Hong Kong University of Science and Technology, Hong Kong
Abstract: Satellite cells (SCs), or muscle stem cells (MuSCs), are the resident somatic stem cells responsible for skeletal muscle regeneration. Most SCs remain quiescent in resting adult muscles but can activate rapidly upon receiving a stimulus. Whereas post-transcriptional regulation by microRNAs or RNA-binding proteins has been reported to regulate SC quiescence and activation, the role of alternative splicing during SC activation remains elusive. Using an in vivo fixation approach to preserve QSCs in situ, we revealed rapid and extensive splicing changes upon SC activation. Genes regulated by alternative splicing during SC activation are enriched in fundamental pathways, including RNA splicing, transcription regulation, chromatin organization, and the cell cycle. We revealed that RNA Binding Fox-1 Homolog 2 (Rbfox2) regulates alternative splicing during SC activation. The loss of Rbfox2 delays SC activation and muscle regeneration. We further demonstrated that Rbfox2 regulate the splicing of Numb, a well-known Notch regulator during SC activation. The inclusion of exon 6 of the Numb transcript is Rbfox2-dependent and required for SC activation. The skipping of Numb exon 6 delays SC activation and upregulates the Notch signaling pathway. Altogether, our study provides an alternative splicing landscape changes during SC activation and demonstrates Rbfox2 as a key splicing regulator in MuSCs. Moreover, we demonstrate that manipulating the splicing of a single gene is sufficient to affect SC activation and essential signaling pathways such as Notch signaling, highlighting the importance of alternative splicing in regulating SC fate decisions.
Funding Source: This study was supported by Hong Kong Research Grant Council (GRF16100322, GRF16102021, C6018-19G, AoE/M-604/16 and T13-605/18W) and partly supported by the Innovation and Technology Commission (ITCPD/17-9).
