miR‐206 family is important for mitochondrial and muscle function, but not essential for myogenesis in vitro [miRNA-Seq]

miR-206, miR-1a-1 and miR-1a-2, foundational members of the myomir family, promote skeletal muscle differentiation and have complete identity in the seed sequence, suggesting functional redundancy. To test if the essential role of these three microRNAs in skeletal myogenesis was masked by redundant function of at least one of the three miRNA left in the cells in previous reports, we generated triple KO (tKO) C2C12 cells by CRISPR/Cas9 (in vitro) and triple KO mice (in vivo model). tKO myoblasts differentiate, producing similar levels of promyogenic mRNAs and normal fusion index. RNAseq analysis confirms tKO clones differentiate but also reveals decrease in mRNA levels of genes related to mitochondrial oxidative phosphorylation. Dimished mitochondria function in tKO cells was confirmed using Seahorse assay. The targets of miR-206/-1a are specifically upregulated during differentiation of tKO myoblasts, when the microRNAs are normally induced, confirming the complete loss of the three microRNA genes. Although we observe partial embryonic lethality of tKO mice, the live mice grow normally to adulthood, have the same size of skeletal muscles as control animals, but perform worse on physical activity tests, which may be partially explained by smaller skeletal muscle fiber diameters. Thus these three myomiRs are not essential for skeletal muscle differentiation but are required for optimal differentiation and provide a clear example of the microRNAs not being a switch but a modulator of differentiation. small RNA-seq on 16 samples; control C2C12 cells population 1 and population 2, miR-206, miR-1a-1 and miR-1a-2 triple KO clone 1 and clone 2; proliferation and differentiation conditions