MicroRNAs involved in skeletal muscle differentiation. J Genet Genomics. 2013;40:107-116. [PMID: 23522383 DOI: 10.1016/j.jgg.2013.02.002]

Integrative Analysis of MicroRNA and mRNA Data Reveals an Orchestrated Function of MicroRNAs in Skeletal Myocyte Differentiation in Response to TNF-α or IGF1

Introduction

Skeletal muscle cell differentiation is impaired by elevated levels of the inflammatory cytokine tumor necrosis factor-α (TNF-α) with pathological significance in chronic diseases or inherited muscle disorders. Insulin like growth factor-1 (IGF1) positively regulates muscle cell differentiation. Both, TNF-α and IGF1 affect gene and microRNA (miRNA) expression in this process. However, computational prediction of miRNA-mRNA relations is challenged by false positives and targets which might be irrelevant in the respective cellular transcriptome context. Thus, this study is focused on functional information about miRNA affected target transcripts by integrating miRNA and mRNA expression profiling data.

Methodology/Principal Findings

Murine skeletal myocytes PMI28 were differentiated for 24 hours with concomitant TNF-α or IGF1 treatment. Both, mRNA and miRNA expression profiling was performed. The data-driven integration of target prediction and paired mRNA/miRNA expression profiling data revealed that i) the quantity of predicted miRNA-mRNA relations was reduced, ii) miRNA targets with a function in cell cycle and axon guidance were enriched, iii) differential regulation of anti-differentiation miR-155-5p and miR-29b-3p as well as pro-differentiation miR-335-3p, miR-335-5p, miR-322-3p, and miR-322-5p seemed to be of primary importance during skeletal myoblast differentiation compared to the other miRNAs, iv) the abundance of targets and affected biological processes was miRNA specific, and v) subsets of miRNAs may collectively regulate gene expression.

Conclusions

Joint analysis of mRNA and miRNA profiling data increased the process-specificity and quality of predicted relations by statistically selecting miRNA-target interactions. Moreover, this study revealed miRNA-specific predominant biological implications in skeletal muscle cell differentiation and in response to TNF-α or IGF1 treatment. Furthermore, myoblast differentiation-associated miRNAs are suggested to collectively regulate gene clusters and targets associated with enriched specific gene ontology terms or pathways. Predicted miRNA functions of this study provide novel insights into defective regulation at the transcriptomic level during myocyte proliferation and differentiation due to inflammatory stimuli.

Overexpression of secretagogin inhibits cell apoptosis and induces chemoresistance in small cell lung cancer under the regulation of miR-494

Secretagogin (SCGN) has recently been identified to play a crucial role in cell apoptosis, receptor signaling and differentiation. However, its clinical significance and functional roles in SCLC chemoresistance remain unknown. Here we examined the expression of SCGN in clinical samples from SCLC patients and evaluated its relation with clinical prognosis. Then up and down-regulation of SCGN were carried out in SCLC cell lines to assess its influence on chemoresistance. Furthermore, luciferase reporter assay was used to evaluate whether SCGN is a novel direct target of miR-494. Our results revealed that elevated expression of SCGN was correlated with the poorer prognosis of SCLC patients and the more significant correlation with chemosensitivity. We also found that knockdown of SCGN expression in H69AR and H446AR cells increased chemosensitivity via increasing cell apoptosis and cell cycle arrest of G0/G1 phase, while over-expression of SCGN reduced chemosensitivity in sensitive H69 and H446 cells. SCGN as a novel target of miR-494 by luciferase reporter assay, up-regulation of miR-494 can sensitize H69AR cells to chemotherapeutic drugs. These results suggest SCGN is involved in the chemoresistance of SCLC under the regulation of miR-494 and may be a potential biomarker for predicting therapeutic response in treatment SCLC.

