The long and short of inverted repeat genes in animals: MicroRNAs, mirtrons and hairpin RNAs
Volume 7, Issue 18
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September 15, 2008
Pages 2840 - 2845http://dx.doi.org/10.4161/cc.7.18.6734
Authors: Katsutomo Okamura, Wei-Jen Chung and Eric C. Lai View affiliations
MicroRNAs (miRNAs) are endogenous animal transcripts that contain intramolecular double stranded RNA (dsRNA) and are processed by Dicer. Their mature products are ~21-24 nucleotides in length, and they collectively regulate a broad network of endogenous transcripts. A subset of miRNAs are produced from mirtrons, short hairpin introns whose splicing bypasses the normal nuclear processing of canonical miRNAs. Recent studies revealed novel, extended intramolecular dsRNA produced by defined transcription units in flies and mammals, termed hairpin RNAs (hpRNAs). Detailed biogenesis studies in Drosophila showed that hpRNAs are not merely "long" miRNAs, but are actually processed by a distinct biogenesis pathway that is related to the canonical RNA interference pathway. We compare and contrast the miRNA and hpRNA pathways in this review, and describe some of the key questions that the recognition of this novel pathway raises.