MicroRNAs

Abstract

MicroRNAs (miRNA) are small, naturally occurring single-stranded RNA of about 21-23 nucleotide in length. They are generated from endogenous transcripts that are encoded in the genomes of humans, animals, viruses, and plants. The first short noncoding miRNA, lin-4 that regulates gene expression in nematode C. elegans was identified by Victor Ambros et al. in 1993 [1]. The miRNA world did not take off until the discovery of let-7, a second miRNA discovered by Ruvkun and Horvitz in 2000 [2], and the rise in interest in another class of short RNA, silencing RNA (siRNA) [3, 4]. The highly conserved nature of let-7 also attracted a great deal of attention to miRNA research. Since its discovery, more miRNAs in various organisms, from protozoans to humans have been identified. Currently, a total of 873 miRNAs have been reported in human (miRBase 11.0, April 2008), and many of them are encoded in polycistronic transcripts. The expression of miRNA, in general, is both organ-specific and dependent on the stage of development [5, 6]. miRNAs have diverse functions including regulation of important cellular processes e.g., cancer, cell metabolism, immune function, cell proliferation, apoptosis, tissue development, and differentiation [7-11]. © 2010 Springer-Verlag Berlin Heidelberg.