Lund Elsebet, Liu Mingzhu, Hartley Rebecca S, Sheets Michael D, Dahlberg James E
Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
RNA. 2009 Dec;15(12):2351-63. doi: 10.1261/rna.1882009. Epub 2009 Oct 23.
We show that microRNA-427 (miR-427) mediates the rapid deadenylation of maternal mRNAs after the midblastula transition (MBT) of Xenopus laevis embryogenesis. By MBT, the stage when the embryonic cell cycle is remodeled and zygotic transcription of mRNAs is initiated, each embryo has accumulated approximately 10(9) molecules of miR-427 processed from multimeric pri-miR-427 transcripts synthesized after fertilization. We demonstrate that the maternal mRNAs for cyclins A1 and B2 each contain a single miR-427 target sequence, spanning less than 30 nucleotides, that is both necessary and sufficient for deadenylation, and that inactivation of miR-427 leads to stabilization of the mRNAs. Although this deadenylation normally takes place after MBT, exogenous miRNAs produced prematurely in vivo can promote deadenylation prior to MBT, indicating that turnover of the maternal mRNAs is limited by the amount of accumulated miR-427. Injected transcripts comprised solely of the cyclin mRNA 3' untranslated regions or bearing a 5' ApppG cap undergo deadenylation, showing that translation of the targeted RNA is not required. miR-427 is not unique in promoting deadenylation, as an unrelated miRNA, let-7, can substitute for miR-427 if the reporter RNA contains an appropriate let-7 target site. We propose that miR-427, like the orthologous miR-430 of zebrafish, functions to down-regulate expression of maternal mRNAs early in development.
我们发现，微小RNA - 427（miR - 427）在非洲爪蟾胚胎发育的中囊胚转换（MBT）后介导母体mRNA的快速去腺苷酸化。到MBT阶段，即胚胎细胞周期重塑且mRNA的合子转录开始之时，每个胚胎已经积累了约10⁹个从受精后合成的多聚体pri - miR - 427转录本加工而来的miR - 427分子。我们证明，细胞周期蛋白A1和B2的母体mRNA各自包含一个单一的miR - 427靶序列，跨度小于30个核苷酸，该序列对于去腺苷酸化是必需且充分的，并且miR - 427的失活会导致mRNA的稳定。虽然这种去腺苷酸化通常在MBT之后发生，但体内过早产生的外源性miRNA可在MBT之前促进去腺苷酸化，这表明母体mRNA的周转受积累的miR - 427量的限制。仅由细胞周期蛋白mRNA的3'非翻译区组成或带有5' ApppG帽的注射转录本会发生去腺苷酸化，这表明不需要靶向RNA的翻译。miR - 427在促进去腺苷酸化方面并非独一无二，因为如果报告RNA包含合适的let - 7靶位点，一种不相关的miRNA，let - 7，可以替代miR - 427。我们提出，miR - 427与斑马鱼的直系同源物miR - 430一样，在发育早期发挥下调母体mRNA表达的作用。