MicroRNAs and Cardiac Regeneration

The human heart has a limited capacity to regenerate lost or damaged cardiomyocytes after cardiac insult. Instead, myocardial injury is characterized by extensive cardiac remodeling by fibroblasts, resulting in the eventual deterioration of cardiac structure and function. Cardiac function would be improved if these fibroblasts could be converted into cardiomyocytes. MicroRNAs (miRNAs), small noncoding RNAs that promote mRNA degradation and inhibit mRNA translation, have been shown to be important in cardiac development. Using this information, various researchers have used miRNAs to promote the formation of cardiomyocytes through several approaches. Several miRNAs acting in combination promote the direct conversion of cardiac fibroblasts into cardiomyocytes. Moreover, several miRNAs have been identified that aid the formation of inducible pluripotent stem cells and miRNAs also induce these cells to adopt a cardiac fate. MiRNAs have also been implicated in resident cardiac progenitor cell differentiation. In this review, we discuss the current literature as it pertains to these processes, as well as discussing the therapeutic implications of these findings.

The mesmiRizing complexity of microRNAs for striated muscle tissue engineering

microRNAs (miRs) are small non-protein-coding RNAs, able to post-transcriptionally regulate many genes and exert pleiotropic effects. Alteration of miR levels in tissues and in the circulation has been associated with various pathological and regenerative conditions. In this regard, tissue engineering of cardiac and skeletal muscles is a fascinating context for harnessing the complexity of miR-based circuitries and signals. In this review, we will focus on miR-driven regulation of cardiac and skeletal myogenic routes in homeostatic and challenging states. Furthermore, we will survey the intriguing perspective of exosomal and circulating miRs as novel paracrine players, potentially useful for current and future approaches of regenerative medicine for the striated muscles.

MiRNA inhibition in tissue engineering and regenerative medicine

MicroRNAs (miRNAs) are noncoding RNAs that provide an endogenous negative feedback mechanism for translation of messenger RNA (mRNA) into protein. Single miRNAs can regulate hundreds of mRNAs, enabling miRNAs to orchestrate robust biological responses by simultaneously impacting multiple gene networks. MiRNAs can act as master regulators of normal and pathological tissue development, homeostasis, and repair, which has motivated expanding efforts toward the development of technologies for therapeutically modulating miRNA activity for regenerative medicine and tissue engineering applications. This review highlights the tools currently available for miRNA inhibition and their recent therapeutic applications for improving tissue repair.

Effects of Dietary Energy Sources on Post Mortem Glycolysis, Meat Quality and Muscle Fibre Type Transformation of Finishing Pigs

Dietary energy source can influence muscle glycogen storage at slaughter. However, few studies have demonstrated whether the diet-induced change of muscle glycogen is achieved by the transformation of muscle fibre type. This study investigated the effects of dietary energy sources on meat quality, post mortem glycolysis and muscle fibre type transformation of finishing pigs. Seventy-two barrows with an average body weight of 65.0 ± 2.0 kg were selected and were allotted to three iso-energetic and iso-nitrogenous diets A, B or C, and each treatment consisted of three replicates (pens) of eight pigs each. Diet A contained 44.1% starch, 5.9% crude fat and 12.6% neutral detergent fiber (NDF); diet B contained 37.6% starch, 9.5% crude fat and 15.4% NDF; and diet C contained 30.9% starch, 14.3% crude fat and 17.8% NDF. The duration of the experiment was 28 days. After feed withdrawal 12 h, 24 pigs (eight per treatment) were slaughtered, samples from M. longissimus lumborum (LL) were collected for subsequent analysis. The results showed that pigs fed diet C had lesser average daily gain, average daily feed intake and back fat depth than those fed diet A (P<0.05). Diet C increased pH_45min (P<0.05) and decreased drip loss (P<0.05) in LL muscles compared with diet A. Meat from pigs fed diet A showed increased contents of lactate and greater glycolytic potential (GP) compared with those fed diet C (P<0.05). Greater mRNA expression of myosin heavy-chain (MyHC)-I and IIa and lesser expression of MyHC-IIx and IIb (P<0.05) in LL muscles were found in pigs fed diet C, than in pigs fed diet A. In addition, pigs fed diet C resulted in downregulation of miR23a and upregulation of miR409 and miR208b (P<0.05), associated with conserved changes of their corresponding targets. These findings indicated that diets containing low starch and high fibre were beneficial in reducing muscle glycolysis, improving meat quality of finishing pigs. This reduction of GP may be partially associated with the improvement of oxidative fibre composition in LL muscle, and the change in myofibre type may be correlated with the change in the miRNA expression.

