Differential expression of miRNAs in slow and fast muscle fibers isolated from GFP-Myh7 mice.

MicroRNAs (miRNAs) are short noncoding RNAs that regulate gene expression in various cell types. Skeletal muscle consists of bundles of muscle fibers, which are classified as either slow-type or fast-type according to their properties. However, the roles of miRNAs in modulating physiological muscle phenotypes remain unclear. Here, we profiled fiber-type-enriched miRNAs to gain insight into differences in gene regulation between the two fiber types. To avoid cross-contamination, we used GFP-Myh7 mice, in which slow-type muscle fibers express green fluorescent protein (GFP), allowing easy discrimination between GFP-positive slow-type fibers and GFP-negative fast-type fibers under fluorescence microscopy. Here, we profiled miRNA expression in two muscle fiber types in GFP-Myh7 mice. Microarray analysis showed that 18 and 12 miRNAs were highly expressed in slow-type and fast-type fibers, respectively, with >2 log2 fold-change (log2FC) relative to their counterparts. These distinct miRNA expressions were largely consistent with polymerase chain reaction (PCR) results. Gene ontology analyses predicted that target genes of these miRNAs were mainly involved in "regulation of transcription" in slow-type muscle fibers, and in "extracellular matrix (ECM)"-related terms in fast-type fibers. Our results suggest that distinct miRNA expression patterns in each fiber type may participate in modulating fiber-type-specific intracellular and extracellular environments.