MicroRNAs (miRNAs) are short, endogenous RNAs that have essential roles in regulating gene expression through the disruption of target genes. The miRNA-induced suppression can occur through Argonaute-mediated cleavage of target mRNAs or by translational inhibition. System-wide studies have underscored the integral role that miRNAs play in regulating the expression of essential genes within bone marrow stromal cells. The miRNA expression has been shown to enhance or inhibit cell differentiation and activity, and elucidating miRNA targets within bone marrow cells has revealed novel regulations during normal bone development. Importantly, multiple studies have shown that miRNA misexpression mediates the progression of bone-related pathologies, including osteopetrosis and osteoporosis, as well as the development and progression of osteosarcoma. Furthermore, recent studies have detailed the capacity for miRNAs to influence bone metastasis from a number of primary carcinomas. Taken together, these findings reveal the significant clinical potential for miRNAs to regulate bone homeostasis, as well as to mediate bone-related pathologies.BoneKEy Reports 3, Article number: 549 (2014) | doi:10.1038/bonekey.2014.44
MiRNA Biogenesis and FunctionThe past decade has seen a torrent of novel research into the post-translational regulation of genes via microRNA-mediated suppression. The microRNAs (miRNAs) are a class of B22-nucleotide-long RNAs that repress gene expression through complementary binding to sites in the 3 0 -untranslated region (UTR) of target mRNAs. 1 Mature miRNAs are generated by the sequential cleavage of longer precursor transcripts, or pri-miRNAs, that are typically transcribed from intragenic or intergenic regions by RNA polymerase II. 2 The initial cleavage step, mediated by Drosha and the DGCR8 complex, occurs in the nucleus and produces a shortened (70-100 nucleotides) pre-miRNA hairpin. Pre-miRNAs are exported from the nucleus by Exportin 5, followed by a second cleavage by the ribonuclease Dicer that produces a double-stranded, B18-25-nucleotide-long mature miRNA. One miRNA strand will then combine with Argonaute (AGO2) proteins to produce an RNAinduced silencing complex, allowing for directed pairing with target mRNAs. 1