Fine-tuning of the PAX-SIX-EYA-DACH network by multiple microRNAs controls embryo myogenesis.

MicroRNAs (miRNAs), short non-coding RNAs, which act post-transcriptionally to regulate gene expression, are of widespread significance during development and disease, including muscle disease. Advances in sequencing technology and bioinformatics led to the identification of a large number of miRNAs in vertebrates and other species, however, for many of these miRNAs specific roles have not yet been determined. LNA in situ hybridisation has revealed expression patterns of somite-enriched miRNAs, here we focus on characterising the functions of miR-128. We show that antagomiR-mediated knockdown (KD) of miR-128 in developing chick somites has a negative impact on skeletal myogenesis. Computational analysis identified the transcription factor EYA4 as a candidate target consistent with the observation that miR-128 and EYA4 display similar expression profiles. Luciferase assays confirmed that miR-128 interacts with the EYA4 3'UTR. In vivo experiments also suggest that EYA4 is regulated by miR-128. EYA4 is a member of the PAX-SIX-EYA-DACH (PSED) network of transcription factors. Therefore, we identified additional candidate miRNA binding sites in the 3'UTR of SIX1/4, EYA1/2/3 and DACH1. Using the miRanda algorithm, we found sites for miR-128, as well as for other myogenic miRNAs, miR-1a, miR-206 and miR-133a, some of these were experimentally confirmed as functional miRNA target sites. Our results reveal that miR-128 is involved in regulating skeletal myogenesis by directly targeting EYA4 with indirect effects on other PSED members, including SIX4 and PAX3. Hence, the inhibitory effect on myogenesis observed after miR-128 knockdown was rescued by concomitant knockdown of PAX3. Moreover, we show that the PSED network of transcription factors is co-regulated by multiple muscle-enriched microRNAs.