Rates of production and degradation together specify microRNA (miRNA) abundance and dynamics. Here, we used approach-to-steady-state metabolic labeling to assess these rates for 176 miRNAs in contact-inhibited mouse embryonic fibroblasts (MEFs), 182 miRNAs in dividing MEFs, and 127 miRNAs in mouse embryonic stem cells (mESCs). MicroRNA duplexes, each comprising a mature miRNA and its passenger strand, are produced at rates as fast as 110 ± 50 copies/cell/min, which exceeds rates reported for any mRNAs. These duplexes are rapidly loaded into Argonaute, with <30 min typically required for duplex loading and silencing-complex maturation. Within Argonaute, guide strands have stabilities that vary by 100-fold. Half-lives also vary globally between cell lines, with median values ranging from 11 to 34 h in mESCs and contact-inhibited MEFs, respectively. Moreover, relative half-lives for individual miRNAs vary between cell types, implying the influence of cell-specific factors in dictating turnover rate. The apparent influence of miRNA regions most important for targeting, together with the effect of one target on miR-7 accumulation, suggest that targets fulfill this role. Analysis of the tailing and trimming of miRNA 3' termini showed that the flux was typically greatest through the isoform tailed with a single uridine, although changes in this flux did not correspond to changes in stability, which suggested that the processes of tailing and trimming might be independent from that of decay. Together, these results establish a framework for describing the dynamics and regulation of miRNAs throughout their life cycle.

中文翻译：

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哺乳动物 microRNA 代谢动态的全局分析。

生成率和降解率共同决定了 microRNA (miRNA) 的丰度和动态。在这里，我们使用接近稳态代谢标记来评估接触抑制的小鼠胚胎成纤维细胞（MEF）中的 176 个 miRNA、分裂的 MEF 中的 182 个 miRNA 以及小鼠胚胎干细胞（mESC）中的 127 个 miRNA 的速率。MicroRNA 双链体各自包含一个成熟的 miRNA 及其过客链，其生成速度高达 110 ± 50 拷贝/细胞/分钟，这超过了任何 mRNA 报道的速度。这些双链体被快速加载到 Argonaute 中，双链体加载和沉默复合物成熟通常需要 <30 分钟。在 Argonaute 中，引导链的稳定性相差 100 倍。细胞系之间的半衰期也存在全球差异，mESC 和接触抑制 MEF 的半衰期中值分别为 11 至 34 小时。此外，各个 miRNA 的相对半衰期因细胞类型而异，这意味着细胞特异性因素对决定周转率的影响。对靶向最重要的 miRNA 区域的明显影响，以及一个靶标对 miR-7 积累的影响，表明靶标履行了这一作用。对 miRNA 3' 末端加尾和修剪的分析表明，通过用单个尿苷加尾的异构体，通量通常最大，尽管该通量的变化与稳定性的变化并不对应，这表明加尾和修剪的过程可能会影响稳定性。独立于腐朽。这些结果共同建立了一个框架来描述 miRNA 在其整个生命周期中的动态和调控。