Identification of miR-2400 gene as a novel regulator in skeletal muscle satellite cells proliferation by targeting MYOG gene

MicroRNAs play critical roles in skeletal muscle development as well as in regulation of muscle cell proliferation and differentiation. Previous study in our laboratory showed that the expression level of miR-2400, a novel and unique miRNA from bovine, had significantly changed in skeletal muscle-derived satellite cells (MDSCs) during differentiation, however, the function and expression pattern for miR-2400 in MDSCs has not been fully understood. In this report, we firstly identified that the expression levels of miR-2400 were down-regulated during MDSCs differentiation by stem-loop RT-PCR. Over-expression and inhibition studies demonstrated that miR-2400 promoted MDSCs proliferation by EdU (5-ethynyl-2' deoxyuridine) incorporation assay and immunofluorescence staining of Proliferating cell nuclear antigen (PCNA). Luciferase reporter assays showed that miR-2400 directly targeted the 3' untranslated regions (UTRs) of myogenin (MYOG) mRNA. These data suggested that miR-2400 could promote MDSCs proliferation through targeting MYOG. Furthermore, we found that miR-2400, which was located within the eighth intron of the Wolf-Hirschhorn syndrome candidate 1-like 1 (WHSC1L1) gene, was down-regulated in MDSCs in a direct correlation with the WHSC1L1 transcript by Clustered regularly interspaced palindromic repeats interference (CRISPRi). In addition, these observations not only provided supporting evidence for the codependent expression of intronic miRNAs and their host genes in vitro, but also gave insight into the role of miR-2400 in MDSCs proliferation.

The miRNA Transcriptome Directly Reflects the Physiological and Biochemical Differences between Red, White, and Intermediate Muscle Fiber Types

MicroRNAs (miRNAs) are small non-coding RNAs that can regulate their target genes at the post-transcriptional level. Skeletal muscle comprises different fiber types that can be broadly classified as red, intermediate, and white. Recently, a set of miRNAs was found expressed in a fiber type-specific manner in red and white fiber types. However, an in-depth analysis of the miRNA transcriptome differences between all three fiber types has not been undertaken. Herein, we collected 15 porcine skeletal muscles from different anatomical locations, which were then clearly divided into red, white, and intermediate fiber type based on the ratios of myosin heavy chain isoforms. We further illustrated that three muscles, which typically represented each muscle fiber type (i.e., red: peroneal longus (PL), intermediate: psoas major muscle (PMM), white: longissimus dorsi muscle (LDM)), have distinct metabolic patterns of mitochondrial and glycolytic enzyme levels. Furthermore, we constructed small RNA libraries for PL, PMM, and LDM using a deep sequencing approach. Results showed that the differentially expressed miRNAs were mainly enriched in PL and played a vital role in myogenesis and energy metabolism. Overall, this comprehensive analysis will contribute to a better understanding of the miRNA regulatory mechanism that achieves the phenotypic diversity of skeletal muscles.

Genome-wide profiling of the microRNA-mRNA regulatory network in skeletal muscle with aging

Skeletal muscle degenerates progressively, losing mass (sarcopenia) over time, which leads to reduced physical ability and often results in secondary diseases such as diabetes and obesity. The regulation of gene expression by microRNAs is a key event in muscle development and disease. To understand genome‐wide changes in microRNAs and mRNAs during muscle aging, we sequenced microRNAs and mRNAs from mouse gastrocnemius muscles at two different ages (6 and 24 months). Thirty‐four microRNAs (15 up‐regulated and 19 down‐regulated) were differentially expressed with age, including the microRNAs miR‐206 and ‐434, which were differentially expressed in aged muscle in previous studies. Interestingly, eight microRNAs in a microRNA cluster at the imprinted Dlk1‐Dio3 locus on chromosome 12 were coordinately down‐regulated. In addition, sixteen novel microRNAs were identified. Integrative analysis of microRNA and mRNA expression revealed that microRNAs may contribute to muscle aging through the positive regulation of transcription, metabolic processes, and kinase activity. Many of the age‐related microRNAs have been implicated in human muscular diseases. We suggest that genome‐wide microRNA profiling will expand our knowledge of microRNA function in the muscle aging process.

