Translational inhibition by deadenylation-independent mechanisms is central to microRNA-mediated silencing in zebrafish.
MicroRNA (miRNA) is a class of small noncoding RNA approximately 22 nt in length. Animal miRNA silences complementary mRNAs via translational inhibition, deadenylation, and mRNA degradation. However, the underlying molecular mechanisms remain unclear. A key question is whether these three outputs are independently induced by miRNA through distinct mechanisms or sequentially induced within a single molecular pathway. Here, we successfully dissected these intricate outputs of miRNA-mediated repression using zebrafish embryos as a model system. Our results indicate that translational inhibition and deadenylation are independent outputs mediated by distinct domains of TNRC6A, which is an effector protein in the miRNA pathway. Translational inhibition by TNRC6A is divided into two mechanisms: PAM2 motif-mediated interference of poly(A)-binding protein (PABP), and inhibition of 5' cap- and poly(A) tail-independent step(s) by a previously undescribed P-GL motif. Consistent with these observations, we show that, in zebrafish embryos, miRNA inhibits translation of the target mRNA in a deadenylation- and PABP-independent manner at early time points. These results indicate that miRNA exerts multiple posttranscriptional outputs via physically and functionally independent mechanisms and that direct translational inhibition is central to miRNA-mediated repression.
Department of Biology, Graduate School of Science, Kobe University, 1-1 Rokkodaicho Nadaku, Kobe, Hyogo 657-8501, Japan. yuichiro.mishima@people.kobe-u.ac.jp
Yuichiro
Y
Mishima
Akira
A
Fukao
Tomoyoshi
T
Kishimoto
Hiroshi
H
Sakamoto
Toshinobu
T
Fujiwara
Kunio
K
Inoue
D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D001324:Autoantigens / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D008156:Luciferases; D035683:MicroRNAs / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D020871:RNA Stability / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D015027:Zebrafish / Q000196:embryology* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism
D001324:Autoantigens; D035683:MicroRNAs; C570983:TNRC6A protein, zebrafish; D029961:Zebrafish Proteins; D049452:Green Fluorescent Proteins; D008156:Luciferases