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。     

Clustered miRNAs and their role in biological functions and diseases

MicroRNAs (miRNAs) are endogenous, small non‐coding RNAs known to regulate expression of protein‐coding genes. A large proportion of miRNAs are highly conserved, localized as clusters in the genome, transcribed together from physically adjacent miRNAs and show similar expression profiles. Since a single miRNA can target multiple genes and miRNA clusters contain multiple miRNAs, it is important to understand their regulation, effects and various biological functions. Like protein‐coding genes, miRNA clusters are also regulated by genetic and epigenetic events. These clusters can potentially regulate every aspect of cellular function including growth, proliferation, differentiation, development, metabolism, infection, immunity, cell death, organellar biogenesis, messenger signalling, DNA repair and self‐renewal, among others. Dysregulation of miRNA clusters leading to altered biological functions is key to the pathogenesis of many diseases including carcinogenesis. Here, we review recent advances in miRNA cluster research and discuss their regulation and biological functions in pathological conditions.     

microRNAs: small molecules with big roles - C. elegans to human cancer

miRNAs (microRNAs) were first discovered as critical regulators of developmental timing events in Caenorhabditis elegans. Subsequent studies have shown that miRNAs and cellular factors necessary for miRNA biogenesis are conserved in many organisms, suggesting the importance of miRNAs during developmental processes. Indeed, mutations in the miRNA-processing pathway induce pleiotropic defects in development, which accompany perturbation of correct expression of target genes. However, control of gene expression in development is not the only function of miRNAs. Recent work has provided new insights into the role of miRNAs in various biological events, including aging and cancer. C. elegans continues to be helpful in facilitating a further understanding of miRNA function in human diseases.     

microRNAs: small molecules with big roles - C. elegans to human cancer.

miRNAs (microRNAs) were first discovered as critical regulators of developmental timing events in Caenorhabditis elegans. Subsequent studies have shown that miRNAs and cellular factors necessary for miRNA biogenesis are conserved in many organisms, suggesting the importance of miRNAs during developmental processes. Indeed, mutations in the miRNA-processing pathway induce pleiotropic defects in development, which accompany perturbation of correct expression of target genes. However, control of gene expression in development is not the only function of miRNAs. Recent work has provided new insights into the role of miRNAs in various biological events, including aging and cancer. C. elegans continues to be helpful in facilitating a further understanding of miRNA function in human diseases.     

PGC-Enriched miRNAs Control Germ Cell Development

Non-coding microRNAs (miRNAs) regulate the translation of target messenger RNAs (mRNAs) involved in the growth and development of a variety of cells, including primordial germ cells (PGCs) which play an essential role in germ cell development. However, the target mRNAs and the regulatory networks influenced by miRNAs in PGCs remain unclear. Here, we demonstrate a novel miRNAs control PGC development through targeting mRNAs involved in various cellular pathways. We reveal the PGC-enriched expression patterns of nine miRNAs, including miR-10b, -18a, -93, -106b, -126-3p, -127, -181a, -181b, and -301, using miRNA expression analysis along with mRNA microarray analysis in PGCs, embryonic gonads, and postnatal testes. These miRNAs are highly expressed in PGCs, as demonstrated by Northern blotting, miRNA in situ hybridization assay, and miRNA qPCR analysis. This integrative study utilizing mRNA microarray analysis and miRNA target prediction demonstrates the regulatory networks through which these miRNAs regulate their potential target genes during PGC development. The elucidated networks of miRNAs disclose a coordinated molecular mechanism by which these miRNAs regulate distinct cellular pathways in PGCs that determine germ cell development.     

A New Short Oligonucleotide-Based Strategy for the Precursor-Specific Regulation of microRNA Processing by Dicer

The precise regulation of microRNA (miRNA) biogenesis seems to be critically important for the proper functioning of all eukaryotic organisms. Even small changes in the levels of specific miRNAs can initiate pathological processes, including carcinogenesis. Accordingly, there is a great need to develop effective methods for the regulation of miRNA biogenesis and activity. In this study, we focused on the final step of miRNA biogenesis; i.e., miRNA processing by Dicer. To test our hypothesis that RNA molecules can function not only as Dicer substrates but also as Dicer regulators, we previously identified by SELEX a pool of RNA oligomers that bind to human Dicer. We found that certain of these RNA oligomers could selectively inhibit the formation of specific miRNAs. Here, we show that these specific inhibitors can simultaneously bind both Dicer and pre-miRNAs. These bifunctional riboregulators interfere with miRNA maturation by affecting pre-miRNA structure and sequestering Dicer. Based on these observations, we designed a set of short oligomers (12 nucleotides long) that were capable of influencing pre-miRNA processing in vitro, both in reactions involving recombinant human Dicer and in cytosolic extracts. We propose that the same strategy may be used to develop effective and selective regulators to control the production of any miRNA. Overall, our findings indicate that the interactions between pre-miRNAs and other RNAs may form very complex regulatory networks that modulate miRNA biogenesis and consequently gene expression.     

Emerging roles of microRNAs in the control of embryonic stem cells and the generation of induced pluripotent stem cells

MicroRNAs (miRNAs) have emerged as critical regulators of gene expression. These small, non-coding RNAs are believed to regulate more than a third of all protein coding genes, and they have been implicated in the control of virtually all biological processes, including the biology of stem cells. The essential roles of miRNAs in the control of pluripotent stem cells were clearly established by the finding that embryonic stem (ES) cells lacking proteins required for miRNA biogenesis exhibit defects in proliferation and differentiation. Subsequently, the function of numerous miRNAs has been shown to control the fate of ES cells and to directly influence critical gene regulatory networks controlled by pluripotency factors Sox2, Oct4, and Nanog. Moreover, a growing list of tissue-specific miRNAs, which are silenced or not processed fully in ES cells, has been found to promote differentiation upon their expression and proper processing. The importance of miRNAs for ES cells is further indicated by the exciting discovery that specific miRNA mimics or miRNA inhibitors promote the reprogramming of somatic cells into induced pluripotent stem (iPS) cells. Although some progress has been made during the past two years in our understanding of the contribution of specific miRNAs during reprogramming, further progress is needed since it is highly likely that miRNAs play even wider roles in the generation of iPS cells than currently appreciated. This review examines recent developments related to the roles of miRNAs in the biology of pluripotent stem cells. In addition, we posit that more than a dozen additional miRNAs are excellent candidates for influencing the generation of iPS cells as well as for providing new insights into the process of reprogramming.