Unique patterns of transcript and miRNA expression in the South American strong voltage electric eel (Electrophorus electricus)

Background

With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs.

Results

We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs’ electric organ, main electric organ, and Hunter’s electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species.

Conclusions

Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1288-8) contains supplementary material, which is available to authorized users.

miRNA expression in control and FSHD fetal human muscle biopsies

Background

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant disorder and is one of the most common forms of muscular dystrophy. We have recently shown that some hallmarks of FSHD are already expressed in fetal FSHD biopsies, thus opening a new field of investigation for mechanisms leading to FSHD. As microRNAs (miRNAs) play an important role in myogenesis and muscle disorders, in this study we compared miRNAs expression levels during normal and FSHD muscle development.

Methods

Muscle biopsies were obtained from quadriceps of both healthy control and FSHD1 fetuses with ages ranging from 14 to 33 weeks of development. miRNA expression profiles were analyzed using TaqMan Human MicroRNA Arrays.

Results

During human skeletal muscle development, in control muscle biopsies we observed changes for 4 miRNAs potentially involved in secondary muscle fiber formation and 5 miRNAs potentially involved in fiber maturation. When we compared the miRNA profiles obtained from control and FSHD biopsies, we did not observe any differences in the muscle specific miRNAs. However, we identified 8 miRNAs exclusively expressed in FSHD1 samples (miR-330, miR-331-5p, miR-34a, miR-380-3p, miR-516b, miR-582-5p, miR-517* and miR-625) which could represent new biomarkers for this disease. Their putative targets are mainly involved in muscle development and morphogenesis. Interestingly, these FSHD1 specific miRNAs do not target the genes previously described to be involved in FSHD.

Conclusions

This work provides new candidate mechanisms potentially involved in the onset of FSHD pathology. Whether these FSHD specific miRNAs cause deregulations during fetal development, or protect against the appearance of the FSHD phenotype until the second decade of life still needs to be investigated.

Could lncRNAs be the missing links in control of mesenchymal stem cell differentiation?

Long suspected, recently recognized, and increasingly studied, non protein-coding RNAs (ncRNAs) are emerging as key drivers of biological control and pathology. Since their discovery in 1993, microRNAs (miRNAs) have been the subject of intense research focus and investigations have revealed striking findings, establishing that these molecules can exert a substantial level of biological control in numerous tissues. More recently, long ncRNAs (lncRNAs), the lesser-studied siblings of miRNA, have been suggested to have a similar robust role in developmental and adult tissue regulation. Mesenchymal stem cells (MSCs) are an important source of multipotent cells for normal and therapeutic tissue repair. Much is known about the critical role of miRNAs in biogenesis and differentiation of MSCs however; recent studies have suggested lncRNAs may play an equally important role in the regulation of these cells. Here we highlight the role of lncRNAs in the regulation of mesenchymal stem cell lineages including adipocytes, chondrocytes, myoblasts, and osteoblasts. In addition, the potential for these noncoding RNAs to be used as biomarkers for disease or therapeutic targets is also discussed.

PARP13 regulates cellular mRNA post-transcriptionally and functions as a pro-apoptotic factor by destabilizing TRAILR4 transcript

Poly(ADP-ribose) Polymerase-13 (PARP13/ZAP/ZC3HAV1) is an antiviral factor, active against specific RNA viruses such as MLV, SINV and HIV. During infection, PARP13 binds viral RNA via its four CCCH-type zinc finger domains and targets it for degradation by recruiting cellular mRNA decay factors such as the exosome complex and XRN1. Here we show that PARP13 binds to and regulates cellular mRNAs in the absence of viral infection. Knockdown of PARP13 results in the misregulation of hundreds of transcripts. Among the most upregulated transcripts is TRAILR4 that encodes a decoy receptor for TRAIL - a pro-apoptotic cytokine that is a promising target for the therapeutic inhibition of cancers. PARP13 destabilizes TRAILR4 mRNA posttranscriptionally in an exosome dependent manner by binding to a region in its 3’UTR. As a consequence, PARP13 represses TRAILR4 expression and increases cell sensitivity to TRAIL-mediated apoptosis, acting as a key regulator of the cellular response to TRAIL.

