High-Throughput Analysis of MicroRNA Gene Expression Using Sensitive Probes

MicroRNAs (miRNAs) represent a new class of noncoding RNAs whose functions are, in most cases, unknown, but are believed to play important biological roles (1 ). These tiny RNAs are genome encoded as primary transcripts, referred to as pri-miRNAs, which are processed in the nucleus by Dorsha, a ribonuclease, into pre-miRNAs approx 60–80 nucleotides (nt) long that form stem-loop hairpin structures (2 ). Subsequent to transport to the cytoplasm, premiRNAs are processed by Dicer to approx 22-nt mature miRNAs, which are incorporated into the ribonucleoprotein (RNP) complex that can direct either mRNA cleavage or translation arrest (see Fig. 1 ). The first identified miRNAs in Caenorhabditis elegans are lineage-4 (lin-4 ) and lethal-7 (let-7 ) (3 ,4 ). Recent data supported a role for lin-4 and let-7 as posttranscriptional negative regulators for several genes, including lin-14 , lin-28 , and lin-41 genes (5 ). In general miRNAs bind to the 3′ untranslated regions (UTRs) of their target mRNAs with imperfect homology (6 ).

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