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      Expression profiling of mammalian microRNAs uncovers a subset of brain-expressed microRNAs with possible roles in murine and human neuronal differentiation

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          Abstract

          Northern blot analysis of 119 previously reported microRNAs in adult organs from mouse and human identified a subset of brain-expressed miRNAs whose expression behavior is conserved in both mouse and human differentiating neurons, implicating these microRNAs in mammalian neuronal development or function

          Abstract

          Background

          The microRNAs (miRNAs) are an extensive class of small noncoding RNAs (18 to 25 nucleotides) with probable roles in the regulation of gene expression. In Caenorhabditis elegans, lin-4 and let-7 miRNAs control the timing of fate specification of neuronal and hypodermal cells during larval development. lin-4, let-7 and other miRNA genes are conserved in mammals, and their potential functions in mammalian development are under active study.

          Results

          In order to identify mammalian miRNAs that might function in development, we characterized the expression of 119 previously reported miRNAs in adult organs from mouse and human using northern blot analysis. Of these, 30 miRNAs were specifically expressed or greatly enriched in a particular organ (brain, lung, liver or skeletal muscle). This suggests organ- or tissue-specific functions for miRNAs. To test if any of the 66 brain-expressed miRNAs were present in neurons, embryonal carcinoma cells were treated with all- trans-retinoic acid to promote neuronal differentiation. A total of 19 brain-expressed miRNAs (including lin-4 and let-7 orthologs) were coordinately upregulated in both human and mouse embryonal carcinoma cells during neuronal differentiation. The mammalian ortholog of C. elegans lin- 28, which is downregulated by lin-4 in worms via 3' untranslated region binding, was also repressed during neuronal differentiation of mammalian embryonal carcinoma cells. Mammalian lin-28 messenger RNAs contain conserved predicted binding sites in their 3' untranslated regions for neuron-expressed miR-125b (a lin-4 ortholog), let-7a, and miR-218.

          Conclusions

          The identification of a subset of brain-expressed miRNAs whose expression behavior is conserved in both mouse and human differentiating neurons implicates these miRNAs in mammalian neuronal development or function.

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          Most cited references 48

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          The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14.

          lin-4 is essential for the normal temporal control of diverse postembryonic developmental events in C. elegans. lin-4 acts by negatively regulating the level of LIN-14 protein, creating a temporal decrease in LIN-14 protein starting in the first larval stage (L1). We have cloned the C. elegans lin-4 locus by chromosomal walking and transformation rescue. We used the C. elegans clone to isolate the gene from three other Caenorhabditis species; all four Caenorhabditis clones functionally rescue the lin-4 null allele of C. elegans. Comparison of the lin-4 genomic sequence from these four species and site-directed mutagenesis of potential open reading frames indicated that lin-4 does not encode a protein. Two small lin-4 transcripts of approximately 22 and 61 nt were identified in C. elegans and found to contain sequences complementary to a repeated sequence element in the 3' untranslated region (UTR) of lin-14 mRNA, suggesting that lin-4 regulates lin-14 translation via an antisense RNA-RNA interaction.
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            Frequent deletions and down-regulation of micro- RNA genes miR15 and miR16 at 13q14 in chronic lymphocytic leukemia.

            Micro-RNAs (miR genes) are a large family of highly conserved noncoding genes thought to be involved in temporal and tissue-specific gene regulation. MiRs are transcribed as short hairpin precursors ( approximately 70 nt) and are processed into active 21- to 22-nt RNAs by Dicer, a ribonuclease that recognizes target mRNAs via base-pairing interactions. Here we show that miR15 and miR16 are located at chromosome 13q14, a region deleted in more than half of B cell chronic lymphocytic leukemias (B-CLL). Detailed deletion and expression analysis shows that miR15 and miR16 are located within a 30-kb region of loss in CLL, and that both genes are deleted or down-regulated in the majority ( approximately 68%) of CLL cases.
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              Identification of novel genes coding for small expressed RNAs.

              In Caenorhabditis elegans, lin-4 and let-7 encode 22- and 21-nucleotide (nt) RNAs, respectively, which function as key regulators of developmental timing. Because the appearance of these short RNAs is regulated during development, they are also referred to as small temporal RNAs (stRNAs). We show that many 21- and 22-nt expressed RNAs, termed microRNAs, exist in invertebrates and vertebrates and that some of these novel RNAs, similar to let-7 stRNA, are highly conserved. This suggests that sequence-specific, posttranscriptional regulatory mechanisms mediated by small RNAs are more general than previously appreciated.
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                Author and article information

                Journal
                Genome Biol
                Genome Biology
                BioMed Central (London )
                1465-6906
                1465-6914
                2004
                16 February 2004
                : 5
                : 3
                : R13
                Affiliations
                [1 ]Department of Genetics, Dartmouth Medical School, Hanover, NH 03755, USA
                [2 ]Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, NH 03755, USA
                [3 ]Department of Molecular Biology, University of Medicine and Dentistry of NJ, Stratford, NJ 08084, USA
                [4 ]Department of Medicine and Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA
                Article
                gb-2004-5-3-r13
                395763
                15003116
                Copyright © 2004 Sempere et al.; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.
                Categories
                Research

                Genetics

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