Next-generation sequencing analysis of miRNA expression in control and FSHD myogenesis

Emerging evidence has demonstrated that miRNA sequences can regulate skeletal myogenesis by controlling the process of myoblast proliferation and differentiation. However, at present a deep analysis of miRNA expression in control and FSHD myoblasts during differentiation has not yet been derived. To close this gap, we used a next-generation sequencing (NGS) approach applied to in vitro myogenesis. Furthermore, to minimize sample genetic heterogeneity and muscle-type specific patterns of gene expression, miRNA profiling from NGS data was filtered with FC≥4 (log₂FC≥2) and p-value<0.05, and its validation was derived by qRT-PCR on myoblasts from seven muscle districts. In particular, control myogenesis showed the modulation of 38 miRNAs, the majority of which (34 out 38) were up-regulated, including myomiRs (miR-1, -133a, -133b and -206). Approximately one third of the modulated miRNAs were not previously reported to be involved in muscle differentiation, and interestingly some of these (i.e. miR-874, -1290, -95 and -146a) were previously shown to regulate cell proliferation and differentiation. FSHD myogenesis evidenced a reduced number of modulated miRNAs than healthy muscle cells. The two processes shared nine miRNAs, including myomiRs, although with FC values lower in FSHD than in control cells. In addition, FSHD cells showed the modulation of six miRNAs (miR-1268, -1268b, -1908, 4258, -4508- and -4516) not evidenced in control cells and that therefore could be considered FSHD-specific, likewise three novel miRNAs that seem to be specifically expressed in FSHD myotubes. These data further clarify the impact of miRNA regulation during control myogenesis and strongly suggest that a complex dysregulation of miRNA expression characterizes FSHD, impairing two important features of myogenesis: cell cycle and muscle development. The derived miRNA profiling could represent a novel molecular signature for FSHD that includes diagnostic biomarkers and possibly therapeutic targets.

The transient expression of miR-203 and its inhibiting effects on skeletal muscle cell proliferation and differentiation

Previous studies have shown that miR-203 is a skin-specific microRNA (miRNA) with a profound role in skin cell differentiation. However, emerging microarray and deep sequencing data revealed that miR-203 is also expressed in embryonic skeletal muscle and myoblasts. In this study, we found that miR-203 was transiently upregulated in chicken embryos on days 10 to 16 (E10-E16) and was sharply downregulated and even not expressed after E16 in chicken embryonic skeletal muscle. Histological profiles and weight variations of embryo skeletal muscle revealed that miR-203 expression is correlated with muscle development. In vitro experiments showed that miR-203 exhibited downregulated expression during myoblast differentiation into myotubes. miR-203 overexpression inhibited myoblast proliferation and differentiation, whereas its loss-of-function increased myoblast proliferation and differentiation. During myogenesis, miR-203 can target and inhibit the expression of c-JUN and MEF2C, which were important for cell proliferation and muscle development, respectively. The overexpression of c-JUN significantly promoted myoblast proliferation. Conversely, knockdown of c-JUN by siRNA suppressed myoblast proliferation. In addition, the knockdown of MEF2C by siRNA significantly inhibited myoblast differentiation. Altogether, these data not only suggested that the expression of miR-203 is transitory during chicken skeletal muscle development but also showed a novel role of miR-203 in inhibiting skeletal muscle cell proliferation and differentiation by repressing c-JUN and MEF2C, respectively.

