences from let-7d, let-7-f1, and let-7 g precursors. The two folded domains of Lin28 recognize two distinct regions of the RNA and are sufficient for inhibition of let-7 in vivo. We also show by NMR spectroscopy that the linker connecting the two folded domains is flexible, accommodating Lin28 binding to diverse let-7 family members. Protein-RNA complex formation imposes specific conformations on both components that could affect downstream recognition by other processing factors. Our data provide a molecular explanation for Lin28 specificity and a model for how it regulates let-7.

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    • "Mono-uridylation by TUT7/4/2 restores the optimal 2-nt 3 0 overhang of group II pre-miRNAs resulting in efficient Dicer processing (Heo et al, 2012). Between the two contrasting roles that TUTs play in miRNA biogenesis, Lin28-dependent oligo-uridylation by TUT4/7 has been intensively characterized via biochemical and structural studies (Heo et al, 2008, 2009; Hagan et al, 2009; Nam et al, 2011; Yeom et al, 2011; Loughlin et al, 2012; Mayr et al, 2012; Thornton et al, 2012), whereas mechanism of monouridylation has been largely unknown. "
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    ABSTRACT: Terminal uridylyl transferases (TUTs) function as integral regulators of microRNA (miRNA) biogenesis. Using biochemistry, single-molecule, and deep sequencing techniques, we here investigate the mechanism by which human TUT7 (also known as ZCCHC6) recognizes and uridylates precursor miRNAs (pre-miRNAs) in the absence of Lin28. We find that the overhang of a pre-miRNA is the key structural element that is recognized by TUT7 and its paralogues, TUT4 (ZCCHC11) and TUT2 (GLD2/PAPD4). For group II pre-miRNAs, which have a 1-nt 3′ overhang, TUT7 restores the canonical end structure (2-nt 3′ overhang) through mono-uridylation, thereby promoting miRNA biogenesis. For pre-miRNAs where the 3′ end is further recessed into the stem (as in 3′ trimmed pre-miRNAs), TUT7 generates an oligo-U tail that leads to degradation. In contrast to Lin28-stimulated oligo-uridylation, which is processive, a distributive mode is employed by TUT7 for both mono- and oligo-uridylation in the absence of Lin28. The overhang length dictates the frequency (but not duration) of the TUT7-RNA interaction, thus explaining how TUT7 differentiates pre-miRNA species with different overhangs. Our study reveals dual roles and mechanisms of uridylation in repair and removal of defective pre-miRNAs.
    The EMBO Journal 05/2015; 34(13). DOI:10.15252/embj.201590931 · 10.43 Impact Factor
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    • "As a result of this knockdown, mature let-7 family miRNAs accumulated , as measured by RT-PCR, relative to transfection of a nontarget (siNT) control (Figure S3C). Also of note, siRNAs against both homologs were necessary to observe an induction of the let-7 family members, demonstrating their known semiredundant roles in let-7 maturation (Nam et al., 2011). "
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    ABSTRACT: It is clear that neural differentiation from human pluripotent stem cells generates cells that are developmentally immature. Here, we show that the let-7 plays a functional role in the developmental decision making of human neural progenitors, controlling whether these cells make neurons or glia. Through gain- and loss-of-function studies on both tissue and pluripotent derived cells, our data show that let-7 specifically regulates decision making in this context by regulation of a key chromatin-associated protein, HMGA2. Furthermore, we provide evidence that the let-7/HMGA2 circuit acts on HES5, a NOTCH effector and well-established node that regulates fate decisions in the nervous system. These data link the let-7 circuit to NOTCH signaling and suggest that this interaction serves to regulate human developmental progression.
    Stem Cell Reports 10/2014; 3(5). DOI:10.1016/j.stemcr.2014.08.015 · 5.37 Impact Factor
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    • "While Lin28B represses let-7 processing in the nucleus to prevent the formation of the precursor form from the primary let-7, Lin28A also blocks cytoplasmic processing of let-7 [6]. It has recently been shown in mouse that deletion of the Lin28 linker domain alters the protein’s three-dimensional structure and is sufficient to disrupt sequestration of the precursor form of let-7 (pre-let-7) [14]. "
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    ABSTRACT: Understanding the control of stem cell (SC) differentiation is important to comprehend developmental processes as well as to develop clinical applications. Lin28 is a conserved molecule that is involved in SC maintenance and differentiation by regulating let-7 miRNA maturation. However, little is known about the in vivo function of Lin28. Here, we report critical roles for lin-28 during oogenesis. We found that let-7 maturation was increased in lin-28 null mutant fly ovaries. We showed that lin-28 null mutant female flies displayed reduced fecundity, due to defects in egg chamber formation. More specifically, we demonstrated that in mutant ovaries, the egg chambers fuse during early oogenesis resulting in abnormal late egg chambers. We also showed that this phenotype is the combined result of impaired germline SC differentiation and follicle SC differentiation. We suggest a model in which these multiple oogenesis defects result from a misregulation of the ecdysone signaling network, through the fine-tuning of Abrupt and Fasciclin2 expression. Our results give a better understanding of the evolutionarily conserved role of lin-28 on GSC maintenance and differentiation.
    PLoS ONE 06/2014; 9(6):e101141. DOI:10.1371/journal.pone.0101141 · 3.23 Impact Factor
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