Global profiling of miRNAs and the hairpin precursors: insights into miRNA processing and novel miRNA discovery

MicroRNAs (miRNAs) constitute an important class of small regulatory RNAs that are derived from distinct hairpin precursors (pre-miRNAs). In contrast to mature miRNAs, which have been characterized in numerous genome-wide studies of different organisms, research on global profiling of pre-miRNAs is limited. Here, using massive parallel sequencing, we have performed global characterization of both mouse mature and precursor miRNAs. In total, 87 369 704 and 252 003 sequencing reads derived from 887 mature and 281 precursor miRNAs were obtained, respectively. Our analysis revealed new aspects of miRNA/pre-miRNA processing and modification, including eight Ago2-cleaved pre-miRNAs, eight new instances of miRNA editing and exclusively 5′ tailed mirtrons. Furthermore, based on the sequences of both mature and precursor miRNAs, we developed a miRNA discovery pipeline, miRGrep, which does not rely on the availability of genome reference sequences. In addition to 239 known mouse pre-miRNAs, miRGrep predicted 41 novel ones with high confidence. Similar as known ones, the mature miRNAs derived from most of these novel loci showed both reduced abundance following Dicer knockdown and the binding with Argonaute2. Evaluation on data sets obtained from Caenorhabditis elegans and Caenorhabditis sp.11 demonstrated that miRGrep could be widely used for miRNA discovery in metazoans, especially in those without genome reference sequences.     

Identification and Characterization of the miRNA Transcriptome of Ovis aries

The discovery and identification of Ovis aries (sheep) miRNAs will further promote the study of miRNA functions and gene regulatory mechanisms. To explore the microRNAome (miRNAome) of sheep in depth, samples were collected that included eight developmental stages: the longissimus dorsi muscles of Texel fetuses at 70, 85, 100, 120, and 135 days, and the longissimus dorsi muscles of Ujumqin fetuses at 70, 85, 100, 120, and 135 d, and lambs at 0 (birth), 35, and 70 d. These samples covered all of the representative periods of Ovis aries growth and development throughout gestation (about 150 d) and 70 d after birth. Texel and Ujumqin libraries were separately subjected to Solexa deep sequencing; 35,700,772 raw reads were obtained overall. We used ACGT101-miR v4.2 to analyze the sequence data. Following meticulous comparisons with mammalian mature miRNAs, precursor hairpins (pre-miRNAs), and the latest sheep genome, we substantially extended the Ovis aries miRNAome. The list of pre-miRNAs was extended to 2,319, expressing 2,914 mature miRNAs. Among those, 1,879 were genome mapped to unique miRNAs, representing 2,436 genome locations, and 1,754 pre-miRNAs were mapped to chromosomes. Furthermore, the Ovis aries miRNAome was processed using an elaborate bioinformatic analysis that examined multiple end sequence variation in miRNAs, precursors, chromosomal localizations, species-specific expressions, and conservative properties. Taken together, this study provides the most comprehensive and accurate exploration of the sheep miRNAome, and draws conclusions about numerous characteristics of Ovis aries miRNAs, including miRNAs and isomiRs.     

Interrogation of rabbit miRNAs and their isomiRs

Rabbit (Oryctolagus cuniculus) is the only lagomorph animal of which the genome has been sequenced. Establishing a rabbit miRNA resource will benefit subsequent functional genomic studies in mammals. We have generated small RNA sequence reads with SOLiD and Solexa platforms to identify rabbit miRNAs, where we identified 464 pre-miRNAs and 886 mature miRNAs. The brain and heart miRNA libraries were used for further in-depth analysis of isomiR distributions. There are several intriguing findings. First, several rabbit pre-miRNAs form highly conserved clusters. Second, there is a preference in selecting one strand as mature miRNA, resulting in an arm selection preference. Third, we analyzed the isomiR expression and validated the expression of isomiR types in different rabbit tissues. Moreover, we further performed additional small RNA libraries and defined miRNAs differentially expressed between brain and heart. We conclude also that isomiR distribution profiles could vary between brain and heart tissues.     

Synthetic pre-microRNAs reveal dual-strand activity of miR-34a on TNF-α

Functional microRNAs (miRNAs) are produced from both arms of their precursors (pre-miRNAs). Their abundances vary in context-dependent fashion spatiotemporarily and there is mounting evidence of regulatory interplay between them. Here, we introduce chemically synthesized pre-miRNAs (syn-pre-miRNAs) as a general class of accessible, easily transfectable mimics of pre-miRNAs. These are RNA hairpins, identical in sequence to natural pre-miRNAs. They differ from commercially available miRNA mimics through their complete hairpin structure, including any regulatory elements in their terminal-loop regions and their potential to introduce both strands into RISC. They are distinguished from transcribed pre-miRNAs by their terminal 5′ hydroxyl groups and their precisely defined terminal nucleotides. We demonstrate with several examples how they fully recapitulate the properties of pre-miRNAs, including their processing by Dicer into functionally active 5p; and 3p-derived mature miRNAs. We use syn-pre-miRNAs to show that miR-34a uses its 5p and 3p miRNAs in two pathways: apoptosis during TGF-β signaling, where SIRT1 and SP4 are suppressed by miR-34a-5p and miR-34a-3p, respectively; and the lipopolysaccharide (LPS)-activation of primary human monocyte-derived macrophages, where TNF (TNFα) is suppressed by miR-34a-5p indirectly and miR-34a-3p directly. Our results add to growing evidence that the use of both arms of a miRNA may be a widely used mechanism. We further suggest that syn-pre-miRNAs are ideal and affordable tools to investigate these mechanisms.     