Involvement of microRNAs in the regulation of muscle wasting during catabolic conditions

Loss of muscle proteins and the consequent weakness has important clinical consequences in diseases such as cancer, diabetes, chronic heart failure, and in aging. In fact, excessive proteolysis causes cachexia, accelerates disease progression, and worsens life expectancy. Muscle atrophy involves a common pattern of transcriptional changes in a small subset of genes named atrophy-related genes or atrogenes. Whether microRNAs play a role in the atrophy program and muscle loss is debated. To understand the involvement of miRNAs in atrophy we performed miRNA expression profiling of mouse muscles under wasting conditions such as fasting, denervation, diabetes, and cancer cachexia. We found that the miRNA signature is peculiar of each catabolic condition. We then focused on denervation and we revealed that changes in transcripts and microRNAs expression did not occur simultaneously but were shifted. Indeed, whereas transcriptional control of the atrophy-related genes peaks at 3 days, changes of miRNA expression maximized at 7 days after denervation. Among the different miRNAs, microRNA-206 and -21 were the most induced in denervated muscles. We characterized their pattern of expression and defined their role in muscle homeostasis. Indeed, in vivo gain and loss of function experiments revealed that miRNA-206 and miRNA-21 were sufficient and required for atrophy program. In silico and in vivo approaches identified transcription factor YY1 and the translational initiator factor eIF4E3 as downstream targets of these miRNAs. Thus miRNAs are important for fine-tuning the atrophy program and their modulation can be a novel potential therapeutic approach to counteract muscle loss and weakness in catabolic conditions.

Cell entry of lymphocytic choriomeningitis virus is restricted in myotubes

In mice persistently infected since birth with the prototypic arenavirus lymphocytic choriomeningitis viurs, viral antigen and RNA are readily detected in most organs and cell types but remarkably absent in skeletal muscle. Here we report that mouse C2C12 myoblasts that are readily infected by LCMV, become highly refractory to LCMV infection upon their differentiation into myotubes. Myotube's resistance to LCMV was not due to an intracellular restriction of virus replication but rather an impaired cell entry mediated by the LCMV surface glycoprotein. Our findings provide an explanation for the observation that in LCMV carrier mice myotubes, which are constantly exposed to blood-containing virus, remain free of viral antigen and RNA despite myotubes express high levels of the LCMV receptor alpha dystroglycan and do not pose an intracellular blockade to LCMV multiplication.

Long noncoding RNAs, emerging players in muscle differentiation and disease

The vast majority of the mammalian genome is transcribed giving rise to many different types of noncoding RNAs. Among them, long noncoding RNAs are the most numerous and functionally versatile class. Indeed, the lncRNA repertoire might be as rich as the proteome. LncRNAs have emerged as key regulators of gene expression at multiple levels. They play important roles in the regulation of development, differentiation and maintenance of cell identity and they also contribute to disease. In this review, we present recent advances in the biology of lncRNAs in muscle development and differentiation. We will also discuss the contribution of lncRNAs to muscle disease with a particular focus on Duchenne and facioscapulohumeral muscular dystrophies.

Converging pathways involving microRNA-206 and the RNA-binding protein KSRP control post-transcriptionally utrophin A expression in skeletal muscle

Several reports have previously highlighted the potential role of miR-206 in the post-transcriptional downregulation of utrophin A in cultured cells. Along those lines, we recently identified K-homology splicing regulator protein (KSRP) as an important negative regulator in the post-transcriptional control of utrophin A in skeletal muscle. We sought to determine whether these two pathways act together to downregulate utrophin A expression in skeletal muscle. Surprisingly, we discovered that miR-206 overexpression in cultured cells and dystrophic muscle fibers causes upregulation of endogenous utrophin A levels. We further show that this upregulation of utrophin A results from the binding of miR-206 to conserved sites located in the 3′-UTR (untranslated region) of KSRP, thus causing the subsequent inhibition of KSRP expression. This miR-206-mediated decrease in KSRP levels leads, in turn, to an increase in the expression of utrophin A due to a reduction in the activity of this destabilizing RNA-binding protein. Our work shows that miR-206 can oscillate between direct repression of utrophin A expression via its 3′-UTR and activation of its expression through decreased availability of KSRP and interactions with AU-rich elements located within the 3′-UTR of utrophin A. Our study thus reveals that two apparent negative post-transcriptional pathways can act distinctively as molecular switches causing repression or activation of utrophin A expression.

