Myf6/MRF4 is a Myogenic Niche Regulator Required for the Maintenance of the Muscle Stem Cell Pool (2020)
Figure 2

Figure 2. Temporally Regulated Occupancy of Myogenic Regulatory Factors (MRFs) to cis-Regulatory Domains of Myokine Genes. A Gene expression analysis of myokines (table EV3) during a five day time course of myogenic differentiation going from cycling myoblasts in growth media (Ham's F10 supplemented with 20% Fetal Bovine Serum, 1% penicillin/streptomycin, 2.5 ng/ml basic Fibroblast Growth Factor) to terminally differentiated myocytes (2 days in differentiation media, DMEM supplemented with 5% horse serum) to post mitotic multinucleated myotubes (5 days in differentiation media). Gene expression was assayed in biological triplicate by microarray (Soleimani et al., 2018; Soleimani et al., 2012a). Expression of each gene was averaged across three replicates and normalized to mean zero and standard deviation of one. Expression values were then truncated at +/- 3 for color display. Blue indicates lower than average expression, while red indicates higher than average expression. B Distribution of Myf6 peaks within 100kb of the TSS of the myokine genes (table EV3), similar to the analysis shown in (A). C-E Snapshots of the UCSC genome browser showing enrichment of Myf6 ChIP-Seq reads compared to control around EGF (C), LIF and OSM (D), and VEGFA (E) loci superimposed on reads for Histone H3 lysine 4 mono methyl (H3K4me1), Histone H3 lysine 4 tri methyl (H3K4me3) and total H3 in myoblasts (pink) and myotubes (green). F Snapshots of representative IGV tracks displaying RNA-Seq data from WT whole muscle (WM), single myofibers (SF) and satellite cells (SC) showing the expression of EGF, EGFR and VEGFA. Ckm and Myf6 are used as positive controls for whole muscle and single fibers. PDGFRA, a marker of fibro/adipogenic progenitor cells, is used as a control to show the lack of niche cells in the single myofiber samples. G-H RNA-Sequencing Reads Per Million (RPM) for EGF (G) and EGFR (H) in satellite cells and single myofibers. RNA-Sequencing libraries were prepared from 1000 satellite cells freshly-isolated by FACS or from a single myofiber as described in the Material and Methods. (n=3 biological replicates per group) bars=mean +/- SD, two-tailed t-test). I Activation of EGFR in MuSCs on EDL myofibers treated with EGF compared to untreated control. Myofibers were cultured for 48 hours and were treated with 40ng/ml of EGF for 10 minutes before fixing and staining with antibodies for PAX7 and phospho-EGFR. Scale bar=30μm. J Activation of EGFR signaling in myoblasts treated with recombinant EGF. Myoblasts were treated with 2 ng/ml of recombinant protein in growth media (Ham's F10 supplemented with 20% FBS, 2.5 ng/ml bFGF) for 15 minutes and lysed in RIPA lysis buffer. Western Blots were performed with antibodies against EGFR and phospho-EGFR (pEGFR-Y1068). K Depletion of Myf6 transcript by siRNAs in differentiated primary myotubes (5DM). (n=3 biological replicates), two-tailed t-test, bars = mean +/- SD L Depletion of Myf6 expression by siRNAs leads to a significant reduction in the gene expression output of Epidermal Growth Factor (EGF). (n=3 biological replicates), two-tailed t-test, bars = mean +/- SD