Deep Sequencing Identifies Tissue-Specific MicroRNAs and Their Target Genes Involving in the Biosynthesis of Tanshinones in Salvia miltiorrhiza

Salvia miltiorrhiza is one of the most popular traditional medicinal herbs in Asian nations. Its dried root contains a number of tanshinones, protocatechuic aldehyde, salvianolic acid B and rosmarinic, and is used for the treatment of various diseases. The finding of microRNAs (miRNAs) and their target genes will help understand their biological role on the biosynthesis of tanshinones in S. miltiorrhiza. In the present study, a total of 452 known miRNAs corresponding to 589 precursor miRNAs (pre-miRNAs), and 40 novel miRNAs corresponding to 24 pre-miRNAs were identified in different tissues of S. miltiorrhiza by high-throughput sequencing, respectively. Among them, 62 miRNAs express only in root, 95 miRNAs express only in stem, 19 miRNAs express only in leaf, and 71 miRNAs express only in flower, respectively. By the degradome analysis, 69 targets potentially cleaved by 25 miRNAs were identified. Among them, acetyl-CoA C-acetyltransferase was cleaved by miR5072, and involved in the biosynthesis of tanshinones. This study provided valuable information for understanding the tissue-specific expression patterns of miRNAs in S. miltiorrhiza, and offered a foundation for future studies of the miRNA-mediated biosynthesis of tanshinones.     

MicroRNA Transcriptome Profile Analysis in Porcine Muscle and the Effect of miR-143 on the MYH7 Gene and Protein

Porcine skeletal muscle fibres are classified based on their different physiological and biochemical properties. Muscle fibre phenotype is regulated by several independent signalling pathways, including the mitogen-activated protein kinase (MAPK), nuclear factor of activated T cells (NFAT), myocyte enhancer factor 2 (MEF2) and peroxisome proliferator-activated receptor (PPAR) signalling pathways. MicroRNAs are non-coding small RNAs that regulate many biological processes. However, their function in muscle fibre type regulation remains unclear. The aim of our study was to identify miRNAs that regulate muscle fibre type during porcine growth to help understand the miRNA regulation mechanism of fibre differentiation. We performed Solexa/Illumina deep sequencing for the microRNAome during 3 muscle growth stages (63, 98 and 161 d). In this study, 271 mature miRNAs and 243 pre-miRNAs were identified. We detected 472 novel miRNAs in the muscle samples. Among the mature miRNAs, there are 23 highest expression miRNAs (over 10000 RPM), account for 85.3% of the total counts of mature miRNAs., including 10 (43.5%) muscle-related miRNAs (ssc-miR-133a-3p, ssc-miR-486, ssc-miR-1, ssc-miR-143-3p, ssc-miR-30a-5p, ssc-miR-181a, ssc-miR-148a-3p, ssc-miR-92a, ssc-miR-21, ssc-miR-126-5p). Particularly, both ssc-miR-1 and ssc-miR-133 belong to the MyomiRs, which control muscle myosin content, myofibre identity and muscle performance. The involvement of these miRNAs in muscle fibre phenotype provides new insight into the mechanism of muscle fibre regulation underlying muscle development. Furthermore, we performed cell transfection experiment. Overexpression/inhibition of ssc-miR-143-3p in porcine skeletal muscle satellite cell induced an/a increase/reduction of the slow muscle fibre gene and protein (MYH7), indicating that miR-143 activity regulated muscle fibre differentiate in skeletal muscle. And it regulate MYH7 through the HDAC4-MEF2 pathway.     

Ancient genome‐wide admixture extends beyond the current hybrid zone between Macaca fascicularis and M. mulatta

Macaca fascicularis and Macaca mulatta are two of the most commonly used laboratory macaques, yet their genetic differences at a genome‐wide level remain unclear. We analysed the multilocus DNA sequence data of 54 autosomal loci obtained from M. fascicularis samples from three different geographic origins and M. mulatta samples of Burmese origin. M. fascicularis shows high nucleotide diversity, four to five times higher than humans, and a strong geographic population structure between Indonesian‐Malaysian and Philippine macaques. The pattern of divergence and polymorphism between M. fascicularis and M. mulatta shows a footprint of genetic exchange not only within their current hybrid zone but also across a wider range for more than 1 million years. However, genetic admixture may not be a random event in the genome. Whereas randomly selected genic and intergenic regions have the same evolutionary dynamics between the species, some cytochrome oxidase P450 (CYP) genes (major chemical metabolizing genes and potential target genes for local adaptation) have a significantly larger species divergence than other genes. By surveying CYP3A5 gene sequences of more than a hundred macaques, we identified three nonsynonymous single nucleotide polymorphisms that were highly differentiated between the macaques. The mosaic pattern of species divergence in the genomes may be a consequence of genetic differentiation under ecological adaptation and may be a salient feature in the genomes of nascent species under parapatry.