Differentially expressed microRNAs in chondrocytes from distinct regions of developing human cartilage

There is compelling in vivo evidence from reports on human genetic mutations and transgenic mice that some microRNAs (miRNAs) play an important functional role in regulating skeletal development and growth. A number of published in vitro studies also point toward a role for miRNAs in controlling chondrocyte gene expression and differentiation. However, information on miRNAs that may regulate a specific phase of chondrocyte differentiation (i.e. production of progenitor, differentiated or hypertrophic chondrocytes) is lacking. To attempt to bridge this knowledge gap, we have investigated miRNA expression patterns in human embryonic cartilage tissue. Specifically, a developmental time point was selected, prior to endochondral ossification in the embryonic limb, to permit analysis of three distinct populations of chondrocytes. The location of chondroprogenitor cells, differentiated chondrocytes and hypertrophic chondrocytes in gestational day 54-56 human embryonic limb tissue sections was confirmed both histologically and by specific collagen expression patterns. Laser capture microdissection was utilized to separate the three chondrocyte populations and a miRNA profiling study was carried out using TaqMan® OpenArray® Human MicroRNA Panels (Applied Biosystems®). Here we report on abundantly expressed miRNAs in human embryonic cartilage tissue and, more importantly, we have identified miRNAs that are significantly differentially expressed between precursor, differentiated and hypertrophic chondrocytes by 2-fold or more. Some of the miRNAs identified in this study have been described in other aspects of cartilage or bone biology, while others have not yet been reported in chondrocytes. Finally, a bioinformatics approach was applied to begin to decipher developmental cellular pathways that may be regulated by groups of differentially expressed miRNAs during distinct stages of chondrogenesis. Data obtained from this work will serve as an important resource of information for the field of cartilage biology and will enhance our understanding of miRNA-driven mechanisms regulating cartilage and endochondral bone development, regeneration and repair.

A miR-30d antisense oligonucleotide inhibits proliferation and promotes apoptosis of colon cancer cells

AIM: To investigate the expression of miR-30d in colon cancer tissues and the effect of a miR-30d antisense oligonucleotide (ASO) on the proliferation and apoptosis of colon cancer cells.

METHODS: The expression of miR-30d in 102 colon cancer tissues and matched tumor-adjacent tissues was detected by real-time quantitative PCR. After colon cancer cells were transfected with a miR-30d ASO, cell proliferation and apoptosis were measured by MTT assay, colony formation assay and flow cytometry.

RESULTS: miR-30d was overexpressed in 52.94% (54/102) of colon cancer tissues, and the positive rate of miR-30d overexpression was significantly higher in colon cancer tissues than in tumor-adjacent colon tissues (P < 0.05). Transfection of miR-30d ASO significantly reduced the expression of miR-30d (P < 0.05), decreased cell survival at 24, 48 and 96 h (all P < 0.05), inhibited colony formation (P < 0.05), and increased apoptosis (P < 0.05) compared with control cells. In addition, the expression of Bcl-2 mRNA and protein was significantly decreased after the expression of miR-30d was down-regulated.

CONCLUSION: MiR-30d is overexpressed in human colon cancer. Inhibition of the expression of miR-30d can effectively inhibit growth and promotes apoptosis of colon cancer cells. MiR-30d may become a new target for the regulation of gene expression in colon cancer.

Roles of microRNAs in the Caenorhabditis elegans nervous system

The first microRNA was discovered in Caenorhabditis elegans in 1993, and since then, thousands of microRNAs have been identified from almost all eukaryotic organisms examined. MicroRNAs function in many biological events such as cell fate determination, metabolism, apoptosis, and carcinogenesis. So far, more than 250 microRNAs have been identified in C. elegans; however, functions for most of these microRNAs are still unknown. A small number of C. elegans microRNAs are associated with known physiological roles such as developmental timing, cell differentiation, stress response, and longevity. In this review, we summarize known roles of microRNAs in neuronal differentiation and function of C. elegans, and discuss interesting perspectives for future studies.