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Let-7b/c enhance the stability of a tissue-specific mRNA during mammalian organogenesis as part of a feedback loop involving KSRP.

ABSTRACT: Gene silencing mediated by either microRNAs (miRNAs) or Adenylate/uridylate-rich elements Mediated mRNA Degradation (AMD) is a powerful way to post-transcriptionally modulate gene expression. We and others have reported that the RNA-binding protein KSRP favors the biogenesis of select miRNAs (including let-7 family) and activates AMD promoting the decay of inherently labile mRNAs. Different layers of interplay between miRNA- and AMD-mediated gene silencing have been proposed in cultured cells, but the relationship between the two pathways in living organisms is still elusive. We conditionally deleted Dicer in mouse pituitary from embryonic day (E) 9.5 through Cre-mediated recombination. In situ hybridization, immunohistochemistry, and quantitative reverse transcriptase-PCR revealed that Dicer is essential for pituitary morphogenesis and correct expression of hormones. Strikingly, αGSU (alpha glycoprotein subunit, common to three pituitary hormones) was absent in Dicer-deleted pituitaries. αGSU mRNA is unstable and its half-life increases during pituitary development. A transcriptome-wide analysis of microdissected E12.5 pituitaries revealed a significant increment of KSRP expression in conditional Dicer-deleted mice. We found that KSRP directly binds to αGSU mRNA, promoting its rapid decay; and, during pituitary development, αGSU expression displays an inverse temporal relationship to KSRP. Further, let-7b/c downregulated KSRP expression, promoting the degradation of its mRNA by directly binding to the 3'UTR. Therefore, we propose a model in which let-7b/c and KSRP operate within a negative feedback loop. Starting from E12.5, KSRP induces the maturation of let-7b/c that, in turn, post-transcriptionally downregulates the expression of KSRP itself. This event leads to stabilization of αGSU mRNA, which ultimately enhances the steady-state expression levels. We have identified a post-transcriptional regulatory network active during mouse pituitary development in which the expression of the hormone αGSU is increased by let7b/c through downregulation of KSRP. Our study unveils a functional crosstalk between miRNA- and AMD-dependent gene regulation during mammalian organogenesis events.

SUBMITTER: Repetto E

PROVIDER: S-EPMC3405994 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:miR828 in Arabidopsis triggers the cleavage of Trans-Acting SiRNA Gene 4 (TAS4) transcripts and production of small interfering RNAs (ta-siRNAs). One siRNA, TAS4-siRNA81(-), targets a set of MYB transcription factors including PAP1, PAP2, and MYB113 which regulate the anthocyanin biosynthesis pathway. Interestingly, miR828 also targets MYB113, suggesting a close relationship between these MYBs, miR828, and TAS4, but their evolutionary origins are unknown. We found that PAP1, PAP2, and TAS4 expression is induced specifically by exogenous treatment with sucrose and glucose in seedlings. The induction is attenuated in abscisic acid (ABA) pathway mutants, especially in abi3-1 and abi5-1 for PAP1 or PAP2, while no such effect is observed for TAS4. PAP1 is under regulation by TAS4, demonstrated by the accumulation of PAP1 transcripts and anthocyanin in ta-siRNA biogenesis pathway mutants. TAS4-siR81(-) expression is induced by physiological concentrations of Suc and Glc and in pap1-D, an activation-tagged line, indicating a feedback regulatory loop exists between PAP1 and TAS4. Bioinformatic analysis revealed MIR828 homologues in dicots and gymnosperms, but only in one basal monocot, whereas TAS4 is only found in dicots. Consistent with this observation, PAP1, PAP2, and MYB113 dicot paralogs show peptide and nucleotide footprints for the TAS4-siR81(-) binding site, providing evidence for purifying selection in contrast to monocots. Extended sequence similarities between MIR828, MYBs, and TAS4 support an inverted duplication model for the evolution of MIR828 from an ancestral gymnosperm MYB gene and subsequent formation of TAS4 by duplication of the miR828* arm. We obtained evidence by modified 5'-RACE for a MYB mRNA cleavage product guided by miR828 in Pinus resinosa. Taken together, our results suggest that regulation of anthocyanin biosynthesis by TAS4 and miR828 in higher plants is evolutionarily significant and consistent with the evolution of TAS4 since the dicot-monocot divergence.

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Let-7b/c enhance the stability of a tissue-specific mRNA during mammalian organogenesis as part of a feedback loop involving KSRP.

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