title: Biogenesis of mammalian microRNAs by a non-canonical processing pathway.
abstract: Canonical microRNA biogenesis requires the Microprocessor components, Drosha and DGCR8, to generate precursor-miRNA, and Dicer to form mature miRNA. The Microprocessor is not required for processing of some miRNAs, including mirtrons, in which spliceosome-excised introns are direct Dicer substrates. In this study, we examine the processing of putative human mirtrons and demonstrate that although some are splicing-dependent, as expected, the predicted mirtrons, miR-1225 and miR-1228, are produced in the absence of splicing. Remarkably, knockout cell lines and knockdown experiments demonstrated that biogenesis of these splicing-independent mirtron-like miRNAs, termed 'simtrons', does not require the canonical miRNA biogenesis components, DGCR8, Dicer, Exportin-5 or Argonaute 2. However, simtron biogenesis was reduced by expression of a dominant negative form of Drosha. Simtrons are bound by Drosha and processed in vitro in a Drosha-dependent manner. Both simtrons and mirtrons function in silencing of target transcripts and are found in the RISC complex as demonstrated by their interaction with Argonaute proteins. These findings reveal a non-canonical miRNA biogenesis pathway that can produce functional regulatory RNAs.
authors.affiliation: Department of Cell Biology and Anatomy, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA.
authors.forename: Mallory A
authors.initials: MA
authors.lastname: Havens
authors.forename: Ashley A
authors.initials: AA
authors.lastname: Reich
authors.forename: Dominik M
authors.initials: DM
authors.lastname: Duelli
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Hastings
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D020868:Gene Silencing; D006801:Humans; D007438:Introns; D051379:Mice; D035683:MicroRNAs / Q000378:metabolism*; D011506:Proteins / Q000502:physiology; D012323:RNA Processing, Post-Transcriptional; D016601:RNA-Binding Proteins; D043244:Ribonuclease III / Q000378:metabolism / Q000502:physiology
chemical_list: C526735:Ago2 protein, mouse; D060565:Argonaute Proteins; C474043:DGCR8 protein, human; C586244:MIRN1225 microRNA, human; D035683:MicroRNAs; D011506:Proteins; D016601:RNA-Binding Proteins; C517918:DROSHA protein, human; D043244:Ribonuclease III