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Molecular left-right (L-R) asymmetry is established at the node of the mouse embryo as a result of the sensing of a leftward fluid flow by immotile cilia of perinodal crown cells and the consequent degradation of Dand5 mRNA on the left side. We here examined how the fluid flow induces Dand5 mRNA decay. We found that the first 200 nucleotides in the 3′ untranslated region (3′-UTR) of Dand5 mRNA are necessary and sufficient for the left-sided decay and to mediate the response of a 3′-UTR reporter transgene to Ca2+, the cation channel Pkd2, the RNA-binding protein Bicc1 and their regulation by the flow direction. We show that Bicc1 preferentially recognizes GACR and YGAC sequences, which can explain the specific binding to a conserved GACGUGAC motif located in the proximal Dand5 3′-UTR. The Cnot3 component of the Ccr4-Not deadenylase complex interacts with Bicc1 and is also required for Dand5 mRNA decay at the node. These results suggest that Ca2+ currents induced by leftward fluid flow stimulate Bicc1 and Ccr4-Not to mediate Dand5 mRNA degradation specifically on the left side of the node., Questioning what regulates left-right asymmetry breaking in the mouse node: the authors identify a 200 bp stretch of the Dand5 3’UTR where Bicc1 binds, and Cnot proteins downstream of calcium flow regulate the post-transcriptional regulation of Dand5 by Bicc1.

RNA transcripts can form a variety of higher-order structures. We developed a large-scale affinity analysis system, FOREST (Folded RNA Element Profiling with Structure Library), to investigate the function of these RNA structures on transcriptome-wide scale. Here we describe a protocol to analyze RNA-protein interactions using FOREST . Users of the protocol prepare an RNA structure library comprised of diverse species of transcripts and perform high-throughput characterization of the RNA-protein interactions to obtain quantitative and comprehensive information on the binding affinities and specificities. Moreover, we demonstrate how FOREST can be used to analyze a non-canonical structure, the RNA G-quadruplex, without sequencing bias, because the quantification is performed directly on a microarray without sequence amplification. FOREST will contribute to the discovery of RNA structure motifs that determine RNA-protein interactions.

SUMMARYMolecular left-right (L-R) asymmetry is established at the node of the mouse embryo as a result of the sensing of a leftward fluid flow by immotile cilia of perinodal crown cells and the consequent degradation of Dand5 mRNA on the left side. We here examined how the fluid flow induces Dand5 mRNA decay. We found that the 3’ untranslated region (3’-UTR) of Dand5 mRNA is necessary and sufficient for the left-sided decay and is responsive to the flow direction, loss of the cation channel Pkd2, and Ca2+. The 200-nucleotide proximal-most portion of the 3’-UTR, which is conserved among mammals, is essential for the asymmetric mRNA decay and binds Bicc1, an RNA binding protein specifically expressed at the node. Bicc1 preferentially recognizes GAC and GACR sequences in RNA, and these motifs are enriched in the 200-nucleotide region of the Dand5 3’-UTR. The Cnot3 component of the Ccr4-Not deadenylase complex interacts with Bicc1 and is also required for Dand5 mRNA decay at the node. Our results thus suggest that leftward fluid flow induces binding of Bicc1 to the 3’-UTR of Dand5 mRNA in crown cells on the left side of the node, and that consequent recruitment of Ccr4-Not mediates mRNA degradation.

Biochemical assays and computational analyses have discovered RNA structures throughout various transcripts. However, the roles of these structures are mostly unknown. Here we develop folded RNA element profiling with structure library (FOREST), a multiplexed affinity assay system to identify functional interactions from transcriptome-wide RNA structure datasets. We generate an RNA structure library by extracting validated or predicted RNA motifs from gene-annotated RNA regions. The RNA structure library with an affinity enrichment assay allows for the comprehensive identification of target-binding RNA sequences and structures in a high-throughput manner. As a proof-of-concept, FOREST discovers multiple RNA-protein interaction networks with quantitative scores, including translational regulatory elements that function in living cells. Moreover, FOREST reveals different binding landscapes of RNA G-quadruplex (rG4) structures-binding proteins and discovers rG4 structures in the terminal loops of precursor microRNAs. Overall, FOREST serves as a versatile platform to investigate RNA structure-function relationships on a large scale., RNA構造のライブラリ化を通じてRNA 構造ごとにおけるRNA-タンパク質相互作用を大規模に解析するシステム「FOREST」の開発 --RNAを標的とする創薬に道--. 京都大学プレスリリース. 2020-12-09.

MicroRNA (miRNA) activity differs with cell type, suggesting it can be used as a cell marker. In this study, we developed novel miRNA-responsive non-viral reporter vectors to continuously monitor and visualize miRNA dynamics during differentiation and to efficiently purify target living cells. Each vector codes miRNA-responsive and reference reporter genes in a single mRNA. These two genes are independent modules but transcribed by a single promoter, which enables us to distinguish miRNA-mediated post-transcriptional repression from transcriptional repression. We generated stable, miRNA-responsive vector-containing human induced pluripotent stem cells (hiPSCs) using the piggyBac transposon or episomal vectors. We could continuously monitor the differentiation status of living hiPSCs by detecting the activity of hiPSC-specific miRNA (miR-302a*). In addition, we could selectively sort hiPSC-derived cardiomyocytes using cardiomyocyte-specific miRNA (miR-208a or miR-1)-reporter vectors. Our miRNA reporter system provides a simple way to quantitatively and continuously monitor and visualize changes in the cellular state and should facilitate a broad range of studies that depend on cellular changes including drug discovery and cell-fate conversion.