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MicroRNAs (miRNAs) are small non-coding RNA molecules that post-transcriptionally regulate gene expression by base-pairing to mRNAs. Hundreds of miRNAs have been identified in various multicellular organisms and many miRNAs are evolutionarily conserved. Although the biological functions of most miRNAs are unknown, miRNAs are predicted to regulate up to 30% of the genes within the human genome. Gradually, we are beginning to understand the functions of individual miRNAs and the general function of miRNA action. Here, we review the recent advances in miRNA biology in animals. Particularly, we focus on the roles of miRNAs in vertebrate development and disease.

MicroRNAs (miRNAs) are 20–23 nucleotide (nt) RNA molecules that regulate gene expression post-transcriptionally. A key step toward understanding the function of the hundreds of miRNAs identified in animals is to determine their expression during development. Here we performed a detailed analysis of conditions for in situ detection of miRNAs in the zebrafish embryo using locked nucleic acid (LNA)-modified DNA probes and report expression patterns for 15 miRNAs in the mouse embryo. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are produced by the Dicer1 enzyme; the role of Dicer1 in vertebrate development is unknown. Here we report target-selected inactivation of the dicer1 gene in zebrafish. We observed an initial build-up of miRNA levels, produced by maternal Dicer1, in homozygous dicer1 mutants, but miRNA accumulation stopped after a few days. This resulted in developmental arrest around day 10. These results indicate that miRNA-producing Dicer1 is essential for vertebrate development. [ABSTRACT FROM AUTHOR]