Myf6/MRF4 is a myogenic niche regulator required for the maintenance of the muscle stem cell pool

Abstract

The function and maintenance of muscle stem cells (Mu SC s) are tightly regulated by signals originating from their niche environment. Skeletal myofibers are a principle component of the Mu SC niche and are in direct contact with the muscle stem cells. Here, we show that Myf6 establishes a ligand/receptor interaction between muscle stem cells and their associated muscle fibers. Our data show that Myf6 transcriptionally regulates a broad spectrum of myokines and muscle‐secreted proteins in skeletal myofibers, including EGF . EGFR signaling blocks p38 MAP kinase‐induced differentiation of muscle stem cells. Homozygous deletion of Myf6 causes a significant reduction in the ability of muscle to produce EGF , leading to a deregulation in EGFR signaling. Consequently, although Myf6‐knockout mice are born with a normal muscle stem cell compartment, they undergo a progressive reduction in their stem cell pool during postnatal life due to spontaneous exit from quiescence. Taken together, our data uncover a novel role for Myf6 in promoting the expression of key myokines, such as EGF , in the muscle fiber which prevents muscle stem cell exhaustion by blocking their premature differentiation.

Application of ATAC-Seq for genome-wide analysis of the chromatin state at single myofiber resolution

“…To further assess the quality of the ATAC-Seq data, we analyzed select genes that are expressed by either MuSCs or myofibers. For instance, in the myofiber samples, we confirmed the presence of ATAC-seq peaks in the promoter regions of Ckm , Actin alpha 1 ( Acta1 ), Myogenic factor 6 ( Myf6 ) and Myosin heavy chain 4 ( Myh4 ), all of which are expressed by myofibers but not MuSCs (14,47,49,50) (Figure 2I-L). On the other hand, in MuSCs we observed peaks in the promoter regions of Paired box 7 ( Pax7 ), and Myf5, genes that are known to be expressed in MuSCs (48, 51) (Figure 2M-N).…”

“…The GSEA between uninjured myofibers and MuSCs revealed that one of the top significantly enriched pathways is myogenesis where we can observe that genes associated with differentiation and myofiber function such as Myf6 , Ckm and Tropomyosin 2 ( Tpm2 ) (14,47,60,61) have higher accessibility in the myofiber compared to MuSCs (Figure 5B-5D). On the other hand, genes associated with quiescence and MuSCs such as alpha 7 integrin ( Itga7 ) and Gpx3 are more accessible in MuSCs compared to the myofiber, as expected (62, 63) (Figure 5C, 5E).…”

“…Myofibers also act as a key signaling component of muscle stem cells (MuSCs) (14), which are in turn required for the regeneration of nascent muscle fiber after injury. Skeletal muscle is a very heterogenous tissue composed not only of myofibers and their associated MuSCs, but also numerous different non-myogenic cell types (15).…”

Epigenetic regulation of satellite cell fate during skeletal muscle regeneration

“…1) [13,18]. Finally, the formation of multinucleated myofibers results in the decreased expression of MYOD1 while MYF6/MRF4 becomes highly expressed in the functional muscle fiber [19][20][21].…”

Discriminative feature of cells characterizes cell populations of interest by a small subset of genes

“…Skeletal muscle satellite cells (MuSCs) are known to be an essential cell population for muscle regeneration, and are activated upon muscle injury and undergo multiple progenitor cell stages until differentiating into myofibers. In this process of muscle regeneration, there is also a self-renewing state in which MuSCs again transition to a quiescent state and refill the MuSC pool 15,16 . Therefore, we attempted to characterize heterogeneous cell populations of MuSCs with multiple transient states by DFC, which has been difficult to capture by a DEG-based approach.…”