动物细胞核内miRNA的加工过程

microRNA(miRNA)是存在于真核生物中的一类大的基因家族,与其靶mRNA分子一起形成了生物体内复杂的调控网络。miRNA在基因表达调节过程中的关键性作用涉及到发育时序的控制、造血细胞的分化、细胞凋亡、细胞增殖以及器官的形成等方面。其中最值得探讨的问题是miRNA的生物发生过程及其调控机制。近年来,miRNA在动物细胞核中加工机制的研究取得了较大的进展。在细胞核中,RNA多聚酶II指导的miRNA基因的转录,微处理器作用下的pri-miRNA的剪切及exportin-5协助下的pre-miRNA的输出过程彼此协调,共同而有序的完成miRNA在细胞核中的加工过程。     

Structural basis of microRNA length variety

The biogenesis of human microRNAs (miRNAs) includes two RNA cleavage steps in which the activities of the RNases Drosha and Dicer are involved. miRNAs of diverse lengths are generated from different genes, and miRNAs that are heterogeneous in length are produced from a single miRNA gene. We determined the solution structures of many miRNA precursors and analysed the structural basis of miRNA length diversity using a new measure: the weighted average length of diced RNA (WALDI). We found that asymmetrical structural motifs present in precursor hairpins are primarily responsible for the length diversity of miRNAs generated by Dicer. High-resolution northern blots of miRNAs and their precursors revealed that both Dicer and Drosha cleavages of imperfect specificity contributed to the miRNA length heterogeneity. The relevance of these findings to the dynamics of the dicing complex, mRNA regulation by miRNA, RNA interference and miRNA technologies are discussed.     

The ATM kinase induces microRNA biogenesis in the DNA damage response

The DNA damage response involves a complex network of processes that detect and repair DNA damage. Here we show that miRNA biogenesis is globally induced upon DNA damage in an ATM-dependent manner. About one-fourth of miRNAs are significantly upregulated after DNA damage, while loss of ATM abolishes their induction. KH-type splicing regulatory protein (KSRP) is a key player that translates DNA damage signaling to miRNA biogenesis. The ATM kinase directly binds to and phosphorylates KSRP, leading to enhanced interaction between KSRP and pri-miRNAs and increased KSRP activity in miRNA processing. Mutations of the ATM phosphorylation sites of KSRP impaired its activity in regulating miRNAs. These findings reveal a mechanism by which DNA damage signaling is linked to miRNA biogenesis.     

Piecing together the mosaic of early mammalian development through microRNAs

The microRNA (miRNA) pathway represents an integral component of the gene regulation circuitry that controls development. In recent years, the role of miRNAs in embryonic stem (ES) cells and mammalian embryogenesis has begun to be explored. A few dozens of miRNAs expressed in mammalian ES cells, either exclusively or nonexclusively, have been cloned. The overall role of miRNAs in ES cells and embryonic development has been assessed by examining the effect of knocking out Dicer, an RNase III enzyme required for miRNA and small interfering RNA biogenesis, as well as DGCR8, a nuclear protein specifically involved in miRNA biogenesis. In addition, the role of a cluster of miRNAs specifically expressed in ES cells, the miR-290-295 group, has been investigated by the knock-out approach. These analyses have revealed the crucial role of miRNAs in ES cell differentiation, lineage specification, and organogenesis, especially neurogenesis and cardiogenesis. Systematic investigation of the role of miRNAs in ES cells and embryos will allow us to find missing pieces of the mosaic of early development.     

Stress response factors as hub‐regulators of microRNA biogenesis: implication to the diseased heart

MicroRNAs (miRNAs) are important regulators of heart function and then an intriguing therapeutic target for plenty of diseases. The problem raised is that many data in this area are contradictory, thus limiting the use of miRNA‐based therapy. The goal of this review is to describe the hub‐mechanisms regulating the biogenesis and function of miRNAs, which could help in clarifying some contradictions in the miRNA world. With this scope, we analyse an array of factors, including several known agents of stress response, mediators of epigenetic changes, regulators of alternative splicing, RNA editing, protein synthesis and folding and proteolytic systems. All these factors are important in cardiovascular function and most of them regulate miRNA biogenesis, but their influence on miRNAs was shown for non‐cardiac cells or some specific cardiac pathologies. Finally, we consider that studying the stress response factors, which are upstream regulators of miRNA biogenesis, in the diseased heart could help in (1) explaining some contradictions concerning miRNAs in heart pathology, (2) making the role of miRNAs in pathogenesis of cardiovascular disease more clear, and therefore, (3) getting powerful targets for its molecular therapy. Copyright © 2015 John Wiley & Sons, Ltd.     

微小RNAs的3'端尿苷化和腺苷化

miRNA是转录后基因表达调节的重要分子,但目前对它们自身的调节机制还知之甚少.最近的研究发现,在很多生物中,miRNA的3'末端都可以无需模板的添加尿苷酸(尿苷化)或腺苷酸(腺苷化),这种修饰可以发生在miRNA的前体上,也可以发生在成熟的miRNA上,其作用不仅可以影响miRNA的生物合成,稳定性,靶向靶标mRNAs的效率,而且还可以作为损伤miRNA的质量控制机制,及其形成mRNAs的异构体,以提高miRNA的作用范围或更精细的发挥基因表达调节作用.越来越多的研究揭示:这种修饰具有miRNA、组织、生物发育阶段和疾病状况等特异性,而且还涉及很多人类的发病机制,如癌症.本文综述了miRNA的3'末端尿苷化或腺苷化的研究进展,并对这种机制的应用前景进行了展望.